| 1. |
- Fan, Lizhou, et al.
(author)
-
3D Core-Shell NiFeCr Catalyst on a Cu Nanoarray for Water Oxidation : Synergy between Structural and Electronic Modulation
- 2018
-
In: ACS Energy Letters. - : AMER CHEMICAL SOC. - 2380-8195. ; 3:12, s. 2865-2874
-
Journal article (peer-reviewed)abstract
- Low cost transition metal-based electrocatalysts for water oxidation and understanding their structure-activity relationship are greatly desired for clean and sustainable chemical fuel production. Herein, a core-shell (CS) NiFeCr metal/metal hydroxide catalyst was fabricated on a 3D Cu nanoarray by a simple electrodeposition-activation method. A synergistic promotion effect between electronic structure modulation and nanostructure regulation was presented on a CS-NiFeCr oxygen evolution reaction (OER) catalyst: the 3D nanoarchitecture facilitates the mass transport process, the in situ formed interface metal/metal hydroxide heterojunction accelerates the electron transfer, and the electronic structure modulation by Cr incorporation improves the reaction kinetics. Benefiting from the synergy between structural and electronic modulation, the catalyst shows excellent activity toward water oxidation under alkaline conditions: overpotential of 200 mV at 10 mA/cm(2) current density and Tafel slope of 28 mV/dec. This work opens up a new window for understanding the structure-activity relationship of OER catalysts and encourages new strategies for development of more advanced OER catalysts.
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| 2. |
- Zhang, Wei, et al.
(author)
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Investigation of Triphenylamine (TPA)-Based Metal Complexes and Their Application in Perovskite Solar Cells
- 2017
-
In: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 2:12, s. 9231-9240
-
Journal article (peer-reviewed)abstract
- Triphenylamine-based metal complexes were designed and synthesized via coordination to Ni(II), Cu(II), and Zn(II) using their respective acetate salts as the starting materials. The resulting metal complexes exhibit more negative energy levels (vs vacuum) as compared to 2,2', 7,7'-tetrakis(N, N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD), high hole extraction efficiency, but low hole mobilities and conductivities. Application of dopants typically used for Spiro-OMeTAD was not successful, indicating a more complicated mechanism of partial oxidation besides the redox potential. However, utilization as hole-transport material was successful, giving a highest efficiency of 11.1% under AM 1.5G solar illumination.
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| 3. |
- Zhang, Wei, et al.
(author)
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Organic Salts as p-Type Dopants for Efficient LiTFSI-Free Perovskite Solar Cells
- 2020
-
In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:30, s. 33751-33758
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Journal article (peer-reviewed)abstract
- Despite the ubiquity and importance of organic hole-transport materials in photovoltaic devices, their intrinsic low conductivity remains a drawback. Thus, chemical doping is an indispensable solution to this drawback and is essentially always required. The most widely used p-type dopant, FK209, is a cobalt coordination complex. By reducing Co(III) to Co(II), Spiro-OMeTAD becomes partially oxidized, and the film conductivity is initially increased. In order to further increase the conductivity, the hygroscopic co-dopant LiTFSI is typically needed. However, lithium salts are normally quite hygroscopic, and thus, water absorption has been suggested as a significant reason for perovskite degradation and therefore limited device stability. In this work, we report a LiTFSI-free doping process by applying organic salts in relatively high amounts. The film conductivity and morphology have been studied at different doping amounts. The resulting solar cell devices show comparable power conversion efficiencies to those based on conventional LiTFSI-doped Spiro-OMeTAD but show considerably better long-term device stability in an ambient atmosphere.
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| 4. |
- Chen, Cheng, et al.
(author)
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Cu(II) Complexes as p-Type Dopants in Efficient Perovskite Solar Cells
- 2017
-
In: ACS Energy Letters. - : American Chemical Society (ACS). - 2380-8195. ; 2:2, s. 497-503
-
Journal article (peer-reviewed)abstract
- In this work, two Cu(II) complex compounds are designed and synthesized for applications as p-type dopants in solid-state perovskite solar cells (PSCs). Through the characterization of the optical and electrochemical properties, the complex Cu(bpcm)(2) is shown to be eligible for oxidization of the commonly used hole-transport material (HTM) SpiroOMeTAD. The reason is the electron-withdrawing effect of the chloride groups on the ligands. When the complex was applied as p-type dopant in PSCs containing Spiro-OMeTAD as HTM, an efficiency as high as 18.5% was achieved. This is the first time a Cu(II) pyridine complex has been used as p-type dopant in PSCs.
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| 5. |
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| 6. |
- Daniel, Quentin, et al.
(author)
-
Water Oxidation Initiated by In Situ Dimerization of the Molecular Ru(pdc) Catalyst
- 2018
-
In: ACS Catalysis. - : AMER CHEMICAL SOC. - 2155-5435. ; 8:5, s. 4375-4382
-
Journal article (peer-reviewed)abstract
- The mononuclear ruthenium complex [Ru(pdc)L-3] (H(2)pdc = 2,6-pyridinedicarboxylic acid, L = N-heterocycles such as 4-picoline) has previously shown promising catalytic efficiency toward water oxidation, both in homogeneous solutions and anchored on electrode surfaces. However, the detailed water oxidation mechanism catalyzed by this type of complex has remained unclear. In order to deepen understanding of this type of catalyst, in the present study, [Ru(pdc)(py)(3)] (py = pyridine) has been synthesized, and the detailed catalytic mechanism has been studied by electrochemistry, UV-vis, NMR, MS, and X-ray crystallography. Interestingly, it was found that once having reached the Ru-IV state, this complex promptly formed a stable ruthenium dimer [Ru-III(pdc)(py)(2)-O-Ru-IV(pdc)(py)(2)](+). Further investigations suggested that the present dimer, after one pyridine ligand exchange with water to form [Ru-III(pdc)(py)(2)-O-Ru-IV(pdc)(py)(H2O)](+), was the true active species to catalyze water oxidation in homogeneous solutions.
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| 7. |
- Fan, Lizhou, et al.
(author)
-
2D MnOx composite catalysts inspired by natural OEC for efficient catalyticwater oxidation
-
Other publication (other academic/artistic)abstract
- Birnessite MnOx is a close inorganic model of natural oxygen-evolving complex (OEC) that hasbeen widely investigated for catalytic water oxidation, yet its activity is limited by the pooractive site exposure and sluggish charge transfer. Herein, starting from typical birnessite MnOx,we fabricated a hybrid of 2D manganese oxide nanosheets and pyridyl modified graphene(MnOx-NS/py-G) for electrocatalytic water oxidation. Benefiting from the synergy of structuralexfoliation, graphene substrate and molecular pyridyl modification, the MnOx-NS/py-G exhibitsabundant catalytically active sites exposure, fast electron transport, and promoted proton transferat catalyst surface, which imitates the key features of natural OEC. Consequently, theMnOx-NS/py-G reached over 600 times higher activity compared to the typical birnessite MnOx.Inspired by nature, this work provides a well-designed and effective strategy to develop highlyactive manganese oxide-based water oxidation catalysts.
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| 8. |
- Fan, Lizhou, et al.
(author)
-
Holistic functional biomimetics : a key to make an efficient electrocatalyst for water oxidation
- 2023
-
In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 11:20, s. 10669-10676
-
Journal article (peer-reviewed)abstract
- Water oxidation is the holy grail reaction of natural and artificial photosynthesis. How to design an efficient water-oxidation catalyst remains a long-term challenge for solar fuel production. The rate of water oxidation in photosystem II by the oxygen-evolving complex (OEC) Mn4CaO5 cluster is as high as 100-400 s−1. Mimicking the structures of the OEC is a straightforward strategy to design water-oxidation catalysts. However, the high efficiency of the OEC relies on not only its highly active site but also its holistic system for well-organized electron transfer and proton transport. Lacking such a holistic functional system makes δ-MnO2 a poor water-oxidation catalyst, although the local structure of δ-MnO2 is similar to that of the Mn4CaO5 cluster. Electrocatalysts simultaneously imitating the catalytically active sites, fast electron transfer, and promoted proton transport in a natural OEC have been rarely reported. The significance of the synergy of a holistic system is underrated in the design of water-oxidation catalysts. In this work, we fabricated holistic functional biomimetic composites of two-dimensional manganese oxide nanosheets and pyridyl-modified graphene (MnOx-NS/py-G) for electrocatalytic water oxidation. MnOx-NS/py-G simultaneously imitates the synergy of catalytically active sites, fast electron transfer, and promoted proton transport in a natural OEC, resulting in overall 600 times higher activity than that of typical δ-MnO2. This work demonstrates the significance of holistic functional biomimetic design and guides the development of highly active electrocatalysts for small molecule activation related to solar energy storage.
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| 9. |
- Fan, Lizhou, et al.
(author)
-
Molecular Functionalization of NiO Nanocatalyst for Enhanced Water Oxidation by Electronic Structure Engineering
- 2020
-
In: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 13:22, s. 5901-5909
-
Journal article (peer-reviewed)abstract
- Tuning the local environment of nanomaterial-based catalysts has emerged as an effective approach to optimize their oxygen evolution reaction (OER) performance, yet the controlled electronic modulation around surface active sites remains a great challenge. Herein, directed electronic modulation of NiO nanoparticles was achieved by simple surface molecular modification with small organic molecules. By adjusting the electronic properties of modifying molecules, the local electronic structure was rationally tailored and a close electronic structure-activity relationship was discovered: the increasing electron-withdrawing modification readily decreased the electron density around surface Ni sites, accelerating the reaction kinetics and improving OER activity, and vice versa. Detailed investigation by operando Raman spectroelectrochemistry revealed that the electron-withdrawing modification facilitates the charge-transfer kinetics, stimulates the catalyst reconstruction, and promotes abundant high-valent gamma-NiOOH reactive species generation. The NiO-C(6)F(5)catalyst, with the optimized electronic environment, exhibited superior performance towards water oxidation. This work provides a well-designed and effective approach for heterogeneous catalyst fabrication under the molecular level.
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| 10. |
- Fan, Lizhou, et al.
(author)
-
Promoting the Fe(VI) active species generation by structural and electronic modulation of efficient iron oxide based water oxidation catalyst without Ni or Co
- 2020
-
In: Nano Energy. - : Elsevier BV. - 2211-2855 .- 2211-3282. ; 72
-
Journal article (peer-reviewed)abstract
- Fe is considered as a promising alternative for OER catalysts owing to its high natural abundance and low cost. Due to the low conductivity and sluggish catalytic kinetics, the catalytic efficiency of Fe-rich catalysts is far from less abundant Ni, Co-rich alternatives and has been hardly improved without the involvement of Ni or Co. The lower activity of Fe-rich catalysts renders the real active center of state-of-the-art NiFe, CoFe catalyst in long-term scientific debate, despite of detection of Fe-based active intermediates in these catalysts during catalytic process. In the present work, we fabricated a series of sub-5 nm Fe1-yCryOx nanocatalysts via a simple solvothermal method, achieving systematically promoted high-valent Fe(VI) species generation by structural and electronic modulation, displaying highly active OER performance without involvement of Ni or Co. Detailed investigation revealed that the high OER activity is related to the ultrasmall nanoparticle size that promotes abundant edge- and corner-site exposure at catalyst surface, which involves in OER as highly reactive site; and the incorporated Cr ions that remarkably accelerate the charge transfer kinetics, providing an effective conduit as well as suitable host for high-valent active intermediate. This work reveals the structural prerequisites for efficient Fe-rich OER catalyst fabrication, inspiring deeper understanding of the structure-activity relationship as well as OER mechanism of Fe-based catalysts.
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| 11. |
- Wang, Linqin, et al.
(author)
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Design and synthesis of dopant-free organic hole-transport materials for perovskite solar cells
- 2018
-
In: Chemical Communications. - : ROYAL SOC CHEMISTRY. - 1359-7345 .- 1364-548X. ; 54:69, s. 9571-9574
-
Journal article (peer-reviewed)abstract
- Two novel dopant-free hole-transport materials (HTMs) with spiro[dibenzo[c,h]xanthene-7,9-fluorene] (SDBXF) skeletons were prepared via facile synthesis routes. A power conversion efficiency of 15.9% in perovskite solar cells is attained by using one HTM without dopants, which is much higher than undoped Spiro-OMeTAD-based devices (10.8%). The crystal structures of both new HTMs were systematically investigated to reveal the reasons behind such differences in performance and to indicate the design principles of more advanced HTMs.
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| 12. |
- Zhang, Biaobiao, et al.
(author)
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Characterization of a trinuclear ruthenium species in catalytic water oxidation by Ru(bda)(pic)(2) in neutral media
- 2016
-
In: Chemical Communications. - : Royal Society of Chemistry. - 1359-7345 .- 1364-548X. ; 52:55, s. 8619-8622
-
Journal article (peer-reviewed)abstract
- A Ru-III-O-Ru-IV-O-Ru-III type trinuclear species was crystallographically characterized in water oxidation by Ru(bda)(pic)(2) (H(2)bda = 2,2'-bipyridine- 6,60-dicarboxylic acid; pic = 4-picoline) under neutral conditions. The formation of a ruthenium trimer due to the reaction of Ru-IV QO with Ru-II-OH2 was fully confirmed by chemical, electrochemical and photochemical methods. Since the oxidation of the trimer was proposed to lead to catalyst decomposition, the photocatalytic water oxidation activity was rationally improved by the suppression of the formation of the trimer.
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| 13. |
- Zhang, Biaobiao, et al.
(author)
-
Defective and "c-Disordered" Hortensia-like Layered MnOx as an Efficient Electrocatalyst for Water Oxidation at Neutral pH
- 2017
-
In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 7:9, s. 6311-6322
-
Journal article (peer-reviewed)abstract
- The development of a highly active manganese-based water oxidation catalyst in the design of an ideal artificial photosynthetic device operating under neutral pH conditions remains a great challenge, due to the instability of pivotal Mn3+ intermediates. We report here defective and "c-disordered" layered manganese oxides (MnOx-300) formed on a fluorine-doped tin oxide electrode by constant anodic potential deposition and subsequent annealing, with a catalytic onset (0.25 mA/cm(2)) at an overpotential (eta) of 280 mV and a benchmark catalytic current density of 1.0 mA/cm(2) at an overpotential (eta) of 330 mV under neutral pH (1 M potassium phosphate). Steady current density above 8.2 mA/cm(2) was obtained during the electrolysis at 1.4 V versus the normal hydrogen electrode for 20 h. Insightful studies showed that the main contributing factors for the observed high activity of MnOx-300 are (i) a defective and randomly stacked layered structure, (ii) an increased degree of Jahn-Teller distorted Mn3+ in the MnO6 octahedral sheets, (iii) effective stabilization of Mn3+, (iv) a high surface area, and (v) improved electrical conductivity. These results demonstrate that manganese oxides as structural and functional models of an oxygen-evolving complex (OEC) in photosystem II are promising catalysts for water oxidation in addition to Ni/Co-based oxides/hydroxides.
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| 14. |
- Zhang, Biaobiao, et al.
(author)
-
Electrocatalytic Water Oxidation Promoted by 3 D Nanoarchitectured Turbostratic Δ-MnOx on Carbon Nanotubes
- 2017
-
In: ChemSusChem. - : Wiley-VCH Verlag. - 1864-5631 .- 1864-564X. ; 10:22, s. 4472-4478
-
Journal article (peer-reviewed)abstract
- The development of manganese-based water oxidation electrocatalysts is desirable for the production of solar fuels, as manganese is earth-abundant, inexpensive, non-toxic, and has been employed by the Photosystem II in nature for a billion years. Herein, we directly constructed a 3 D nanoarchitectured turbostratic δ-MnOx on carbon nanotube-modified nickel foam (MnOx/CNT/NF) by electrodeposition and a subsequent annealing process. The MnOx/CNT/NF electrode gives a benchmark catalytic current density (10 mA cm−2) at an overpotential (η) of 270 mV under alkaline conditions. A steady current density of 19 mA cm−2 is obtained during electrolysis at 1.53 V for 1.0 h. To the best of our knowledge, this work represents the most efficient manganese-oxide-based water oxidation electrode and demonstrates that manganese oxides, as a structural and functional model of oxygen-evolving complex (OEC) in Photosystem II, can also become comparable to those of most Ni- and Co-based catalysts.
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| 15. |
- Zhang, Peili, et al.
(author)
-
Dendritic core-shell nickel-iron-copper metal/metal oxide electrode for efficient electrocatalytic water oxidation
- 2018
-
In: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 9:1
-
Journal article (peer-reviewed)abstract
- Electrochemical water splitting requires efficient water oxidation catalysts to accelerate the sluggish kinetics of water oxidation reaction. Here, we report a promisingly dendritic core-shell nickel-iron-copper metal/metal oxide electrode, prepared via dealloying with an electrodeposited nickel-iron-copper alloy as a precursor, as the catalyst for water oxidation. The as-prepared core-shell nickel-iron-copper electrode is characterized with porous oxide shells and metallic cores. This tri-metal-based core-shell nickel-iron-copper electrode exhibits a remarkable activity toward water oxidation in alkaline medium with an overpotential of only 180 mV at a current density of 10 mA cm-2. The core-shell NiFeCu electrode exhibits pH-dependent oxygen evolution reaction activity on the reversible hydrogen electrode scale, suggesting that non-concerted proton-electron transfers participate in catalyzing the oxygen evolution reaction. To the best of our knowledge, the as-fabricated core-shell nickel-iron-copper is one of the most promising oxygen evolution catalysts.
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| 16. |
- Zhang, Peili, et al.
(author)
-
Gas-templating of hierarchically structured Ni-Co-P for efficient electrocatalytic hydrogen evolution
- 2017
-
In: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 5:16, s. 7564-7570
-
Journal article (peer-reviewed)abstract
- One of the grand challenges for developing scalable and sustainable hydrogen producing systems is the lack of efficient and robust earth-abundant element based catalysts for the hydrogen evolution reaction (HER). Herein, a hierarchically structured Ni-Co-P film was fabricated via a gas templating electro-deposition method. This film exhibits remarkably high catalytic performance for the HER in 1 M KOH with respective current densities of -10 and -500 mA cm(-2) at the overpotentials of -30 and -185 mV with a Tafel slope of 41 mV dec(-1). A controlled potential electrolysis experiment demonstrates that the as-prepared Ni-Co-P film is an efficient and robust catalyst with a faradaic efficiency close to 100%. Systematic characterization suggests that the unique hierarchical structure and the mutual participation of nano-sized Ni/Co based components are responsible for the high HER catalytic activity.
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| 17. |
- Zhang, Peili, et al.
(author)
-
Paired Electrocatalytic Oxygenation and Hydrogenation of Organic Substrates with Water as the Oxygen and Hydrogen Source
- 2019
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In: Angewandte Chemie International Edition. - : Wiley-VCH Verlagsgesellschaft. - 1433-7851 .- 1521-3773. ; 58:27, s. 9155-9159
-
Journal article (peer-reviewed)abstract
- The use of water as an oxygen and hydrogen source for the paired oxygenation and hydrogenation of organic substrates to produce valuable chemicals is of utmost importance as a means of establishing green chemical syntheses. Inspired by the active Ni3+ intermediates involved in electro-catalytic water oxidation by nickel-based materials, we prepared NiBx as a catalyst and used water as the oxygen source for the oxygenation of various organic compounds. NiBx was further employed as both an anode and a cathode in a paired electrosynthesis cell for the respective oxygenation and hydrogenation of organic compounds, with water as both the oxygen and hydrogen source. Conversion efficiency and selectivity of >= 99% were observed during the oxygenation of 5-hydroxy-methylfurfural to 2,5-furandicarboxylic acid and the simultaneous hydrogenation of p-nitrophenol to p-aminophenol. This paired electrosynthesis cell has also been coupled to a solar cell as a stand-alone reactor in response to sunlight.
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| 18. |
- Zhang, Wei, 1989-, et al.
(author)
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Single crystal structure and opto-electronic properties of oxidized Spiro-OMeTAD
- 2020
-
In: Chemical Communications. - : Royal Society of Chemistry. - 1359-7345 .- 1364-548X. ; 56:10, s. 1589-1592
-
Journal article (peer-reviewed)abstract
- Single crystals of Spiro(TFSI)2 were grown, the optical and electronic properties were characterized and compared with neutral Spiro-OMeTAD. Density-functional theory was used to get insights into binding and band structure properties. The flat valence bands indicate a rather limited orbital overlap in Spiro(TFSI)2.
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| 19. |
- Zhang, Wei, et al.
(author)
-
The Central Role of Ligand Conjugation for Properties of Coordination Complexes as Hole-Transport Materials in Perovskite Solar Cells
- 2019
-
In: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 2:9, s. 6768-6779
-
Journal article (peer-reviewed)abstract
- Two zinc-based coordination complexes Y3 and Y4 have been synthesized and characterized, and their performance as hole-transport materials (HTMs) for perovskite solar cells (PSCs) has been investigated. The complex Y3 contains two separate ligands, and the molecular structure can be seen as a disconnected porphyrin ring. On the other hand, Y4 consists of a porphyrin core and therefore is a more extended conjugated system as compared to Y3. The optical and redox properties of the two different molecular complexes are comparable. However, the hole mobility and conductivity of Y4 as macroscopic material are remarkably higher than that of Y3. Furthermore, when employed as hole-transport materials in perovskite solar cells, cells containing Y4 show a power conversion efficiency (PCE) of 16.05%, comparable to the Spiro-OMeTAD-based solar cells with an efficiency around 17.08%. In contrast, solar cells based on Y3 show a negligible efficiency of about 0.01%. The difference in performance of Y3 and Y4 is analyzed and can be attributed to the difference in packing of the nonplanar and planar building blocks in the corresponding materials.
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| 20. |
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| 21. |
- Biaobiao, Zhang, et al.
(author)
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Modifying Ru-bda Backbone with Steric Hindrance and Hydrophilicity: Influence of Secondary Coordination Environments on Water-Oxidation Mechanism.
-
Journal article (other academic/artistic)abstract
- Understanding the seven coordination and O−O coupling pathway of the distinguished Ru-bda catalysts is essential for the development of next generation efficient water-oxidation catalysts based on earth-abundant metals. This work reports the synthesis, characterization and catalytic properties of a monomeric ruthenium catalyst Ru-bnda (H2bnda = 2,2'-bi(nicotinic acid)-6,6'-dicarboxylic acid) featuring steric hindrance and enhanced hydrophilicity on the backbone. Combining experimental evidence with systematic density functional theory calculations on the Ru-bnda and related catalysts Ru-bda, Ru-pda and Ru-biqa, we emphasized that seven coordination clearly determines presence of RuV=O with high spin density on the ORuV=O atom, i.e. oxo with radical properties, which is one of the necessary conditions for reacting through the O−O coupling pathway. However, an additional factor to make the condition sufficient is the favorable intermolecular face-to-face interaction for the generation of the pre-reactive [RuV=O···O=RuV], which is significantly influenced by the secondary coordination environments. This work provides a new understanding of the structure-activity relationship of water-oxidation catalysts and their potential to adopt I2M pathway for O−O bond formation.
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| 22. |
- Cuartero, Maria, et al.
(author)
-
Ferrocene self assembled monolayer as a redox mediator for triggering ion transfer across nanometer-sized membranes
- 2019
-
In: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 315, s. 84-93
-
Journal article (peer-reviewed)abstract
- Modulation of ion-transfer processes across nanometer-sized voltammetry membranes by ferrocene-based self-assembled monolayer on regular glassy carbon electrode is herein demonstrated. The composition of the membrane is advantageously tuned to promote either cation or anion transfer: the presence of an exchangeable cation results in cation transfer, whereas a lipophilic salt induces anion transfer through the fulfilment of the electroneutrality of the system. When an anodic scan oxidizes ferrocene moieties in the monolayer, these are stabilized by the pairing of lipophilic anions present in the membrane. As a result, either, hydrophilic cations present in the membrane are expelled into the solution or anions enter from the solution generating hence reversible and voltammetric waves for these transfers. The use of a redox active monolayer rather than a conducting polymer film or a redox active compound into the membrane overcomes a number of drawbacks previously manifested by these systems. The confinement of the redox process in a thin film at the immediate vicinity of the membrane allows to avoid the need of elevated number of redox moieties to be sued in the membrane, therefore suppressing its acute leaching and being compatible with the incorporation of both cation and anion ionophores for the first time. In this sense, assisted transfer of lithium and chloride are shown as proof-of-concept. Here, the peak potential of the associated voltammetric waves shifts according to the Nernst equation, in analogy to potentiometric sensors. Analytical detection of lithium and chloride ions in real samples is additionally presented.
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| 23. |
- Daniel, Quentin, et al.
(author)
-
Re-Investigation of Cobalt Porphyrin for Electrochemical Water Oxidation on FTO Surface : Formation of CoOx as Active Species
- 2017
-
In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 7:2, s. 1143-1149
-
Journal article (peer-reviewed)abstract
- The use of cobalt porphyrin complexes as efficient and cost-effective molecular catalysts for water oxidation has been investigated previously. However, by combining a set of analytical techniques (electrochemistry, ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and synchrotron-based photoelectron spectroscopy (SOXPES and HAXPES)), we have demonstrated that three different cobalt porphyrins, deposited on FTO glasses, decompose promptly into a thin film of CoOx on the surface of the electrode during water oxidation under certain conditions (borate buffer pH 9.2). It is presumed that the film is composed of CoO, only detectable by SOXPES, as conventional techniques are ineffective. This newly formed film has a high turnover frequency (TOF), while the high transparency of the CoOx-based electrode is very promising for future application in photoelectrochemical cells.
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| 24. |
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| 25. |
- Fan, Ke, et al.
(author)
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Amorphous WO3 induced lattice distortion for a low-cost and high-efficient electrocatalyst for overall water splitting in acid
- 2020
-
In: Sustainable Energy & Fuels. - : ROYAL SOC CHEMISTRY. - 2398-4902. ; 4:4, s. 1712-1722
-
Journal article (peer-reviewed)abstract
- The development of highly active and durable catalysts for water oxidation under acidic conditions is necessary but challenging for renewable energy conversion. Ir-based catalysts are highly efficient for water oxidation in acid, but their large scale application is hindered by the high cost and scarcity of iridium. Herein, we use an amorphous WO3 induced lattice distortion (AWILD) strategy to reduce the Ir content to only 2 wt% in the final material. The optimized hybrid nitrogen-doped carbon (NC)/WO3/IrO2 can efficiently catalyze water oxidation with a low overpotential of 270 mV at 10 mA cm(-2) current density (eta (10)) and a high turnover frequency of over 2 s(-1) at 300 mV overpotential in 0.5 M H2SO4, a performance that surpasses that of commercial IrO2 significantly. Introducing the layer of amorphous WO3 between IrO2 nanoparticles and NC can distort the lattice of IrO2, exposing more highly active sites for water oxidation. The AWILD effect compensates for the lower Ir content and dramatically reduces the cost of the catalyst without sacrificing the catalytic activity. Additionally, this catalyst also exhibits high activity in acid for hydrogen evolution with only 65 mV of eta (10) attributed to the AWILD effect, exhibiting efficient bifunctionality as a Janus catalyst for overall water splitting. The AWILD approach provides a novel and efficient strategy for low-cost and highly efficient electrocatalysts for acidic overall water splitting with an extremely low content of noble metals.
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| 26. |
- Fan, Ke, et al.
(author)
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Sacrificial W Facilitates Self-Reconstruction with Abundant Active Sites for Water Oxidation
- 2022
-
In: Marine and Petroleum Geology. - : Wiley. - 0264-8172 .- 1873-4073. ; 138
-
Journal article (peer-reviewed)abstract
- Water oxidation is an important reaction for multiple renewable energy conversion and storage-related devices and technologies. High-performance and stable electrocatalysts for the oxygen evolution reaction (OER) are urgently required. Bimetallic (oxy)hydroxides have been widely used in alkaline OER as electrocatalysts, but their activity is still not satisfactory due to insufficient active sites. In this research, A unique and efficient approach of sacrificial W to prepare CoFe (oxy)hydroxides with abundant active species for OER is presented. Multiple ex situ and operando/in situ characterizations have validated the self-reconstruction of the as-prepared CoFeW sulfides to CoFe (oxy) hydroxides in alkaline OER with synchronous W etching. Experiments and theoretical calculations show that the sacrificial W in this process induces metal cation vacancies, which facilitates the in situ transformation of the intermediate metal hydroxide to CoFe-OOH with more high-valence Co(III), thus creating abundant active species for OER. The Co(III)-rich environment endows the in situ formed CoFe oxyhydroxide with high catalytic activity for OER on a simple flat glassy carbon electrode, outperforming those not treated by the sacrificial W procedure. This research demonstrates the influence of etching W on the electrocatalytic performance, and provides a low-cost means to improve the active sites of the in situ self-reconstructed bimetallic oxyhydroxides for OER.
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| 27. |
- Fan, Ke, et al.
(author)
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Surface and bulk reconstruction of CoW sulfides during pH-universal electrocatalytic hydrogen evolution
- 2021
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 9:18, s. 11359-11369
-
Journal article (peer-reviewed)abstract
- Electrocatalytic water splitting is an efficient means of producing energy carriers, such as H2. The hydrogen evolution reaction (HER) requires high-efficiency electrocatalysts. Understanding the active site structures of the HER electrocatalysts is essential for the rational design and development of water splitting devices. In this study, porous CoW sulfides were employed as model electrocatalysts for pH-universal HER. Multiple characterization studies, such as X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and operando X-ray diffraction, were systematically used to investigate the reconstruction of the active species at the surface and in the bulk. The results show that during the HER, the structural transformation of the species CoW sulfides is strongly dependent on the pH of the electrolyte. Electrolytes of varying pH lead to varied reconstruction and influence the true catalytically active species responsible for the HER. The surface and the bulk of the electrocatalysts transform to different oxides/hydroxides when subjected to the HER. This is the first time that the pH-dependent bulk and surface structural evolution in the HER has been revealed. This study reveals the reconstruction and potential active site evolution of mixed-metal sulfides for the HER. We believe that the present study not only provides an idealized "pre-catalyst"for pH-universal highly-efficient HER, but also provides a thorough understanding about the identification of the real active sites and the mechanism of the structural evolution of the electrocatalysts during hydrogen evolution.
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| 28. |
- Grądzka-Kurzaj, Iwona, et al.
(author)
-
Effects of molecular modifications for water splitting enhancement of BiVO4
- 2020
-
In: International journal of hydrogen energy. - : Elsevier Ltd. - 0360-3199 .- 1879-3487. ; 45:30, s. 15129-15141
-
Journal article (peer-reviewed)abstract
- Combined organic (molecular adsorption) and inorganic (TiO2 passivation) modifications for enhancing water splitting efficiency of porous bismuth vanadate electrodes are tested. The catalytic activity of BiVO4 is increased after adsorption of a newly prepared ruthenium catalyst. TiO2 passivation and sensitization with RuP dye does not show straightforward improvements to the complex photocatalytic behaviour depending on the configuration of the (two- or three-electrode) photoelectrochemical cell, type of the experiment and sample aging. The time constant for electron transport in BiVO4 electrodes (in the range of seconds, revealed by electrochemical impedance measurements) was found to correlate with the stable photocurrent of the cells. The femtosecond transient absorption studies confirm the negligible effects of RuP on the population of the photoexcited carriers in BiVO4. The transient absorption studies also show that the processes responsible for the differences in photocurrents of the modified BiVO4 samples occur on a time scale longer than the first nanoseconds.
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| 29. |
- Guo, Yu, et al.
(author)
-
Necessity of structural rearrangements for O[sbnd]O bond formation between O5 and W2 in photosystem II
- 2021
-
In: Journal of Energy Challenges and Mechanics. - : Elsevier B.V.. - 2056-9386. ; 57, s. 436-442
-
Journal article (peer-reviewed)abstract
- Numerous aspects of the water oxidation mechanism in photosystem II have not been fully elucidated, especially the O[sbnd]O bond formation pathway. However, a body of experimental evidences have identified the O5 and W2 ligands of the oxygen-evolving complex as the highly probable substrate candidates. In this work, we studied O[sbnd]O bond formation between O5 and W2 based on the native Mn4Ca cluster by density functional calculations. Structural rearrangements before the formation of the S4 state were found as a prerequisite for O[sbnd]O bond formation between O5 and W2, regardless if the suggested pathways involving the typical Mn1(IV)-O[rad] species or the recently proposed Mn4(VII)(O)2 species. Possible alternatives for the S2 → S3 and S3 → S4 transitions accounting for such required rearrangements are discussed. These findings reflect that the structural flexibility of the Mn4Ca cluster is essential to allow structural rearrangements during the catalytic cycle.
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| 30. |
- Jiang, Yi, et al.
(author)
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Chemical and photocatalytic water oxidation by mononuclear Ru catalysts
- 2013
-
In: Cuihuà xuébào. - 0253-9837 .- 1872-2067. ; 34:8, s. 1489-1495
-
Journal article (peer-reviewed)abstract
- Four mononuclear Ru complexes with different substituents on the para position of the pyridine ligand of Ru(bda)(pic)(2) (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; pic = picoline) were synthesized and characterized by H-1 nuclear magnetic resonance or X-ray crystallography. The electrochemical properties of this series of compounds in acidic and neutral conditions were studied by cyclic voltammetry. Their catalytic activity towards water oxidation was investigated using a chemical oxidant ([Ce(NH4)(2)(NO3)(6)] (Ce-IV) in acidic solution, or driven by visible light in a three-component system containing a photosensitizer ([Ru(bpy)(3)](2+)) and an electron acceptor (S2O82-). For the chemical water oxidation, complex 1 was found to be the most effective, exhibiting a turnover number (TON) of up to 4000. The pyridine substituent at the 4-position in 1 may be protonated giving an intensive electron-withdrawing effect. Complex 2 bears the most electron-withdrawing trifluoromethyl group under neutral conditions and showed the highest photocatalytic activity with a TON of 270 over 2 h. It was concluded that the more electron-withdrawing substituents led to higher activity towards oxygen evolution for this type of Ru catalysts in the oxidation of water.
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| 31. |
- Jiang, Yi, et al.
(author)
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Promoting the Activity of Catalysts for the Oxidation of Water with Bridged Dinuclear Ruthenium Complexes
- 2013
-
In: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 52:12, s. 3398-3401
-
Journal article (peer-reviewed)abstract
- Solar fuels: Dinuclear ruthenium catalysts prepared from two covalently bridged monomeric catalytic units show outstanding activities towards the oxidation of water with high turnover numbers up to 43 000 and turnover frequencies up to 40 s-1 (see picture). Direct comparison of the performance parameters indicates that the dimers are significantly more active as catalysts than the monomers.
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| 32. |
- Kravchenko, Oleksandr, et al.
(author)
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Improving the Stability of Ru-bda Molecular Water Oxidation Catalysts via π‑System Extension of Backbone Ligand
-
Other publication (other academic/artistic)abstract
- Originating from natural enzymes, molecular catalysts often serve as models for studying certain catalytic processes. Despite well-established mechanisms and structure-activity relationships, molecular electrocatalysts are much less used in industry than materials. Wide application of molecular complexes is primarily limited by their insufficient stability, and many efforts are devoted to addressing this problem. Design of water oxidation catalysts experienced gradual development, associated with the gains in stability, e.g., through well-defined coordination modes, moderate flexibility, oxidatively stable and negatively charged ligands. Herein we report a simple yet effective modification of state-of-the-art Ru-bda based water oxidation catalysts. Extension of the π-system of equatorial bipyridine ligand improves electron density delocalization and stabilizes molecular orbitals with high 3d contribution, which are partly responsible for axial ligand bonding. This feature allows catalysts to reach turnover numbers up to 20000, operating for hours in pH 1 solution at concentrations lower than 5 μM.
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| 33. |
- Kravchenko, Oleksandr, et al.
(author)
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Modulation of the First and Second Coordination Sphere Effects by Backbone Substitution in Ru(bda)L2 Water Oxidation Catalysts
-
Other publication (other academic/artistic)abstract
- Active research in the field of renewable energy has provided numerous molecular water oxidation catalysts for efficient water splitting, such as Ru-bda. As the most stable and active catalysts are based on ruthenium, a larger focus is put on the understanding, which properties of the ligands can be leveraged in cheap and sustainable catalysts to compensate the drawbacks of non-noble metals. Most modifications of the bda ([2,2'-bipyridine]-6,6'-dicarboxylate) ligand do not yield in more efficient catalysts and in general constitute a complicated structure-activity relationship. Herein, we report two new modifications of bda with strong electron-donating and electron-withdrawing substituents and their implications on the intra- and intermolecular interactions.
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| 34. |
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| 35. |
- Li, Fei, et al.
(author)
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Highly efficient oxidation of water by a molecular catalyst immobilized on carbon nanotubes
- 2011
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In: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 50:51, s. 12276-12279
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Journal article (peer-reviewed)abstract
- A successful team: A molecular device based on multiwalled carbon nanotubes functionalized by a mononuclear ruthenium catalyst has been shown to split water electrochemically (see picture; ITO=indium tin oxide). The readily prepared electrode showed excellent electrocatalytic activity for the oxidation of water, a high current density, and a low overpotential, and constitutes one step forward in the design of artificial photosynthetic systems.
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| 36. |
- Li, Fei, et al.
(author)
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Towards A Solar Fuel Device : Light-Driven Water Oxidation Catalyzed by a Supramolecular Assembly
- 2012
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In: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 51:10, s. 2417-2420
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Journal article (peer-reviewed)abstract
- Time to split: Supramolecular assemblies containing both photosensitizers and a ruthenium water-oxidation catalyst were prepared and characterized. The pictured assembly exhibits, for the first time, enhanced visible-light-driven water oxidation activity.
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| 37. |
- Li, Hua, et al.
(author)
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Visible Light-Driven Water Oxidation Promoted by Host-Guest Interaction between Photosensitizer and Catalyst with A High Quantum Efficiency
- 2015
-
In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 137:13, s. 4332-4335
-
Journal article (peer-reviewed)abstract
- A highly active supramolecular system for visible light-driven water oxidation was developed with cyclodextrin-modified ruthenium complex as the photosensitizer, phenyl-modified ruthenium complexes as the catalysts, and sodium persulfate as the sacrificial electron acceptor. The catalysts were found to form 1:1 host-guest adducts with the photosensitizer. Stopped-flow measurement revealed the host-guest interaction is essential to facilitate the electron transfer from catalyst to sensitizer. As a result, a remarkable quantum efficiency of 84% was determined under visible light irradiation in neutral aqueous phosphate buffer. This value is nearly 1 order of magnitude higher than that of noninteraction system, indicating that the noncovalent incorporation of sensitizer and catalyst is an appealing approach for efficient conversion of solar energy into fuels.
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| 38. |
- Liu, Tianqi, et al.
(author)
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Iron-Based Molecular Water Oxidation Catalysts : Abundant, Cheap, and Promising
- 2019
-
In: Chemistry - An Asian Journal. - : WILEY-V C H VERLAG GMBH. - 1861-4728 .- 1861-471X. ; 14:1, s. 31-43
-
Research review (peer-reviewed)abstract
- An efficient and robust water oxidation catalyst based on abundant and cheap materials is the key to converting solar energy into fuels through artificial photosynthesis for the future of humans. The development of molecular water oxidation catalysts (MWOCs) is a smart way to achieve promising catalytic activity, thanks to the clear structures and catalytic mechanisms of molecular catalysts. Efficient MWOCs based on noble-metal complexes, for example, ruthenium and iridium, have been well developed over the last 30 years; however, the development of earth-abundant metal-based MWOCs is very limited and still challenging. Herein, the promising prospect of iron-based MWOCs is highlighted, with a comprehensive summary of previously reported studies and future research focus in this area.
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| 39. |
- Liu, Tianqi, et al.
(author)
-
Isolation and Identification of Pseudo Seven-Coordinate Ru(III) Intermediate Completing the Catalytic Cycle of Ru-bda Type of Water Oxidation Catalysts
- 2022
-
In: CCS Chemistry. - : Chinese Chemical Society. - 2096-5745. ; 4:7, s. 2481-2490
-
Journal article (peer-reviewed)abstract
- Isolation of RuIII-bda (17-electron specie) complex with an aqua ligand (2-electron donor) is challenging due to violation of the 18-electron rule. Although considerable efforts have been dedicated to mechanistic studies of water oxidation by the Ru-bda family, the structure and initial formation of the RuIII-bda aqua complex are still controversial. Herein, we challenge this often overlooked step by designing a pocket-shape Ru-based complex 1. The computational studies showed that 1 possesses the crucial hydrophobicity at the RuV(O) state as well as similar probability of access of terminal O to solvent water molecules when compared with classic Ru-bda catalysts. Through characterization of single-crystal structures at the RuII and RuIII states, a pseudo seven-coordinate “ready-to-go” aqua ligand with RuIII...O distance of 3.62 Å was observed. This aqua ligand was also found to be part of a formed hydrogen-bonding network, providing a good indication of how the RuIII-OH2 complex is formed.
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| 40. |
- Liu, Tianqi, et al.
(author)
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Promoting O–O Radical Coupling of Water Oxidation Catalyst via Secondary Interaction
-
Other publication (other academic/artistic)abstract
- Interaction of two metal–oxyl radicals (I2M) mechanism can theoretically provide water oxidation catalysts with lower overpotentials because they avoid forming the high-energy metal-OOH intermediate. However, only two Ru-based catalytic systems have been reported involving intermolecular I2M pathway. Herein, a Ru-pda-type (pda is 1,10-phenanthroline-2,9-dicarboxylate acid) water oxidation catalyst was designed and synthesized. Through synergistic modulation of oxo spin-density and organizational entropy, mechanism switching from the water nucleophilic attack (WNA) to I2M was realized, accompanied by a rate increase of around two orders of magnitude.
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| 41. |
- Liu, Tianqi, et al.
(author)
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Promoting Proton Transfer and Stabilizing Intermediates in Catalytic Water Oxidation via Hydrophobic Outer Sphere Interactions
- 2022
-
In: Chemistry - A European Journal. - : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 28:24
-
Journal article (peer-reviewed)abstract
- The outer coordination sphere of metalloenzyme often plays an important role in its high catalytic activity, however, this principle is rarely considered in the design of man-made molecular catalysts. Herein, four Ru-bda (bda=2,2 '-bipyridine-6,6 '-dicarboxylate) based molecular water oxidation catalysts with well-defined outer spheres are designed and synthesized. Experimental and theoretical studies showed that the hydrophobic environment around the Ru center could lead to thermodynamic stabilization of the high-valent intermediates and kinetic acceleration of the proton transfer process during catalytic water oxidation. By this outer sphere stabilization, a 6-fold rate increase for water oxidation catalysis has been achieved.
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| 42. |
- Meng, Qijun, et al.
(author)
-
Efficient BiVO4 Photoanodes by Postsynthetic Treatment : Remarkable Improvements in Photoelectrochemical Performance from Facile Borate Modification
- 2019
-
In: Angewandte Chemie International Edition. - : Wiley-VCH Verlagsgesellschaft. - 1433-7851 .- 1521-3773. ; 58:52, s. 19027-19033
-
Journal article (peer-reviewed)abstract
- Water-splitting photoanodes based on semiconductor materials typically require a dopant in the structure and co-catalysts on the surface to overcome the problems of charge recombination and high catalytic barrier. Unlike these conventional strategies, a simple treatment is reported that involves soaking a sample of pristine BiVO4 in a borate buffer solution. This modifies the catalytic local environment of BiVO4 by the introduction of a borate moiety at the molecular level. The self-anchored borate plays the role of a passivator in reducing the surface charge recombination as well as that of a ligand in modifying the catalytic site to facilitate faster water oxidation. The modified BiVO4 photoanode, without typical doping or catalyst modification, achieved a photocurrent density of 3.5 mA cm−2 at 1.23 V and a cathodically shifted onset potential of 250 mV. This work provides an extremely simple method to improve the intrinsic photoelectrochemical performance of BiVO4 photoanodes.
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| 43. |
- Meng, Qijun, 1990-, et al.
(author)
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Remarkable synergy of borate and interfacial hole transporter on BiVO4 photoanodes for photoelectrochemical water oxidation
- 2021
-
In: Materials Advances. - : Royal Society of Chemistry (RSC). - 2633-5409. ; 2:13, s. 4323-4332
-
Journal article (peer-reviewed)abstract
- Bismuth vanadate (BiVO4) is one of the most fascinating building blocks for the design and assembly of highly efficient artificial photosynthesis devices for solar water splitting. Our recent report has shown that borate treated BiVO4 (B-BiVO4) results in an improved water oxidation performance. In this study, further improvement of both the photoelectrochemical (PEC) activity and stability of B-BiVO4 was successfully achieved by introducing NiFeV LDHs as an oxygen evolution catalyst and interfacial hole transporter. Benefiting from the synergistic effect of co-catalyst and borate pretreatment, the as-prepared NiFeV/B-BiVO4 exhibited a high photocurrent density of 4.6 mA cm−2 at 1.23 VRHE and an outstanding onset potential of ∼0.2 VRHE with good long-term stability. More importantly, NiFeV was found to play a pivotal role in the critically efficient suppression of charge combination on the BiVO4 surface and acceleration of charge transfer rather than a mere electrocatalyst for water oxidation.
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| 44. |
- Sheng, Xia, et al.
(author)
-
Hierarchical micro-reactor as electrodes for water splitting by metal rod tipped carbon nanocapsule self-assembly in carbonized wood
- 2020
-
In: Applied Catalysis B. - : Elsevier. - 0926-3373 .- 1873-3883. ; 264
-
Journal article (peer-reviewed)abstract
- Materials design of efficient electrochemical micro-reactors is challenging, although hierarchically structured, self-standing electrodes with catalyst arrays offer promise. Herein, catalyst function in compact micro-reactor electrodes is designed by nanostructural tailoring of carbonized wood for efficient water splitting. Specifically, NiFe rod tipped, N-doped graphitic carbon nanocapsule arrays are self-assembled in hierarchical wood, and the benefit of this unique presentation and its promotive effect on accessibility of the catalyst surfaces is apparent. This report also comprises the first wood based micro-reactor electrodes for electrocatalytic water oxidation demonstrating excellent performance. The overpotential for oxygen evolution reaction was as low as 180 mV for 10 mA cm−2 current density and TOFredox was high at a level of 5.8 s−1 (at 370 mV overpotential). This hierarchical electrode can also work as bifunctional catalyst (both as anodic and as cathodic electrode) for total water splitting with a cell potential of 1.49 V for 10 mA cm−2 in alkaline solution, suggestive of their potential also in other electrochemical applications.
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| 45. |
- Timmer, Brian, et al.
(author)
-
Electronic Influence of the 2,2 '-Bipyridine-6,6 '-dicarboxylate Ligand in Ru-Based Molecular Water Oxidation Catalysts
- 2021
-
In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:2, s. 1203-1208
-
Journal article (peer-reviewed)abstract
- Water provides an ideal source for the production of protons and electrons required for generation of renewable fuels. Among the most-prominent electrocatalysts capable of water oxidation at low overpotentials are Ru(bda)L-2-type catalysts. Although many studies were dedicated to the investigation of the influence of structural variations, the true implication of the bda backbone on catalysis remains mostly unclarified. In this work, we further investigated if electronic effects are contributing to catalysis by Ru(bda)(pic)(2) or if the intrinsic catalytic activity mainly originates from the structural features of the ligand. Through introduction of pyrazines in the bda backbone, forming Ru(N-1-bda)(pic)(2) and Ru(N-2-bda)(pic)(2), electronic differences were maximized while minimizing changes in the geometry and other intermolecular interactions. Through a combination of electrochemical analysis, chemical oxygen evolution, and density functional theory calculations, we reveal that the catalytic activity is unaffected by the electronic features of the backbone and that the unique bimolecular reactivity of the Ru(bda)L-2 family of catalysts thus purely depends on the spatial geometry of the ligand.
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| 46. |
- Timmer, Brian, et al.
(author)
-
Electronic Influence of the 2,2′-Bipyridine-6,6′-dicarboxylate Ligand in Ru-based Type Water Oxidation Catalysts
-
Other publication (other academic/artistic)abstract
- Water provides an ideal source for the production of protons and electrons required for generation of renewable fuels. Amongst the most prominent electrocatalysts capable of water oxidation at low overpotentials are Ru(bda)L2 type catalysts. Although many studies were dedicated to investigate the influence of structural variations, the true implication of the bda-backbone on catalysis remains mostly unknown. In this work, we investigated if electronic effects are contributing to catalysis by Ru(bda)(pic)2 or if the intrinsic catalytic activity mainly originates from the structural features of the ligand. Through introduction of pyrazines in the bda-backbone, forming Ru(N1-bda)(pic)2 and Ru(N1-bda)(pic)2, electronic differences were maximized whilst minimizing changes in geometry. Through a combination of electrochemical analysis, chemical oxygen evolution and DFT calculations we reveal that the catalytic activity is largely unaffected by the electronic features of the backbone and that the unique reactivity of the Ru(bda)L2 family of catalysts thus originates purely from their spatial geometry and intermolecular interactions.
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| 47. |
- Timmer, Brian, et al.
(author)
-
Off-set Interactions for Low Concentration Water Splitting Catalysis with Ru(bda)L2
-
Other publication (other academic/artistic)abstract
- Production of renewable fuels like hydrogen requires protons and electrons, which can be simultaneously generated through an ideal pathway, i.e., water oxidation. However, detailed molecular level understanding of the formation of the O-O bond is essential for achieving high efficiencies. O-O bond formation with Ru(bda)L2-type catalysts is well-known to proceed through a bimolecular reaction pathway, limiting the potential application of this catalyst at lower concentration. Herein, we report that by simple structural considerations in the axial pyridine ligands high efficiencies have been achieved with mononuclear catalysts, with TOFs as high as 449 ± 24 s-1 at high catalyst concentrations and 31 ± 3 s-1 at only 1 μM catalyst concentration. We propose that introduction of an off-set in the interaction between the two catalytic units reduces the kinetic barrier of the second-order O-O bond formation, maintaining a longer first order dependence on the catalyst. This hypothesis, combined with the previously proposed π-π interactions, further rationalizes the high activity observed for Ru(bda)(isoq)2 type catalysts and offers inspiration to overcome the limitations of 2nd order catalysis.
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| 48. |
- Timmer, Brian, et al.
(author)
-
Off-Set Interactions of Ruthenium–bda Type Catalysts for Promoting Water-Splitting Performance
- 2021
-
In: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 60:26, s. 14504-14511
-
Journal article (peer-reviewed)abstract
- O−O bond formation with Ru(bda)L2-type catalysts is well-known to proceed through a bimolecular reaction pathway, limiting the potential application of these catalysts at low concentrations. Herein, we achieved high efficiencies with mononuclear catalysts, with TOFs of 460±32 s−1 at high catalyst loading and 31±3 s−1 at only 1 μM catalyst concentration, by simple structural considerations on the axial ligands. Kinetic and DFT studies show that introduction of an off-set in the interaction between the two catalytic units reduces the kinetic barrier of the second-order O−O bond formation, maintaining high catalytic activity even at low catalyst concentrations. The results herein furthermore suggest that π–π interactions may only play a minor role in the observed catalytic activity, and that asymmetry can also rationalize high activity observed for Ru(bda)(isoq)2 type catalysts and offer inspiration to overcome the limitations of 2nd order catalysis.
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| 49. |
- Yi, Jiajia, et al.
(author)
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Electrostatic Interactions Accelerating Water Oxidation Catalysis via Intercatalyst O-O Coupling
- 2021
-
In: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 143:6, s. 2484-2490
-
Journal article (peer-reviewed)abstract
- Intercatalyst coupling has been widely applied in the functional mimics for binuclear synergy in natural metal enzymes. Herein, we introduce two facile and effective design strategies, which facilitate the coupling of two catalytic units via electrostatic interactions. The first system is based on a catalyst molecule functionalized with both a positively charged and a negatively charged group in the structure being able to pair with each other in an antiparallel manner arranged by electrostatic interactions. The other system consists of a mixture of two different of catalysts modified with either positively or negatively charged groups to generate intermo-lecular electrostatic interactions. Applying these designs to Ru(bda) (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylic acid) water-oxidation catalysts improved the catalytic performance by more than an order of magnitude. The intermolecular electrostatic interactions in these two systems were fully identified by H-1 NMR, TEM, SAXS, and electrical conductivity experiments. Molecular dynamics simulations further verified that electrostatic interactions contribute to the formation of prereactive dimers, which were found to play a key role in dramatically improving the catalytic performance. The successful strategies demonstrated here can be used in designing other intercatalyst coupling systems for activation and formation of small molecules and organic synthesis.
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| 50. |
- Yu, Fengshou, et al.
(author)
-
Efficient Electrocatalytic Water Oxidation by a Copper Oxide Thin Film in Borate Buffer
- 2015
-
In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 5:2, s. 627-630
-
Journal article (peer-reviewed)abstract
- A robust water oxidation catalyst based on copper oxide was prepared by facile electrodeposition of Cu2+ from borate buffer solution under near neutral conditions. The Cu-B-i thin film exhibits high activity and long-term stability in Cu2+-free pH 9 borate buffer. A steady current density of 1.2 mA/cm(2) was sustained for at least 10 h at 1.3 V versus NHE without iR compensation, which sets a new benchmark for copper-based OEC.
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