| 1. |
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| 2. |
- 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.
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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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| 3. |
- Cai, Bin, et al.
(author)
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Organic Polymer Dots Photocatalyst for CO2 Reduction in Aqueous Solution
-
Other publication (other academic/artistic)abstract
- Developing low-cost and efficient photocatalysts to convert CO2 into valuable fuels is desirable to realize a carbon-neutral society. In this work, we report that polymer dots (Pdots) of poly[(9,9′-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-thiadiazole)] (PFBT) without adding any extra co-catalyst can photocatalytic reduction of CO2 into CO in aqueous solution, rendering a CO production rate of 57 μmol g-1 h-1 with a detectable selectivity of up to 100%. 5 cycles of CO2 re-purging experiments show no distinct decline in CO amount and reaction rate, indicating the promising photocatalytic stability of PFBT Pdots in photocatalytic CO2 reduction reaction. Mechanistic study reveals that photo-excited PFBT Pdots are reduced by TEOA first, then the reduced PFBT Pdots can bind CO2 and reduce it into CO via their intrinsic active sites. This work highlights the application of organic Pdots for CO2 reduction in the aqueous solution, which therefore provides a strategy to develop highly efficient and environmental-friendly nanoparticular photocatalysts for CO2 reduction.
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| 4. |
- Cai, Bin, et al.
(author)
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Organic Polymer Dots Photocatalyze CO2 Reduction in Aqueous Solution
- 2023
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In: Angewandte Chemie International Edition. - : John Wiley & Sons. - 1433-7851 .- 1521-3773. ; 62:45
-
Journal article (peer-reviewed)abstract
- Developing low-cost and efficient photocatalysts to convert CO2 into valuable fuels is desirable to realize a carbon-neutral society. In this work, we report that polymer dots (Pdots) of poly[(9,9 ' -dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-thiadiazole)] (PFBT), without adding any extra co-catalyst, can photocatalyze reduction of CO2 into CO in aqueous solution, rendering a CO production rate of 57 mu mol g(-1) h(-1 )with a detectable selectivity of up to 100 %. After 5 cycles of CO2 re-purging experiments, no distinct decline in CO amount and reaction rate was observed, indicating the promising photocatalytic stability of PFBT Pdots in the photocatalytic CO2 reduction reaction. A mechanistic study reveals that photoexcited PFBT Pdots are reduced by sacrificial donor first, then the reduced PFBT Pdots can bind CO(2 )and reduce it into CO via their intrinsic active sites. This work highlights the application of organic Pdots for CO2 reduction in aqueous solution, which therefore provides a strategy to develop highly efficient and environmentally friendly nanoparticulate photocatalysts for CO2 reduction.
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| 5. |
- Cheng, Fangwen, et al.
(author)
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Interfacial Property Tuning Enables Copper Electrodes in High-Performance n-i-p Perovskite Solar Cells
- 2023
-
In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 145:36, s. 20081-20087
-
Journal article (peer-reviewed)abstract
- Developing cost-effective metal electrodes is essential for reducing the overall cost of perovskite solar cells (PSCs). Although copper is highly conductive and economical, it is rarely used as a positive electrode in efficient n-i-p PSCs due to its unmatched Fermi level and low oxidation threshold. We report herein that modification for the inner surface of electrodes using mercaptopyridine-based molecules readily tunes the electronic and chemical properties of copper, which has been achieved by fine-tuning the substituents of mercaptopyridines. The systematic adjustment for the Fermi level and oxidation potential of copper facilitates interfacial hole extraction and enhances the oxidation resistance of copper electrodes, which enables pure copper electrodes to be used in high-performance n-i-p PSCs with different hole transport materials. The resulting PSCs with copper electrodes display excellent power conversion efficiency and long-term stability, even comparable to those of the gold electrodes, showing great potential in the manufacturing and commercialization of PSCs.
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| 6. |
- Fan, Ting, et al.
(author)
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Why Is There a Barrier in the Coupling of Two Radicals in the Water Oxidation Reaction?
- 2016
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 6:12, s. 8308-8312
-
Journal article (peer-reviewed)abstract
- Two radicals can form a bond without an energetic barrier. However, the radical coupling mechanism in ruthenium catalyzed water oxidation has been found to be associated with substantial activation energies. Here we have investigated the coupling reaction of [Ru=O(bda)L-2](+) catalysts with different axial L ligands. The interaction between the two oxo radical moieties at the Ru(V) state was found to have a favorable interaction in the transition state in comparison to the prereactive complex. To further understand the existence of the activation energy, the activation energy has been decomposed into distortion energy and interaction energy. No correlation between the experimental rates and the calculated coupling barriers of different axial L was found, showing that more aspects such as solvation, supramolecular properties, and solvent dynamics likely play important roles in the equilibrium between the free Ru-v=0 monomer and the [Ru-v=O center dot center dot center dot O=Ru-v] dimer. On the basis of our findings, we give general guidelines for the design of catalysts that operate by the radical coupling mechanism.
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| 7. |
- Fu, Xianbiao, et al.
(author)
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High-Entropy Alloy Nanosheets for Fine-Tuning Hydrogen Evolution
- 2022
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 12:19, s. 11955-11959
-
Journal article (peer-reviewed)abstract
- The electrolysis of water is promising for hydrogen production. The development of high-performance and low-cost hydrogen evolution reaction (HER) electrocatalysts is particularly important for the wide application of water electrolyzers. Tuning the hydrogen binding energy (HBE) of materials is an effective way to optimize the HER electrocatalysts, particularly for applications in an acidic environment. Here, we report the discovery of a Pt-free combination, PdMoGaInNi, which has the HBE optimum, via computer-facilitated screening. As the exploratory example of the two-dimensional high-entropy alloy (HEA) for HER, the PdMoGaInNi HEA nanosheets were synthesized to realize the predicted Pt-free combination with optimal HBE. The PdMoGaInNi HEA nanosheets exhibit a high HER activity with low overpotentials of 13 mV at 10 mA cm-2, outperforming commercial Pd/C and Pt/C catalysts. Given the high entropy, lattice distortion, and sluggish diffusion effects of HEA, the PdMoGaInNi shows great long-term durability for at least 200 h in a proton exchange membrane water electrolyzer.
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| 8. |
- Guo, Yaxiao, et al.
(author)
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Molybdenum and boron synergistically boosting efficient electrochemical nitrogen fixation
- 2020
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In: Nano Energy. - : Elsevier Ltd. - 2211-2855 .- 2211-3282. ; 78
-
Journal article (peer-reviewed)abstract
- Ammonia production consumes ~2% of the annual worldwide energy supply, therefore strategic alternatives for the energy-intensive ammonia synthesis through the Haber-Bosch process are of great importance to reduce our carbon footprint. Inspired by MoFe-nitrogenase and the energy-efficient and industrially feasible electrocatalytic synthesis of ammonia, we herein establish a catalytic electrode for artificial nitrogen fixation, featuring a carbon fiber cloth fully grafted by boron-doped molybdenum disulfide (B-MoS2/CFC) nanosheets. An excellent ammonia production rate of 44.09 μg h–1 cm–2 is obtained at −0.2 V versus the reversible hydrogen electrode (RHE), whilst maintaining one of the best reported Faradaic efficiency (FE) of 21.72% in acidic aqueous electrolyte (0.1 M HCl). Further applying a more negative potential of −0.25 V renders the best ammonia production rate of 50.51 μg h–1 cm–2. A strong-weak electron polarization (SWEP) pair from the different electron accepting and back-donating capacities of boron and molybdenum (2p shell for boron and 5d shell for molybdenum) is proposed to facilitate greatly the adsorption of non-polar dinitrogen gas via N≡N bond polarization and the first protonation with large driving force. In addition, for the first time a visible light driven photo-electrochemical (PEC) cell for overall production of ammonia, hydrogen and oxygen from water + nitrogen, is demonstrated by coupling a bismuth vanadate BiVO4 photo-anode with the B-MoS2/CFC catalytic cathode.
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| 9. |
- Huang, Xiaofeng, et al.
(author)
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Solvent Gaming Chemistry to Control the Quality of Halide Perovskite Thin Films for Photovoltaics
- 2022
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In: ACS CENTRAL SCIENCE. - : American Chemical Society (ACS). - 2374-7943 .- 2374-7951. ; 8:7, s. 1008-1016
-
Journal article (peer-reviewed)abstract
- Research on solvent chemistry, particularly for halide perovskite intermediates, has been advancing the development of perovskite solar cells (PSCs) toward commercial applications. A predictive understanding of solvent effects on the perovskite formation is thus essential. This work systematically discloses the relationship among the basicity of solvents, solvent-contained intermediate structures, and intermediate-to-perovskite alpha-FAPbI(3) evolutions. Depending on their basicity, solvents exhibit their own favorite bonding selection with FA(+) or Pb2+ cations by forming either hydrogen bonds or coordination bonds, resulting in two different kinds of intermediate structures. While both intermediates can be evolved into alpha-FAPbI(3) below the delta-to-alpha thermodynamic temperature, the hydrogen-bond-favorable kind could form defect-less alpha-FAPbI(3) via sidestepping the break of strong coordination bonds. The disclosed solvent gaming mechanism guides the solvent selection for fabricating high-quality perovskite films and thus high-performance PSCs and modules.
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| 10. |
- Huang, Xiaofeng, et al.
(author)
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Solvent racing crystallization : Low-solvation dispersion cosolvents for high-quality halide perovskites in photovoltaics
- 2023
-
In: Joule. - : Elsevier. - 2542-4351. ; 7:7, s. 1556-1573
-
Journal article (peer-reviewed)abstract
- The solvation capacity of dispersion solvents plays a crucial role in the solution processing of metal halide perovskites. For instance, N,N-dimethylformamide (DMF), a widely used dispersion solvent, possesses high solvation capacity but often generates suboptimal film quality due to slow crystallization kinetics. We propose using low-solvation binary cosolvents (nitrile-and ether-type solvents) to achieve a balance between solvation (i.e., sufficient solubility of precursors) and desolvation (i.e., rapid crystallization of films) pro-cesses during perovskite synthesis. The polarity and hydrogen -bonding property of these cosolvents synergistically enhance their solvation capacity, facilitating perovskite precursor dissolution. Moreover, the low-solvation cosolvents accelerate the crystalliza-tion of well-defined intermediate films, yielding higher-quality pe-rovskites than those synthesized with DMF. The optimized modules achieved an active-area efficiency of 22.27%, with a certified aper-ture-area efficiency of 16.10% and corresponding active-area effi-ciency of 20.75%. This research on solvation regulation provides universal guidelines for innovatively preparing high-quality halide perovskites.
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| 11. |
- Li, Yingzheng, et al.
(author)
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Influence of O-O formation pathways and charge transfer mediator on lipid bilayer membrane-like photoanodes for water oxidation
- 2024
-
In: Journal of Energy Chemistry. - : Elsevier. - 2095-4956 .- 2096-885X. ; 93, s. 526-537
-
Journal article (peer-reviewed)abstract
- Inspired by the function of crucial components in photosystem II (PSII), electrochemical and dyesensitized photoelectrochemical (DSPEC) water oxidation devices were constructed by the selfassembly of well-designed amphipathic Ru(bda)-based catalysts (bda = 2,2'-bipyrdine-6,6'-dicarbonoxyl acid) and aliphatic chain decorated electrode surfaces, forming lipid bilayer membrane (LBM)-like structures. The Ru(bda) catalysts on electrode-supported LBM films demonstrated remarkable water oxidation performance with different O-O formation mechanisms. However, compared to the slow charge transfer process, the O-O formation pathways did not determine the PEC water oxidation efficiency of the dyesensitized photoanodes, and the different reaction rates for similar catalysts with different catalytic paths did not determine the PEC performance of the DSPECs. Instead, charge transfer plays a decisive role in the PEC water oxidation rate. When an indolo[3,2-b] carbazole derivative was introduced between the Ru (bda) catalysts and aliphatic chain-modified photosensitizer in LBM films, serving as a charge transfer mediator for the tyrosine-histidine pair in PSII, the PEC water oxidation performance of the corresponding photoanodes was dramatically enhanced.
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| 12. |
- Li, Yingzheng, et al.
(author)
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Switching the O-O Bond Formation Pathways of Ru-pda Water Oxidation Catalyst by Third Coordination Sphere Engineering
- 2021
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In: RESEARCH. - : American Association for the Advancement of Science (AAAS). - 2639-5274. ; 2021
-
Journal article (peer-reviewed)abstract
- Water oxidation is a vital anodic reaction for renewable fuel generation via electrochemical- and photoelectrochemical-driven water splitting or CO2 reduction. Ruthenium complexes, such as Ru-bda family, have been shown as highly efficient water-oxidation catalysts (WOCs), particularly when they undergo a bimolecular O-O bond formation pathway. In this study, a novel Ru(pda)-type (pda(2-) = 1,10-phenanthroline-2,9-dicarboxylate) molecular WOC with 4-vinylpyridine axial ligands was immobilized on the glassy carbon electrode surface by electrochemical polymerization. Electrochemical kinetic studies revealed that this homocoupling polymer catalyzes water oxidation through a bimolecular radical coupling pathway, where interaction between two Ru(pda)-oxyl moieties (I2M) forms the O-O bond. The calculated barrier of the I2M pathway by density-functional theory (DFT) is significantly lower than the barrier of a water nucleophilic attack (WNA) pathway. By using this polymerization strategy, the Ru centers are brought closer in the distance, and the O-O bond formation pathway by the Ru (pda) catalyst is switched from WNA in a homogeneous molecular catalytic system to I2M in the polymerized film, providing some deep insights into the importance of third coordination sphere engineering of the water oxidation catalyst.
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| 13. |
- Liu, Tianqi, et al.
(author)
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Bioinspired Active Site with a Coordination-Adaptive Organosulfonate Ligand for Catalytic Water Oxidation at Neutral pH
- 2023
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 145:21, s. 11818-11828
-
Journal article (peer-reviewed)abstract
- Many enzymes use adaptive frameworks to preorganize substrates, accommodate various structural and electronic demands of intermediates, and accelerate related catalysis. Inspired by biological systems, a Ru-based molecular water oxidation catalyst containing a configurationally labile ligand [2,2′:6′,2″-terpyridine]-6,6″-disulfonate was designed to mimic enzymatic framework, in which the sulfonate coordination is highly flexible and functions as both an electron donor to stabilize high-valent Ru and a proton acceptor to accelerate water dissociation, thus boosting the catalytic water oxidation performance thermodynamically and kinetically. The combination of single-crystal X-ray analysis, various temperature NMR, electrochemical techniques, and DFT calculations was utilized to investigate the fundamental role of the self-adaptive ligand, demonstrating that the on-demand configurational changes give rise to fast catalytic kinetics with a turnover frequency (TOF) over 2000 s–1, which is compared to oxygen-evolving complex (OEC) in natural photosynthesis.
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| 14. |
- 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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| 15. |
- Wang, Ying, et al.
(author)
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Nucleophilic Attack by OH2 or OH- : A Detailed Investigation on pH Dependent Performance of a Ru Catalyst
- 2019
-
In: Organometallics. - : AMER CHEMICAL SOC. - 0276-7333 .- 1520-6041. ; 38:6, s. 1264-1268
-
Journal article (peer-reviewed)abstract
- The considerable rate enhancements along with the increase in pH values may be due to the direct involvement of hydroxide anion in attacking electrophilic [Ru-V(tda)(py)(2)O](+) (1; tda = [2,2':6',2 ''-terpyridine]-6,6 ''-dicarboxylate, py = pyridine). The enhanced reaction rate is well in agreement with the descending activation barriers in our calculation. The addition of four extra water molecules in the geometry optimization plays a key role in stabilizing hydroxide anion as well as building a reasonable hydrogen-bonding network, and three of these molecules are required to stabilize the OH as an anion instead of a radical.
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| 16. |
- Yang, Hao, et al.
(author)
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Intramolecular hydroxyl nucleophilic attack pathway by a polymeric water oxidation catalyst with single cobalt sites
- 2022
-
In: Nature Catalysis. - : Springer Nature. - 2520-1158. ; 5:5, s. 414-429
-
Journal article (peer-reviewed)abstract
- Exploration of efficient water oxidation catalysts (WOCs) is the primary challenge in conversion of renewable energy into fuels. Here we report a molecularly well-defined heterogeneous WOC with Aza-fused, pi-conjugated, microporous polymer (Aza-CMP) coordinated single cobalt sites (Aza-CMP-Co). The single cobalt sites in Aza-CMP-Co exhibited superior activity under alkaline and near-neutral conditions. Moreover, the molecular nature of the isolated catalytic sites makes Aza-CMP-Co a reliable model for studying the heterogeneous water oxidation mechanism. By a combination of experimental and theoretical results, a pH-dependent nucleophilic attack pathway for O-O bond formation was proposed. Under alkaline conditions, the intramolecular hydroxyl nucleophilic attack (IHNA) process with which the adjacent -OH group nucleophilically attacks Co4+=O was identified as the rate-determining step. This process leads to lower activation energy and accelerated kinetics than those of the intermolecular water nucleophilic attack (WNA) pathway. This study provides significant insights into the crucial function of electrolyte pH in water oxidation catalysis and enhancement of water oxidation activity by regulation of the IHNA pathway.
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| 17. |
- Yang, Jing, et al.
(author)
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From Ru-bda to Ru-bds : a step forward to highly efficient molecular water oxidation electrocatalysts under acidic and neutral conditions
- 2021
-
In: Nature Communications. - : Springer Nature. - 2041-1723. ; 12:1
-
Journal article (peer-reviewed)abstract
- Significant advances during the past decades in the design and studies of Ru complexes with polypyridine ligands have led to the great development of molecular water oxidation catalysts and understanding on the O-O bond formation mechanisms. Here we report a Ru-based molecular water oxidation catalyst [Ru(bds)(pic)(2)] (Ru-bds; bds(2-) = 2,2-bipyridine-6,6 ' -disulfonate) containing a tetradentate, dianionic sulfonate ligand at the equatorial position and two 4-picoline ligands at the axial positions. This Ru-bds catalyst electrochemically catalyzes water oxidation with turnover frequencies (TOF) of 160 and 12,900s(-1) under acidic and neutral conditions respectively, showing much better performance than the state-of-art Ru-bda catalyst. Density functional theory calculations reveal that (i) under acidic conditions, the high valent Ru intermediate Ru-V=O featuring the 7-coordination configuration is involved in the O-O bond formation step; (ii) under neutral conditions, the seven-coordinate Ru-IV=O triggers the O-O bond formation; (iii) in both cases, the I2M (interaction of two M-O units) pathway is dominant over the WNA (water nucleophilic attack) pathway. Developing efficient molecular water oxidation catalysts for artificial photosynthesis is a challenging task. Here the authors introduce a ruthenium based complex with negatively charged sulfonate groups to effectively drive water oxidation under both acidic and neutral conditions.
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| 18. |
- 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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| 19. |
- You, Pengyao, et al.
(author)
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Interfacial oxidized Pd species dominate catalytic hydrogenation of polar unsaturated bonds
- 2024
-
In: Nano Reseach. - : Springer. - 1998-0124 .- 1998-0000. ; 17:1, s. 235-244
-
Journal article (peer-reviewed)abstract
- The determination of catalytically active sites is crucial for the design of efficient and stable catalysts toward desired reactions. However, the complexity of supported noble metal catalysts has led to controversy over the locations of catalytically active sites (e.g., metal, support, and metal/support interface). Here we develop a structurally controllable catalyst system (Pd/SBA-15) to reveal the catalytic active sites for the selective hydrogenation of ketones to alcohol using acetophenone hydrogenation as model reaction. Systematic investigations demonstrated that unsupported Pd nanocrystals have no catalytic activity for acetophenone hydrogenation. However, oxidized Pd species were catalytically highly active for acetophenone hydrogenation. The catalytic activity decreased with the decreased oxidation state of Pd. This work provides insights into the hydrogenation mechanism of ketones but also other unsaturated compounds containing polar bonds, e.g., nitrobenzene, N-benzylidene-benzylamine, and carbon dioxide.
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| 20. |
- Zhan, Shaoqi, et al.
(author)
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Capturing the Role of Explicit Solvent in the Dimerization of Ru-V(bda) Water Oxidation Catalysts
- 2017
-
In: Angewandte Chemie International Edition. - : Wiley-VCH Verlagsgesellschaft. - 1433-7851 .- 1521-3773. ; 56:24, s. 6962-6965
-
Journal article (peer-reviewed)abstract
- A ground-breaking empirical valence bond study for a soluble transition-metal complex is presented. The full reaction of catalyst monomers approaching and reacting in the Ru-V oxidation state were studied. Analysis of the solvation shell in the reactant and along the reaction coordinate revealed that the oxo itself is hydrophobic, which adds a significant driving force to form the dimer. The effect of the solvent on the reaction between the prereactive dimer and the product was small. The solvent seems to lower the barrier for the isoquinoline (isoq) complex while it is increased for pyridines. By comparing the reaction in the gas phase and solution, the proposed p-stacking interaction of the isoq ligands is found to be entirely driven by the water medium.
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| 21. |
- Zhan, Shaoqi, et al.
(author)
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Dynamics and Reactions of Molecular Ru Catalysts at Carbon Nanotube-Water Interfaces
- 2018
-
In: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 140:24, s. 7498-7503
-
Journal article (peer-reviewed)abstract
- Immobilization of molecular catalysts to electrode surfaces can improve the recyclability and electron transfer rates. The drawback is that most experimental techniques and theoretical methods are not applicable. Here we present results from a study of a ruthenium water oxidation catalyst [(RuO)-O-V(bda)L-2] in explicit water at a carbon nanotube water interface, forming the key O-O bond between two 128 atom catalysts, all fully dynamically. Our methodology is based on a recently developed empirical valence bond (EVB) model. We follow the key steps of the reaction including diffusion of the catalysts at the interface, formation of the prereactive dimer, and the bond formation between the two catalysts. On the basis of the calculated parameters, we compute the turnover frequency (TOF) at the experimental loading, in excellent agreement with the experiments. The key O-O bond formation was significantly retarded at the surface, and limiting components were identified that could be improved by catalyst modification.
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| 22. |
- Zhan, Shaoqi, et al.
(author)
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Dynamics with Explicit Solvation Reveals Formation of the Prereactive Dimer as Sole Determining Factor for the Efficiency of Ru(bda)L-2 Catalysts
- 2018
-
In: ACS Catalysis. - : AMER CHEMICAL SOC. - 2155-5435. ; 8:9, s. 8642-8648
-
Journal article (peer-reviewed)abstract
- This report describes all key steps in the O-O bond formation from two separated [Ru-V=O(bda)L-2](+) cations to form the dinuclear [(bda)L2RuIV-O-Ru-IV(bda)L-2](2+) in explicit solvent. The three steps involve the diffusion of the catalysts in the water phase, formation of the prereactive dimer, and the bond formation between the two catalysts. On the basis of the calculated parameters, we compute the rate constant of two catalysts with different L-ligands, isoquinoline and picoline, and the computed values are in excellent agreement with the experimental ones. The interaction of the axial ligands is key to the improved rates of the larger ligand, mainly by facilitating the formation of the prereactive dimer from the solvated monomer. By comparing the binding free energy of hydrophilic Ru-IV-OH and hydrophobic Ru-V=O, the hydrophobic driving force of Ru-V=O in this system has been estimated to 1 kcal mol(-1).
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| 23. |
- Zhan, Shaoqi, et al.
(author)
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Hydrophobic/Hydrophilic Directionality Affects the Mechanism of Ru-Catalyzed Water Oxidation Reaction
- 2020
-
In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 10:22, s. 13364-13370
-
Journal article (peer-reviewed)abstract
- From the study of supramolecular dimers of [(RuO)-O-V(pda)](+) (pda = 1,10-phenanthroline-2,9-dicarboxylic acid) and [(RuO)-O-V(bda)](+) (bda = 2,2'-bipyridine-6,6'-dicarboxylate) complexes, the O-O bond-forming intermediates in water oxidation, we found orientational distinction induced by the pda and bda ligands. The bda complex prefers the front-to-front geometry, while the pda complex favors the front-to-back geometry in the formation of prereactive geometry. In the bda complex, the hydrophobic oxo will point at another oxo with the bda directed toward water, which favors the I2M mechanism. In the pda complex, the hydrophobic oxo instead is directed toward a more hydrophobic phenanthroline moiety of the pda of another species, which disfavors I2M. The binding free energy of the nonproductive front-to-back of pda is 3 kcal mol(-1) more stable than that of the prereactive dimer. This incorrect orientation leads to an additional rearrangement required before the O-O bond can be formed. Estimation of the rate constant shows 2 orders of magnitude lower reactivity for the I2M mechanism of the pda complex relative to the bda complex, which makes the water nucleophilic attack mechanism competitive.
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| 24. |
- Zhan, Shaoqi, et al.
(author)
-
The Carboxylate Ligand as an Oxide Relay in Catalytic Water Oxidation.
-
Journal article (other academic/artistic)abstract
- Carboxylate groups have diverse functionality in ligands of transiton metal catalysts. Here we present a conceptuallydifferent function of the carboxylates – the oxide relay. It functions by providing an intramolecular nucleophilic oxygen close tothe oxo group to facilitate O-O bond formation, and at a later stage a remote electrophilic center to facilitate OH- nucleophilic attack.EVB-MD models were generated for key bond forming steps, diffusion coefficients and binding free energies from potentialof mean force estimations were calculated from MD simulations, activation free energies of chemical steps were calculated usingdensity functional theory. The catalyst studied is the extremely active Ru(tda)(py)2 water oxidation catalyst. The combination ofsimulation methods allowed for estimation of the turnover frequencies, which were within one order of magnitude from the experimentalresults at different pH values. From the calculated reaction rates we find that at low pH the OH- anion nucleophilic attack isthe rate-limiting step, which changes at high pH to the O-O bond formation step. Both steps are extremely rapid and key to theefficiency is the oxide relay functionality of a pendant carboxylate group. The functionality was discovered for a ruthenium catalyst,but since there is nothing in the mechanism restricting it to this metal, the oxide relay functionality could open new ways todesign the next generation water oxidation catalysts with improved activity.
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| 25. |
- Zhan, Shaoqi, et al.
(author)
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The Carboxylate Ligand as an Oxide Relay in Catalytic Water Oxidation
- 2019
-
In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 141:26, s. 10247-10252
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Journal article (peer-reviewed)abstract
- Carboxylate groups have diverse functionalities in ligands of transition metal catalysts. Here we present a conceptually different function of the carboxylates: the oxide relay. It functions by providing an intramolecular nucleophilic oxygen close to the oxo group to facilitate O-O bond formation and at a later stage a remote electrophilic center to facilitate OH- nucleophilic attack. Empirical valence bond-molecular dynamics (EVB-MD) models were generated for key bond forming steps, diffusion coefficients and binding free energies from potential of mean force estimations were calculated from molecular dynamics (MD) simulations, activation free energies of chemical steps were calculated using density functional theory (DFT). The catalyst studied is the extremely active Ru(tda)(py)(2) water oxidation catalyst. The combination of simulation methods allowed for estimation of the turnover frequencies, which were within 1 order of magnitude from the experimental results at different pH values. From the calculated reaction rates we find that at low pH the OH- anion nucleophilic attack is the rate limiting step, which changes at high pH to the O-O bond formation step. Both steps are extremely rapid, and key to the efficiency is the oxide relay functionality of a pendant carboxylate group. We cannot exclude all alternative mechanisms and suggest isotope experiments using O-18-labeled water to support or invalidate the oxide relay mechanism. The functionality was discovered for a ruthenium catalyst, but since there is nothing in the mechanism restricting it to this metal, the oxide relay functionality could open new ways to design the next-generation water oxidation catalysts with improved activity.
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| 26. |
- Zhan, Shaoqi, 1988-
(author)
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Theoretical Studies on Water Oxidation Catalysts - from Solvent to Interfaces
- 2019
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Doctoral thesis (other academic/artistic)abstract
- Water splitting contains two half-reactions, the water oxidation reaction and the hydrogen reduction reaction. In water oxidation, protons and electrons will be generated to offer two elemental components for production of fuels, such as H2 and CH3OH. To overcome the overpotential of the reaction, a large amount of water oxidation catalysts (WOCs) have been synthesized. In the second chapter, a variety of homogeneous and heterogenous catalysts have been introduced. The homogeneous catalysts include Ru-based catalysts, Ir-based catalysts, and first-row transition metal-based catalysts. Among these catalysts, a family of Ru(bda)L2 complexes was found in experiment to have a comparable turnover frequency (TOF) at acidic pH with photosystem II. A similar catalyst, Ru(tda)(py)2, was found to have an impressive TOF of 50 000 s-1 at pH 10.0. The heterogenous catalysts include heterogenous oxide and heterogenized molecular catalysts that catalyze the reaction using either electrochemical driving force or photoelectrochemical driving force.Understanding the details of the mechanism can help to design a better catalyst with high catalytic performance. For this purpose, several theoretical methods have been applied. Density functional theory (DFT) was employed to study the rate limiting reaction in implicit solvent. The empirical valence bond (EVB) method is a powerful tool for describing environment effects. This approach was used to get insight into the solvent and surface effects on the reaction pathway. Molecular dynamics (MD) and potential of mean force (PMF) methods are applied to perform simulations for large systems at long time-scales. The Ru(bda)L2 catalysts have been found to have high TOF, up to 1000 s-1 and react via an I2M (Interaction of two metal centers) pathway. By using B3LYP-D3 functional to study the diradical coupling of the O-O bond formation, we found that there is no intrinsic barrier between the two RuV=O fragments of RuV=O complexes. On the basis of the study of the solvent role on the reaction using an EVB-MD model, the oxo of the RuV=O species was shown to be hydrophobic. The hydrophobic oxo explained why the Ru(bda)L2 complexes proceed the reaction via the I2M pathway. To study the full dimerization of two separated RuV=O species in fully explicit solvent, we calculated the diffusion of individual catalysts from MD simulations, association of pre-reactive dimer from PMF simulations, and the coupling reaction in explicit solvation using the EVB approach. The formation of the prereactive dimer was found to be the sole determining factor for the efficiency of the Ru(bda)L2 catalysts. In the study of four Ru complexes with different equatorial ligands, the secondary coordination environments, such as flexibility, hydrophilicity were proposed to be the affecting the different catalytic pathways.To make an efficient electrocatalyst, the Ru(bda)L2 catalyst has been modified by Sun and co-workers with pyrene groups at the axial L-ligands to be adhered on the CNT functionalized electrodes. A computational model of the RuV=O catalyst tethered on the CNT surface was built to study the O-O bond formation in heterogenous system. By using the same combination of MD, PMF, and EVB, we studied the full dimerization reaction of the catalyst at CNT-water interfaces with full dynamics. The reasons for the lower the TOF of the surface catalyst and methods to improve the lower TOF were addressed in this study.With the pH dependent Ru(tda)(py)2 complex, we used the same combination methods and proposed a conceptually new function of the dangling carboxylate – the oxide relay. The oxide relay provides a highly nucleophilic oxygen atom close to the oxo to facilitate the O-O bond formation at the first step, and a highly electrophilic center to react with the OH- even at neutral pH at the second step. The rate-limiting step is the O-O bond formation at high pH, OH- nucleophilic attack at neutral pH.In summary, several key properties of the water oxidation catalyzed by Ru-based complexes, such as solvent and surface effects, hydrophobicity, and oxide relay have been investigated in detail by using several computational techniques. Our studies can shed light on the design of molecular WOCs with high catalytic activity and will help the development of artificial photosysnthesis devices.
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| 27. |
- Zhang, Biaobiao, 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
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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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| 28. |
- Zhang, Biaobiao, et al.
(author)
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Switching O–O bond formation mechanism between WNA and I2M pathways by modifying the Ru-bda backbone ligands of water-oxidation catalysts
- 2021
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In: Journal of Energy Challenges and Mechanics. - : Elsevier B.V.. - 2056-9386. ; 54, s. 815-821
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Journal article (peer-reviewed)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 (H2bda = 2,2ʹ-bipyridine-6,6ʹ-dicarboxylic acid), Ru-pda (H2pda = 1,10-phenanthroline-2,9-dicarboxylic acid), and Ru-biqa (H2biqa = (1,1ʹ-biisoquinoline)-3,3ʹ-dicarboxylic acid), we emphasized that seven coordination clearly determines presence of RuV[dbnd]O with high spin density on the ORuV[dbnd]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[dbnd]O···O[dbnd]RuV], which may be 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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| 29. |
- Zhang, Wuyong, et al.
(author)
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Coordinative Stabilization of Single Bismuth Sites in a Carbon-Nitrogen Matrix to Generate Atom-Efficient Catalysts for Electrochemical Nitrate Reduction to Ammonia
- 2023
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In: Advanced Science. - : John Wiley & Sons. - 2198-3844. ; 10:28
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Journal article (peer-reviewed)abstract
- Electrochemical nitrate reduction to ammonia powered by renewable electricity is not only a promising alternative to the established energy-intense and non-ecofriendly Haber-Bosch reaction for ammonia generation but also a future contributor to the ever-more important denitrification schemes. Nevertheless, this reaction is still impeded by the lack of understanding for the underlying reaction mechanism on the molecular scale which is necessary for the rational design of active, selective, and stable electrocatalysts. Herein, a novel single-site bismuth catalyst (Bi-N-C) for nitrate electroreduction is reported to produce ammonia with maximum Faradaic efficiency of 88.7% and at a high rate of 1.38 mg h(-1) mg(cat)(-1) at -0.35 V versus reversible hydrogen electrode (RHE). The active center (described as BiN2C2) is uncovered by detailed structural analysis. Coupled density functional theory calculations are applied to analyze the reaction mechanism and potential rate-limiting steps for nitrate reduction based on the BiN2C2 model. The findings highlight the importance of model catalysts to utilize the potential of nitrate reduction as a new-generation nitrogen-management technology based on the construction of efficient active sites.
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| 30. |
- Zhang, Yazhou, et al.
(author)
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Heterogeneous Hydrogenation with Hydrogen Spillover Enabled by Nitrogen Vacancies on Boron Nitride-Supported Pd Nanoparticles
- 2023
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In: Angewandte Chemie International Edition. - : Wiley-VCH Verlagsgesellschaft. - 1433-7851 .- 1521-3773. ; 62:9
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Journal article (peer-reviewed)abstract
- Heterogeneous hydrogenation with hydrogen spillover has been demonstrated as an effective route to achieve high selectivity towards target products. More effort should be paid to understand the complicated correlation between the nature of supports and hydrogenation involving hydrogen spillover. Herein, we report the development of the hydrogenation system of hexagonal boron nitride (h-BN)-supported Pd nanoparticles for the hydrogenation of aldehydes/ketones to alcohols with hydrogen spillover. Nitrogen vacancies in h-BN determine the feasibility of hydrogen spillover from Pd to h-BN. The hydrogenation of aldehydes/ketones with hydrogen spillover from Pd proceeds on nitrogen vacancies on h-BN. The weak adsorption of alcohols to h-BN inhibits the deep hydrogenation of aldehydes/ketones, thus leading to high catalytic selectivity to alcohols. Moreover, the hydrogen spillover-based hydrogenation mechanism makes the catalyst system exhibit a high tolerance to CO poisoning.
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| 31. |
- Zhang, Zhicheng, et al.
(author)
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The Editorial
- 2023
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In: Chemistry - An Asian Journal. - : John Wiley & Sons. - 1861-4728 .- 1861-471X. ; 18:6
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Journal article (other academic/artistic)abstract
- Surface and interface engineering has been considered as a promising strategy to enhance the performance of catalysts towards CO2 reduction. In their editorial to this special collection, guest editors Zhicheng Zhang, Zhen Zhang, Zhenyu Sun, Shaoqi Zhan and Guoxiong Wang provide a brief overview of this field and highlight the state-of-the-art contributions featured in this special collection.
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| 32. |
- Zhao, Ziqi, et al.
(author)
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Molecular Engineering of Photocathodes based on Polythiophene Organic Semiconductors for Photoelectrochemical Hydrogen Generation
- 2021
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:34, s. 40602-40611
-
Journal article (peer-reviewed)abstract
- Organic semiconductors provide significant potentials for the construction of photoelectrochemical (PEC) cells for solar hydrogen production because of their highly tunable properties. Herein, on carbon fiber paper (CFP) surface, pyridyl (Py), and 4,4'-bipyridin-1-ium (Py-2(+)) groups were introduced into polythiophene (pTH) semiconductor by electrochemical copolymerization, respectively. After assembly with the Co(dmgBF(2))(2) type catalyst (CoB, dmgBF(2) = difluoroboryldimethylglyoximate), the CoB@Py-2(+)-pTH/CFP photocathode displayed nearly twice the photocurrent enhancement (550 mu A cm(-2) at 0.15 V vs reversible hydrogen electrode, RHE) comparing to that generated by the CoB@Py-pTH/CFP photocathode (290 mu A cm(-2) at 0.15 V vs RHE) for light-driven H-2 generation under AM 1.5 solar illumination. Investigation of the mechanism revealed that the introduction of the positively charged pyridinium groups could improve the intrinsic Co(dmgBF(2))(2) catalyst activity for the H-2 generation reaction. Meanwhile, the positively charged pyridinium groups serve as p-type dopants to increase the semiconductor bulk charge transfer rate and act as electron transfer mediators to promote the interfacial charge transfer kinetics between the catalyst and the pTH-based organic semiconductor.
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| 33. |
- Zhou, Yue, et al.
(author)
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Stabilized and Controlled Release of Radicals within Copper Formate-Based Nanozymes for Biosensing
- 2023
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 15:37, s. 43431-43440
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Journal article (peer-reviewed)abstract
- Fenton-like radical processes are widely utilized to explain catalytic mechanisms of peroxidase-like nanozymes, which exhibit remarkable catalytic activity, cost-effectiveness, and stability. However, there is still a need for a comprehensive understanding of the formation, stabilization, and transformation of such radicals. Herein, a copper formate-based nanozyme (Cuf-TMB) was fabricated via a pre-catalytic strategy under ambient conditions. The as-prepared nanozyme shows comparable catalytic activity (K-m, 1.02 x 10(-5) mM(-1); K-cat, 3.09 x 10(-2) s(-1)) and kinetics to those of natural peroxidase toward H2O2 decomposition. This is attributed to the feasible oxidation by *OH species via the *O intermediate, as indicated by density functional theory calculations. The key .OH radicals were detected to be stable for over 52 days and can be released in a controlled manner during the catalytic process via in situ electron spin-resonance spectroscopy measurements. Based on the understanding, an ultrasensitive biosensing platform was constructed for the sensitive monitoring of biochemical indicators in clinic settings.
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| 34. |
- Zhuo, Q., et al.
(author)
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Tuning the O–O bond formation pathways of molecular water oxidation catalysts on electrode surfaces via second coordination sphere engineering
- 2021
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In: Cuihuà xuébào. - : Science Press. - 0253-9837 .- 1872-2067. ; 42:3, s. 460-469
-
Journal article (peer-reviewed)abstract
- A molecular [Ru(bda)]-type (bda = 2,2’-bipyridine-6,6’-dicarboxylate) water oxidation catalyst with 4-vinylpyridine as the axial ligand (Complex 1) was immobilized or co-immobilized with 1-(trifluoromethyl)-4-vinylbenzene (3F) or styrene (St) blocking units on the surface of glassy carbon (GC) electrodes by electrochemical polymerization, in order to prepare the corresponding poly-1@GC, poly-1+P3F@GC, and poly-1+PSt@GC functional electrodes. Kinetic measurements of the electrode surface reaction revealed that [Ru(bda)] triggers the O–O bond formation via (1) the radical coupling interaction between the two metallo-oxyl radicals (I2M) in the homo-coupling polymer (poly-1), and (2) the water nucleophilic attack (WNA) pathway in poly-1+P3F and poly-1+PSt copolymers. The comparison of the three electrodes revealed that the second coordination sphere of the water oxidation catalysts plays vital roles in stabilizing their reaction intermediates, tuning the O–O bond formation pathways and improving the water oxidation reaction kinetics without changing the first coordination structures.
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