| 1. |
- Liu, Aijie, et al.
(författare)
-
In Situ Preparation and Immobilization of Semiconducting Polymer Dots on Microbeads for Efficient and Stable Photocatalytic Hydrogen Evolution
- 2021
-
Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 4:5, s. 4308-4312
-
Tidskriftsartikel (refereegranskat)abstract
- Organic semiconducting polymers dots (Pdots) have recently shown efficient photocatalytic activity for hydrogen evolution in an aqueous phase. However, colloidal Pdots face problems of aggregation and precipitation during the photocatalytic reaction due to unavoidable collisions between particles, thus resulting in a short catalytic lifetime. In this work, in situ preparation of PFBT Pdots on the surface of microbeads is reported. Results indicate that, with this facile method and support of a template, the photocatalytic properties of PFBT Pdots can be highly enhanced.
|
|
| 2. |
- Tian, Lei, et al.
(författare)
-
Understanding the Role of Surface States on Mesoporous NiO Films
- 2020
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 142:43
-
Tidskriftsartikel (refereegranskat)abstract
- Surface states of mesoporous NiO semiconductor films have particular properties differing from the bulk and are able to dramatically influence the interfacial electron transfer and adsorption of chemical species. To achieve a better performance of NiO-based p-type dye-sensitized solar cells (p-DSCs), the function of the surface states has to be understood. In this paper, we applied a modified atomic layer deposition procedure that is able to passivate 72% of the surface states on NiO by depositing a monolayer of Al2O3. This provides us with representative control samples to study the functions of the surface states on NiO films. A main conclusion is that surface states, rather than the bulk, are mainly responsible for the conductivity in mesoporous NiO films. Furthermore, surface states significantly affect dye regeneration (with I–/I3– as redox couple) and hole transport in NiO-based p-DSCs. A new dye regeneration mechanism is proposed in which electrons are transferred from reduced dye molecules to intra-bandgap states, and then to I3– species. The intra-bandgap states here act as catalysts to assist I3– reduction. A more complete mechanism is suggested to understand the particular hole transport behavior in p-DSCs, in which the hole transport time is independent of light intensity. This is ascribed to the percolation hole hopping on the surface states. When the concentration of surface states was significantly reduced, the light-independent charge transport behavior in pristine NiO-based p-DSCs transformed into having an exponential dependence on light intensity, similar to that observed in TiO2-based n-type DSCs. These conclusions on the function of surface states provide new insight into the electronic properties of mesoporous NiO films.
|
|
| 3. |
- Amaro-Gahete, Juan, et al.
(författare)
-
Catalytic systems mimicking the [FeFe]-hydrogenase active site for visible-light-driven hydrogen production
- 2021
-
Ingår i: Coordination chemistry reviews. - : Elsevier. - 0010-8545 .- 1873-3840. ; 448
-
Forskningsöversikt (refereegranskat)abstract
- A global hydrogen economy could ensure environmentally sustainable, safe and cost-efficient renewable energy for the 21st century. Solar hydrogen production through artificial photosynthesis is a key strategy, and the activity of natural hydrogenase metalloenzymes an inspiration for the design of synthetic catalyst systems. [FeFe]-hydrogenase enzymes, present in anaerobic bacteria and green algae, are the most efficient class of biological catalysts for hydrogen evolution. The enzymes operate in an aqueous environment, utilizing electrons that ultimately stem from photosynthesis as the only energy source. Functional synthetic models of the [FeFe]-hydrogenase enzyme active site have garnered intense interest as potential catalysts for the reduction of protons to molecular hydrogen. Herein, we take an extensive journey through the field of biomimetic hydrogenase chemistry for lightdriven hydrogen production. We open with a brief presentation of the structure and redox mechanism of the natural enzyme. Synthetic methodologies, structural characteristics, and hydrogen generation metrics relevant to the synthetic diiron catalysts ([2Fe2S]) are discussed. We first examine multicomponent photocatalysis systems with the [2Fe2S] cluster, followed by photosensitizer-[2Fe2S] dyads and molecular triads. Finally, strategies for the incorporation of [2Fe2S] complexes into supramolecular assemblies, semiconductor supports, and hybrid heterogeneous platforms are laid out. We analyze the individual properties, scope, and limitations of the components present in the photocatalytic reactions. This review illuminates the most useful aspects to rationally design a wide variety of biomimetic catalysts inspired by the diiron subsite of [FeFe]-hydrogenases, and establishes design features shared by the most stable and efficient hydrogen producing photosystems. (C) 2021 The Author(s). Published by Elsevier B.V.
|
|
| 4. |
- Amaro-Gahete, Juan, et al.
(författare)
-
Hydroxyl-Decorated Diiron Complex as a [FeFe]-Hydrogenase Active Site Model Complex : Light-Driven Photocatalytic Activity and Heterogenization on Ethylene-Bridged Periodic Mesoporous Organosilica
- 2022
-
Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 12:3
-
Tidskriftsartikel (refereegranskat)abstract
- A biomimetic model complex of the [FeFe]-hydrogenase active site (FeFeOH) with an ethylene bridge and a pendant hydroxyl group has been synthesized, characterized and evaluated as catalyst for the light-driven hydrogen production. The interaction of the hydroxyl group present in the complex with 3-isocyanopropyltriethoxysilane provided a carbamate triethoxysilane bearing a diiron dithiolate complex (NCOFeFe), thus becoming a potentially promising candidate for anchoring on heterogeneous supports. As a proof of concept, the NCOFeFe precursor was anchored by a grafting procedure into a periodic mesoporous organosilica with ethane bridges (EthanePMO@NCOFeFe). Both molecular and heterogenized complexes were tested as catalysts for light-driven hydrogen generation in aqueous solutions. The photocatalytic conditions were optimized for the homogenous complex by varying the reaction time, pH, amount of the catalyst or photosensitizer, photon flux, and the type of light source (light-emitting diode (LED) and Xe lamp). It was shown that the molecular FeFeOH diiron complex achieved a decent turnover number (TON) of 70 after 6 h, while NCOFeFe and EthanePMO@NCOFeFe had slightly lower activities showing TONs of 37 and 5 at 6 h, respectively.
|
|
| 5. |
- Axelsson, Martin, 1993-
(författare)
-
Illuminating Benzothiadiazole : Mechanistic Insights into its Role in Fuel-Forming Reactions
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Development and understanding of catalytic reactions involved in fuel formation are crucial to be able to make the energy transition into a sustainable future. One intriguing type of catalyst for these types of reactions is organic material catalysts, which combine some of the tunable nature of molecular catalysts with the scalability and robust nature of material catalysts. The understanding of the catalytic mechanisms in these types of materials is still a work in progress. In the last decade D-A type polymers have gotten a lot of attention as potential photocatalysts for fuel-forming reactions but currently, the mechanisms in which these reactions take place are very limited.This thesis focuses on the molecular unit benzothiadiazole (BT) and its role in catalytic fuel-forming reactions across various molecules and polymers. In paper I: The hydrogen evolution reaction (HER) is investigated on the small molecule 2,1,3-benzothiadiazole-4,7dicarbonitrile (BT). The study reveals that BTDN serves as an electrocatalyst for the HER. Some catalytic intermediates were identified spectroscopically and a catalytic mechanism was proposed.In papers II and III: Polymeric nanoparticles (Pdots) based on the polymer poly(9,9- dioctylfluorene-alt-2,1,3-benzothiadiazole (PFBT) were investigated for photocatalytic fuel-forming reactions. First, the HER was explored and it emphasised the significance of proton binding to the BT unit as a catalytic intermediate. It also showed that changing to basic conditions can quench the HER and make place for CO2 reduction to CO and that PFBT Pdots exhibit good selectivity in catalyzing this reaction.Finally, in Paper IV, the binding and reduction of CO2 on the molecule BTDN were investigated. It was shown that BTDN can bind CO2 in multiple reduced states and reduce it to CO and oxalate in a third reduction, albeit with seemingly low efficiencies.
|
|
| 6. |
- Axelsson, Martin, et al.
(författare)
-
Small Organic Molecule Based on Benzothiadiazole for Electrocatalytic Hydrogen Production
- 2021
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:50, s. 21229-21233
-
Tidskriftsartikel (refereegranskat)abstract
- A small organic molecule 2,1,3-benzothiadiazole-4, 7-dicarbonitrile (BTDN) is assessed for electrocatalytic hydrogen evolution on glassy carbon electrode and shows a hydrogen production Faradaic efficiency of 82% in the presence of salicylic acid. The key catalytic intermediates of reduced species BTDN-. and protonated intermediates are characterized or hypothesized by using various spectroscopic methods and density functional theory (DFT)-based calculations. With the experimental and theoretical results, a catalytic mechanism of BTDN for electrocatalytic H-2 evolution is proposed.
|
|
| 7. |
- Axelsson, Martin, 1993-, et al.
(författare)
-
The Role of Benzothiadiazole Unit in Organic Polymers on Photocatalytic Hydrogen Production
- 2024
-
Ingår i: JACS Au. - : American Chemical Society (ACS). - 2691-3704. ; 4:2, s. 570-577
-
Tidskriftsartikel (refereegranskat)abstract
- Organic polymers based on the donor–acceptor structure are a promising class of efficient photocatalysts for solar fuel production. Among these polymers, poly(9,9-dioctylfluorene-alt-1,2,3-benzothiadiazole) (PFBT) consisting of fluorene donor and benzothiadiazole acceptor units has shown good photocatalytic activity when it is prepared into polymer dots (Pdots) in water. In this work, we investigate the effect of the chemical environment on the activity of photocatalysis from PFBT Pdots for hydrogen production. This is carried out by comparing the samples with various concentrations of palladium under different pH conditions and with different sacrificial electron donors (SDs). Moreover, a model compound 1,2,3-benzothiadiazole di–9,9-dioctylfluorene (BTDF) is synthesized to investigate the mechanism for protonation of benzothiadiazole and its kinetics in the presence of an organic acid–salicylic acid by cyclic voltammetry. We experimentally show that benzothiadiazole in BTDF can rapidly react with protons with a fitted value of 0.1–5 × 1010 M–1 s–1 which should play a crucial role in the photocatalytic reaction with a polymer photocatalyst containing benzothiadiazole such as PFBT Pdots for hydrogen production in acidic conditions. This work gives insights into why organic polymers with benzothiadiazole work efficiently for photocatalytic hydrogen production.
|
|
| 8. |
- Bagnall, Andrew J., et al.
(författare)
-
Ultrafast Electron Transfer from CuInS2 Quantum Dots to a Molecular Catalyst for Hydrogen Production : Challenging Diffusion Limitations
- 2024
-
Ingår i: ACS Catalysis. - 2155-5435. ; 14:6, s. 4186-4201
-
Tidskriftsartikel (refereegranskat)abstract
- Systems integrating quantum dots with molecular catalysts are attracting ever more attention, primarily owing to their tunability and notable photocatalytic activity in the context of the hydrogen evolution reaction (HER) and CO2 reduction reaction (CO2RR). CuInS2 (CIS) quantum dots (QDs) are effective photoreductants, having relatively high-energy conduction bands, but their electronic structure and defect states often lead to poor performance, prompting many researchers to employ them with a core–shell structure. Molecular cobalt HER catalysts, on the other hand, often suffer from poor stability. Here, we have combined CIS QDs, surface-passivated with l-cysteine and iodide from a water-based synthesis, with two tetraazamacrocyclic cobalt complexes to realize systems which demonstrate high turnover numbers for the HER (up to >8000 per catalyst), using ascorbate as the sacrificial electron donor at pH = 4.5. Photoluminescence intensity and lifetime quenching data indicated a large degree of binding of the catalysts to the QDs, even with only ca. 1 μM each of QDs and catalysts, linked to an entirely static quenching mechanism. The data was fitted with a Poissonian distribution of catalyst molecules over the QDs, from which the concentration of QDs could be evaluated. No important difference in either quenching or photocatalysis was observed between catalysts with and without the carboxylate as a potential anchoring group. Femtosecond transient absorption spectroscopy confirmed ultrafast interfacial electron transfer from the QDs and the formation of the singly reduced catalyst (CoII state) for both complexes, with an average electron transfer rate constant of ≈ (10 ps)−1. These favorable results confirm that the core tetraazamacrocyclic cobalt complex is remarkably stable under photocatalytic conditions and that CIS QDs without inorganic shell structures for passivation can act as effective photosensitizers, while their smaller size makes them suitable for application in the sensitization of, inter alia, mesoporous electrodes.
|
|
| 9. |
- Banin, U., et al.
(författare)
-
Nanotechnology for catalysis and solar energy conversion
- 2021
-
Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 32:4
-
Tidskriftsartikel (refereegranskat)abstract
- This roadmap on Nanotechnology for Catalysis and Solar Energy Conversion focuses on the application of nanotechnology in addressing the current challenges of energy conversion: 'high efficiency, stability, safety, and the potential for low-cost/scalable manufacturing' to quote from the contributed article by Nathan Lewis. This roadmap focuses on solar-to-fuel conversion, solar water splitting, solar photovoltaics and bio-catalysis. It includes dye-sensitized solar cells (DSSCs), perovskite solar cells, and organic photovoltaics. Smart engineering of colloidal quantum materials and nanostructured electrodes will improve solar-to-fuel conversion efficiency, as described in the articles by Waiskopf and Banin and Meyer. Semiconductor nanoparticles will also improve solar energy conversion efficiency, as discussed by Boschloo et al in their article on DSSCs. Perovskite solar cells have advanced rapidly in recent years, including new ideas on 2D and 3D hybrid halide perovskites, as described by Spanopoulos et al 'Next generation' solar cells using multiple exciton generation (MEG) from hot carriers, described in the article by Nozik and Beard, could lead to remarkable improvement in photovoltaic efficiency by using quantization effects in semiconductor nanostructures (quantum dots, wires or wells). These challenges will not be met without simultaneous improvement in nanoscale characterization methods. Terahertz spectroscopy, discussed in the article by Milot et al is one example of a method that is overcoming the difficulties associated with nanoscale materials characterization by avoiding electrical contacts to nanoparticles, allowing characterization during device operation, and enabling characterization of a single nanoparticle. Besides experimental advances, computational science is also meeting the challenges of nanomaterials synthesis. The article by Kohlstedt and Schatz discusses the computational frameworks being used to predict structure-property relationships in materials and devices, including machine learning methods, with an emphasis on organic photovoltaics. The contribution by Megarity and Armstrong presents the 'electrochemical leaf' for improvements in electrochemistry and beyond. In addition, biohybrid approaches can take advantage of efficient and specific enzyme catalysts. These articles present the nanoscience and technology at the forefront of renewable energy development that will have significant benefits to society.
|
|
| 10. |
- Brnovic, Andjela, et al.
(författare)
-
Mechanistic Insights into the Photocatalytic Hydrogen Production of Y5 and Y6 Nanoparticles
- 2023
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:26, s. 12631-12639
-
Tidskriftsartikel (refereegranskat)abstract
- Utilization of solarenergy in organic semiconductorsrelies oncomplicated photophysical processes due to the strong electron-holeinteractions. To gain a better understanding of these processes andtheir effect on the photocatalytic performance of non-fullerene acceptors(NFAs) within nanoparticles (NPs), we compared the excited-state dynamicsand photocatalytic hydrogen production activity of two NFA-based NPs,Y5 and Y6. Our results show that under LED light irradiation, Y5 NPsexhibit 14 times better hydrogen production activity than Y6 NPs.The hydrogen production activity was also evaluated under Xenon lightirradiation (AM1.5G, 100 mW & BULL;cm(-2)) for Y5 NPs,yielding 410 mmol/g after 24 h. Time-resolved spectroscopy experimentsrevealed a longer triplet lifetime for Y5 compared to Y6 NPs, andthe lifetime was reduced upon addition of the electron donor ascorbate.This suggests the involvement of the triplet state in reductive quenchingand better hydrogen evolution reaction performance for Y5 NPs. Thegood agreement between fluorescence and triplet lifetimes observedfor Y5 NPs was attributed to reverse intersystem crossing, which repopulatesthe excited singlet state through thermally activated delayed fluorescence(TADF). The absence of TADF in Y6 NPs could limit its efficiency forhydrogen evolution reaction, in addition to the intrinsically shortertriplet lifetime and reduction potential difference, making it animportant factor to consider in Y series-based NPs.
|
|
| 11. |
- Cai, Bin, et al.
(författare)
-
Organic Polymer Dots Photocatalyze CO2 Reduction in Aqueous Solution
- 2023
-
Ingår i: Angewandte Chemie International Edition. - : John Wiley & Sons. - 1433-7851 .- 1521-3773. ; 62:45
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 12. |
- Cheng, Fangwen, et al.
(författare)
-
Embedding biocatalysts in a redox polymer enhances the performance of dye-sensitized photocathodes in bias-free photoelectrochemical water splitting
- 2024
-
Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 15:1
-
Tidskriftsartikel (refereegranskat)abstract
- Dye-sensitized photoelectrodes consisting of photosensitizers and molecular catalysts with tunable structures and adjustable energy levels are attractive for low-cost and eco-friendly solar-assisted synthesis of energy rich products. Despite these advantages, dye-sensitized NiO photocathodes suffer from severe electron-hole recombination and facile molecule detachment, limiting photocurrent and stability in photoelectrochemical water-splitting devices. In this work, we develop an efficient and robust biohybrid dye-sensitized NiO photocathode, in which the intermolecular charge transfer is enhanced by a redox polymer. Owing to efficient assisted electron transfer from the dye to the catalyst, the biohybrid NiO photocathode showed a satisfactory photocurrent of 141±17 μA·cm−2 at neutral pH at 0 V versus reversible hydrogen electrode and a stable continuous output within 5 h. This photocathode is capable of driving overall water splitting in combination with a bismuth vanadate photoanode, showing distinguished solar-to-hydrogen efficiency among all reported water-splitting devices based on dye-sensitized photocathodes. These findings demonstrate the opportunity of building green biohybrid systems for artificial synthesis of solar fuels.
|
|
| 13. |
- Cheng, Haoliang, et al.
(författare)
-
Assessing the effect of surface states of mesoporous NiO films on charge transport and unveiling an unexpected light response phenomenon in tandem dye-sensitized solar cells
- 2022
-
Ingår i: Energy Advances. - : Royal Society of Chemistry. - 2753-1457. ; 1:5, s. 303-311
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the role of NiO surface states is assessed in a tandem dye-sensitized solar cell (t-DSSC) consisting of a 4-(Bis-{4-[5-(2,2-dicyano-vinyl)-thiophene-2-yl]-phenyl}-amino)-benzoic acid (P1) dye-sensitized NiO photocathode, a VG1-C8 dye-sensitized TiO2 photoanode and the I−/I3− redox couple. The NiO surface states are proved to participate in the reduction of the I−/I3− electrolyte in the t-DSSCs. By adjusting the thickness of the TiO2 film, the charge transport processes of the t-DSSCs are significantly affected by the photocurrent and the NiO surface states, resulting in various photovoltaic properties. This work also proves that the NiO surface states together with energy transfer between the desorbed P1 dye from the NiO photocathode and the VG1-C8 dye from the TiO2 photoanode are responsible for the light response from both dyes observed in the IPCE spectra of the t-DSSCs.
|
|
| 14. |
- Cheng, Haoliang, et al.
(författare)
-
Atomic Layer Deposition of SnO2 as an Electron Transport Material for Solid-State P-type Dye-Sensitized Solar Cells
- 2022
-
Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:10, s. 12022-12028
-
Tidskriftsartikel (refereegranskat)abstract
- Tin oxide (SnO2) as an electron transport material was prepared by atomic layer deposition in dye-sensitized NiO films to fabricate solid-state p-type dye-sensitized solar cells using two organic dyes PB6 and TIP as photosensitizers. Due to the excellent electron mobility and satisfactory penetration of SnO2 material into the NiO film, a record photocurrent density over 1 mA cm–2 was achieved with a power conversion efficiency of 0.14%. The effect of an inserted Al2O3 layer between the dye-sensitized NiO and SnO2 layer on photovoltaic performance of the devices was also investigated. The results suggest that the charge recombination between NiO and SnO2 can be significantly suppressed, showing prolonged charge lifetime and enhanced photovoltage.
|
|
| 15. |
- Dürr, Robin N., et al.
(författare)
-
From NiMoO4 to γ-NiOOH : Detecting the Active Catalyst Phase by Time Resolved in Situ and Operando Raman Spectroscopy
- 2021
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 15:8, s. 13504-13515
-
Tidskriftsartikel (refereegranskat)abstract
- Water electrolysis powered by renewable energies is a promising technology to produce sustainable fossil free fuels. The development and evaluation of effective catalysts are here imperative; however, due to the inclusion of elements with different redox properties and reactivity, these materials undergo dynamical changes and phase transformations during the reaction conditions. NiMoO4 is currently investigated among other metal oxides as a promising noble metal free catalyst for the oxygen evolution reaction. Here we show that at applied bias, NiMoO4·H2O transforms into γ-NiOOH. Time resolved operando Raman spectroscopy is utilized to follow the potential dependent phase transformation and is collaborated with elemental analysis of the electrolyte, confirming that molybdenum leaches out from the as-synthesized NiMoO4·H2O. Molybdenum leaching increases the surface coverage of exposed nickel sites, and this in combination with the formation of γ-NiOOH enlarges the amount of active sites of the catalyst, leading to high current densities. Additionally, we discovered different NiMoO4 nanostructures, nanoflowers, and nanorods, for which the relative ratio can be influenced by the heating ramp during the synthesis. With selective molybdenum etching we were able to assign the varying X-ray diffraction (XRD) pattern as well as Raman vibrations unambiguously to the two nanostructures, which were revealed to exhibit different stabilities in alkaline media by time-resolved in situ and operando Raman spectroscopy. We advocate that a similar approach can beneficially be applied to many other catalysts, unveiling their structural integrity, characterize the dynamic surface reformulation, and resolve any ambiguities in interpretations of the active catalyst phase.
|
|
| 16. |
- Dürr, Robin N.
(författare)
-
Potential Electrocatalysts for Water Splitting Devices : A Journey Through the Opportunities and Challenges of Catalyst Classes
- 2022
-
Konstnärligt arbete (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis work, different classes of catalysts and their suitability for integration into an electrolyzer cell has been investigated.Ruthenium based molecular catalysts have shown high activities and stabilities towards water oxidation in neutral pH. Especially the oligomeric catalysts exhibited a superior performance. The electrical conductivity of the electrode and the low loading of catalyst might impose limitations on reaching high current densities at reasonable potentials.Among the tested transition metal single atom catalysts, synthesized by pyrolyzing transition metal doped ZIF-8 structures, cobalt has shown the highest activity towards hydrogen evolution and a stable behaviour in acidic pH. The enhanced stability of single atomic sites compared to the corresponding nanoparticles was proposed. However, also for this class of catalyst, the low number of active sites seems to present a difficulty need to be overcome.With the novel method presented to fabricate a membrane electrode assembly, the usage of commonly used expensive membranes could possibly be avoided.Both nickel molybdate hydrate nanoparticle shapes have been proposed to transform in an electrochemical activation step into γ-NiOOH as active phase for the oxygen evolution reaction in alkaline pH. With the removal of molybdenum, a high electrochemical surface area with a large number of exposed nickel sites was indicated to be the origin behind the high catalytic activity of the nanoparticles. Molybdenum was suggested to only serve as structure and pore forming agent. Preliminary results indicated a higher activity for the rod structure towards the oxygen evolution reaction. An essential outcome is that it is uncertain if rods can be isolated synthesized on a nickel foam and hence the absence of the sheet structure should be verified, which could be done for example by selective molybdenum leaching combined with Raman spectroscopy. Furthermore, the two nanostructures are fundamentally different materials and characterized by various techniques.Among all different classes of catalysts investigated, the nanoparticle catalysts seem to be the most promising for a successful integration in a large scale electrolyzer cell for widespread use.
|
|
| 17. |
- Eliasson, Nora, et al.
(författare)
-
Ultrafast Dynamics in Cu-Deficient CuInS2 Quantum Dots : SubBandgap Transitions and Self-Assembled Molecular Catalysts
- 2021
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:27, s. 14751-14764
-
Tidskriftsartikel (refereegranskat)abstract
- The photophysical properties of Cu-deficient Cu01.2In1Sx quantum dots synthesized through a facile aqueous-based procedure have been investigated. Transient absorption experiments were carried out probing in the UV-vis, near-IR, and mid-IR regions, with the aim to (i) study the photophysical properties of the quantum dots and (ii) monitor kinetics of electron transfer to a molecular catalyst. When pumping subbandgap transitions, negative (bleach) signals were observed that were spectrally and kinetically distinct from those observed with bandgap pump wavelengths. Herein, these distinct contributions are suggested to result from the overlapping bleaching of state filling electrons and trapped holes. Such an interpretation highlights the importance of considering the hole-contributions to the bleach for the proper determination of carrier kinetics in similar systems. A model complex of the [Fe-2]-hydrogenase active site was introduced to explore the potential of the quantum dots as photosensitizers for molecular catalysts. The quantum dot photoluminescence was quenched upon catalyst addition, and direct evidence of the singly reduced catalyst was found by transient absorption in the UV-vis and mid-IR. The catalyst accepted reducing equivalents on a subpicosecond time scale upon photoexcitation of the quantum dots, despite no covalent linking chemistry being applied. This implies that charge transfer is not limited by diffusion rates, thus confirming the presence of spontaneous quantum dot and catalyst self-assembly.
|
|
| 18. |
- Gao, Jiajia, et al.
(författare)
-
Electrochemical impedance and X-ray absorption spectroscopy analyses of degradation in dye-sensitized solar cells containing cobalt tris(bipyridine) redox shuttles
- 2022
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:31, s. 18888-18895
-
Tidskriftsartikel (refereegranskat)abstract
- Electrochemical impedance spectroscopy (EIS) is a commonly used steady-state technique to examine the internal resistance of electron-transfer processes in solar cell devices, and the results are directly related to the photovoltaic performance. In this study, EIS was performed to study the effects of accelerated ageing, aiming for insights into the degradation mechanisms of dye-sensitized solar cells (DSSCs) containing cobalt tris(bipyridine) complexes as redox mediators. Control experiments based on aged electrolytes differing in concentrations of the redox couple components and cation co-additives were conducted to reveal the correlation of the cell degradation with external and internal properties. The failure modes of the cells emerged as changes in the kinetics of charge- and ion-transfer processes. An insufficient concentration of the redox complexes, in particular Co(iii), was found to be the main reason for the inferior performance after ageing. The related characterization of electrolytes aged outside the solar cell devices confirms the loss of active Co(iii) complexes in the device electrolytes. A new EIS feature at low frequencies emerged during ageing and was analysed. The new EIS feature demonstrates the presence of an unexpected rate-limiting, charge-transfer process in aged devices, which can be attributed to the TiO2/electrolyte interface. High-resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS) was performed to identify the reduction of a part of Co(iii) to Co(II) after ageing, by investigating the Co K absorption edge. The HERFD-XAS data suggested a partial reduction of Co(iii) to Co(ii), accompanied by a difference in symmetry of the reduced species.
|
|
| 19. |
- Hola, Katerina, et al.
(författare)
-
Carbon Dots and [FeFe] Hydrogenase Biohybrid Assemblies for Efficient Light-Driven Hydrogen Evolution
- 2020
-
Ingår i: ACS Catalysis. - : AMER CHEMICAL SOC. - 2155-5435. ; 10:17, s. 9943-9952
-
Tidskriftsartikel (refereegranskat)abstract
- Artificial photosynthesis is seen as a path to convert and store solar energy into chemical energy for our society. In this work, highly fluorescent aspartic acid-based carbon dots (CDs) are synthesized and employed as a photosensitizer to drive photocatalytic hydrogen evolution with an [FeFe] hydrogenase (CrHydA1). The direct interaction in CDs from L-aspartic acid (AspCDs)/CrHydA1 self-assembly systems, which is visualized from native gel electrophoresis, has been systematically investigated to understand the electron-transfer dynamics and its impact on photocatalytic efficiency. The study discloses the significant influence of the electrostatic surrounding generated by sacrificial electron donors on the intimate interplay within the oppositely charged subunits of the biohybrid assembly as well as the overall photocatalytic performance. The system reaches an external quantum efficiency of 1.7% at 420 nm and an initial activity of 1.73 mu mol(H-2) mg(-1) (hydrogenase) min(-1) under favorable electrostatic conditions. Owing to the ability of the synthesized AspCDs to operate efficiently under visible light, in contrast to other materials that require UV illumination, the stability of the biohybrid assembly in the presence of a redox mediator extends beyond 1 week.
|
|
| 20. |
- Lalaoui, Noemie, et al.
(författare)
-
Gold nanoparticle-based supramolecular approach for dye-sensitized H-2-evolving photocathodes
- 2022
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 51:41, s. 15716-15724
-
Tidskriftsartikel (refereegranskat)abstract
- Solar conversion of water into the storable energy carrier H-2 can be achieved through photoelectrochemical water splitting using light adsorbing anodes and cathodes bearing O-2 and H-2 evolving catalysts, respectively. Herein a novel photocathode nanohybrid system is reported. This photocathode consists of a dye-sensitized p-type nickel oxide (NiO) with a perylene-based chromophore (PCA) and a tetra-adamantane modified cobaloxime reduction catalyst (Co) that photo-reduces aqueous protons to H-2. An original supramolecular approach was employed, using beta-cyclodextrin functionalized gold nanoparticles (beta-CD-AuNPs) to link the alkane chain of the PCA dye to the adamantane moieties of the cobaloxime catalyst (Co). This new architecture was investigated by photoelectrochemical measurements and via femtosecond-transient absorption spectroscopy. The results show that irradiation of the complete NiO|PCA|beta-CD-AuNPs|Co electrode leads to ultrafast hole injection into NiO (pi = 3 ps) from the excited dye, followed by rapid reduction of the catalyst, and finally H-2 evolution.
|
|
| 21. |
- Liu, Aijie, et al.
(författare)
-
Excited-state and charge-carrier dynamics in binary conjugated polymer dots towards efficient photocatalytic hydrogen evolution
- 2023
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 25:4, s. 2935-2945
-
Tidskriftsartikel (refereegranskat)abstract
- Aqueous dispersed conjugated polymer dots (Pdots) have shown promising application in photocatalytic hydrogen evolution. To efficiently extract photogenerated charges from type-II heterojunction Pdots for hydrogen evolution, the mechanistic study of photophysical processes is essential for Pdot optimization. Within this work, we use a PFODTBT donor (D) polymer and an ITIC small molecule acceptor (A) as a donor/acceptor (D/A) model system to study their excited states and charge/energy transfer dynamics via steady-state and time-resolved photoluminescence spectroscopy, respectively. Charge-carrier generation and the recombination dynamics of binary Pdots with different D/A ratios were followed using femtosecond transient absorption spectroscopy. A significant spectral relaxation of photoluminescence was observed for individual D Pdots, implying an energetic disorder by nature. However, this was not seen for charge carriers in binary Pdots, probably due to the ultrafast charge generation process at an early time (<200 fs). The results showed slower charge recombination upon increasing the ratio of ITIC in binary Pdots, which further resulted in an enhanced photocatalytic hydrogen evolution, twice that as compared to individual D Pdots. Although binary Pdots prepared via the nanoprecipitation method exhibit a large interfacial area that allows high charge generation efficiencies, it also provides a high possibility for charge recombination and limits the further utilization of free charges. Therefore, for the future design of type-II heterojunction Pdots, suppressing the charge carrier recombination via increasing the crystallinity and proper phase segregation is necessary for enhanced photocatalytic hydrogen evolution.
|
|
| 22. |
- Liu, Aijie, et al.
(författare)
-
Panchromatic Ternary Polymer Dots Involving Sub-Picosecond Energy and Charge Transfer for Efficient and Stable Photocatalytic Hydrogen Evolution
- 2021
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:7, s. 2875-2885
-
Tidskriftsartikel (refereegranskat)abstract
- Panchromatic ternary polymer dots (Pdots) consisting of two conjugated polymers (PFBT and PFODTBT) based on fluorene and benzothiadiazole groups, and one small molecular acceptor (ITIC) have been prepared and assessed for photocatalytic hydrogen production with the assistance of a Pt cocatalyst. Femtosecond transient absorption spectroscopic studies of the ternary Pdots have revealed both energy and charge transfer processes that occur on the time scale of sub-picosecond between the different components. They result in photogenerated electrons being located mainly at ITIC, which acts as both electron and energy acceptor. Results from cryo-transmission electron microscopy suggest that ITIC forms crystalline phases in the ternary Pdots, facilitating electron transfer from ITIC to the Pt cocatalyst and promoting the final photocatalytic reaction yield. Enhanced light absorption, efficient charge separation, and the ideal morphology of the ternary Pdots have rendered an external quantum efficiency up to 7% at 600 nm. Moreover, the system has shown a high stability over 120 h without obvious degradation of the photocatalysts.
|
|
| 23. |
- Materna, Kelly L., et al.
(författare)
-
Understanding the Performance of NiO Photocathodes with Alkyl-Derivatized Cobalt Catalysts and a Push-Pull Dye
- 2020
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:28, s. 31372-31381
-
Tidskriftsartikel (refereegranskat)abstract
- Mesoporous NiO photocathodes containing the push-pull dye PB6 and alkyl-derivatized cobaloxime catalysts were prepared using surface amide couplings and analyzed for photocatalytic proton reduction catalysis. The length of the alkyl linker used to derivatize the cobalt catalysts was found to correlate to the photocurrent with the highest photocurrent observed using shorter alkyl linkers but the lowest one for samples without linker. The alkyl linkers were also helpful in slowing dye-NiO charge recombination. Photoelectrochemical measurements and femtosecond transient absorption spectroscopic measurements suggested electron transfer to the surfaceimmobilized catalysts occurred; however, H-2 evolution was not observed. Based on UV-vis, X-ray fluorescence spectroscopy (XRF), and X-ray photoelectron spectroscopy (XPS) measurements, the cobalt catalyst appeared to be limiting the photocathode performance mainly via cobalt demetallation from the oxime ligand. This study highlights the need for a deeper understanding of the effect of catalyst molecular design on photocathode performance.
|
|
| 24. |
- Materna, Kelly L., et al.
(författare)
-
Using Surface Amide Couplings to Assemble Photocathodes for Solar Fuel Production Applications
- 2020
-
Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 12:4, s. 4501-4509
-
Tidskriftsartikel (refereegranskat)abstract
- A facile surface amide-coupling method was examined to attach dye and catalyst molecules to silatrane-decorated NiO electrodes. Using this method, electrodes with a push-pull dye were assembled and characterized by photoelectrochemistry and transient absorption spectroscopy. The dye-sensitized electrodes exhibited hole injection into NiO and good photoelectrochemical stability in water, highlighting the stability of the silatrane anchoring group and the amide linkage. The amide-coupling protocol was further applied to electrodes that contain a molecular proton reduction catalyst for use in photocathode architectures. Evidence for catalyst reduction was observed during photoelectrochemical measurements and via photocathodes.
|
|
| 25. |
- Pandey, Gaurav Kumar, et al.
(författare)
-
Visible-light photoredox catalysis with organic polymers
- 2023
-
Ingår i: CHEMICAL PHYSICS REVIEWS. - : American Institute of Physics (AIP). - 2688-4070. ; 4:1
-
Forskningsöversikt (refereegranskat)abstract
- The development of photocatalysts to drive organic reactions is a frontier research topic. Organic polymers can be well tuned in terms of structural and photophysical properties and, therefore, constitute a promising class of photocatalysts in photoredox catalysis for organic synthesis. In this review article, we provide an overview of the concept of photoredox catalysis and recent developments in organic polymers as photocatalysts including porous organic polymers, graphitic carbon nitride, carbon dots, and polymer dots with adjustable reactivity that have undergone state-of-the-art advancement in different photoredox catalytic organic reactions.
|
|
