Nanoporous BiVO4 Photoanodes with Dual-Layer Oxygen Evolution Catalysts for Solar Water Splitting
28 Feb 2014-Science (American Association for the Advancement of Science)-Vol. 343, Iss: 6174, pp 990-994
TL;DR: It is demonstrated that a nanoporous morphology effectively suppresses bulk carrier recombination without additional doping, manifesting an electron-hole separation yield of 0.90 at 1.23 volts (V) versus the reversible hydrogen electrode (RHE).
Abstract: Bismuth vanadate (BiVO4) has a band structure that is well-suited for potential use as a photoanode in solar water splitting, but it suffers from poor electron-hole separation. Here, we demonstrate that a nanoporous morphology (specific surface area of 31.8 square meters per gram) effectively suppresses bulk carrier recombination without additional doping, manifesting an electron-hole separation yield of 0.90 at 1.23 volts (V) versus the reversible hydrogen electrode (RHE). We enhanced the propensity for surface-reaching holes to instigate water-splitting chemistry by serially applying two different oxygen evolution catalyst (OEC) layers, FeOOH and NiOOH, which reduces interface recombination at the BiVO4/OEC junction while creating a more favorable Helmholtz layer potential drop at the OEC/electrolyte junction. The resulting BiVO4/FeOOH/NiOOH photoanode achieves a photocurrent density of 2.73 milliamps per square centimenter at a potential as low as 0.6 V versus RHE.
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TL;DR: This review attempts to summarize the recent progress in the rational design and fabrication ofheterojunction photocatalysts, such as the semiconductor-semiconductor heterojunction, the semiconductors-metal heterojunctions, the silicon-carbon heteroj junction and the multicomponent heteroj conjunction.
Abstract: Semiconductor-mediated photocatalysis has received tremendous attention as it holds great promise to address the worldwide energy and environmental issues. To overcome the serious drawbacks of fast charge recombination and the limited visible-light absorption of semiconductor photocatalysts, many strategies have been developed in the past few decades and the most widely used one is to develop photocatalytic heterojunctions. This review attempts to summarize the recent progress in the rational design and fabrication of heterojunction photocatalysts, such as the semiconductor–semiconductor heterojunction, the semiconductor–metal heterojunction, the semiconductor–carbon heterojunction and the multicomponent heterojunction. The photocatalytic properties of the four junction systems are also discussed in relation to the environmental and energy applications, such as degradation of pollutants, hydrogen generation and photocatalytic disinfection. This tutorial review ends with a summary and some perspectives on the challenges and new directions in this exciting and still emerging area of research.
3,013 citations
TL;DR: Measurements of activity as a function of film thickness on Au and glassy carbon substrates are consistent with the hypothesis that Fe exerts a partial-charge-transfer activation effect on Ni, similar to that observed for noble-metal electrode surfaces.
Abstract: Fe plays a critical, but not yet understood, role in enhancing the activity of the Ni-based oxygen evolution reaction (OER) electrocatalysts. We report electrochemical, in situ electrical, photoelectron spectroscopy, and X-ray diffraction measurements on Ni1–xFex(OH)2/Ni1–xFexOOH thin films to investigate the changes in electronic properties, OER activity, and structure as a result of Fe inclusion. We developed a simple method for purification of KOH electrolyte that uses precipitated bulk Ni(OH)2 to absorb Fe impurities. Cyclic voltammetry on rigorously Fe-free Ni(OH)2/NiOOH reveals new Ni redox features and no significant OER current until >400 mV overpotential, different from previous reports which were likely affected by Fe impurities. We show through controlled crystallization that β-NiOOH is less active for OER than the disordered γ-NiOOH starting material and that previous reports of increased activity for β-NiOOH are due to incorporation of Fe-impurities during the crystallization process. Through...
2,419 citations
11 Jan 2017
TL;DR: In this article, the authors investigate progress towards photo-electrocatalytic water-splitting systems, with special emphasis on how they might be incorporated into photoelectrocaralyst systems.
Abstract: Sunlight is by far the most plentiful renewable energy resource, providing Earth with enough power to meet all of humanity's needs several hundred times over. However, it is both diffuse and intermittent, which presents problems regarding how best to harvest this energy and store it for times when the sun is not shining. Devices that use sunlight to split water into hydrogen and oxygen could be one solution to these problems, because hydrogen is an excellent fuel. However, if such devices are to become widely adopted, they must be cheap to produce and operate. Therefore, the development of electrocatalysts for water splitting that comprise only inexpensive, earth-abundant elements is critical. In this Review, we investigate progress towards such electrocatalysts, with special emphasis on how they might be incorporated into photoelectrocatalytic water-splitting systems and the challenges that remain in developing these devices. Splitting water is an attractive means by which energy — either electrical and/or light — is stored and consumed on demand. Active and efficient catalysts for anodic and cathodic reactions often require precious metals. This Review covers base-metal catalysts that can afford high performance in a more sustainable and available manner.
2,369 citations
TL;DR: It is shown that a pair of perovskite cells connected in series can power the electrochemical breakdown of water into hydrogen and oxygen efficiently, and the combination of the two yields a water-splitting photocurrent density and a solar-to-hydrogen efficiency of 12.3%.
Abstract: Although sunlight-driven water splitting is a promising route to sustainable hydrogen fuel production, widespread implementation is hampered by the expense of the necessary photovoltaic and photoelectrochemical apparatus. Here, we describe a highly efficient and low-cost water-splitting cell combining a state-of-the-art solution-processed perovskite tandem solar cell and a bifunctional Earth-abundant catalyst. The catalyst electrode, a NiFe layered double hydroxide, exhibits high activity toward both the oxygen and hydrogen evolution reactions in alkaline electrolyte. The combination of the two yields a water-splitting photocurrent density of around 10 milliamperes per square centimeter, corresponding to a solar-to-hydrogen efficiency of 12.3%. Currently, the perovskite instability limits the cell lifetime.
2,140 citations
TL;DR: Li et al. as mentioned in this paper provided an overview of the concept of heterojunction construction and more importantly, the current state-of-the-art for the efficient, visible-light driven junction water splitting photo(electro)catalysts reported over the past ten years.
Abstract: Solar driven catalysis on semiconductors to produce clean chemical fuels, such as hydrogen, is widely considered as a promising route to mitigate environmental issues caused by the combustion of fossil fuels and to meet increasing worldwide demands for energy. The major limiting factors affecting the efficiency of solar fuel synthesis include; (i) light absorption, (ii) charge separation and transport and (iii) surface chemical reaction; therefore substantial efforts have been put into solving these problems. In particular, the loading of co-catalysts or secondary semiconductors that can act as either electron or hole acceptors for improved charge separation is a promising strategy, leading to the adaptation of a junction architecture. Research related to semiconductor junction photocatalysts has developed very rapidly and there are a few comprehensive reviews in which the strategy is discussed (A. Kudo and Y. Miseki, Chemical Society Reviews, 2009, 38, 253–278, K. Li, D. Martin, and J. Tang, Chinese Journal of Catalysis, 2011, 32, 879–890, R. Marschall, Advanced Functional Materials, 2014, 24, 2421–2440). This critical review seeks to give an overview of the concept of heterojunction construction and more importantly, the current state-of-the art for the efficient, visible-light driven junction water splitting photo(electro)catalysts reported over the past ten years. For water splitting, these include BiVO4, Fe2O3, Cu2O and C3N4, which have attracted increasing attention. Experimental observations of the proposed charge transfer mechanism across the semiconductor/semiconductor/metal junctions and the resultant activity enhancement are discussed. In parallel, recent successes in the theoretical modelling of semiconductor electronic structures at interfaces and how these explain the functionality of the junction structures is highlighted.
1,891 citations
References
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TL;DR: The biggest challenge is whether or not the goals need to be met to fully utilize solar energy for the global energy demand can be met in a costeffective way on the terawatt scale.
Abstract: Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2
8,037 citations
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TL;DR: The food-quality iron oxides are primarily distinguished from technical grades by their comparatively low levels of contamination by other metals; this is achieved by the selection and control of the source of the iron or by the extent of chemical purification during the manufacturing process as discussed by the authors.
Abstract: DEFINITION Iron oxides are produced from ferrous sulfate by heat soaking, removal of water, decomposition, washing, filtration, drying and grinding. They are produced in either anhydrous or hydrated forms. Their range of hues includes yellows, reds, browns and blacks. The food-quality iron oxides are primarily distinguished from technical grades by their comparatively low levels of contamination by other metals; this is achieved by the selection and control of the source of the iron or by the extent of chemical purification during the manufacturing process.
3,866 citations
TL;DR: Observations suggest that the OER is catalyzed by Ni in Ni-Fe films and that the presence of Fe alters the redox properties of Ni, causing a positive shift in the potential at which Ni(OH)2/NiOOH redox occurs.
Abstract: A detailed investigation has been carried out of the structure and electrochemical activity of electrodeposited Ni-Fe films for the oxygen evolution reaction (OER) in alkaline electrolytes. Ni-Fe films with a bulk and surface composition of 40% Fe exhibit OER activities that are roughly 2 orders of magnitude higher than that of a freshly deposited Ni film and about 3 orders of magnitude higher than that of an Fe film. The freshly deposited Ni film increases in activity by as much as 20-fold during exposure to the electrolyte (KOH); however, all films containing Fe are stable as deposited. The oxidation of Ni(OH)2 to NiOOH in Ni films occurs at potentials below the onset of the OER. Incorporation of Fe into the film increases the potential at which Ni(OH)2/NiOOH redox occurs and decreases the average oxidation state of Ni in NiOOH. The Tafel slope (40 mV dec(-1)) and reaction order in OH(-) (1) for the mixed Ni-Fe films (containing up to 95% Fe) are the same as those for aged Ni films. In situ Raman spectra acquired in 0.1 M KOH at OER potentials show two bands characteristic of NiOOH. The relative intensities of these bands vary with Fe content, indicating a change in the local environment of Ni-O. Similar changes in the relative intensities of the bands and an increase in OER activity are observed when pure Ni films are aged. These observations suggest that the OER is catalyzed by Ni in Ni-Fe films and that the presence of Fe alters the redox properties of Ni, causing a positive shift in the potential at which Ni(OH)2/NiOOH redox occurs, a decrease in the average oxidation state of the Ni sites, and a concurrent increase in the activity of Ni cations for the OER.
1,951 citations
TL;DR: In this paper, highly crystalline monoclinic and tetragonal BiVO4 photocatalysts were obtained by the reaction of layered potassium vanadate powder (KV3O8 and K3V5O14) with Bi(NO3)3 for 3 days in aqueous media at room temperature.
Abstract: BiVO4 photocatalysts for O2 evolution, which work under visible light irradiation, were prepared by an aqueous process. The BiVO4 photocatalysts were obtained by the reaction of layered potassium vanadate powder (KV3O8 and K3V5O14) with Bi(NO3)3 for 3 days in aqueous media at room temperature. Highly crystalline monoclinic and tetragonal BiVO4 were selectively synthesized by changing the ratio of vanadium to bismuth in the starting materials. X-ray diffraction and scanning electron microscopy measurements showed that the monoclinic BiVO4 was formed via a tetragonal BiVO4 intermediate. Tetragonal BiVO4 with a 2.9 eV band gap mainly possessed an ultraviolet absorption band while monoclinic BiVO4 with a 2.4 eV band gap had a characteristic visible light absorption band in addition to the UV band. The UV bands observed in the tetragonal and monoclinic BiVO4 were assigned to the band transition from O2p to V3d whereas the visible light absorption was due to the transition from a valence band formed by Bi6s or ...
1,761 citations
Book•
01 Jan 1968
TL;DR: In this paper, the authors proposed a method of particle size distribution determination based on the Coulter principle, which is the alternative derivation of Kozeny's equation using equivalent capillaries.
Abstract: Sampling of powders sampling of dusty gases in gas streams sampling and sizing from the atmosphere - air technology, Atcor Net 2000, Bausch and Lomb, Beckman, Centre for Air Environmental Studies, Climet Series 7000, Coulter Model 550 contamination monitor, Dynac, Gardner, GCA Miniram, Insitec PCSV-P, Kratel Partoscope, Leitz Tyndalloscope, Met One particle counters, Pacific Scientific Hiac/Royco particle counting systems, particle measuring systems, RAC particle monitors, Rotheroe and Mitchell digital dust indicator, Saab photometer, Sartorius, Sinclair Particle size, shape and distribution - shape regeneration by Fourier analysis, the Rosinn-Rammler distribution, mean particle sizes and specific surface evaluation for Rosinn-Rammler distribution Sieving microscopy interaction between particles and fluids in a gravitational field dispersion of powders incremental methods of particle size determination cumulative methods of sedimentation size analysis fluid classification - the Warmain cyclosizer, the Humboldt particle size analyzer TDS, the cross-flow elbow classifier, the Bahco classifier, the BCURA centrifugal elutriator, Analysette 9, the Donaldson classifier, the Micromeritics classifier Centrifugal methods - early instruments - the Marshall centrifuge and the MSA particle size analyser, the Alpine sedimentation centrifuge, the Mikropul Sedimentputer, the LADAL X-ray centrifuge, the LADAL pipette withdrawal centrifuge The electrical sensing zone method of particle size distribution determination (the Coulter principle) radiation scattering methods of particle size determination high-order Tyndall spectr (HOTS) permeametry and gas diffusion - alternative derivation of Kozeny's equation using equivalent capillaries Gas adsorption - BET isotherm for multilayer adsorption, comparison between BET and HJr methods, the Frenkel-Halsey-Hill equation (FHH), the Dubinin-Radushkevich equation (D-R), Kiselev's equation Other methods for determining surface area - Langmuir trough, Gravimetric method, the Rayleigh interferometer Determination of pore size distribution by gas adsorption - the Kelvin equation On-line particle analysis - Brinkmann analyser, Climet particle counting systems, Flowvision, Hiac/Royco (Pacific Scientific) particle counters, Horiba particle size analysers, the Insitic particle counter, Kane May particle size analysers, Kratel Partascope, Lasentec, Talbot optical-electronic method, the Erdco acoustical counter, the Coulter on-line monitor screening - the Cyclosensor, non-Newtonian rheological properties Appendix 1 Equipment and suppliers, manufacturers' and suppliers' addresses
1,592 citations