Efficient Solar Water Splitting, Exemplified by RuO<sub>2</sub>-Catalyzed AlGaAs/Si Photoelectrolysis

Licht, Stuart; Wang, and B.; Mukerji, Sudeshna; Soga, Tetsuo; Umeno, Masayoshi; Tributsch, H.

doi:10.1021/jp002083b

Cited by 366 publications

(244 citation statements)

References 28 publications

(60 reference statements)

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“…The electrocatalysts may or may not be in physical contact with the PV electrodes, but in all such systems the photovoltage generated by the structure is independent of the nature of the electrocatalyst/electrolyte interface. Examples of PV-biased electrosynthetic cells include AlGaAs/Si tandem structures, 9 amorphous hydrogenated Si (a-Si:H) triple-junction structures, [10][11][12] triple-junction structures based on CuInGaSe 2 ( Fig. 2b-d), 13 and n-Si/SiO x /In-doped tin oxide (ITO) structures.…”

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confidence: 99%

A taxonomy for solar fuels generators

Nielander

Shaner

Papadantonakis

et al. 2015

Energy Environ. Sci.

179

175

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A number of approaches to solar fuels generation are being developed, each of which has associated advantages and challenges. Many of these solar fuels generators are identified as "photoelectrochemical cells" even though these systems collectively operate based on a suite of fundamentally different physical principles. To facilitate appropriate comparisons between solar fuels generators, as well as to enable concise and consistent identification of the state-of-the-art for designs based on comparable operating principles, we have developed a taxonomy and nomenclature for solar fuels generators based on the source of the asymmetry that separates photogenerated electrons and holes. Three basic device types have been identified: photovoltaic cells, photoelectrochemical cells, and particulate/molecular photocatalysts. We outline the advantages and technological challenges associated with each type, and provide illustrative examples for each approach as well as for hybrid approaches. Broader contextSolar fuels generators are devices that harness energy from sunlight to drive the synthesis of chemical fuels. A number of approaches to solar fuels generation are being pursued, many of which can be differentiated by the physical principles on which they are based. Herein, we propose a nomenclature and taxonomy based on three basic device types: photovoltaic cells, photoelectrochemical cells, and photoelectrosynthetic particulate/molecular photocatalysts. An understanding of the inherent operating principles and the advantages and challenges associated with each of these device types will facilitate clear comparisons between devices as well as help guide research efforts toward improving these devices and achieving the ultimate goal of sustainable fuel production.

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confidence: 99%

A taxonomy for solar fuels generators

Nielander

Shaner

Papadantonakis

et al. 2015

Energy Environ. Sci.

179

175

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“…The most abundant of renewable energy resource for electrical generation is solar energy, and as early as 2001 we were driving stable solar electrolytic water splitting to hydrogen fuels at over 18% solar to chemical energy conversion by using efficient multiple bandgap solar cells. 6 One of the challenges to the use of illuminated junctions to drive electrochemical or photoelectrochemical water splitting is that the bandgap of efficient semiconductors lies in the visible spectrum which generate a photo-potential less than the minimum needed rest potential of 1.23 volt required to split water to hydrogen and oxygen at room temperature and pressure. In 2002, a theory was presented demonstrating that thermal, sub-bandgap solar energy was sufficient to increase the temperature of water splitting and decrease the required potential to split water 7,8 sufficiently to use common semiconductors.…”

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confidence: 99%

Comparison of Alternative Molten Electrolytes for Water Splitting to Generate Hydrogen Fuel

Licht

Liu

Cui

et al. 2016

J. Electrochem. Soc.

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This study explores a new high temperature molten hydroxide domain to electrochemically split water into hydrogen fuel. Hydrogen fuel, if produced without greenhouse gas emissions, is a promising fuel for transportation. This study opens a pathway to low energy water splitting and the electrolytic production of hydrogen fuel without carbon dioxide emission. A wide range of pure and mixed alkali and alkali earth hydroxide electrolytes are explored at temperatures ranging from 200 to 700 • C. Higher temperature leads to improved (lower voltage) water splitting and improved rates of charge transfer, but carries challenges (increased rates of parasitic side reactions as the molten electrolytes dehydrate with increasing temperature). This study extends the range of hydrogen formation in alkaline electrolysis water splitting to over 600 • C, and demonstrates that lithium and/or barium hydroxide electrolytes remain hydrated at high temperatures, and in the high temperature domain are advantageous over sodium or potassium hydroxide electrolytes. In pure LiOH, the coulombic efficiency for hydrogen generation decreases with temperature and is measured respectively at η H 2 = 88%, 21%, 4% and 0%, respectively at 500, 600, 700 and 800 • Hydrogen has advantageous features compared to fossil fuels. It has a higher specific energy, is not polluting, has a combustion product of water, and in particular it does not emit the greenhouse gas carbon dioxide. Challenges of hydrogen storage are being addressed and hydrogen powered vehicles have been introduced to the commercial marketplace.1-4 Unfortunately, the predominant fraction of hydrogen generated today is produced by steam reformation of fossil fuel by reacting the fossil fuel with steam to release H 2 and CO 2 . Steam reformation is a substantial source of CO 2 emissions, negating the climate mitigation effect of using H 2 as a fuel. Thus, a process to efficiently generate hydrogen without carbon dioxide emissions is needed.The development of electrolytic splitting of water dates back to 1802. 5 The electrolysis of water produces hydrogen and oxygen directly without CO 2 emission (if the energy source used to generate the electricity did not release CO 2 ). Utilization of renewable or nuclear energy to generate the electricity for this electrolysis can drive this electrolytic water splitting to produce hydrogen as a fuel without carbon dioxide emissions. The most abundant of renewable energy resource for electrical generation is solar energy, and as early as 2001 we were driving stable solar electrolytic water splitting to hydrogen fuels at over 18% solar to chemical energy conversion by using efficient multiple bandgap solar cells.6 One of the challenges to the use of illuminated junctions to drive electrochemical or photoelectrochemical water splitting is that the bandgap of efficient semiconductors lies in the visible spectrum which generate a photo-potential less than the minimum needed rest potential of 1.23 volt required to split water to hydrogen and oxygen at room te...

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“…[1][2][3][4][5] Since the discovery of light driven electrochemical water splitting in the early 1970s by Fujishima and Honda, 6 there has been continuing research into the development of photoelectrochemical (PEC) cells which has resulted in systems with solar to hydrogen conversion efficiencies as high as 18%. [7][8][9] These laboratory-scale demonstrations have tended to rely on multi-junction photovoltaic (PV) components, water splitting catalysts, and other complex components that have limited stability under electrolytes necessary for efficient operation (i.e. strong acids or bases).…”

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confidence: 99%

Robust production of purified H₂in a stable, self-regulating, and continuously operating solar fuel generator

Modestino

Walczak

Berger

et al. 2014

Energy Environ. Sci.

107

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The development of practical solar-driven electrochemical fuel generators requires the integration of light absorbing and electrochemical components into an architecture that must also provide easy separation of the product fuels. Unfortunately, many of these components are not stable under the extreme pH conditions necessary to facilitate ionic transport between redox reaction sites. By using a controlled recirculating stream across reaction sites, this work demonstrates a stable, self-regulating and continuous purified solarhydrogen generation from near neutral pH electrolytes that yield continuous nearly pure H 2 streams with solar-fuel efficiencies above 6.2%.Converting solar energy directly into chemical fuel (i.e. articial photosynthesis) could potentially provide a carbon-neutral alternative to fossil fuels.1-5 Since the discovery of light driven electrochemical water splitting in the early 1970s by Fujishima and Honda, 6 there has been continuing research into the development of photoelectrochemical (PEC) cells which has resulted in systems with solar to hydrogen conversion efficiencies as high as 18%.7-9 These laboratory-scale demonstrations have tended to rely on multi-junction photovoltaic (PV) components, water splitting catalysts, and other complex components that have limited stability under electrolytes necessary for efficient operation (i.e. strong acids or bases). 10,11Recently, systems composed of multi-junction amorphous silicon PV cells and cobalt-based catalysts have been developed that operate at high efficiencies and under near-neutral buffered electrolytes.12,13 Importantly, with few exceptions, 9 previous device demonstrations co-evolve hydrogen and oxygen in a common electrolyte solution. For practical implementation of solar-fuel generators, the reduction (i.e. H 2 for water splitting) and oxidation (O 2 ) products need to be produced at physically separated sites. This is of vital importance for several reasons.(1) The gaseous fuel can be collected in its pure form avoiding the need for expensive gas separation steps. (2) Potential losses due to crossover of the reduction product to the oxidation site can be minimized and (3) the accumulation of explosive mixtures of fuels and oxidants can be avoided. To achieve the required product separation, integrated devices incorporate ion-conducting and product impermeable membranes to physically separate the electrodes and allow for the electrochemical production of fuels, 14,15 an approach analogous to that used in commercial electrolysis systems. 16-19Operation under moderate pH conditions relaxes the stability constraints of practical light absorbing and catalyst components (e.g. silicon based PV components and earthabundant catalysts) 12,13 and mitigates the risks associated with managing large volumes of highly corrosive solutions. However, operation of water splitting systems under near neutral Broader contextPractical solar fuel generators will likely require the use of economically viable components, the operation under environmental...

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Efficient Solar Water Splitting, Exemplified by RuO₂-Catalyzed AlGaAs/Si Photoelectrolysis

Cited by 366 publications

References 28 publications

A taxonomy for solar fuels generators

A taxonomy for solar fuels generators

Comparison of Alternative Molten Electrolytes for Water Splitting to Generate Hydrogen Fuel

Robust production of purified H₂in a stable, self-regulating, and continuously operating solar fuel generator

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Efficient Solar Water Splitting, Exemplified by RuO2-Catalyzed AlGaAs/Si Photoelectrolysis

Cited by 366 publications

References 28 publications

A taxonomy for solar fuels generators

A taxonomy for solar fuels generators

Comparison of Alternative Molten Electrolytes for Water Splitting to Generate Hydrogen Fuel

Robust production of purified H2in a stable, self-regulating, and continuously operating solar fuel generator

Contact Info

Product

Resources

About

Efficient Solar Water Splitting, Exemplified by RuO₂-Catalyzed AlGaAs/Si Photoelectrolysis

Robust production of purified H₂in a stable, self-regulating, and continuously operating solar fuel generator