Perspectives on the photoelectrochemical storage of solar energy
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Review Perspectives on the photoelectrochemical storage of solar energy
Roel van de Krol, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institute for Solar Fuels, Berlin 14109, Germany Bruce A. Parkinson, Department of Chemistry and School of Energy Resources, University of Wyoming, Laramie, Wyoming 80271, USA Address all correspondence to Roel van de Krol at roel.vandekrol@ helmholtz-berlin.de (Received 24 August 2017; accepted 31 October 2017)
ABSTRACT Direct photoelectrochemical water splitting offers several advantages over PV-powered electrolysis and may become the technology of choice in the future. However, significant R&D efforts and breakthroughs are needed to accomplish this goal. The sustainable production of hydrogen would be an important first step for both powering fuel cells and for enabling large-scale and technologically mature gas phase processes to reduce CO2 and nitrogen to get desired products. Specifically, the central challenge is to produce hydrogen from water using sunlight. Photovoltaics and wind-powered electrolysis are likely to be the technology of choice to produce renewable hydrogen for the next few decades. However, the integration of light absorption and catalysis in ‘direct’ photoelectrolysis routes offers several advantages, such as lower current densities and better heat management, and may become technologically relevant in the second half of this century. This article discusses the research and development efforts and needed breakthroughs to achieve this goal. New chemically stable semiconductors with a band gap between 1.5 and 2.0 eV and long carrier lifetimes are urgently needed to make efficient tandem devices. Scale-up of these research level devices beyond a few cm2 introduces mass transport limitations that require creative electrochemical engineering solutions. Last but not least, standardized methods for measuring efficiencies and stabilities need to be implemented and should lead to official benchmarking and certification laboratories to guide commercial scale up efforts. Keywords: photochemical; energy storage; energy generation
DISCUSSION POINTS • W ater splitting will be a central challenge for any future fossil fuel-free energy infrastructure that relies on liquid or gaseous chemical fuels. • W hile the main materials challenge for solar- and wind-driven electrolysis is the development of better catalysts, the main challenge for photoelectrochemical water splitting is to find new chemically stable optimal-bandgap semiconducting light absorbers. • F urther progress in the development of photo-driven water splitting generators requires significant additional efforts in electrochemical engineering and the development of standardized methods for benchmarking device performance and stability.
Introduction There has been a world-wide effort in the last decade to accelerate the progress of research on converting and storing solar
energy especially in the form of chemical bonds. Major centers for solar fuels research, and programs within the nation
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