http://pubs.acs.org/journal/aelccp
Addressing the Key Aspects of Photoelectrocatalytic Systems for Solar Fuel Production
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researchers that tackle the key challenges of solar fuel production. With over 100 presentations from all around the world, the symposium covered all of the fundamental aspects of photoelectrocatalytic energy conversion, spanning from small to large architectures, from catalyst and nanostructure design to assembled devices and systems, toward practical utilization of the resulting technology. Important themes were discovery and nanostructuring approaches of novel materials. Presentations on photocatalytic particles, semiconductor photoelectrodes, protection layers, and hydrogen/oxygen evolution catalysts showed impressive progress on finding suitable materials with maximized light harvesting, excellent charge separation and transfer properties, and good capability for driving surface redox reactions for solar fuel production. Starting with some conventional photoactive materials with relatively large bandgaps like TiO2, Prof. Gang Liu from the Chinese Academy of Sciences reported the strategies of doping and hetorostructure forming to increase the light-absorbing properties of TiO2 and C3N4 materials. Dr. Ian D. Sharp from Lawrence Berkeley National Laboratory discussed the fundamental understanding of excited-state processes and charge transfer kinetics on smaller bandgap oxide-based photoanodes. The investigations on new-generation photoelectrode systems including III−V group and 2D semiconductors, chalcogenides, and oxynitrides were also discussed in much detail. Dr. Todd Deutsch from the National Renewable Energy Laboratory discussed recent advances in III−V multijunction absorbers for water splitting, for which efficiencies above 15% and noteworthy improvements in stability have been achieved. Interfacial engineering plays a critical role in the photoelectrochemical systems because it drastically affects the charge transport behavior. Work from Prof. Shannon Boettcher’s group at the University of Oregon highlighted this interfacial issue, with particular focus on the fundamental understanding of the charge transfer process at the catalyst/semiconductor photoelectrode interface. Prof. Dunwei Wang’s team from Boston College studied the energetics and kinetics of interfacial charge transfer with synchrotron methods and optoelectrical impedance methods, revealing different mechanisms for the observed photocurrent enhancements depending on the type of catalyst. From the design and selection of semiconductor light absorbers and catalysts, new materials discovery clearly lays an essential foundation for photoelectrocatalytic systems, while fundamental understanding of the electronic structures,
o address global grand challenges of energy supply and climate change, we are forced to explore low-cost, clean, and sustainable energy conversion and storage systems. Solar fuels produced from (photo)electrocatalytic water splitting and/or CO2 reduction have been considered as one of the ultimate solutions, not only to solve the production and supply challenge of bulk renewable energy but also to reduce our carbon footprint without competing with food stocks. However, despite decades of intensive research endeavors, the efficient and selective conversion of water/ CO2 to valuable chemical fuels with (photo)electrocatalytic systems still remains one of the Holy Grails of chemistry. To promote the advances of this highly challenging yet critically important research field, the symposium ES7 - “(Photo)electrocatalytic Materials and Integrated Assemblies for Solar Fuels ProductionDiscovery, Characterization and Performance” at the MRS 2017 Spring Meeting in Phoenix aimed to provide a platform for world-leading researchers to discuss their latest research progress and to exchange ideas toward the practical utilization of sustainable solar fuels. As the intention of its organizers (Figure 1), this symposium featured a multidisciplinary and interdisciplinary cohort of
Figure 1. Photo of the organizers of symposium ES7 - “(Photo)electrocatalytic Materials and Integrated Assemblies for Solar Fuels ProductionDiscovery, Characterization and Performance” at the MRS 2017 Spring Meeting in Phoenix. Left to right: Akihiko Kudo, Francesca Maria Toma, Roel Van de Krol, Lianzhou Wang. (Photo courtesy of F. M. Toma.) © XXXX American Chemical Society
Received: October 31, 2017 Accepted: November 2, 2017
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DOI: 10.1021/acsenergylett.7b01079 ACS Energy Lett. 2017, 2, 2725−2726
Energy Focus
Cite This: ACS Energy Lett. 2017, 2, 2725-2726
Energy Focus
ACS Energy Letters
our colleagues in this discipline. We as the organizers would like to express our congratulations and appreciation to all of the authors for their excellent contributions in this challenging yet highly promising research field and very much look forward to the next related symposium at the 2017 MRS Fall meeting. We believe that symposia on photoelectrocatalytic systems for solar fuel production will further promote the advances of photoelectrocatalysis for better utilization of renewable solar energy.
interfacial band-edge energetics, and mitigation of loss mechanisms is critical for rational improvement and further development of these systems. To this end, theory and modeling, as well as advanced in situ and in operando measurements, are rapidly gaining importance in the field. Professor Giulia Galli from the University of Chicago applied first-principles calculations to elucidate the nature of charge transport properties of various semiconductor light absorbers, which provides important insights for the experimentalists to consider. Dr Junko Yano from Lawrence Berkeley National Laboratory applied soft and hard X-ray spectroscopy to in situ characterize the mechanism and processes of CO2 reduction catalysis. The electrochemical reduction of CO2 to valuable chemical fuels was a particular highlight of this symposium. Prof. Harry A. Atwater from the California Institute of Technology and the Joint Centre for Artificial Photosynthesis (JCAP) provided an excellent overview on the progress and state-of-the-art in CO2 reduction and on the remaining challenges in terms of selectivity and efficiency. Dr. Takeshi Morikawa from Toyota Central R&D laboratories proposed an interesting bifunctional design to couple photoinduced CO2 reduction with a simultaneous water oxidation process, based on a metal complex/semiconductor hybrid system. Such systems may offer new opportunities toward the better utilization of solar energy. Our ultimate dream for photoelectrocatalytic solar fuel production is to mimic nature’s photosynthetic process while exceeding its energy conversion efficiencies (1−2%). Thus, a photoelectrocatalytic device must be an integrated system that covers all of the architectural design and assemblies of the reactor to accomplish the light harvesting, charge and mass transport, catalytic reactions, and product separation and collection processes. Toward this goal, the research team must be multidisciplinary to include not only chemists, physicists, and material scientists but also researchers in engineering. Professor Nathan Lewis from the California Institute of Technology discussed the latest advances on integrated photoelectrochemcial water splitting systems that used membranes as the separator and support to facilitate sunlight-driven hydrogen production. Excitingly, a stable solardriven water splitting device supported with a bipolar membrane led to 10% solar to hydrogen (STH) conversion efficiency. In another invited talk, Professor Jong Hyeok Park from Yonsei University (Korea) presented their recent progress on the design of a photoelectrochemcial tandem reactor by incorporating a water-resistant dye-sensitized solar cell that can achieve 7% STH. In a highly creative attempt toward a practical solar fuel system, Prof. Daniel G. Nocera from Harvard University combined a biological system with inorganic counterparts to form an integrated hybrid device, which has the function of mimicking the true nature of photosynthesis, i.e., water splitting plus CO2 reduction. With efficiencies above 6%, this so-called “bionic leaf” greatly exceeds the efficiency of nature’s photosynthesis process. In summary, the 5 day program covered a broad range of the research topics in this exciting research field, which may pave a solid pathway toward the realization of our long-standing dream of sustainable artificial photosynthesis, addressing both our grand energy and climate change challenges. It was impressive to see, even at the last Friday afternoon session of the symposium, that there were still over 20 researchers in the audience, clearly reflecting the commitment and enthusiasm of
Francesca Maria Toma*,† Akihiko Kudo*,‡ Roel Van de Krol*,§ Lianzhou Wang*,⊥
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† Chemical Science Division, Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States ‡ Department of Applied Chemistry, Tokyo University of Science, Tokyo 162-8601, Japan § Institute for Solar Fuels, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 14109 Berlin, Germany ⊥ School of Chemical Engineering, The University of Queensland, St. Lucia, Queensland 4072, Australia
AUTHOR INFORMATION
Corresponding Authors
*E-mail: *E-mail: *E-mail: *E-mail:
[email protected] (F.M.T.).
[email protected] (A.K.).
[email protected] (R.V.d.K.).
[email protected] (L.W.).
Notes
Views expressed in this Energy Focus are those of the authors and not necessarily the views of the ACS. The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The organizers of the meeting (the authors) thank support from ACS Energy Letters, California Institute of Technology, Bruker Nanosurfaces, and the Materials Research Society.
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DOI: 10.1021/acsenergylett.7b01079 ACS Energy Lett. 2017, 2, 2725−2726
