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Published November 13, 2013 | Supplemental Material
Journal Article Open

Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction

Abstract

Objective evaluation of the activity of electrocatalysts for water oxidation is of fundamental importance for the development of promising energy conversion technologies including integrated solar water-splitting devices, water electrolyzers, and Li-air batteries. However, current methods employed to evaluate oxygen-evolving catalysts are not standardized, making it difficult to compare the activity and stability of these materials. We report a protocol for evaluating the activity, stability, and Faradaic efficiency of electrodeposited oxygen-evolving electrocatalysts. In particular, we focus on methods for determining electrochemically active surface area and measuring electrocatalytic activity and stability under conditions relevant to an integrated solar water-splitting device. Our primary figure of merit is the overpotential required to achieve a current density of 10 mA cm^(–2) per geometric area, approximately the current density expected for a 10% efficient solar-to-fuels conversion device. Utilizing the aforementioned surface area measurements, one can determine electrocatalyst turnover frequencies. The reported protocol was used to examine the oxygen-evolution activity of the following systems in acidic and alkaline solutions: CoO_x, CoPi, CoFeO_x, NiO_x, NiCeO_x, NiCoO_x, NiCuO_x, NiFeO_x, and NiLaO_x. The oxygen-evolving activity of an electrodeposited IrO_x catalyst was also investigated for comparison. Two general observations are made from comparing the catalytic performance of the OER catalysts investigated: (1) in alkaline solution, every non-noble metal system achieved 10 mA cm^(–2) current densities at similar operating overpotentials between 0.35 and 0.43 V, and (2) every system but IrO_x was unstable under oxidative conditions in acidic solutions.

Additional Information

© 2013 American Chemical Society. Received: July 11, 2013. Publication Date (Web): October 30, 2013. This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under award no. DE-SC0004993. We are grateful for the many useful insights we have received regarding this work from various members of the electrochemistry community. In particular, we would like to acknowledge useful discussions with Allen J. Bard, Fred C. Anson, Nathan S. Lewis, Carl A. Koval, Manuel P. Soriaga, and Hans-Joachim Lewerenz. XPS data was collected at the Molecular Materials Research Center of the Beckman Institute of the California Institute of Technology. The authors declare no competing financial interest.

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