Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction

摘要

Objective evaluation of the activity of electro-catalysts 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 electro-deposited 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.