Water-Splitting Standards

Abstract

Chemistry Widespread use of functional electrocatalytic water-splitting systems in conjunction with solar power infrastructure will probably require a composition of Earth-abundant materials that remain stable under the reaction conditions and operate efficiently at minimal overpotential (a measure of how much of the input energy gets stored in the products' chemical bonds for later use when the Sun has set, rather than lost as heat). Numerous reports highlight favorable features of particular experimental catalysts in this context, but cross-comparisons have proven challenging in the absence of established standards for the testing conditions. McCrory et al. offer a preliminary framework for making apples-to-apples comparisons of catalysts for the oxygen-evolving half of the couple. They report benchmark tests of nine representative non–precious metal catalysts deposited on glassy carbon electrodes, under standardized acidic (1 M sulfuric acid) and basic (1 M sodium hydroxide) conditions. After first assessing the active surface area for normalization, the authors measured the overpotential necessary to attain a current density of 10 mA/cm2 and then tracked performance over 2 hours. None of the tested non–precious metal catalysts were stable in acid, highlighting a priority for further research. In base, the overpotentials across the test set varied relatively little, spanning a range between 350 and 430 mV. J. Am. Chem. Soc. 135 , 16977 (2013).