Electrocatalytic water oxidation is a key transformation in many strategies designed to harness solar energy and store it as chemical fuels. Understanding the mechanism(s) of the best electrocatalysts for water oxidation has been a fundamental chemical challenge for decades. Here, we quantitate evolved dioxygen isotopologue composition via gas-phase EPR spectroscopy to elucidate the mechanisms of water oxidation on metal oxide electrocatalysts with high precision. Isotope fractionation is paired with computational and kinetic modeling, showing that this technique is sensitive enough to differentiate O–O bond-forming steps. Strong agreement between experiment and theory indicates that for the nickel-iron layered double hydroxide─one of the best earth-abundant electrocatalysts to be studied─water oxidation proceeds via a dioxo coupling mechanism to form a side-bound peroxide rather than a hydroxide attack to form an end-bound peroxide.

中文翻译：

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电子顺磁共振波谱法从水氧化电催化中分离出氧同位素体

电催化水氧化是许多旨在利用太阳能并将其存储为化学燃料的策略中的关键转变。几十年来，了解水氧化的最佳电催化剂的机制一直是一个基本的化学挑战。在这里，我们通过气相 EPR 光谱定量了演化的双氧同位素体组成，以高精度阐明金属氧化物电催化剂上水氧化的机制。同位素分馏与计算和动力学模型相结合，表明该技术足够灵敏，可以区分 O-O 键形成步骤。实验与理论之间的高度一致表明，对于镍铁层状双氢氧化物（地球上最丰富的待研究电催化剂之一）来说，水氧化通过二氧偶联机制进行，形成侧键过氧化物，而不是氢氧化物攻击形成末端结合的过氧化物。