The oxygen evolution reaction has an important role in many alternative-energy schemes because it supplies the protons and electrons required for converting renewable electricity into chemical fuels1-3. Electrocatalysts accelerate the reaction by facilitating the required electron transfer4, as well as the formation and rupture of chemical bonds5. This involvement in fundamentally different processes results in complex electrochemical kinetics that can be challenging to understand and control, and that typically depends exponentially on overpotential1,2,6,7. Such behaviour emerges when the applied bias drives the reaction in line with the phenomenological Butler-Volmer theory, which focuses on electron transfer8, enabling the use of Tafel analysis to gain mechanistic insight under quasi-equilibrium9-11 or steady-state assumptions12. However, the charging of catalyst surfaces under bias also affects bond formation and rupture13-15, the effect of which on the electrocatalytic rate is not accounted for by the phenomenological Tafel analysis8 and is often unknown. Here we report pulse voltammetry and operando X-ray absorption spectroscopy measurements on iridium oxide to show that the applied bias does not act directly on the reaction coordinate, but affects the electrocatalytically generated current through charge accumulation in the catalyst. We find that the activation free energy decreases linearly with the amount of oxidative charge stored, and show that this relationship underlies electrocatalytic performance and can be evaluated using measurement and computation. We anticipate that these findings and our methodology will help to better understand other electrocatalytic materials and design systems with improved performance.

中文翻译：

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化学与偏压在电催化析氧中的关键作用

析氧反应在许多替代能源方案中具有重要作用，因为它提供将可再生电力转化为化学燃料所需的质子和电子1-3。电催化剂通过促进所需的电子转移 4 以及化学键的形成和断裂 5 来加速反应。这种参与根本不同的过程会导致复杂的电化学动力学，理解和控制可能具有挑战性，并且通常以指数方式取决于过电位 1,2,6,7。当应用偏压驱动反应符合现象学 Butler-Volmer 理论时，就会出现这种行为，该理论侧重于电子转移 8，从而使使用 Tafel 分析能够在准平衡 9-11 或稳态假设 12 下获得机械洞察力。然而，偏压下催化剂表面的充电也会影响键的形成和断裂 13-15，其对电催化速率的影响未由现象学 Tafel 分析 8 解释，并且通常是未知的。在这里，我们报告了对氧化铱的脉冲伏安法和原位 X 射线吸收光谱测量，以表明施加的偏压不直接作用于反应坐标，而是通过催化剂中的电荷积累影响电催化产生的电流。我们发现活化自由能随着存储的氧化电荷量线性降低，并表明这种关系是电催化性能的基础，可以通过测量和计算进行评估。