Understanding the nature of active sites is central to controlling (electro)catalytic activity. Here we employed surface X-ray scattering coupled with density functional theory and surface-enhanced infrared absorption spectroscopy to examine the oxygen evolution reaction on RuO₂ surfaces as a function of voltage. At 1.5 V_RHE, our results suggest that there is an –OO group on the coordinatively unsaturated ruthenium (Ru_CUS) site of the (100) surface (and similarly for (110)), but adsorbed oxygen on the Ru_CUS site of (101). Density functional theory results indicate that the removal of –OO from the Ru_CUS site, which is stabilized by a hydrogen bond to a neighbouring –OH (–OO–H), could be the rate-determining step for (100) (similarly for (110)), where its reduced binding on (100) increased activity. A further reduction in binding energy on the Ru_CUS site of (101) resulted in a different rate-determining step (–O + H₂O – (H⁺ + e⁻) → –OO–H) and decreased activity. Our study provides molecular details on the active sites, and the influence of their local coordination environment on activity.

了解活性位点的性质对于控制（电）催化活性至关重要。在这里，我们采用表面X射线散射，密度泛函理论和表面增强红外吸收光谱技术，研究了RuO ₂表面上的氧气逸出反应与电压的关系。在1.5伏_RHE，我们的结果表明，有一个-OO组对配位不饱和钌（Ru _CUS的（100）面的）位点（并且类似地为（110）），但在Ru吸附的氧_CUS的位点（ 101）。密度泛函理论结果表明从Ru _CUS中去除–OO通过与相邻的–OH（–OO–H）的氢键稳定的位点可能是（100）（与（110）类似）的速率确定步骤，其中其对（100）的结合减少而活性增加。（101）的Ru _CUS位点上结合能的进一步降低导致了不同的速率确定步骤（–O + H ₂ O –（H ⁺  + e ⁻）→–OO–H）和活性降低。我们的研究提供了有关活性位点的分子细节，以及它们的局部配位环境对活性的影响。