The development of surface-immobilized molecular redox catalysts is an emerging research field with promising applications in sustainable chemistry. In electrocatalysis, paramagnetic species are often key intermediates in the mechanistic cycle but are inherently difficult to detect and follow by conventional in situ techniques. We report a new method, operando film-electrochemical electron paramagnetic resonance spectroscopy (FE-EPR), which enables mechanistic studies of surface-immobilized electrocatalysts. This technique enables radicals formed during redox reactions to be followed in real time under flow conditions, at room temperature and in aqueous solution. Detailed insight into surface-immobilized catalysts, as exemplified here through alcohol oxidation catalysis by a surface-immobilized nitroxide, is possible by detecting active-site paramagnetic species sensitively and quantitatively operando, thereby enabling resolution of the reaction kinetics. Our finding that the surface electron-transfer rate, which is of the same order of magnitude as the rate of catalysis (accessible from operando FE-EPR), limits catalytic efficiency has implications for the future design of better surface-immobilized catalysts.

表面固定化分子氧化还原催化剂的开发是一个新兴的研究领域，在可持续化学中具有广阔的应用前景。在电催化中，顺磁性物质通常是机械循环中的关键中间体，但本质上很难通过传统的原位技术检测和跟踪。我们报告了一种新方法，即原位薄膜电化学电子顺磁共振波谱（FE-EPR），它可以对表面固定化电催化剂进行机理研究。该技术能够在流动条件下、室温和水溶液中实时跟踪氧化还原反应过程中形成的自由基。通过灵敏且定量地检测活性位点顺磁性物质，可以详细了解表面固定催化剂（如此处通过表面固定氮氧自由基进行醇氧化催化所例示的），从而能够解析反应动力学。我们发现表面电子转移速率与催化速率（可从操作 FE-EPR 获得）处于同一数量级，限制了催化效率，这对未来更好的表面固定催化剂的设计具有影响。