Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Photonics and Interfaces, Station 6, CH-1015 Lausanne, Switzerland.
Nat Commun. 2017 Feb 24;8:14280. doi: 10.1038/ncomms14280.
Multi-electron heterogeneous catalysis is a pivotal element in the (photo)electrochemical generation of solar fuels. However, mechanistic studies of these systems are difficult to elucidate by means of electrochemical methods alone. Here we report a spectroelectrochemical analysis of hydrogen evolution on ruthenium oxide employed as an electrocatalyst and as part of a cuprous oxide-based photocathode. We use optical absorbance spectroscopy to quantify the densities of reduced ruthenium oxide species, and correlate these with current densities resulting from proton reduction. This enables us to compare directly the catalytic function of dark and light electrodes. We find that hydrogen evolution is second order in the density of active, doubly reduced species independent of whether these are generated by applied potential or light irradiation. Our observation of a second order rate law allows us to distinguish between the most common reaction paths and propose a mechanism involving the homolytic reductive elimination of hydrogen.
多电子多相催化是（光电）电化学太阳能燃料生成的关键因素。然而，仅通过电化学方法很难阐明这些体系的机理研究。在这里，我们报告了在用作电催化剂的氧化钌和基于氧化亚铜的光阴极部分上进行的析氢的光谱电化学分析。我们使用光吸收光谱法来量化还原氧化钌物种的密度，并将其与质子还原产生的电流密度相关联。这使我们能够直接比较暗电极和光电极的催化功能。我们发现，无论这些活性双还原物种是由外加电位还是光辐照产生，其还原氢的反应级数均为二级。我们对二级反应速率定律的观察可以区分最常见的反应途径，并提出一种涉及氢的均裂还原消除的机理。
