<i>In situ</i> fiber-optic detection of photocorrosion in electrochemically grown CuO photocathodes

Semiconductor metal oxides with narrow bandgap have emerged as a promising platform for photoelectrochemical reactions, yet their photoelectron-induced photocorrosion effect has been a limitation for their wider applications. Understanding the conversion processes concomitant with photoelectrochemical reaction at the electrode–electrolyte interface plays a crucial role in revealing the corrosion mechanisms and advancing the development of efficient photocathodes. However, accurately and in situ tracking these dynamic chemical events remains a great challenge due to the fact that reaction processes occur at nanoscale interfaces. Here, we track the electrochemical growth and conversion of copper nanostructures at interface by the evanescent field of the surface plasmon wave by using a gold-coated optical fiber as an electrochemical electrode and light sensing probe. The results exhibit correlation between redox processes of copper species and plasmonic resonances. Furthermore, in situ fiber-optic detection reveals the photocorrosion dynamics under photoelectrochemical reaction, including photoelectron-induced self-reduction of copper oxide and self-oxidation of cuprous oxide. These demonstrations facilitate not only the diagnosis for the health condition of photocathode nanomaterial, but also the understanding of the underlying reaction mechanism, and thus are potentially crucial for advancing the development of highly efficient photocathodes in future energy applications.