AbstractThe ongoing problems in western countries connected to the global energy supply urgently force the research community to strive in finding new methodologies for boosting the functional properties of earth‐abundant raw materials, for example, the largely available cupreous oxide. In this work, the authors focus on the surface sensitization of this metal oxide semiconductor with an argon plasma treatment, that promotes, during photoelectrochemical hydrogen evolution, the formation of metallic copper nanostructures. Interestingly, these copper‐based hierarchical nano‐branches, having inherent plasmonic properties, are at the origin of the improved shelf‐life of the modified Cu2O photocathode, as is demonstrated by advanced structural and photophysical analyses. This proposed photophysical mechanism for an operando electrode stabilization suggests that a self‐healing process can occur within the Cu2O/plasmonic Cu heterostructure. These findings pave the way to the implementation of new, easy‐to‐make strategies to improve the properties of low‐cost, low‐toxicity energy materials.