Insights into the efficiency and stability of Cu-based nanowires for electrocatalytic oxygen evolution

Copper oxide nanowires with varying oxidation states are prepared and their activity for water oxidation is studied. The nanowires with a CuO phase are found to be the most active, and their degree of crystallinity is important in achieving efficient water oxidation. For the crystalline CuO nanowires in a weakly basic Na₂CO₃ electrolyte, a Tafel slope of 41 mV/decade, an overpotential of approximately 500 mV at ~ 10 mA/cm² (without compensation for the solution resistance), and a faradaic efficiency of nearly 100% are obtained. This electrode maintains a stable current for over 15 h. The low overpotential of 500 mV at 10 mA/cm², small Tafel slope, long-term stability, and low cost make CuO one of the most promising catalysts for water oxidation. Moreover, the evolution of the CuO nanowire morphology over time is studied by electron microscopy, revealing that the diffusion of Cu ions from the interior of the nanowires to their surface causes the aggregation of individual nanowires over time. However, despite this aggregation, the current density remains nearly constant, because the total electrochemically active surface area of CuO does not change.