Cu₂O Nanoneedle Arrays for Photoelectrochemical H₂ Evolution Coupled with Rhodamine B Degradation

High-quality Cu2O nanoneedles were prepared through potentiostatic anodization of Cu-mesh followed by a calcination method. The effects of anodic voltage and time on the morphology and phase composition of the Cu(OH)2 precursor were systematically studied. Optimized conditions for preparing Cu(OH)2 nanoneedles are determined to be anodizing at 1.4 V for 800 s. Then, the phase evolution from Cu(OH)2 to Cu2O nanoneedles during the calcination process was investigated. The Cu2O nanoneedles with high-purity were obtained by calcination of Cu(OH)2 nanoneedles at 550 °C. For the first time, COMSOL Multiphysics simulation was employed to prove that the curving of nanoneedles is related to the thermal treating expansion stress caused by the nonuniform formation Cu2O on CuO nanoneedles during the calcination process. The optimum Cu2O photoelectrode exhibited a strong visible light absorption, small charge transfer resistance, high photocurrent, and suitable band alignment, making it capable to produce H2 at the Cu2O photoelectrode and degrade Rhodamine B (RhB) at the Pt electrode. The hydrogen evolution over the Cu2O photoelectrode is obtained to be 45 μmol cm–2 h–1 at – 0.8 V. A degradation efficiency of 80% is achieved at the Pt electrode after 2 h reaction. The cyclic voltammetry coupled with in situ Raman spectroscopy confirmed the instability of the Cu2O electrode at negative voltage due to the transformation between different Cu valence states. The successful hydrogen production and RhB degradation highlight the potential of Cu2O nanoneedles for simultaneous clean energy production and environmental remediation. This work also paved the way for the synthesis of a high-quality 1D-Cu2O electrode by a controllable method.