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

High-quality Cu 2 O 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 Cu 2 O nanoneedles during the calcination process was investigated. The Cu 2 O 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 Cu 2 O on CuO nanoneedles during the calcination process. The optimum Cu 2 O photoelectrode exhibited a strong visible light absorption, small charge transfer resistance, high photocurrent, and suitable band alignment, making it capable to produce H 2 at the Cu 2 O photoelectrode and degrade Rhodamine B (RhB) at the Pt electrode. The hydrogen evolution over the Cu 2 O 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 Cu 2 O electrode at negative voltage due to the transformation between different Cu valence states. The successful hydrogen production and RhB degradation highlight the potential of Cu 2 O nanoneedles for simultaneous clean energy production and environmental remediation. This work also paved the way for the synthesis of a high-quality 1D-Cu 2 O electrode by a controllable method.