Oxygen Evolution Reaction at Low Overpotential Catalyzed by Nanostructured CuO derived from 2 nm-Sized Colloidal Clusters generated by Laser Ablation at The Air-Liquid Interface

Because oxygen evolution reaction is one of the key factors for artificial photosynthesis of chemicals or fuels from CO₂, a lot of catalysts have been developed. Here, we report CuO catalyst derived from 2 nm-sized Cu based clusters prepared by laser ablation at the air-liquid interface using a colloidal solution as a target[1]. First, colloidal solution was prepared by laser ablation of Cu powder precipitated in a flask filled with pure water. Pulsed laser light was irradiated through the bottom of the flask. After laser irradiation for 1 h, we obtained colloidal solution. Then, laser ablation at the air-liquid interface using a colloidal solution was carried out. After laser ablation at the air-liquid interface, a drastic color change from black to a transparent green was observed. Scanning transmission electron microscopy image revealed monodispersed small cluster formation (ca. 2 nm). Colloidal clusters were stably dispersed in water without any chemical reagents for a few years. To investigate the electrocatalytic activity toward oxygen evolution reaction, colloidal solution was deposited on a carbon paper substrate. After deposition, X-ray diffraction pattern revealed Cu₂(NO₃)(OH)₃ formation on carbon paper. After pre-electrolysis in Ar-purged 1.0 M aqueous Na₂CO₃ solution (pH 11.3) at an applied potential of 1.72 V vs RHE for 1h, most of Cu₂(NO₃)(OH)₃ was changed into CuO. Tafel slope of 54 mV/dec and overpotential of 540 mV was required for 10 mA/cm² in Ar-purged aqueous 1.0M Na2CO3 solution. In addition to 1.0 M Na₂CO₃, electrocatalytic activity in KBi buffer (pH 9.2) was also measured. Tafel slope of 88 mV/dec and overpotential of 570 mV at 1.0 mA/cm² was required. In the stability test in both electrolytes for 24h, stable current density were recorded. Scanning electron microscopy images obtained after electrolysis revealed nanostructured CuO formation. Our catalyst exhibited the lowest overpotential for OER rather than those for the previously reported CuO catalyst.<br/><br/>[1] T. Nishi et al., ACS Appl.Energy Mater. 2020, 3 8383-8392.