A low overpotential photoelectrochemical reduction of carbon dioxide to methanol with highly photoactive hierarchical structured cuprous oxide

Abstract In this study, two different highly scalable hierarchical structured photocathodes of Cu2O nanowire (NW) and microyarn (MY), were prepared and evaluated for their photoelectrochemical (PEC) reduction of CO2 (PECRC) to methanol activity. Notably, Cu2O NW showed a considerably higher photoactivity than Cu2O MY, and the highest ever reported in terms of photoconversion efficiency in comparison with similar material. The enhancement is ascribed to the increased in light entrapment, carrier density, and reduced charge transfer resistance as a result of highly dense and uniform NW arrays. Additionally, the PECRC to methanol for both Cu2O photocathodes in this study was operated at considerably low positive bias potential (+0.2 V vs. Ag/AgCl). The yield for methanol achieved in this study is also comparable to that of surface-modified Cu2O photocathode prepared by using a more costly technique. The physicochemical characterization of the photocathodes after the PECRC reaction revealed a periodical appearance of CuCO3.Cu(OH)2, Cu, and CuO on the Cu2O photocathode after the PECRC reaction, which is hypothesized to work synergistically during the PECRC to methanol. Without surface modification, bare Cu2O was adequate to catalyze PECRC to methanol. Overall, the integration of highly scalable and photoactive Cu2O NW photocathode and considerably low overpotential for PECRC will be a promising approach to realize the PECRC to methanol in the future.