Fabrication and characterization of a p-type Cu3Nb2O8 photocathode toward photoelectrochemical reduction of carbon dioxide

We report a new p-type Cu3Nb2O8 as a thin film photocathode, which was fabricated through spin-coating by a metal organic decomposition method. The p-type Cu3Nb2O8 photocathode exhibited a strong cathodic photocurrent, and the incident photon-to-current conversion efficiency plot confirmed that the p-type Cu3Nb2O8 photocathode has the ability to utilize the visible light (lambda < ca. 480 nm). Furthermore, we demonstrated photoelectrochemical reduction of carbon dioxide with the primary product being carbon monoxide by utilizing the p-type Cu3Nb2O8 photocathode under AM 1.5 G solar light irradiation. From the results of Mott-Schottky analysis, UV-vis measurement and ultraviolet photoemission spectroscopy, the conduction band potential of p-type Cu3Nb2O8 was estimated to be -1.21 V versus a normal hydrogen electrode (NHE) at pH 7 with its conduction band edge located at a more negative potential than the reduction potential of carbon dioxide to carbon monoxide. Although the cathodic photocurrent of the p-type Cu3Nb2O8 photocathode gradually decayed with time, it recovered upon thermal annealing in air. This behavior suggests that the photocurrent response of the p-type Cu3Nb2O8 photocathode is intimately related to variation of the valence state of copper ions. In this paper, the photoelectrochemical properties of the p-type Cu3Nb2O8 photocathode are described in conjunction with optical, electrical and structural properties, and characteristics of the p-type Cu3Nb2O8 photocathode for the photoelectrochemical reduction of carbon dioxide are discussed. (C) 2015 Elsevier B.V. All rights reserved.