Fabricating highly efficient heterostructured CuBi2O4 photocathodes for unbiased water splitting

Developing photocathodes with a high photocurrent density and large onset potential is crucial for achieving solar driven water splitting. Herein, we report an efficient copper bismuth oxide (CuBi2O4) photocathode with a unique two-dimensional (2D) porous heterojunction structure. By designing a type II heterojunction structure with CuO, the resultant CuBi2O4/CuO photocathode exhibits a photocurrent density of 1.49 mA cm−2 at 0.6 VSHE, which is over 2 times that of the pristine CuBi2O4 photocathode. Further anodization treatment leads to an improved photocurrent density of 1.87 mA cm−2 at 0.6 VSHE, which is the highest photoresponse for CuBi2O4-based photocathodes. The synergistic effect of high surface area, short charge transfer distance in the 2D structure, efficient charge transfer and improved conductivity are the key reasons for the good performance of the CuBi2O4/CuO photocathodes. Moreover, the onset potential of the anodized CuBi2O4/CuO photocathode was over 1.1 VSHE, enabling an unbiased photoelectrochemical water splitting process by combining with a BiVO4 photoanode. This work highlights the good potential of CuBi2O4 in achieving a spontaneous overall water splitting process.