Ag and N-doped graphene quantum dots co-modified CuBi2O4 submicron rod photocathodes with enhanced photoelectrochemical activity

Photoelectrochemical (PEC) water splitting that can mimic natural photosynthesis to directly harvest and convert solar energy into clean and sustainable hydrogen energy, has been known as a promising avenue for addressing environmental pollution and energy crisis. Spinel-type CuBi2O4 semiconductor as a promising photocathode material for solar water reduction has attracted much attention because of its many unique advantages. However, PEC activity of pristine CuBi2O4 is far from satisfying because of its poor charge carrier transport and transfer efficiency. Herein we report that Ag+ ions and N-doped graphene quantum dots (NGQDs) co-modified CuBi2O4 submicron rods (NGQDs/Ag-CBO SMRs) photocathode can show enhanced PEC activity. Our work demonstrated that one-dimensional structure, Ag+ ions doping, and NGQDs loading benefited the separation and transfer of photogenerated carriers and improved light harvesting ability, which were collectively contributed to enhanced PEC activity of NGQDs/Ag-CBO SMRs photocathode. As a result, the photocurrent density achieved on NGQDs/Ag-CBO SMRs photocathode under AM1.5G simulated sunlight at 0.3 V vs. RHE was 8.8, 2.3, 1.8, and 5.9-times larger than those obtained on CBO SMRs, Ag-CBO SMRs, NGQDs/CBO SMRs, and NGQDs/Ag-CBO microspheres (MSs) ones, respectively. The present study provides a new strategy for designing low-cost and highly efficient photocathodes.