In-situ generation of g-C3N4 on BiVO4 photoanode for highly efficient photoelectrochemical water oxidation

Abstract Constructing a heterojunction photoelectrode is an effective way to promote the photogenerated charge separation in photoelectrochemical (PEC) water oxidation. In this work, we successfully fabricated C3N4/BiVO4 hybrid electrodes by integrating g-C3N4 onto the nanoporous BiVO4 via a simple in-situ synthesis method. The as-prepared C3N4/BiVO4 photoanodes were systematically studied by Electrochemical Impedance Spectroscopy, steady-state surface photovoltage (SPV), transient SPV, Open circuit potential and Photoluminescence measurements. With an optimal loading of g-C3N4, the 2-C3N4/BiVO4 electrode showed a high photocurrent density of 4.06 mA/cm2 at 1.23 V (vs. RHE) for water oxidation, a 2.8 times enhancement over that of the BiVO4. It is found that g-C3N4 improved the PEC performance of the photoanodes by simultaneously promoting the charge separation and surface reaction kinetics. When a NiOOH co-catalyst was immobilized onto the 2-C3N4/BiVO4 electrode, both the PEC property and stability of the photoanode were enhanced. An extremely high photocurrent density of 5.44 mA/cm2 at 1.23 V was achieved. The largest half-cell solar energy conversion efficiency for NiOOH/2-C3N4/BiVO4 was 1.43% at 0.78 V, corresponding to 8.4 times that of unmodified BiVO4 (0.17% at 0.97 V). This work brings new insight into the development of C3N4-based devices for application in solar to fuel conversion.