Solar-Driven H2O2 Generation From H2O and O2 Using Earth-Abundant Mixed-Metal Oxide@Carbon Nitride Photocatalysts

Light-driven generation of H2O2 only from water and molecular oxygen could be an ideal pathway for clean production of solar fuels. In this work, a mixed metal oxide/graphitic-C3N4 (MMO@C3N4) composite was synthesized as a dual-functional photocatalyst for both water oxidation and oxygen reduction to generate H2O2. The MMO was derived from a NiFe-layered double hydroxide (LDH) precursor for obtaining a high dispersion of metal oxides on the surface of the C3N4 matrix. The C3N4 is in the graphitic phase and the main crystalline phase in MMO is cubic NiO. The XPS analyses revealed the doping of Fe3+ in the dominant NiO phase and the existence of surface defects in the C3N4 matrix. The formation and decomposition kinetics of H2O2 on the MMO@C3N4 and the control samples, including bare MMO, C3N4 matrix, Ni- or Fe-loaded C3N4 and a simple mixture of MMO and C3N4, were investigated. The MMO@C3N4 composite produced 63molL(-1) of H2O2 in 90min in acidic solution (pH3) and exhibited a significantly higher rate of production for H2O2 relative to the control samples. The positive shift of the valence band in the composite and the enhanced water oxidation catalysis by incorporating the MMO improved the light-induced hole collection relative to the bare C3N4 and resulted in the enhanced H2O2 formation. The positively shifted conduction band in the composite also improved the selectivity of the two-electron reduction of molecular oxygen to H2O2.