The development of cobalt phosphide co-catalysts on BiVO4 photoanodes to improve H2O2 production

Photoanodic hydrogen peroxide (H2O2) production via water oxidation is limited by low yields and poor selectivity. Herein, four variations of cobalt phosphides, including pristine CoP and Co2P crystals, and two mixed-phase cobalt phosphides (CoP/Co2P) with different ratios, were applied as co-catalysts on the BiVO4 (BVO) photoanode to improve H2O2 production. The optimal yield and selectivity were approximately 9.6 µmol‧h-1‧cm-2 and 25.2 % at a voltage bias of 1.7 V vs reversible hydrogen electrode (VRHE) under sunlight illumination, respectively. This performance is approximately 1.8 times that of pristine BVO photoanode. The roles of the Co and P sites were investigated. In particular, the Co site promotes the breaking of one HO bond in water to form OH• radicals, which is the rate-determining step in H2O2 production. The P site plays an important role in the desorption of H2O2 formed from the catalyst, which is responsible for the recovery of fresh catalytic sites. Among the four samples, Co2P exhibited the best performance for H2O2 production because it had the highest rate of OH• formation owing to its improved accumulation property. This study offers a rational design strategy for co-catalysts for photoanodic H2O2 production.