The development of cobalt phosphide co-catalysts on BiVO photoanodes to improve HO production.

Photoanodic hydrogen peroxide (HO) production via water oxidation is limited by low yields and poor selectivity. Herein, four variations of cobalt phosphides, including pristine CoP and CoP crystals, and two mixed-phase cobalt phosphides (CoP/CoP) with different ratios, were applied as co-catalysts on the BiVO (BVO) photoanode to improve HO production. The optimal yield and selectivity were approximately 9.6 µmol‧h‧cm and 25.2 % at a voltage bias of 1.7 V vs reversible hydrogen electrode (V) 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 HO production. The P site plays an important role in the desorption of HO formed from the catalyst, which is responsible for the recovery of fresh catalytic sites. Among the four samples, CoP exhibited the best performance for HO 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 HO production.