An MgO passivation layer and hydrotalcite derived spinel Co 2 AlO 4 synergically promote photoelectrochemical water oxidation conducted using BiVO 4 -based photoanodes.

M x Co 3- x O 4 co-catalysed photoanodes with high potential for improvement in PEC water-oxidizing properties are reported. However, it is difficult to control the recombination of photogenerated carriers at the interface between the catalyst and cocatalyst. Here, an ultra-thin MgO passivation layer was introduced into the M x Co 3- x O 4 /BiVO 4 coupling system to construct a ternary composite photoanode Co 2 AlO 4 /MgO/BiVO 4 . The photocurrent density of the electrode is 3.52 mA cm -2 , which is 3.2 times that of BiVO 4 (at 1.23 V vs. RHE). The photocurrent is practically increased by 0.86 mA cm -2 and 1.56 mA cm -2 in comparison with that of Co 2 AlO 4 /BiVO 4 and MgO/BiVO 4 electrodes, respectively. Meanwhile, the Co 2 AlO 4 /MgO/BiVO 4 electrode has the highest charge separation efficiency, the lowest charge transfer resistance ( R ct ) and best stability. The excellent PEC performance could be attributed to the inhibitive effect provided by the MgO passivation layer that efficaciously suppresses the electron-hole recombination at the interface and drives the hole transfer outward, which is induced by Co 2 AlO 4 to capture the electrode/electrolyte interface for efficient water oxidation reaction. In order to understand the origin of this improvement, first-principles calculations with density functional theory (DFT) were performed. The theoretical investigation converges to our experimental results. This work proposes a novel idea for restraining the recombination of photogenerated carriers between interfaces and the rational design of efficient photoanodes.