MnCo2O4 as a Photothermal Modifier for BiVO4 Photoanode to Achieve Efficient Photoelectrochemical Water Oxidation

Spinel oxides are widely used to enhance photoanodes’ photoelectrochemical (PEC) water oxidation performance. In this paper, we demonstrate that a p-type photothermal MnCo2O4 layer, inserted between BiVO4 and FeOOH cocatalysts, can significantly enhance PEC performance. On the one hand, the charge recombination is greatly suppressed since p-type MnCo2O4 can form a p–n heterojunction with n-type BiVO4. On the other hand, upon near-infrared (NIR) light irradiation, the deposited MnCo2O4 shows excellent photothermal conversion performance that can further facilitate charge transfer and accelerate the water oxidation process by elevating the operating temperature. In addition, the FeOOH cocatalyst is introduced to fully utilize the holes reaching the surface and further enhance the surface oxygen evolution kinetics. Consequently, the carefully constructed BiVO4/MnCo2O4/FeOOH photoanode shows excellent photocurrent (4.71 mA cm–2) at 1.23 V vs RHE (VRHE) and superior applied bias photon-to-current efficiency (1.62%) at 0.6 VRHE. The photocurrent density maintains more than 90% of the initial photocurrent after 4 h of combined solar and NIR light irradiation. Enhancing the PEC catalytic activity of photoelectrodes using photothermal materials is a simple and effective strategy, which can be used to explore PEC activity enhancement in other photoelectrodes.