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 (V_RHE) and superior applied bias photon-to-current efficiency (1.62%) at 0.6 V_RHE. 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.