NdCo₃ Molecular Catalyst Coupled with a BiVO₄ Photoanode for Photoelectrochemical Water Splitting

Abstract

Photoelectrochemical water splitting is a promising strategy for harvesting and converting solar energy to green hydrogen energy. However, the current inferior performance restricts further improvement of the solar-to-hydrogen efficiency. In this work, a molecular catalyst [NdCo3(btp-3H)2(Ac)2(NO3)2] (NO3)·2H2O (referred to as NdCo3 herein) was deposited onto a porous BiVO4 photoanode using a drop-casting method, and the molecular catalyst was held in place on the BiVO4 surface via intermolecular forces. The photoelectrochemical water oxidation performance of the BiVO4/NdCo3 photoanode reached 2.25 mA cm–2 at 1.23 V vs RHE under AM 1.5G illumination (100 mW cm–2), which was much higher than the pristine BiVO4 photoanode (1.49 mA cm–2). The enhanced performance could be attributed to the improvement of the charge carrier transfer efficiency, resulting in the acceleration of the water oxidation kinetics and inhibiting charge carrier recombination. In addition, the electrocatalytic properties of the homogeneous system were also studied. It was found that a heterogeneous catalytic film was formed due to the water solubility of NdCo3, which enabled a long electrolysis process to be maintained. The electrocatalytic performance of a homogeneous system reached 1 mA cm–2 at 2.31 V vs RHE and was different from the heterogeneous catalytic film (reached 1 mA cm–2 at 2.10 V vs RHE). This integrated system showed that the combination of a molecular catalyst with a photoelectrode helped to promote charge-carrier transport and separation, reducing the amount of charge-carrier recombination. Our approach may be applicable to other materials, helping to provide ideas for developing material combinations capable of achieving greater solar-to-hydrogen efficiencies.