Adjusting the electronic structure of Keggin-type polyoxometalates to construct S-scheme heterojunction for photocatalytic hydrogen evolution

Abstract

The sluggish electron migration rate and pronounced electron-hole recombination, pose significant obstacles to achieving high photocatalytic efficiency. The utilization of multiple catalysts for the construction of heterojunctions can effectively enhance charge separation. A series of Keggin-type hollow dodecahedral polyoxometalates were prepared via hydrothermal synthesis, and their molecular orbitals were modified through the addition of metal elements. The incorporation of metal elements modulated the electronic structure of polyoxometalates, effectively enhancing the electron aggregation capability of polyoxometalates. Single-component catalysts often face serious hole-electron recombination. In order to solve this problem, the scheme of constructing heterojunction is proposed to improve the electron transport efficiency. By immobilizing ZnCdS nanoparticles onto the polyoxometalate surface, the heterojunction architecture was engineered to significantly enhance the interfacial charge transfer capability. Density Functional Theory (DFT) calculations and the experimental results indicate that the modulation of metallic components renders the polyoxometalate a more favorable energy-level orbital. The catalytic mechanism of ZnCdS and KMoP S-scheme heterojunction was also verified. The formation of S-scheme heterojunctions further improves the electron transfer efficiency compared to other traditional heterojunctions, achieving efficient utilization of photo generated electrons and holes. Additionally, the S-scheme heterojunction shifts the catalystʼs d-band center closer to the Fermi level, thereby improving electrical conductivity. This article provides a new approach for energy level regulation of polyoxometalates and the design of S-scheme heterojunctions.