Supercritical CO2-Directed Exposure of {111} Crystal Facets in ZnSn(OH)6 for Enhanced Quantum Spin Exchange and Photocatalytic CO2 Reduction

Abstract

The enhancement of photocatalytic efficiency is limited by exciton dynamics, where photogenerated electrons and holes rapidly recombine due to strong Coulomb attraction. The manipulation of electron spin, involving the control of electron spin and spin states, has emerged as a promising strategy to improve photocatalytic performance via spin-polarization-facilitated charge separation. In this work, we demonstrate a spin-polarization effect achieved by treating ZnSn(OH)6 (ZHS) with supercritical CO2 (SC CO2), which accelerates exciton dissociation and spin-dependent electron migration, thereby enhancing the efficiency of photocatalytic CO2 reduction to CO. Mechanistic investigations reveal that SC CO2 treatment induces oxygen vacancies in ZHS, generates spin-polarized electrons, and selectively exposes highly active {111} crystal facets. Experimentally, it reveals that the oxygen vacancies, together with adjacent hydroxyl groups, construct frustrated Lewis pairs (FLPs). Through enhanced quantum spin exchange interactions (QSEIs), the recombination of photogenerated charge carriers is significantly suppressed, and then their lifetime is prolonged, and CO2 adsorption and activation are simultaneously enhanced. It was found that, under treatment at 16 MPa of SC CO2, the CO production rate of ZHS reaches 144.82 μmol·g–1·h–1, which is 29.37 times that of the untreated sample. Therefore, this study demonstrates that manipulating spin-polarized electrons in photocatalytic semiconductors is an effective strategy to boost CO2RR efficiency, offering new insights for the design of efficient spin-dependent photocatalysts toward solar energy conversion.