Optimizing Reaction Kinetics and Thermodynamics for Photocatalytic CO2 Reduction through Spin Polarization Manipulation

Abstract

The intrinsic properties of electrons, “spin”, significantly influence chemical reactions, particularly in catalysis, in terms of reaction rates and pathways. Notably, the effect of electron spin polarization (SP) has been demonstrated to significantly impact photocatalytic processes, yet the exact mechanism remains unclear. In this study, we achieved a controlled manipulation of the material’s SP degree by strategically modulating the Co vacancies (V_Co) within Co_3–xO₄ as corroborated by magnetic circular dichroism (MCD), positron annihilation spectroscopy, X-ray absorption fine structure (XAFS), and density functional theory (DFT) calculations. Carrier kinetic investigation reveals that the inherent SP of the material and external magnetic field augmented SP significantly enhances charge carrier mobility while attenuating the recombination of photoinduced carriers. Significantly, SP confers a thermodynamic benefit in CO₂ reduction, favoring reactant adsorption and concurrently diminishing the free energy requisite for the rate-determining step. Remarkably, a CO production rate of 0.354 μmol h^–1 (5 mg of catalyst) with 100% selectivity is achieved through manipulation of SP within Co_3–xO₄ and applying an external magnetic field. This work reveals the mechanisms of SP effects on photocatalytic reactions, offering insights into the design of CO₂ reduction photocatalysts.