Inducing spin polarization via Co doping in the BiVO4 cell to enhance the built-in electric field for promotion of photocatalytic CO2 reduction

Abstract

The efficiency of CO₂ photocatalytic reduction is severely limited by inefficient separation and sluggish transfer. In this study, spin polarization was induced and built-in electric field was strengthened via Co doping in the BiVO₄ cell to boost photocatalytic CO₂ reduction. Results showed that owing to the generation of spin-polarized electrons upon Co doping, carrier separation and photocurrent production of the Co-doped BiVO₄ were enhanced. CO production during CO₂ photocatalytic reduction from the Co-BiVO₄ was 61.6 times of the BiVO₄. Notably, application of an external magnetic field (100 mT) further boosted photocatalytic CO₂ reduction from the Co-BiVO₄, with 68.25 folds improvement of CO production compared to pristine BiVO₄. The existence of a built-in electric field (IEF) was demonstrated through density functional theory (DFT) simulations and kelvin probe force microscopy (KPFM). Mechanism insights could be elucidated as follows: doping of magnetic Co into the BiVO₄ resulted in increased the number of spin-polarized photo-excited carriers, and application of a magnetic field led to an augmentation of intrinsic electric field due to a dipole shift, thereby extending carrier lifetime and suppressing charges recombination. Additionally, HCOO^- was a crucial intermediate in the process of CO₂RR, and possible pathways for CO₂ reduction were proposed. This study highlights the significance of built-in electric fields and the important role of spin polarization for promotion of photocatalytic CO₂ reduction.

Keywords: Built-in electric field; Carriers separation; Magnetic metal doping; Photocatalytic CO(2) reduction; Spin polarization.