Deciphering the Quantitative Relationship Between the Photocatalytic Activity and the Built-In Electric Field of Heterojunction.

Abstract

The principle of heterojunction in physics has been extensively referenced in heterogeneous photocatalysis, but it appears to have been utilized qualitatively more as a concept than as a method. The reason is that the quantitative correlation between the intensity of the built-in electric field (BIEF) and photocatalytic activity has not been established, primarily due to the challenges in directly measuring the BIEF of nanosized photocatalysts. To address this, both powder-type and single-crystal-type SiC@WO_3-x-T heterostructures are prepared to quantitatively investigate the dependence of photocatalytic CO₂ reduction activities on BIEF intensity. A strong linear correlation between the effective photoelectron number (N_EPN) for CO₂ reduction and the BIEF intensity is revealed for the first time. Specifically, N_EPN increases by 0.25 µmol g^-1 when V_bi (built-in potential) increases by 1 kV for the powder sample. In contrast, for the single-crystal sample, N_EPN rises by 0.16 µmol with a 1 kV cm^-1 increase in E_bi (built-in electric field). This study not only bridges a critical gap in heterojunction photocatalysis research but also demonstrates a method to amplify the built-in electric field by engineering the interface species, thereby enhancing the photocatalytic performance.