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 CO 2 reduction activities on BIEF intensity. A strong linear correlation between the effective photoelectron number ( N EPN ) for CO 2 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.