Abstract: The facile recombination of photogenerated charge carriers remains a major bottleneck limiting photocatalytic hydrogen evolution efficiency. Cd_0.6Zn_0.4S (CZS), a ternary metal sulfide, possesses several favorable properties; however, its relatively weak internal electric field (IEF) still impedes the effective separation of photogenerated charges, thereby constraining its overall photocatalytic performance. In this study, Mo was incorporated into the CZS lattice, inducing an asymmetric charge distribution on surrounding atoms. This modification significantly enhanced the unit cell dipole moment along both the X-axis (from 2.036 to 10.091 eÅ) and the Y-axis (from 1.761 to 8.112 eÅ). Consequently, Mo-doped CZS exhibits a strengthened IEF, as evidenced by the increase in surface potential from 39 mV to 50 mV. The optimal carrier separation efficiency was achieved at a Mo content of 10%. The hydrogen evolution rate of 10% Mo CdZnS (10MCZS) reaches 8.75 mmol g^-1 h^-1, which is 36.5 times higher than that of pristine CZS (0.24 mmol g^-1 h^-1). In summary, this work provides insight into a strategy for enhancing the IEF via augmentation of the crystallographic dipole moment and disruption of electronic symmetry, thereby advancing photocatalytic performance.

Key words: Photocatalysis, Internal electric field, Crystal cell dipole moment, Photocatalytic hydrogen production, Electron symmetry