Atomic-scale anisotropic local electric field of BiOCl for enhanced photoelectrochemical seawater reduction

Although the built-in local electric field (LEF) triggered by surface oxygen vacancy (O V ) plays a positive role in photoelectrochemical (PEC) water splitting, the migration of electrons is inevitably retarded and trapped by internal O V . In this work, Se/Cu co-doped BiOCl nanosheets (NSs) were synthesized for PEC seawater reduction. The results reveal that, firstly, the O V of BiOCl NSs could be completely eliminated and filled by Se atoms. Secondly, the lattice of BiOCl is distorted by Se/Cu atoms, resulting in an atomic-scale anisotropic LEF that varies in intensity about twice around the Se/Cu atoms, and a synergistic catalytic optimization for H 2 evolution. Thirdly, the gap width of BiOCl is not narrowed after Cu/Se-doping, but the defect levels appear inside the band gap, thus the photoelectrons maintain high kinetics even when excited by visible light. Moreover, the center of Cu 3 d mid-gap state of the Cu/Se co-doped sample has an upward shift than that of the only Cu-doped one. Resultantly, Cu 1% Se 1% BiOCl NSs demonstrate a highly enhanced PEC current density of −0.015 mA/cm 2 at −0.2 V RHE in natural seawater under AM 1.5G solar illumination. This work provides a practical strategy towards non-O V induced anisotropic LEF, and a durable PEC cathode for seawater reduction.