Mixed ion/electron conduction engineering of Li⁺-intercalated CdPS₃ for low-bias photoelectrochemical ammonia synthesis

Photoelectrochemical nitrate reduction reaction is a promising route for sustainable ammonia synthesis under ambient conditions. However, conventional semiconductor photocathodes are often limited by sluggish charge transport, severe electron-hole recombination, and inefficient interfacial electron transfer, especially under low applied bias. Herein, Li⁺ ions are introduced into layered CdPS₃ crystals through an ion-intercalation strategy to construct a mixed ion/electron conductive photocathode, Cd_0.89PS₃Li_0.11. Owing to the two-dimensional van der Waals structure of CdPS₃, the intercalated Li⁺ ions can migrate within the interlayer space, providing an additional ionic transport pathway and facilitating charge compensation. As a result, the conduction behavior of CdPS₃ is transformed from conventional photoelectron-dominated transport to mixed ion/electron conduction, which accelerates charge transfer and enhances photoelectrocatalytic nitrate reduction. The optimized Cd_0.89PS₃Li_0.11 exhibits a high ionic conductivity of 2.8 × 10^-3 S/cm and an electronic conductivity of 4.2 × 10^-7 S/cm. Theoretical calculations further reveal that Li incorporation reduces the energy barrier of the N-O bond dissociation step, thereby promotes the efficient PEC ammonia synthesis. Consequently, Cd_0.89PS₃Li_0.11 achieves an ammonia yield rate of 129.76 mmol g^-1h^-1 (64.88 μmol cm^-2h^-1) with a Faradaic efficiency of 65.63 % at a low bias of −0.3 V versus the reversible hydrogen electrode. This work highlights mixed ion/electron conduction engineering as an effective strategy for designing high-performance photoelectrodes for low-bias ammonia synthesis.