Ni-regulated TiO2/MgIn2S4 photoanodes for low-bias photoelectrochemical H2S valorization via band-alignment and surface-state engineering

Photoelectrochemical H 2 S valorization offers a low-bias route for converting toxic H 2 S-derived alkaline sulfide streams into recoverable sulfur, but its practical efficiency is limited by insufficient sulfide tolerance, sluggish charge separation, and inefficient interfacial hole utilization on photoanodes. Herein, Ni-regulated TiO 2 /MgIn 2 S 4 heterojunction photoanodes were constructed by in situ growth of Ni 2 + -doped MgIn 2 S 4 nanosheets on TiO 2 nanorod arrays for low-bias photoelectrochemical sulfide oxidation. In this architecture, TiO 2 serves as an electron-transport scaffold, while MgIn 2 S 4 functions as a sulfide-compatible visible-light absorber. Ni 2+ incorporation enables coupled band-alignment and surface-state engineering in the TiO 2 /MgIn 2 S 4 heterostructure. Specifically, Ni-induced modulation of the MgIn 2 S 4 band positions optimizes the interfacial band alignment with TiO 2 , thereby promoting directional electron extraction across the Type-II heterojunction and suppressing electron-hole recombination. Meanwhile, Ni-induced productive surface states act as hole-storage reservoirs, facilitating the capture of photogenerated holes and their subsequent transfer to S 2− /HS − species. Benefiting from the coupled regulation of electron extraction and interfacial hole utilization, the optimized TiO 2 /MgIn 2 S 4 -6%Ni photoanode delivers a photocurrent density of 1.30 mA cm −2 at 0.14 V vs. RHE for sulfide oxidation, representing a 3.6-fold enhancement over pristine MgIn 2 S 4 . The recovery of elemental sulfur further verifies the feasibility of low-bias PEC H 2 S valorization. This work demonstrates that Ni-regulated band-alignment and surface-state engineering provide an effective charge-management strategy for designing sulfide-tolerant photoanodes toward environmental sulfide treatment and sulfur resource recovery.