Photo-assisted Fe-doped ZnS photocathodes for long-life and high-efficiency Li–CO2 batteries

Photo-assisted lithium‑carbon dioxide battery (Li-CO 2 ) can utilize the charge carriers generated at the cathode by light to reduce the kinetic barriers of carbon dioxide reduction and lithium carbonate decomposition reactions. However, rapid recombination of photogenerated carriers and sluggish interfacial charge transfer still lead to high overpotentials and limited cycle life in photo-assisted Li-CO 2 batteries. Therefore, it is crucial to design highly efficient photocatalysts that can suppress carrier recombination and accelerate interfacial charge transfer for rational optimization. Herein, we adopted the design strategy of metal ion doping and synthesized a Fe-doped ZnS (Zn 1-x Fe x S, denoted as ZFS-x) photocathode by the hydrothermal synthesis method. The doping of iron ions effectively regulates the electronic structure of ZnS, inhibits the recombination of photogenerated carriers, and accelerates the interfacial charge transfer kinetics. The photo-assisted ZFS-x cathode delivers a markedly prolonged cycling lifetime of up to 300 cycles (600 h) at a current density of 0.01 mA cm −2 , substantially exceeding that achieved under dark conditions (144 h). Furthermore, the single-cycle overpotential is significantly reduced from 2.27  V in the dark to 0.49  V under illumination. Morphology studies confirm that appropriate Fe-ion doping significantly enhances the uniformity of the discharge products, which are present as uniformly dispersed nanoscale particles rather than densely packed plate-like or aggregated structures. Moreover, their highly reversible decomposition during charging effectively mitigates pore blockage and interfacial passivation. These results indicate that the incorporation of iron can improve charge separation and regulate the formation and decomposition of Li 2 CO 3 , thereby effectively modulating the ZnS photocathode and ultimately enabling the development of photo-assisted Li-CO 2 batteries with low overpotential and long cycle life.