Developing Indium-based Ternary Spinel Selenides for Efficient Solid Flexible Zn-Air Batteries and Water Splitting

Exploring economic, efficient, and corrosion-resistant oxygen electrocatalysts contributes to further development of zinc-air batteries and overall water splitting. Herein, a novel ternary spinel CoIn₂Se₄ nanomaterial, with Co²⁺ and In³⁺ occupying the tetrahedral and octahedral sites of the crystalline structure, has been fabricated using a facile and environment-friendly method. Moreover, CoIn₂Se₄ nanosheets outperform pristine CoSe₂ and In₂Se₃ in catalyzing both oxygen evolution reaction (an overpotential of 315 mV at 10 mA cm^-2) and oxygen reduction reaction (an onset overpotential of 0.88 V). The reduced charge resistance and increased active site exposure ratio contribute to the superior performance of CoIn₂Se₄. Moreover, density of theory (density functional theory-DFT) calculations suggest a significantly reduced reaction energy barrier after introducing indium into the spinel, and therefore the reaction kinetics are facilitated. Based on the advantages described above, CoIn₂Se₄ is used as the air cathode for a solid flexible zinc-air battery (FZAB). The system displays an efficient performance that outperforms the Pt@Ir/C catalyst: a significantly enhanced specific capacity of 733 mAh g_Zn^-1, a high energy density of 931 Wh kg^-1, and an excellent flexibility with long cycle life performance (over 400 cycles). The CoIn₂Se₄-based two-series-connected FZABs successfully power light-emitting diode (LED) screens for over 10 h. Meanwhile, CoIn₂Se₄ also shows a significantly enhanced hydrogen evolution reaction (HER) performance than other samples. Finally, the CoIn₂Se₄-based electrolyzer shows an efficient overall water-splitting performance with high stability. This work demonstrates that the indium-based ternary selenides show promising applications in developing renewable energy and water-splitting devices.