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 gZn–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.