Designing an Fe^III-Doped Nickel Sulfide/Carbon Nanotube Hybrid Catalyst for Alkaline Electrolyte Membrane Water Electrolyzers and Zn–Air Battery Performances

The development of an electrocatalyst with high performance using nonprecious metals/metal oxides as well as its applications in flexible and rechargeable Zn–air batteries and water electrolyzers is in strong demand from industries. In this study, we have designed and synthesized a new (Fe3NiS8−δ)−4+δ carbon nanotube (CNT) hybrid electrocatalyst and revealed that the catalyst shows a very high oxygen evolution reaction (1.55 V at 10 mA/cm2) and oxygen reduction reaction (E1/2 = 0.82 V vs RHE) performances. Based on the analyses by in situ electrochemical X-ray diffraction together with structure analysis software, in situ electrochemical Fourier transform infrared spectroscopy, transmission electron microscopy, and computer simulations, such a high performance is derived from the sulfur vacancies that were formed via the self-doped d–p orbitals of FeIII in (Fe3NiS8−δ)−4+δ. Here, we describe an adequate explanation about the role of the iron doping in the nickel sulfides in the catalyst. Furthermore, the fabricated flexible and rechargeable Zn–air and water electrolyzer batteries using the catalyst show a low charge–discharge overpotential gap of 0.66 V and a 237 mA/cm2 current density at 1.9 V, which is very important for the development of a rechargeable Zn–air battery and water electrolyzer with a high performance. First-principles calculations are employed to investigate the reaction mechanisms and elucidate the effect of the CNT support for the catalytic activity.