Low-Cost Rapid Template-Free Synthesis of Nanoscale Zinc Spinels for Energy Storage and Electrocatalytic Applications

Aravind Baby Baskar Senthilkumar, Prabeer Barpanda

doi.org/10.1021/acsaem.9b00054/ACS Appl. Energy Mater. 2019, 2, 5, 3211-3219

Abstract

Spinels form an interesting class of compounds, finding applications in metal-ion batteries and as catalysts for metal–air batteries and fuel cells. Here, we report a fast, template-free solution combustion method to synthesize nanoscale zinc spinels for applications as cathodes in low-cost aqueous zinc-ion batteries and oxygen reduction reaction (ORR) catalysts. It leads to the formation of phase-pure spinels with near-spherical nanoscale morphology. Three spinels—ZnCo₂O₄ (ZCO), ZnMn₂O₄ (ZMO), and ZnMnCoO₄ (ZMCO)—were investigated. ZMO and, for the first time, ZMCO were observed to show reversible Zn (de)insertion involving Mn⁴⁺/Mn³⁺ redox couple with a first discharge capacity of 109.4 mAh/g (i.e., >99% of theoretical capacity). Further, these Zn-based spinels showed appreciable oxygen reduction reaction (ORR) electrocatalytic activity. The ORR activity in alkaline solution was characterized by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) using a rotating disk electrode (RDE) and was observed to be comparable to Pt/C with similar chronoamperometric stability. This enhanced ORR activity can be rooted to the optimal tuning of Co³⁺–O bond strength because of the presence of Mn³⁺. This work presents a robust synthesis route to prepare ZnMnCoO₄ spinel acting as an economic cathode material for large-scale Zn-ion batteries for grid storage applications as well as an efficient and stable alternate ORR catalyst in alkaline solution.

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