Tailored MnO2 Nanoparticles as Electrocatalysts for Metal-Air Batteries

In next-generation electronics, electrified transportation and energy storage, metal-air batteries represent one class of promising power sources thanks to their remarkably high theoretical energy and light weight [1]. The main feature of metal-air batteries is the combination of a metal anode with high energy density and an air electrode with open structure that facilitates the drawing of cathode active materials (i.e. oxygen) from air [1]. In these types of devices, Gas Diffusion Electrodes (GDEs) are widely used as cathodes [2]. However, one of the main drawbacks related to the cathodic reaction (ORR) is the overpotential loss (about 0.3-0.4 V) under operative conditions. Thus, lots of efforts were spent to inhibit the voltage loss requiring an effective ORR catalyst [1,3]. One of the most promising materials, in terms of both performances and costs, seems to be MnOx. According to the recent literature, MnO2 would ensure capacities comparable to those of platinum, letting higher capacity retention to be reached in non-aqueous electrolytes to prevent Li decomposition [1]. In the present work, the electrochemical performances of either bare or Fe/Co-doped MnO2 nano-electrocatalysts are evaluated by Linear Sweep Voltammetries (LSVs). The crystal structure and the surface properties are examined by means of XRPD, BET-BJH, TEM, SEM/EDX and XPS analyses. Correlations between their physico-chemical features and the final electrocatalytic performances are drawn. Experimental results reveal that the as-synthesized powders have excellent electrochemical properties in organic electrolytes (0.15 M LiNO3 in propylene carbonate, PC) showing a shift of the onset potential of about 150 mV with 2% Co-doped MnO2, thus resulting very promising candidates to be used in lithium-air batteries [4].