Efficient Bifunctional Catalysts Based on Electronic Structure-Engineered Mn-Doped CoFeP in Zinc-Air Batteries

Abstract

As one of the candidates for storage and conversion of new energy devices, zinc-air batteries have great advantages in terms of energy density/power density, safety, greenness, and cost. However, the slow kinetics of the oxygen reaction during the charging and discharging processes severely hinder the application of zinc-air batteries. This paper designs metal phosphides rationally to obtain a low-cost, highly efficient, and stable bifunctional catalyst Mn–CoFeP-2. The excellent performance of this catalyst for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is attributed to the doping of Mn, which optimizes the electronic structure of CoFeP and exposes more active sites. The Mn–CoFeP-2 catalyst exhibited excellent ORR performance (E_onset = 0.853 V) and significantly enhanced OER electrocatalytic activity (overpotential of 443 mV at a current density of 10 mA cm^–2). Density functional theory calculations show that the doping of Mn can effectively reduce the energy barrier of Co–Fe sites at the ORR and OER rate-limiting steps. In addition, the Mn–CoFeP-2-based rechargeable zinc-air battery can be cycled for 140 h at a current density of 2 mA cm^–2, which exhibits a better cycling stability performance than the Pt/C–RuO₂ battery (110 h). These outstanding results indicate that Mn–CoFeP-2 is a promising bifunctional catalyst for zinc-air batteries.