Biomass-derived FeNi alloy and nitrogen-codoped porous carbons as highly efficient oxygen reduction and evolution bifunctional electrocatalysts for rechargeable Zn-air battery

Developing a highly efficient and low cost bifunctional oxygen catalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is significantly important for practical applications of Zn-air battery. Here, we, for the first time, use abundantly available peanut shells as precursors and small amount of iron and nickel salts as non-precious metal sources to successfully synthesize FeNi alloy and nitrogen-codoped porous carbon (FeNi-NC) electrocatalyst. The as-synthesized FeNi-NC catalyst exhibits not only excellent ORR electrocatalytic activities with almost the same onset (0.98 V, versus RHE) and half-wave potentials (0.83 V, versus RHE) and limiting current as commercial 20% Pt/C, but also satisfactory OER performance with the similar activity with IrO2 in alkaline electrolyte. Moreover, the overpotential (E-OER-E-ORR) of the FeNi-NC electrocatalyst is 0.81 V, which is smaller than the 20% Pt/C and IrO2 system. Interestingly, a home-made Zn-air battery with FeNi-NC as oxygen electrode displays an excellent charging and discharging polarization curves and robust cycle stability, which is superior to the 20% Pt/C+IrO2-based one. This work provides a facile route to change waste peanut shells into non-precious metal and nitrogen-codoped porous carbons as a valuable bi-functional oxygen electrocatalyst for rechargeable Zn-air batteries.