A Low-Cost, Durable Bifunctional Electrocatalyst Containing Atomic Co and Pt Species for Flow Alkali-Al/Acid Hybrid Fuel Cell and Zn–Air Battery

Transition metal single atoms anchored on nitrogen-doped carbon (M-N-C) matrix with M-N-C active sites have shown to be promising catalysts for both hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). Herein, a hybrid catalyst with low-level loading of atomic Pt and Co species encapsulated in nitrogen-doped graphene (Pt@CoN₄-G) is developed. The Pt@CoN₄-G shows low overpotential for HER in wide-pH electrolyte and manifests improved mass activity with almost eight times greater than that of Pt/C at an overpotential of 50 mV. The Pt@CoN₄-G also exhibits a top-level ORR activity (half-wave potential, E_1/2 = 0.893 V) and robust stability (>200 h) in alkaline medium. Using theoretical calculations and comprehensive characterizations, the strong metal–support interactions between Pt species and CoN₄-G support and synergistical cooperation of multiple active sites are clarified. A flow alkali-Al/acid hybrid fuel cell using Pt@CoN₄-G as cathode catalyst delivers a large power density of 222 mW cm⁻² with excellent stability to achieve simultaneously hydrogen evolution and electricity generation. In addition, Pt@CoN₄-G endows a flow Zn-air battery with high power density (316 mW cm⁻²), good stability under large current density (>100 h at 100 mA cm⁻²), and long cycle life (over 600 h at 5 mA cm⁻²).