Accelerated intermediate conversion through nickel doping into mesoporous Co-N/C nanopolyhedron for efficient ORR

Engineering non-precious metals into nitrogen-doped carbon is employed to improve electrocatalyst activity towards oxygen reduction reaction (ORR). A nickel-doped Co-N/C mesoporous nanopolyhedron is successfully evoluted from a Ni-doped ZIF-67 precursor. The Ni & Co synergistic N/C catalyst exhibits a half-wave potential of 0.895 V (vs. reversible hydrogen electrode (RHE)) with a diffusion-limiting current density of 6.1 mA cm−2 for alkaline ORR at 1600 r min−1, which is competitive to commercial Pt/C in terms of cost, methanol tolerance, and long-term stability. In situ surface-enhanced Raman scattering (SERS) study reveals the formation and fast conversion of superoxide ion (O2-) intermediate on the catalyst surface. Density functional theory (DFT) calculations demonstrate the decrease of energy barrier for potential-determining step (O* protonation) by Co-Ni synergy as well as the reduction of adsorption energy on catalyst surface upon nickel doping. The joint results of in situ SERS study and DFT calculations suggest a favourable ORR process on nickel-doped Co-N/C.