Carbon Nanosheets Containing Discrete Co-N x -B y -C Active Sites for Efficient Oxygen Electrocatalysis and Rechargeable Zn-Air Batteries.

Structural and compositional engineering of atomic-scaled metal-N-C catalysts is important yet challenging in boosting their performance for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Here, boron (B)-doped Co-N-C active sites confined in hierarchical porous carbon sheets (denoted as Co-N,B-CSs) were obtained by a soft template self-assembly pyrolysis method. Significantly, the introduced B element gives an electron-deficient site that can activate the electron transfer around the Co-N-C sites, strengthen the interaction with oxygenated species, and thus accelerate reaction kinetics in the 4e- processed ORR and OER. As a result, the catalyst showed Pt-like ORR performance with a half-wave potential (E1/2 ) of 0.83 V versus (vs) RHE, a limiting current density of about 5.66 mA cm-2 , and higher durability (almost no decay after 5000 cycles) than Pt/C catalysts. Moreover, a rechargeable Zn-air battery device comprising this Co-N,B-CSs catalyst shows superior performance with an open-circuit potential of ∼1.4 V, a peak power density of ∼100.4 mW cm-2 , as well as excellent durability (128 cycles for 14 h of operation). DFT calculations further demonstrated that the coupling of Co-Nx active sites with B atoms prefers to adsorb an O2 molecule in side-on mode and accelerates ORR kinetics.