Boosting the Oxygen Reduction Reaction in Zn-Air Batteries via a Uniform Trace N-Doped Carbon-based Pore Structure

Qi Yang ^†, Rumeng Liu ^†, Juanjuan Gao ^†, Yue Liu ^†, Shen Hu ^†, Haiou Song ^{‡, §}, Shupeng Zhang ^{†, §, *}

ABSTRACT

Zn-air batteries (ZABs) have attracted significant research interest due to their low cost, high safety and large energy density. The oxygen reduction reaction (ORR) in ZABs can be boosted by employing an effective catalyst. The construction of an ORR catalyst comparable to commercial Pt/C remains a considerable challenge without introducing metal atoms due to the sluggish reaction kinetics. Herein, a nitrogen-doped carbon-based material with a uniform porous structure was constructed by the ingenious cooperation of urea and sodium chloride. The obtained catalyst (USPC) exhibited an onset potential of 0.939 V, a half-wave potential of 0.849 V and a limiting current of 5.72 mA cm^-2 in a 0.1 M KOH electrolyte. After 5000 CV cycles, the limiting current density of the USPC decreased by 0.16 mA cm^-2 and there was no negative shift in the half-wave potential. The assembled ZAB displayed a maximum power density of 167 mW cm^-2 with an excellent specific capacity of 782 mA h g^-1 at 10 mA cm^-2 and good galvanostatic discharge-charge cycling durability, which were significantly improved compared to those of Pt/C. The pore size, chemical composition and nitrogen content were not the controlling factors for the USPC in improving the ORR performance. Doping trace amounts of nitrogen could significantly promote the onset potential (vs. RHE), and the uniform and fine nanopores could effectively increase the limiting current. That is, the improvement of ORR activity. This work illustrated the importance of the origin of catalytic activity and promoted the development of high performance ZABs.

KEYWORDS: Oxygen Reduction Reaction; Zn-Air Battery; N-Doped; NaCl Activation; Porous Carbon