A Rational Approach to Suppress Hydrogen Evolution Reaction and its Concurrent Zinc Corrosion in Zinc-air Batteries: A Uniform Dispersion of Carbon Nanodots in the Electrolyte

Abstract

Zinc-air batteries (ZABs) have garnered tremendous attention due to their higher theoretical energy density, cost-free fuel from the atmosphere, ease of fabrication, and environmental friendliness. However, the poor kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) happening at the air-cathode, the hydrogen evolution reaction (HER), and its concurrent zinc corrosion occurring at the anode contribute to the failures of ZABs. While various electrocatalysts are developed to accelerate ORR and OER, the strategies explored to mitigate the issues of anode involve modification of either the zinc anode or the electrolyte. Though the modification of the anode or the electrolyte suppresses HER, it affects the oxygen reactions taking place at the air-cathode. Herein, HER and its concurrent zinc corrosion are suppressed by uniform dispersion of carbon nanodots in the native electrolyte. In addition, this rational approach accelerates both the ORR and OER. The carbon nanodots are prepared electrochemically and characterized using absorption and emission spectroscopy and microscopic studies. Subsequently, carbon nanodots are uniformly dispersed in 6 M KOH (CNF) and used as the electrolyte. The CNF suppresses HER by increasing the overpotential and impedes the zinc corrosion.