Engineering morphology and porosity of N,S‐doped carbons by ionothermal carbonisation for increased catalytic activity towards oxygen reduction reaction

Abstract

A facile and one-pot method using NaCl/KCl as a molten salt medium was developed to tune the porous structure of N,S-doped carbon derived from biomass at high temperature. With increasing the NaCl/KCl amount, the structures of the obtained carbons revealed by scanning electron microscopy become more and more open. N2 adsorption/desorption isotherm shows that the hierarchical porous structure could be efficiently tuned by adjusting the amount of NaCl/KCl salt mixture. Specific surface area (SSA) of as-prepared N,S-doped carbon could reach 1478.6 m2 g−1. The relative ratio of micropore/mesopore drops with the increased NaCl/KCl. When the obtained carbons are used as the catalysts for oxygen reduction reaction (ORR), high catalytic activities are obtained, which result from the porous structure and doping effect of N atoms. Meanwhile, a volcano trend of the electrochemical performance for as-prepared carbons is also shown, which is a result of multiple factors possessing the opposite effect on ORR. Importantly, producing N,S-doped carbon from egg white in NaCl/KCl molten salt medium could provide a promising approach to synthesise the opened N,S-doped carbons with a controllably porous structure and large SSA based on biomass precursors.