Proliferation of pH-universal oxygen reduction performance by morphology modulation in NiS-N,S doped carbon microflowers

Transition metal/doped carbon hybrid nanostructures with precisely controlled morphological features are emerging as the prospective electroactive materials to meet the futuristic sustainable energy demands. Here, gas template-assisted hydrothermal preparation of NiS impregnated on N, S-rich nanocarbon composite is reported for pH-universal oxygen reduction reaction (ORR) electrocatalysis for hydrogen fuel cell and metal-air battery applications. The unique microflower-like superstructures formed by assembly of interconnected nanosheets as visualized through electron microscopic studies pave the way towards achieving the proliferation of ORR performance by providing pathways for gas transport and charge transfer during the reaction. The onset potential of 0.95 V vs. reversible hydrogen electrode (RHE), half-wave potential of 0.74 V vs. RHE, and ORR current density of 5.96 mA/cm 2 (at 0.05 V vs. RHE) in an alkaline medium are achieved in this study. The most active electrocatalyst is tested for ORR activity in an acidic medium, as well. The prepared electrocatalyst exhibits excellent current durability and stability in a methanol-saturated environment compared to the state-of-the-art electrocatalyst in both media. In a nutshell, this study presents a precursor-morphology-performance correlation in pH-universal ORR electrocatalysis in addition to serving as a reference study for gas template-assisted hydrothermal synthesis . • Unique 3-D microflower structure comprising suitable channels for mass and charge transport as a result of facile hydrothermal preparation. • Influence of a gas template (NH 4 Cl) on the morphology, chemical functionalities, and hence the ORR characteristics. • pH-universal ORR activity with reduced overpotential and enhanced current durability is achieved.