Seeded-growth synthesis of dispersed Co9S8 nanoparticles loaded in carbon aerogel as efficient bi-catalysts towards the ORR and HER

Abstract

In this work, a high density of dispersed Co₉S₈ nanoparticles (NPs) loaded in carbon aerogels as bi-catalysts (Co₉S₈^7.5NP/CA catalysts) were successfully prepared by virtue of the seeded-growth method that is widely used for the synthesis of noble metal NPs. It is found that the optimal molar ratio of Co²⁺-to-Fe³⁺ ions for the formation of a high density of dispersed Co₉S₈ NPs with average sizes of 90 nm is determined to be 7.5 (represented by the superscript number) at the fixed concentration of tannic acid (TA) ([TA] : [Fe³⁺] = 1 : 1). Moreover, the concentration of Fe³⁺ precursors is the key that can guarantee the formation of dispersed Co₉S₈ NPs by the overgrowth of in situ Fe SA-NCs as seeds by the spatial confinement effect during the pyrolysis. Thanks to the multiple valence states of elemental Co in the Co₉S₈ NPs and their good dispersity in the as-prepared Co₉S₈^7.5NP/CA catalysts, the half-wave potential (E_1/2) and the overpotential at 10 mA cm⁻² (η₁₀) towards the alkaline oxygen reduction reaction (ORR) and the acidic hydrogen evolution reaction (HER) can be improved up to 0.891 V and 177 mV, respectively.