Reduced Graphene Oxide Sheet-Wrapped Heterotrimetallic Sulfide Nanoparticles for Efficient Alkaline Hydrogen Evolution

Reduced graphene oxide (rGO) sheet-wrapped heterotrimetallic sulfide nanoparticles (Fe3Co3Ni3S8 (FCNS)) with a layered structure (FCNS@rGO) were synthesized through self-assembly of graphene oxide (GO) sheets and FCNS particle precursors, followed by annealing under nitrogen at 800 °C for 2 h. Elemental analyses confirmed the formation of the Fe3Co3Ni3S8 composition, while XRD revealed a pure pentlandite crystal structure between GO sheets. The optimized composition (FCNS@rGO-3) was obtained using different amounts of GO and FCNS. We further investigated the effect of 5% Sustainion XA-9 alkaline ionomer in ethanol and Nafion (5 wt %) perfluorinated resin solution binders on the electrocatalytic hydrogen evolution reaction (HER) of the optimized FCNS@rGO-3 composite in 1.0 M KOH. By employing a 5% Sustainion XA-9 alkaline ionomer in ethanol, the FCNS@rGO-3 composite achieved a current density of −100 mA cm-2 at 371 and 199 mV dec-1, significantly outperforming the rGO and FCNS single phases and the FCNS@rGO-3 supported on a Nafion (5 wt %) perfluorinated resin (561 and 591 mV dec-1). The FCNS@rGO-3 supported with the Sustainion binder exhibited performance roughly comparable to the benchmark Pt/C40% catalyst (223 mV and 99.6 mV dec-1) under identical conditions. During a long-term stability test at -100 mA cm-2, the catalyst demonstrated persistent performance with additional activation (0.021 V/h), achieving -0.57 V vs the reversible hydrogen electrode (RHE). Density functional theory (DFT) calculations suggested that the optimized FCNS@rGO-3 composite possesses more active sites than the single phases (i.e., rGO, FCNS) and considerably reduces the hydrogen adsorption free energy (ΔGH), thereby improving HER performance.