NiCoPt/graphene-dot nanosponge as a highly stable electrocatalyst for efficient hydrogen evolution reaction in acidic electrolyte

Abstract

This work reports the large-scale and simple synthesis of highly effective, stable, and cheap 3D nanosponge catalysts, nanoporous NiCoPt alloys wrapped in graphene dots (NiCoPt/G-dot), for the hydrogen evolution reaction (HER). The simultaneous co-reduction of the metal precursors and carbon dots was confirmed by TEM, XPS, and Raman analyses. The SEM result indicated that the G-dots act as a structure-directing agent, assisting in the generation of the 3D nanosponge complex structure, in which the metal alloy constituents with the outer G-dots synergistically stimulate the electrochemical catalytic activity. Optimization of the alloy composition, while lowering the Pt loading, resulted in the highest HER catalytic activity by the Ni48Co48Pt4/G-dot nanohybrid with a precursor molar ratio of Ni:Co:Pt = 48:48:4. XPS analysis revealed that the nanohybrid surface was enriched with Pt (up to 86.7 at%), suggesting that the alloy composition is controlled by the tendency of Pt metal to segregate towards the surface. The resulting surface electronic structure led to the superior catalytic activity of Ni48Co48Pt4/G-dot, which generated an overpotential of only 45.54 mV at a current density of 10 mA cm−2 in acidic solution. The Ni48Co48Pt4/G-dot exhibited the highest catalytic activity, which correlated well with its having the lowest charge transfer resistance and the highest electrochemical surface area value of 57.51 cm2. The Ni48Co48Pt4/G-dot showed good stability, retaining 94% of its current density after 21 h of operation. This was attributed to the existence of the G-dots, which acted as a protective layer. The developed 3D NiCoPt/G-dot nanosponge may be considered a promising alternative catalyst for hydrogen production.