Highly Stable Transition Metal Alloy Catalysts Wrapped with C-Dots for Hydrogen Evolution Reaction in Acidic Solution

Abstract

This work reports a large-scale and low-cost synthesis of highly effective, durable, and cheap NiCoPt/C-dot catalysts for hydrogen evolution reaction (HER). Simultaneous co-reduction of the metal precursors and carbon dots (C-dots) was confirmed by TEM, XPS, and Raman techniques. The SEM result clearly indicates that C-dots act as a structure-directing agent assisting to generate 3D nanosponge complex structure, which has an abundance of the electrochemically active sites. Synthesis procedure yields NiCoPt/C-dot nanoporous alloy wrapped with graphene, where the synergetic effect of the metal alloy constituents with outer graphene dots stimulates the electrochemical catalytic activity. Graphene dots additionally act as a protective layer. The optimization of the alloy composition along with lowering Pt loading (down to 0.04mM) for the highest catalytic activity for HER yields Ni48Co48Pt4/C-dot nanohybrid. XPS analysis revealed the nanohybrid surface is enriched up to 86.7 at% of Pt, suggesting that the surface composition of an alloy is controlled by the tendency of Pt metal segregation towards the surface. Such surface electronic structure led to the superior catalytic activity of Ni48Co48Pt4/C-dot, which generates an overpotential of only 45.54 mV at a current density of 10 mAcm-2 in acidic solution. The highest catalytic activity correlates well with the lowest charge transfer resistance in conjunction with the highest ECSA value of 57.51 cm2 of the nanohybrid. The synthesized nanocomposite showed good stability retaining 94% of current density after 21 hours of operation. The catalytic activity and durability of developed nanocomposite catalyst are comparable to those of the commercial Pt/C. The aforementioned advantages allow stating that 3D Ni48Co48Pt4/C-dot nanosponge is a low-cost, durable, and efficient electrocatalyst for hydrogen evolution. The developed nanohybrid may be considered as an upcoming alternative catalyst for hydrogen gas production. Figure 1