Tuning the Activity of Carbon for Electrocatalytic Hydrogen Evolution via an Iridium-Cobalt Alloy Core Encapsulated in Nitrogen-Doped Carbon Cages

Abstract

Graphene, a 2D material consisting of a single layer of sp²-hybridized carbon, exhibits inert activity as an electrocatalyst, while the incorporation of heteroatoms (such as N) into the framework can tune its electronic properties. Because of the different electronegativity between N and C atoms, electrons will transfer from C to N in N-doped graphene nanosheets, changing inert C atoms adjacent to the N-dopants into active sites. Notwithstanding the achieved progress, its intrinsic activity in acidic media is still far from Pt/C. Here, a facile annealing strategy is adopted for Ir-doped metal-organic frameworks to synthesize IrCo nanoalloys encapsulated in N-doped graphene layers. The highly active electrocatalyst, with remarkably reduced Ir loading (1.56 wt%), achieves an ultralow Tafel slope of 23 mV dec⁻¹ and an overpotential of only 24 mV at a current density of 10 mA cm⁻² in 0.5 m sulfuric acid solution. Such superior performance is even superior to the noble-metal catalyst Pt. Surface structural and computational studies reveal that the superior behavior originates from the decreased ΔG_H* for HER induced by the electrons transferred from the alloy core to the graphene layers, which is beneficial for enhancing CH binding.

Benefiting from the strong interaction between the coated N-enriched graphene layers and implanted IrCo alloy core, which provides modulated electronic structure, nitrogen-doped graphene nanolayers achieve superior activity toward the hydrogen evolution reaction in acidic electrolyte. The achieved activity exceeds that of state-of-the-art commercial noble-metal catalysts including Pt/C catalysts. The carbon cages act as active sites and as anticorrosive chainmail.

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