Monolayer Covalent C₆₀ Networks Anchored with Uniform Ultrasmall Iridium Nanoparticles for Boosting Electrocatalytic Hydrogen Evolution

The design of highly active and durable acidic hydrogen evolution reaction (HER) electrocatalysts remains a critical challenge for advancing hydrogen production technologies. Monolayer graphullerene, a two-dimensional (2D) carbon network derived from C₆₀ fullerenes, exhibits exceptional properties such as structural stability, high specific surface area, superior in-plane electron conductivity, and distinctive electron-accepting behavior, positioning it as an ideal catalyst support. In this work, we report the synthesis of ultrafine iridium nanoparticles (∼1.7 nm) anchored on monolayer graphullerene (Ir NP@MLG) and demonstrate its excellent HER performance in acidic media. Comprehensive morphological and structural analyses confirm the atomic-scale dispersion of Ir nanoparticles on the monolayer graphullerene framework. The Ir NP@MLG hybrid catalyst achieves excellent HER activity with an ultralow overpotential of η₁₀ = 18 mV (vs RHE) and a Tafel slope of 16.54 mV dec^-1, surpassing most reported Ir-based catalysts. Notably, it exhibits a mass activity of 3.48 A mg^-1 at an overpotential of -50 mV (vs RHE), representing one of the highest values among state-of-the-art Ir catalysts. Stability tests reveal exceptional durability, with negligible activity loss after 260 h of continuous operation. The superior performance originates from (1) the monolayer graphullerene's 2D conductive network facilitating rapid charge transfer and (2) strong metal-support interactions optimizing electronic structure and nanoparticle stabilization. This study establishes monolayer graphullerene as an interesting carbon support for developing electrocatalysts, providing deep insights into the design of efficient hydrogen energy systems.