Inverted carbon-shell iridium-core mesoporous structured electrocatalyst for HER

Abstract In water electrolysis, the nanostructural design of electrocatalysts and their supports is crucial for enhancing catalytic efficiency by reducing overpotential. Platinum (Pt), which is widely used for the hydrogen evolution reaction (HER) at the cathode, is expensive, so core–shell structures are utilized to decrease the amount required. Typically, Pt nanoparticles (NPs) of 1 to 2 nm diameter are uniformly dispersed on carbon black supports to form these structures. Core–shell catalysts have been extensively studied, and various derivatives have been systematically developed and evaluated. In this paper, an inverted structure, referred to as a shell–core structure, where the catalyst forms the core and support forms the shell, is demonstrated. Ir NPs with diameters of 1 to 3 nm are successfully synthesized as the catalyst core, encapsulated in a mesoporous carbon shell derived from polydopamine using dopamine polymerization. At an Ir content below 1 wt%, this inverted shell–core catalyst exhibits catalytic activity comparable to that of commercial Ir NPs catalysts. Specifically, the synthesized catalyst achieves approximately 34 mV at 10 mA/cm² for HER, comparable to commercial metal-based Ir NP catalysts. This approach reduces the requirement for platinum-group metals (PGMs) to below 1 wt% Ir, shifting the focus from support-centered catalyst coatings to catalyst-centered support synthesis.