Confined growth and dispersion of FeP nanoparticles in highly mesoporous carbons as efficient electrocatalysts for the hydrogen evolution reaction

We report the performance of a series of iron monophosphide (FeP) catalysts supported on highly mesoporous carbons (HMCs) with distinct mesopore size (6–17 nm) and mesopore volume (2–3 cm³ g⁻¹) for the hydrogen evolution reaction (HER). Our findings suggest that the mesopore size of the carbon is a key design parameter. The mesopores serve as nanoreactors and control the growth and the dispersion of FeP nanoparticles, which, in turn, determine the HER performance of the electrode. Carbons with smaller mesopore sizes confine and control the size of FeP leading to finely dispersed and fairly small (<5 nm) FeP nanocrystals, while carbons with larger mesopore size result in agglomerated, larger nanoparticles (>10 nm) and, thus, less active electrocatalysts. Electrocatalysts based on FeP immobilized on the mesoporous carbons show lower overpotential and lower Tafel slope and outperform those based on FeP immobilized on commercial activated carbon. This study establishes for the first time some correlations between HER performance and mesopore size and pore volume of the carbon. The findings provide further understanding and might pave the way towards a rational design of highly active electrocatalysts by delineating key design parameters for materials development.