Highly Dense and Ultrasmall Pt Nanoislands Confined in 2D Assemblies with Positive Charge for Electrocatalytic Hydrogen Evolution

Platinum (Pt) nanoparticles supported on a carbon substrate have been regarded as benchmark electrocatalysts for the hydrogen evolution reaction (HER). However, they still face challenges in achieving a uniform distribution with high density on carbon due to Ostwald ripening. Herein, we report the synthesis of ultrasmall and highly dense Pt nanoislands supported on GQD assemblies (PG) through a metal-ion-triggered assembly of graphene quantum dots (GQDs). The peripheral oxygen-involved functional groups (e.g., –OH, –COOH) on GQDs coordinate with Pt 4+ ions to induce the formation of 2D assemblies, confining the subsequent reduction to form highly dense and uniform Pt nanoislands in the cavities isolated by the nanosized sp 2 conjugation plane of GQDs. Spectroscopic analysis combined with density functional theory (DFT) calculations reveals that such Pt nanoislands are electron-deficient with electron-transfer from Pt to the π-conjunction in GQDs through the C–O–Pt pathway, optimizing the hydrogen adsorption energy (Δ G *H ) compared with that in commercialized Pt/C (Pt–C) to facilitate HER kinetics. As a result, such prepared PG delivers a mass activity of 0.19 A mg –1, which is 2 times that of commercial Pt/C with long-term stability. This work provides an alternative and variable kind of carbon substrate for highly dense catalyst design.