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 Pt4+ 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 sp2 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 (ΔG*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.