Ultralow Loading Ruthenium Nanoparticles on Nitrogen-Doped Graphene Aerogel for Trifunctional Electrocatalysis

A three-dimensional (3 D) nitrogen-doped graphene aerogel (NGA) with confined ultrasmall ruthenium nanoparticles (2–4 nm) was prepared through a hydrothermal reaction of graphene oxide (GO), ammonia solution, and ruthenium trichloride hydrate, followed by high-temperature annealing and oxidation. The reactants self-assemble into a 3 D porous structure with Ru nanoparticles embedded inside. With ultralow N and Ru contents of 2.40 and 1.21 at %, the introduction of Ru and N in the 3 D graphene aerogel gives rise to multifunctional catalytic performance in oxygen- and hydrogen-involved reactions. Particularly, its performance in the oxygen evolution reaction (OER) surpassed those of commercial Pt/C and RuO₂ in terms of both smaller potential (1.62 V vs. RHE) to reach 10 mA cm⁻² and larger current densities across the applied potential range of 1 to 2 V (vs. RHE). Structural and chemical characterization revealed that the nanoparticle size and Ru/RuO₂ ratio played decisive roles in determining the aerogel's electrocatalytic performance. Hence, this study demonstrates that the synergistic effect of nanosized Ru and a porous NGA can be applied to achieve effective multifunctional electrocatalysis, for which the Ru nanoparticles can be tailored to achieve optimized performance with the lowest-necessary doping concentration.