Ru Prussian blue analogue-derived Ru nanoparticles composited with a trace amount of Pt as an efficacious electrocatalyst for the hydrogen evolution reaction

Abstract

In this work, we designed a straightforward and highly reproducible synthetic methodology to prepare Ru⁰–Pt⁰ composites. We report a significant improvement in the electrocatalytic performance upon compositing Ru with a very trace amount of Pt. In particular, Ru nanoparticles were derived from a Ru-Prussian blue analogue (Ru PBA) and composited with (0.1, 0.5, and 1 mmol) metallic platinum following an optimized chemical reduction method. Interestingly, the composite with 0.5 mmol of Pt (Ru@C/Pt_0.5) required low overpotentials of 32 and 140 mV to achieve current densities of 10 and 100 mA cm⁻², respectively. Furthermore, Ru@C/Pt_0.5 exhibited a smaller Tafel slope (26 mV dec⁻¹), robust durability with 50 hours of long-term stability and a higher turnover frequency (TOF: 5.6 s⁻¹@η_{10 mA cm⁻²}) than commercial Pt/C (TOF: 4.1 s⁻¹@η_{10 mA cm⁻²}). First-principles calculations using density functional theory (DFT) revealed that the existence of Pt islands on the Ru nanoparticles weakened the strength of the adsorption of hydrogen at the Ru interstitials due to electrostatic repulsion caused by charge retention at Ru atoms near the corner of the islands, leading to rapid dissociation of hydrogen. This created a significant impact on the improvement of the electrocatalytic HER activity of the Ru@C/Pt_0.5 electrocatalyst. It appears that restricting the concentration of Pt to trace amounts is a necessary condition for the observed catalytic efficiency, as the catalytic efficiency decreases with an increasing island size due to stronger binding of atomic hydrogen on peripheral Pt atoms and stabilization of adsorbed atomic hydrogen caused by softening of phonon modes with increasing island size. This study opens up a novel avenue for the exploration of highly efficient electrocatalysts for hydrogen evolution reactions.