P-doped Ru-Pt Alloy Catalyst toward High Performance Alkaline Hydrogen Evolution Reaction

Abstract

Electrocatalytic water splitting represents grand promise for hydrogen fuel in modern energy equipment, and the design and fabrication of higher performance catalysts are at the central. Herein, we report the sequential phosphorus (P)-doping into ruthenium (Ru) nanoparticles (Ru-P/C) by thermal annealing of Ru nanoparticles in phosphine (PH₃) atmosphere and deposition of extremely low concentration of platinum (Pt) to obtain P-doped Ru-Pt alloy catalyst supported on carbon nanotubes (CNTs), which is denoted as (Ru-P)#Pt/C. The data by X-ray diffraction spectroscopy and transmission electron microscopy show that the Ru nanoparticles existed in the form of hexagonal close-packed (hcp) phase with low crystallinity. The results by high-resolution X-ray photoelectron spectroscopy indicate that Ru was mainly in metallic state, and Pt was slightly and positively charged, ascribing to the bonding with P atoms. This indicates that the highly diluted Pt atoms may be dispersed on the surface of Ru nanoparticles through Ru-P-Pt bonds. Accordingly, the as-prepared (Ru-P)#Pt/C alloy catalysts displayed excellent alkaline hydrogen evolution activity, revealing only 17 mV vs. RHE at a current density of 10 mA·cm^-2 and a Tafel slope value of 27 mV·dec^-1, superior to those of the controlled samples Ru-P/C and trace amount of Pt loaded P-doped CNTs (Pt/C-P). Density functional theory (DFT) calculation suggests that P-doping into Ru can enhance the adsorption of water molecules and the activation for water splitting, while the Pt site on Ru-Pt alloy can behave as the hydrogen desorption site. Thus, the superior performance of (Ru-P)#Pt/C alloy catalyst might be attributed to the synergistic effect of P-doped Ru sites and Pt sites, which significantly improves the alkaline hydrogen evolution reaction kinetics.

Keywords

Ru-Pt alloy / Phosphorus-doping / Synergistic effect / Dual active sites

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