Enhancing Alkaline Hydrogen Evolution Reaction on Ru-Decorated TiO2 Nanotube Layers: Synergistic Role of Ti3+, Ru Single Atoms and Ru Nanoparticles

Abstract

Synergistic interplays involving multiple active centers originating from TiO2 nanotube layers (TNT) and ruthenium (Ru) species comprising of both single atoms (SAs) and nanoparticles (NPs) augment the alkaline hydrogen evolution reaction (HER) by enhancing Volmer kinetics from rapid water dissociation and improving Tafel kinetics from efficient H* desorption. Atomic Layer Deposition of Ru with 50 process cycles results in a mixture of Ru SAs and 2.8 ± 0.4 nm NPs present on TNT layers, and it emerges with the highest HER activity among all the electrodes synthesized. A detailed study of the Ti and Ru species using different high-resolution techniques confirmed the presence of Ti3+ states and the coexistence of Ru SAs and NPs. With insights from literature, the role of Ti3+, appropriate work functions of TNT layers and Ru, and the synergistic effect of Ru SAs and Ru NPs in improving the performance of alkaline HER was elaborated and justified. The aforementioned characteristics led to a remarkable performance by having 9 mV onset potentials and 33 mV dec-1 of Tafel slopes and a higher turnover frequency of 1.72 H2 s-1 at 30 mV. Besides, a notable stability from 28 h staircase chronopotentiometric measurements for TNT@Ru surpasses TNT@Pt in comparison.