Fine-tuning surface oxidation states of ruthenium nanoparticles to enhance hydrogen electrode reactions

Abstract

The surface oxidation state of nano-sized electro-catalysts is a critical yet often overlooked factor for their electro-catalysis. Neglecting this aspect can lead to misinterpretation of the underlying catalytic mechanism and hinder progress in developing high-performance electro-catalysts. Herein, we focus on elucidating the relationship between the surface oxidation state and catalytic activity towards the hydrogen evolution/oxidation reaction (HER/HOR) by precisely modulating the oxidation state of surface atoms on ruthenium nanoparticles (Ru-NPs). Aberration-corrected scanning transmission electron microscopy and depth-profiling X-ray photoelectron spectroscopy confirm the existence of oxidized Ru atoms on the surface of Ru-NPs, while the oxidation state of these surface atoms can be controlled by varying the NP size aided by the kinetics analysis for the electro-oxidation of underpotential deposited Cu. The intrinsic activities of the as-prepared catalysts present a volcano-type trend that depends on the surface oxidation state, and the maximum activities can be achieved on the specific oxidized surfaces of 1.9 and 5.3 nm Ru-NPs toward the HER/HOR respectively. Notably, operando X-ray absorption spectroscopy persuasively corroborates the structural stability of oxidized Ru atoms on the surface, even at reduction potential. Theoretical simulations further elucidate the role of surface Ru oxides in enhancing mechanisms for the HER/HOR. This study provides valuable insights into the design of high-performance electro-catalysts and advanced nanomaterials for energy conversion applications.