Excessive Se on RuSe2 nanocrystals to accelerate water dissociation for the enhanced electrocatalytic hydrogen evolution reaction

Abstract

Selenium-enriched RuSe₂ (Ru_xSe) nanocrystals as electrocatalysts for the HER in basic media have been synthesized via a facile hydrothermal method followed by a calcination process. The catalytic activity of the obtained Ru_xSe nanocrystals is greatly dependent on calcination temperatures. The nanocrystals obtained at 400 °C (Ru_xSe-400) demonstrate the highest HER activity with a low overpotential of 45 mV to deliver a current density of 10 mA cm⁻² and a small Tafel slope of 31.4 mV dec⁻¹. The enhanced catalytic HER performance of Ru_xSe-400 could be attributed to the excessive Se on the RuSe₂ nanocrystal surface. Density functional theory (DFT) calculations reveal that the excessive Se would lower the energy barrier for water dissociation and lessen the dependence on the Ru sites for OH* adsorption but have a negligible effect on hydrogen adsorption energy, leading to an accelerated HER process. Furthermore, the excessive Se on the nanocrystal surface further endows the catalyst with promoted charge-transfer kinetics, ensuring a more efficient catalytic reaction. The strategy herein for the design of highly efficient HER catalysts by engineering the separation of different intermediate (H* and OH*) adsorption sites is expected to be extended to other electrocatalysts for high-efficiency energy conversion.