Fundamental Study of Facile and Stable Hydrogen Evolution Reaction at Electrospun Ir and Ru Mixed Oxide Nanofibers

Abstract

Electrochemical hydrogen evolution reaction (HER) has been an interesting research topic in terms of the increasing need of renewable and alternative energy conversion devices. In this article, Ir_<i>x</i>Ru_1–<i>x</i>O_<i>y</i> (<i>y</i> = 0 or 2) nanofibers with diverse compositions of Ir/IrO₂ and RuO₂ are synthesized by electrospinning and calcination procedures. Their HER activities are measured in 1.0 M NaOH. Interestingly, the HER activities of Ir_<i>x</i>Ru_1–<i>x</i>O_<i>y</i> nanofibers improve gradually during repetitive cathodic potential scans for HER, and then eventually reach the steady-state consistencies. This cathodic activation is attributed to the transformation of the nanofiber surface oxides to the metallic alloy. Among a series of Ir_<i>x</i>Ru_1–<i>x</i>O_<i>y</i> nanofibers, the cathodically activated Ir_0.80Ru_0.20O_<i>y</i> shows the best HER activity and stability even compared with IrO_<i>y</i> and RuO_<i>y</i>, commercial Pt and commercial Ir (20 wt % each metal loading on Vulcan carbon), where a superior stability is possibly ascribed to the instant generation of active Ir and Ru metals on the catalyst surface upon HER. Density functional theory calculation results for hydrogen adsorption show that the energy and adsorbate–catalyst distance at metallic Ir_0.80Ru_0.20 are close to those at Pt. This suggests that mixed metallic Ir and Ru are significant contributors to the improved HER activity of Ir_0.80Ru_0.20O_<i>y</i> after the cathodic activation. The present findings clearly demonstrate that the mixed oxide of Ir and Ru is a very effective electrocatalytic system for HER