Iridium-cobalt alloy nanotubes as a bifunctional electrocatalyst for pH-universal overall water splitting

Abstract

Bimetallic IrxCo1-x alloy nanotubes (x = 0.25, 0.50 and 0.75, the atomic ratios of Ir precursor out of the total metal precursor) were prepared via the thermal H-2-reduction of IrxCo1-xOy nanotubes which were synthesized by electrospinning and post calcination. Ir and Co atoms were well mixed to form the alloy in IrxCo1-x nanotubes. Their phase structures were different depending on the composition ratios. Ir0.75Co0.25 and Ir0.50Co0.50 had Ir fcc phase where some Ir atoms were substituted with Co. In contrast, Ir0.25Co0.75 was in Ir-substituting Co hcp phase. Among the IrxCo1-x alloy nanotubes, Ir0.50Co0.50 showed the highest catalytic activity for overall electrochemical water splitting in acidic, neutral, and alkaline conditions, better than pure metallic Ir and Co counterparts. The activity and stability of Ir0.50Co0.50 nanotubes for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) were superior to commercial Ir/C and Pt/C, respectively.