Hydrogen evolution at Ir-Ni bimetallic deposits prepared by galvanic replacement

Ir-Ni layers have been formed by a galvanic replacement method whereby Ni electrodeposited on glassy carbon substrates (Ni/GC) has been partially replaced by Ir upon immersion of the former into an Ir(IV) solution. The resulting Ir-Ni/GC electrodes have been subjected to electrochemical treatment to ensure uncovered Ni anodic dissolution and film re-organisation into an Ir shell - Ir-Ni core structure (denoted as Ir(Ni)/GC). The existence of a thin Ir shell and an Ir-Ni core has been confirmed by surface voltammetry in deaerated acid (which showed pure Ir characteristics), sputter-etch XPS experiments (which confirmed surface enrichment in Ir and depletion of Ni) and EDS results (which gave a ca. 3.5 Ir ÷ Ni atom ratio in the bimetallic material). The Ir(Ni)/GC electrodes have been tested as cathodes for the hydrogen evolution reaction (HER) from acid solutions by electrochemical impedance spectroscopy (EIS) and steady-state current-potential measurements and exhibited a significant increase in intrinsic catalytic activity when compared to bulk Ir electrodes. This has been attributed to the effect of the Ni underlayers on H adsorption affinity of the Ir shell.