Ternary IrO2-Pt-Ni deposits prepared by galvanic replacement as bifunctional oxygen catalysts

Abstract

Abstract Bifunctional oxygen catalysts with IrO2 and Pt active components have been prepared by means of galvanic partial replacement of Ni layers electrodeposited on glassy carbon substrates (Ni/GC). The resulting IrO2Pt(Ni)/GC electrodes have a homogeneous and compact morphology (SEM), while surface electrochemistry and spectroscopic measurements (EDS, XPS) confirm the ternary bulk structure (EDS: 56.39% Ir – 7.60% Pt – 36.01% Ni atomic ratio) and the existence of a IrO2-Pt thin skin on the outermost layers of the deposits (XPS: Ir÷Pt atomic ratio of 21.7). IrO2Pt(Ni)/GC electrodes were evaluated as bifunctional electrocatalysts for oxygen evolution (OER) and oxygen reduction (ORR) reactions in acid, by means of steady-state current-potential measurements and linear sweep voltammetry at a Rotating Disc Electrode (RDE) respectively. The OER overpotential required for a current density (per substrate geometric area) of 1 (η1) and 10 mA cm‐−2 (η10) on the prepared electrodes was 235 and 302 mV respectively, which is in the range of some typical thermally produced IrO2-based DSAs. Their intrinsic OER catalytic activity (as estimated by normalization of the recorded currents at an overpotential of 260 mV by the oxides charge) was found to be 0.29 mA mC−1 comparable or better to other thermally produced IrO2 and Pt-IrO2 systems. Koutecky-Levich analysis shows that ORR proceeds on the ternary catalysts via the four electrons pathway. The overall ORR catalytic activity (0.4 mA cm−2 at +0.8 V vs. SHE) is found to be in the range of that recorded on nanoparticle catalysts, while a suppression of the intrinsic activity compared to bulk Pt is observed most probably due to the presence of IrO2, the latter being in line with similar non-alloyed Pt-IrO2 systems reported in the literature.