Ir Decorated Fractal Ni Catalysts for the Oxygen Evolution Reaction

Abstract

Porous and fractal Ni electrode synthesized by the Dynamic Hydrogen Bubbling Template (DHBT) method (Ni DHBT electrode) have shown very promising performances for the oxygen evolution reaction (OER) in alkaline electrolyte. This was thought to arise as a result of the extended electrochemical active surface area and its superaerophilic properties that facilitates the release of oxygen bubbles[1]. Herein, we report on a method to decorate the Ni DHBT electrode with Ir atoms via a galvanic replacement (GR) reaction. The resulting electrode has very low loadings of Ir (0.26 atom % as determined by EDX). As shown in Figure 1, micrometer-sized pores are observed at the surface of deposits, with pore walls exhibiting a highly porous cauliflower-like secondary structure, with much smaller pore diameter (typically less than 500 nm). The structure seen in Figure 1 was observed over the entire 0.32 cm2 geometric surface area of the deposits. The morphology of the Ir-modified electrode is not changed with respect to Ni DHBT electrode, indicating that the GR reaction is occurring only at the surface of the deposit. Voltammetry cyclic tests in 1M KOH solution showed hydrogen adsorption/desorption (Hupd) peaks of Ir as well as the redox peaks of Ni(OH)2 which suggested the coexistence of Ir and Ni content at electrode/electrolyte interface. The activity for the OER of Ni DHBT electrode was further improved by decoration with Ir, resulting in an overpotential of 195mV at 10 mA/cm2 and a Tafel slope of 46 mV/dec. To the best of our acknowledgment, this is one of the best performing Ni based OER catalysts reported so far. The interaction of oxygen bubbles with the electrode surface will also be assessed using both optical imaging and acoustic emission characterization.[1] M. Hao et al., “Hydrogen Bubble Templating of Fractal Ni Catalysts for Water Oxidation in Alkaline Media,” ACS Appl. Energy Mater., vol. 2, no. 8, pp. 5734–5743, Aug. 2019. Figure 1