Ir-Ni Bimetallic OER Catalysts Prepared by Controlled Ni Electrodeposition on Irpoly and Ir(111)

Ebru Özer,Ilya Sinev,Andrea Mingers,Beatriz Cuenya,Peter Strasser,Thomas Kropp,Jorge Araujo,Manos Mavrikakis,Karl Mayrhofer

doi:10.3390/surfaces1010013

Abstract

The alteration of electrocatalytic surfaces with adatoms lead to structural and electronic modifications promoting adsorption, desorption, and reactive processes. This study explores the potentiostatic electrodeposition process of Ni onto polycrystalline Ir (Irpoly) and assesses the electrocatalytic properties of the resulting bimetallic surfaces. The electrodeposition resulted in bimetallic Ni overlayer (OL) structures and in combination with controlled thermal post-deposition annealing in bimetallic near-surface alloys (NSA). The catalytic oxygen evolution reaction (OER) activity of these two different Ni-modified catalysts is assessed and compared to a pristine, unmodified Irpoly. An overlayer of Ni on Irpoly showed superior performance in both acidic and alkaline milieu. The reductive annealing of the OL produced a NSA of Ni, which demonstrated enhanced stability in an acidic environment. The remarkable activity and stability improvement of Ir by Ni modification makes both systems efficient electrocatalysts for water oxidation. The roughness factor of Irpoly is also reported. With the amount of deposited Ni determined by inductively coupled plasma mass spectrometry (ICP-MS) and a degree of coverage (monolayer) in the dependence of deposition potential is established. The density functional theory (DFT) assisted evaluation of H adsorption on Irpoly enables determination of the preferred Ni deposition sites on the three low-index surfaces (111), (110), and (100).

Highlights

Iridium is one of the most important electrode materials for basic surface science and industrial applications especially those in the field of electrochemistry due to its enhanced catalytic properties in water splitting electrolyzers [1,2]
The Ni-depleted active catalyst structure is expected to be composed of oxygen atoms protonated from the electrolyte to form surface hydroxyl groups, which presumably act as crucial intermediates in the oxygen evolution reaction (OER) mechanism
We can conclude that Ni in the near-surface alloys (NSA) configuration is not able to perform as a sacrificial catalyst component as effectively as Ni in the over layer (OL) configuration

Summary

Introduction

Iridium is one of the most important electrode materials for basic surface science and industrial applications especially those in the field of electrochemistry due to its enhanced catalytic properties in water splitting electrolyzers [1,2]. Surfaces 2018, 1 hydrogen production are the high potential losses at the anode side and the high Ir material costs In this context, studies on low index surfaces of single crystals offer a meaningful opportunity for a fundamental understanding and, based on it, the rational design of enhanced electrocatalytic materials. Potential-controlled deposition results in the growth of a new two-dimensional phase, which is believed to have electronic properties that differ significantly from those of the respective bulk materials. The deposition of metal adatoms on foreign metal substrates provides attractive systems with highly controllable surface coverages by using the electrode potential and deposition time. Due to its practical importance in surface chemistry and electrocatalysis, a number of ex situ and in situ techniques such as cyclic voltammetry (CV), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and low-energy electron diffraction (LEED) have been applied to augment the process of deposition at the molecular and atomic level [10]

Methods

Results

Conclusion