Enhanced Electrochemical Properties and OER Performances by Cu Substitution in NiCo2O4 Spinel Structure.

Hyerim Park,Jae Hong Kim,Young-Sang Youn,Byung Hyun Park,Jaeyoung Choi,Seyeon Kim,Namgyu Son,Taesung Kim,Misook Kang

doi:10.3390/nano10091727

Hyerim Park, Jae Hong Kim + Show 7 more

Open Access

https://doi.org/10.3390/nano10091727

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Journal: Nanomaterials	Publication Date: Aug 31, 2020
Citations: 42	License type: CC BY 4.0

Affiliation: Yeungnam University

Abstract

In order to improve the electrochemical performance of the NiCo2O4 material, Ni ions were partially substituted with Cu2+ ions having excellent reducing ability. All of the electrodes were fabricated by growing the Ni1−xCuxCo2O4 electrode spinel-structural active materials onto the graphite felt (GF). Five types of electrodes, NiCo2O4/GF, Ni0.875Cu0.125Co2O4/GF, Ni0.75Cu0.25Co2O4/GF, Ni0.625Cu0.375Co2O4/GF, and Ni0.5Cu0.5Co2O4/GF, were prepared for application to the oxygen evolution reaction (OER). As Cu2+ ions were substituted, the electrochemical performances of the NiCo2O4-based structures were improved, and eventually the OER activities were also greatly increased. In particular, the Ni0.75Cu0.25Co2O4/GF electrode exhibited the best OER activity in a 1.0 M KOH alkaline electrolyte: the cell voltage required to reach a current density of 10 mA cm−2 was only 1.74 V (η = 509 mV), and a low Tafel slope of 119 mV dec−1 was obtained. X-ray photoelectron spectroscopy (XPS) analysis of Ni1−xCuxCo2O4/GF before and after OER revealed that oxygen vacancies are formed around active metals by the insertion of Cu ions, which act as OH-adsorption sites, resulting in high OER activity. Additionally, the stability of the Ni0.75Cu0.25Co2O4/GF electrode was demonstrated through 1000th repeated OER acceleration stability tests with a high faradaic efficiency of 94.3%.

Highlights

With the increase in environmental pollution due to excessive use of fossil fuels, studies on new energy conversion and storage systems such as water decomposition devices, fuel cells, and batteries are actively being conducted
Hydrogen energy produced by water splitting is an ideal clean energy and has the advantage of having the largest energy efficiency per unit mass compared to other energy sources [1]
It is known that noble metal materials can reduce the over-potential, and noble metals such as Ir and Ru are already used as efficient electrode active materials [3,4]

Summary

Introduction

With the increase in environmental pollution due to excessive use of fossil fuels, studies on new energy conversion and storage systems such as water decomposition devices, fuel cells, and batteries are actively being conducted. Co-based bimetal oxides having a spinel structure as a non-noble metal active material have attracted wide attention in the field of energy storage and conversion. NiCo2O4 has high electrical conductivity and stability, attracting much attention from scientists, and is known as a reliable OER electrode active material with excellent repeatability [8]. Nickel-cobalt bimetal oxide (NiCo2O4) is a material that has been studied extensively for a long time and shows ideal electrochemical performance in super capacitors or batteries such as LiB [10], Zn-Air [11], and Li-Air [12]. In order to improve the electrochemical performance of the NiCo2O4 electrode active material, Ni ions were partially substituted with Cu ions having excellent reducing ability. Instead of Ni in the NiCo2O4 spinel structure, Cu was partially substituted, the optimal amount was confirmed, and the OER performance was checked to investigate their correlation

Materials and Methods

Evaluation of Physicochemical Properties of Electrodes

Electrochemical Characterizations of Electrodes

Results and Discussion