Electrocatalytic activity of high-entropy alloys toward oxygen evolution reaction
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Research Letter
Electrocatalytic activity of high-entropy alloys toward oxygen evolution reaction Xiaodan Cui, Boliang Zhang, Congyuan Zeng, and Shengmin Guo, Department of Mechanical & Industrial Engineering, Louisiana State University, Baton Rouge, Louisiana 70803, USA Address all correspondence to Shengmin Guo at [email protected] (Received 26 May 2018; accepted 15 June 2018)
Abstract Due to the special crystal structures and electron configurations, high-entropy alloys (HEAs) are expected to have favorable activities for electrocatalytic reactions. In this paper, a set of oxygen evolution reaction (OER) criteria are applied for the HEA-based electrocatalyst design. Specifically, FeNiMnCrCu HEA is predicted to have a better OER performance than the baseline FeCoNiCrAl HEA. To demonstrate this design approach, both FeNiMnCrCu and FeCoNiCrAl samples are prepared and tested. Their crystal structures and electrocatalytic performance are examined. This paper demonstrates the potential of using finely tuned HEAs for OER applications.
Background Due to the rapidly increasing demand for renewable and clean energy sources, water electrolysis has been examined frequently as a possible route for hydrogen generation.[1] However, owing to the common usage of high-cost noble metal-based electrocatalysts for oxygen evolution reaction (OER), such as Ir, Ru, and Pt, the large-scale industrialization of water electrolysis is impeded.[2] Recently, many low-cost materials have been explored to replace noble metals for OER.[3,4] Among them, first row transition metals, such as Ni, Fe, Co, Cu, and Mn, are especially appealing, due to their special electronic structures and the abundance on earth.[5] High-entropy alloys (HEAs), a new type of alloys, constructed of five or more metallic elements at equal or near-equal molecular ratios,[6,7] are emerging into an attractive category of functional metallic materials in the past decade.[8] Due to the varied atomic radius and geometrical configurations of different elements, the crystal lattices of HEAs can be finely tuned over a certain range, and the crystal lattices of HEAs can be severely distorted with significant residual strain remaining.[9] Such a high level of crystal imperfection could effectively increase the amount of active catalytic sites.[10] Moreover, due to the highly complex combination of transition metals with different electron configurations, the d-band vacancy number of HEA can be altered to tune its binding strength toward reaction species.[11] Because few studies have been conducted on the catalytic performance of HEAs, this paper examines the hypothesis that by tuning the HEAs compositions, an improved OER performance would be achieved.
HEA design for improved OER performance The binding strength of the reaction species toward the surfaces of an electrocatalyst determines the activity of the electrocatalyst.
For selected metallic catalysts, the volcano plot of catalytic activity versus the absorption energy of atomic oxygen[12] reveals that a moderate binding strength leads
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