Title

Phase Exploration and Identification of Multinary Transition-Metal Selenides as High-Efficiency Oxygen Evolution Electrocatalysts through Combinatorial Electrodeposition

Abstract

Designing high-efficiency electrocatalysts for water oxidation has become an increasingly important concept in the catalysis community due to its implications in clean energy generation and storage. In this respect transition-metal-doped mixed-metal selenides incorporating earth-abundant elements such as Ni and Fe have attracted attention due to their unexpectedly high electrocatalytic activity toward the oxygen evolution reaction (OER) with low overpotential in alkaline medium. In this article, quaternary mixed-metal selenide compositions incorporating Ni-Fe-Co were investigated through combinatorial electrodeposition by exploring the ternary phase diagram of Ni-Fe-Co systems. The OER electrocatalytic activity of the resultant quaternary and ternary mixed-metal selenide compositions was measured in order to systematically investigate the trend of catalytic activity as a function of catalyst composition. Accordingly, the composition(s) exhibiting the best catalytic efficiency for the quaternary Fe-Co-Ni mixed-metal selenide was identified. It was observed that the quaternary selenide outperformed the binary as well as the ternary metal selenides in this Ni-Fe-Co phase space. The elemental composition and relative abundance of the elements in the catalyst film was ascertained from energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Mapping of the OER catalytic activity as a function of catalyst composition indicated that catalytic efficiency was more pronounced in the Fe-rich region with moderate amounts of Ni and trace amounts of Co doping, and the best performance was exhibited by (Ni0.25Fe0.68Co0.07)3Se4, which showed an overpotential of 230 mV (vs RHE) at 10 mA cm-2 with stability exceeding 8 h for continuous oxygen generation. It was also observed that typically the quaternary metal selenide composition was close to AB2Se4, which shows a spinel structure type. Electrochemical measurements along with density functional theory (DFT) calculations were performed to correlate the enhancement of catalytic activity toward the Fe-rich region with composition. First-principles DFT calculations were used to estimate the hydroxyl adsorption energy (Eads) on the surface of the mixed-metal selenides with varying compositions. This adsorption energy could be directly correlated to the onset of OER activity, and the results matched very well with the experimentally observed trend with respect to onset overpotential. The knowledge of the trend of catalytic activity as a function of composition will be very important for catalyst design through targeted material synthesis. This work represents an example of a systematic phase exploration for quaternary metal selenides and provides a strong foundation which can be expanded to study other mixed-metal selenide combinations.

Department(s)

Materials Science and Engineering

Second Department

Chemistry

Comments

The authors acknowledge financial support from the National Science Foundation (DMR 1710313), American Chemical Society Petroleum Research Fund (54793-ND10), and Energy Research and Development Center (ERDC) Missouri S&T.

Keywords and Phrases

Calculations; Cobalt alloys; Cobalt compounds; Density functional theory; Design for testability; Electrocatalysts; Electrodeposition; Electrodes; Energy dispersive spectroscopy; Iron alloys; Nickel compounds; Oxygen; Phase space methods; Selenium compounds; Semiconductor doping; Ternary alloys; Transition metals; X ray photoelectron spectroscopy, Catalytic efficiencies; Clean energy generation; Electrocatalytic activity; Electrochemical measurements; Energy dispersive spectroscopies (EDS); First-principles DFT calculations; Oxygen evolution reaction; Ternary phase diagrams, Catalyst activity

International Standard Serial Number (ISSN)

2155-5435

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2018 American Chemical Society (ACS), All rights reserved.

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