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 (E ads) 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.

A Molecular Tetrahedral Cobalt–Seleno-Based Complex as an Efficient Electrocatalyst for Water Splitting

“…The smaller Tafel slope shown by CoSe 4 -modified electrodes compared to RuO 2 further confirms faster kinetics for OER and consequently better electrocatalytic efficiency of CoSe 4 . The Tafel slope for CoSe 4 is also comparable to reported values for other transition-metal–chalcogenide-based catalysts [ 14 , 24 ]. The CoSe 4 @Au-glass was also analyzed through electroimpedance spectroscopy (EIS) to estimate the charge transfer resistance (R CT ) at the catalyst–electrolyte interface.…”

“…Increased covalency in the chalcogenides also leads to alteration of the electronic band structure and proper alignment of the valence and conduction band edges with the water oxidation/reduction levels, respectively, leading to more facile charge transfer at the electrocatalyst–electrolyte interface which subsequently reduces the overpotential required for the electrochemical conversion [ 22 , 23 ]. Similar effects have also been observed by doping in transition metal sites which also redistributes electron density around the catalytically active site [ 24 ].…”

Electrocatalysts by Electrodeposition: Recent Advances, Synthesis Methods, and Applications in Energy Conversion

“…Nath and co-workers have developed earth-abundant quaternary mixed transition (Ni, Fe, and Co) metal-doped selenides (Se) incorporating electrocatalyst (FeCoNi) 3 Se 4 via combinatorial electrodeposition method for OER. [63] According to their comparative study, the quaternary (Ni 0.25 Fe 0.68 Co 0.07 ) 3 Se 4 exhibited the best performance at a very low overpotential of 230 mV (vs RHE) at 10 mA cm -2 with 8 h stability than binary and the ternary metal selenides.…”

Cryomilled Ni-Co-Se Enables Water Oxidation Electrocatalysts Durable at High Current Densities

“…The improved activity has been attributed to an increase in covalency in the metal-chalcogenide bond due to the smaller associated electronegativity and better conductivity. [14][15][16][17][18][19][20][21] However, several reports have shown that S and Se, in particular, are thermodynamically unstable at high pH during OER and ascribed the outstanding activity to increased nanoporosity in the structure, disordering in the lattice, or high number of defective surface sites after S and Se ions leave the strcuture. [22][23][24] In this work we will use cryomilling in addition to a chalcogenide (Se) scaffold to synthesize nanocrystalline Ni-Co-Se with high concentrations of Co in Ni.…”