Plasma‐Triggered Synergy of Exfoliation, Phase Transformation, and Surface Engineering in Cobalt Diselenide for Enhanced Water Oxidation

Abstract

Various strategies,s uch as increasing active site numbers and structural and surface engineering, have been used to improve the oxygen evolution reaction (OER) performance of transition-metal dichalcogenides.H owever,i t is challenging to combine these strategies in one system to realizet he full catalytic potential. Now,a nA r/O 2 plasma method is used to simultaneously induce exfoliation, surface reorganization (formation of an oxidative layer with rich oxygen vacancies), and phase transformation (cubic-to-orthorhombic) on CoSe 2 to generate an exceptionally outstanding OER electrocatalysts.T he as-made samples require an overpotential of only 251 mV at 10 mA cm À2 ,o utperforming commercial RuO 2 and most reported OER catalysts.T he striking catalytic activity originates from the optimizedc hemical and electronic environment. This work provides valuable insights into the design of promising OER electrocatalysts with high natural abundance via multilevel structural modulation.The global energy crisis and environmental problems have stimulated researchers to develop the next-generation clean and sustainable energy technologies for replacement of traditional fossil fuels. [1] Hydrogen, with ahigh energy density, is regarded as an attractive candidate. [2] Water splitting,a s agreen way to generate hydrogen, is technically hindered by the inherent sluggish kinetics and high overpotential of oxygen evolution reaction (OER). [3] To date,n oble-metal oxides,s uch as RuO 2 and IrO 2 ,r emain the workhorse catalysts to accelerate the process. [4] Nevertheless,t he high cost and limited resources have seriously impeded their large-scale utilization. [5] Therefore,i ti su rgent to explore more economical alternatives with equivalent or better activity and stability based on earth-abundant elements for achieving sustainable water electrolysis technology.Tr ansition-metal (M = Fe,C o, Ni)d ichalcogenides (X 2 = S 2 ,Se 2 ,T e 2 )have been recently attractive for promoting OER electrocatalysis owing to their intriguing structural and electronic properties. [6] So far, diverse strategies have been adopted to bring favorable interface and structural modulation on MX 2 for optimizing their electrocatalytic efficiencies.F or instance,e xfoliation of bulk materials into twodimensional (2D) ultrathin nanosheets can effectively increase the number of exposed active sites,t hus boosting the catalytic activity. [7] Selective control of the crystal structure is another effective way. [8] TheM X 2 minerals exist in two phases (stable cubic pyrite-type and metastable orthorhombic marcasite-type) in nature,w here the subtle structural distinction can affect their binding ability of reaction intermediates,w hich thereby leads to different gains in catalytic performance. [9] Although cubic-to-orthorhombic (c-to-o) transition has been described through at hermal method [10] and the reverse change theoretically can be realized by rotating half of the X 2 2À groups, [11] there is still lack of facile means to actually establish this convers...

The Role of Defect Sites in Nanomaterials for Electrocatalytic Energy Conversion

“…24 It is also noteworthy that the plasma technology with good controllability (e.g., Ar, O 2 , and/or N 2 plasma source type, power density, and processing time) is another promising approach to obtaining uniformly vacancy defects in carbon-or metal-compound-based nanomaterials. 25,26 Furthermore, the obtained defect structures in carbons, transition-metal oxides, and TMDs (e.g., MoS 2 and CoSe 2 ) can be further processed by non-metal-and metal-atom doping to form various dopant-defect coordination motifs to not only stabilize the topological structures of defects but also further manipulate the local electronic distribution through the diverse coordinated configurations. 27,28 Analogous to plasma technology, a high-pressure hydrogenation process has been recently reported to treat a 2D iron-cobalt oxide (Fe 1 Co 1 O x ) via controllable hydrogen pressure and annealing temperature with the purpose of tuning its oxygen vacancy density.…”

“…Since then, such a plasma-engraving strategy has also been employed in exfoliation of bulk 2D materials, such as CoSe 2 , to introduce defects and exposure more active sites. 26 Besides anion defects, cation defects have also been proved to promote OER properties. Shao and co-workers found that the A-site cation defect of a perovskite type (ABX 3 ) LaFeO 3 can greatly enhance both the OER and ORR activities because of 60 Copyright 2016 American Chemical Society.…”

Amorphization activated ruthenium-tellurium nanorods for efficient water splitting

“…However, a high voltage is still needed to drive the reaction process because of the sluggish kinetics for OER, especially in acidic conditions 8–11 . Significant efforts have been undertaken to design novel catalysts to overcome this obstacle, including heteroatoms doping, functionalization, and so on 12–16 . Although much progress in developing bifunctional electrocatalysts for alkaline water splitting has been realized, the overpotential and corrosion resistance are still far from satisfactory under harsh acidic conditions, which hamper the development of proton exchange membrane water electrolyzers 17–19 .…”

A Co-Doped Nanorod-like RuO2 Electrocatalyst with Abundant Oxygen Vacancies for Acidic Water Oxidation

“…Electrochemical water splitting, including hydrogen evolution reaction and oxygen evolution reaction (OER), provide an efficient and environmentally friendly way for large-scale hydrogen production with high purity. To date, alkaline water splitting technologies have been well established and are commercially available for industrial H 2 production (Jin et al, 2016;Suen et al, 2017;Zheng et al, 2016;Wang et al, 2018aWang et al, , 2018bZhuang et al, 2019;Zhou et al, 2019). Nevertheless, compared with alkaline water splitting, acidic water splitting using proton exchange membrane (PEM) electrolyzer offers great advantages such as higher ionic conductivity, fewer unfavorable reactions, high voltage efficiency, and faster system response (Nong et al, 2015;Sardar et al, 2014).…”