Hexagonal Single-Crystal CoS Nanosheets: Controllable Synthesis and Tunable Oxygen Evolution Performance

Abstract

Cobalt-based sulfides with variable valence states and unique physical and chemical properties have shown great potential as oxygen evolution reaction (OER) catalysts for electrochemical water-splitting reactions. However, poor morphological characteristics and a small specific surface area limit its further application. Here, hexagonal single-crystal two-dimensional (2D) CoS nanosheets with different thicknesses are successfully prepared by an atmospheric-pressure chemical vapor deposition method. Because of the advantages of the 2D structure, more exposed catalytic active sites, better reactant adsorption ability, accelerated electron transfer, and enhanced electrical conductivities can be achieved from the thinnest 5 nm CoS nanosheets (CoS-5), significantly improving OER performance. The electrochemical tests manifest that CoS-5 show an overpotential of 290 mV at 10 mA cm–2 and a Tafel slope of 65.6 mV dec–1 in the OER in an alkaline solution, superior to those for other thicknesses of CoS, bulk CoS, and RuO2. For the mechanistic investigation, the lowest charge transfer resistance (R ct) and the highest double-layer capacitance (C dl) were obtained for CoS-5, demonstrating the faster OER kinetics and the larger active area. Density functional theory calculations further reveal the enhanced density of states around the Fermi level and higher H2O molecule adsorption energy for thinner CoS nanosheets, promoting its intrinsic catalytic activity. Moreover, the two-electrode system with CoS-5 as the anode and Pt/C as the cathode requires only 1.56 V to attain 10 mA cm–2 in the overall water-splitting reaction. We believe that this study will provide a fresh view for thickness-dependent catalytic performance and offers a new material for the study of electronic and energy devices.

Recent Advances in Synergistic Modulation of Transition-Metal-Based Electrocatalysts for Water Oxidation: A Mini Review

“…In recent years, transition metal sulfides (Ni x S y , Co x S y , and Fe x S y ), phosphides (Ni x P y , Co x P y , and Fe x P y ), and borides have also shown excellent catalytic activity in the field of electrocatalytic OER [66][67][68][69][70][71]. Hexagonal 2D CoS nanosheets with varying thicknesses were synthesized by chemical vapor deposition [72]. The thinnest 5 nm-CoS nanosheets showed optimal OER performance (290 mV at 10 mA cm −2 ) due to more exposed catalytic active sites, stronger intermediate adsorption, and promoted electron transfer.…”

Cobalt‐based zeolitic imidazole framework derived hollow Co3S4 nanopolyhedrons for supercapacitors

“…They have attracted much attention as potential supercapacitor electrode materials. [7][8][9][10][11][12][13] In particular, cobalt sulfides with high electrical conductivity have been widely studied in many applications due to their excellent electrochemical properties 14 Much work has gone into creating different cobalt sulfide nanostructures over the last 20 years, including nanoparticles 15,16 nanosphere, 17 nanorods, 18,19 nanoarrays, 20 nanoneedles, 21 nanosheets, 22 nanofilms, 23 and hollow nanostructures, [24][25][26][27] for use in electrochemical energy storage systems. Among these structures, hollow nanostructures are expected to deliver superior performance because of the following advantages.…”

Rational Phase Control in the Synthesis of Cobalt Sulfides

“…11 Linnaeite (Co 3 S 4 ) is useful as a stable cathode material in Li/S batteries, while under nearinfrared illumination, linnaeite (Co 3 S 4 ) causes oxidative modifications and disassociates Alzheimer's beta-amyloid oligomers. Jaipurite (CoS) has also been reported to have great electrocatalytic activity for oxygen evolution reactions, 12 as well as great potential as a supercapacitor electrode. 13 In order to improve these applications, reliable synthetic routes to each of these materials must be established.…”