Copper Cobalt Sulfide Nanosheets Realizing a Promising Electrocatalytic Oxygen Evolution Reaction

Abstract

High Resolution Image Download MS PowerPoint Slide Nanostructured CuCo 2 S 4, a mixed metal thiospinel, is found to be a benchmark electrocatalyst for oxygen evolution reaction (OER) in this study with a low overpotential, a low Tafel slope, a high durability, and a high turnover frequency (TOF) at lower mass loadings. Nanosheets of CuCo 2 S 4 are realized from a hydrothermal synthesis method in which the average thickness of the sheets is found to be in the range of 8–15 nm. Aggregated nanosheets form a highly open hierarchical structure. When used as an electrocatalyst, CuCo 2 S 4 nanosheets offer an overpotential value of 310 mV at a 10 mA cm –2 current density, which remains consistent for 10000 measured cycles in a 1 M KOH electrolyte. A chronoamperometric study reveals constant oxygen evolution for 12 h at a 10 mV s –1 scan rate without any degradation of the activity. Furthermore, the calculated mass activity of the CuCo 2 S 4 electrocatalyst is found to be 14.29 A/g and to afford a TOF value of 0.1431 s –1 at 310 mV at a mass loading of 0.7 mg cm –2 . For comparison, nanostructures of Co 3 S 4 and Cu 0.5 Co 2.5 S 4 have been synthesized using a similar method followed for CuCo 2 S 4 . When compared to the OER activities among these three thiospinels and standard IrO 2, CuCo 2 S 4 nanosheets offered the highest OER activities at the same mass loading (0.7 mg/cm 2 ). Extensive X-ray photoelectron spectroscopy and electron paramagnetic resonance analyses for a mechanistic study reveal that introduction of Cu into the Co 3 S 4 lattice enhances the oxygen evolution and kinetics by offering Cu 2+ sites for utilitarian adsorption of OH, O, and OOH reactive species and also by offering a highly active high-spin state of octahedral Co 3+ for OER catalysis.