Nanosheet assembled microspheres of metal (Zn, Ni, and Cu) indium sulfides for highly selective CO2 electroreduction to methane

Abstract

Herein, metal indium sulfides (ZnIn₂S₄, NiIn₂S₄, and CuInS₂) were synthesized using a hydrothermal method. Nanosheet-assembled microspheres were observed. According to cyclic voltammetry, CuInS₂ revealed 19 and 6-fold current density enhancement compared to ZnIn₂S₄ and NiIn₂S₄, respectively. Also, linear sweep voltammetry results suggested a higher current density of CuInS₂ than the others. The lowest Tafel plot of CuInS₂ (189.15 mV dec⁻¹) suggested the improvement of electrocatalytic activity compared to those of ZnIn₂S₄ (282.53 mV dec⁻¹) and NiIn₂S₄ (247.32 mV dec⁻¹). An H-type cell was used for selective electrochemical reduction of CO₂ into CH₄. The gaseous and liquid products were analyzed by gas chromatography and ¹H NMR, respectively. A higher Faraday efficiency (FE) was observed in CuInS₂ (80.11%) compared to those in ZnIn₂S₄ (67.78%) and NiIn₂S₄ (75.31%) towards the electrocatalytic reduction of CO₂ into methane (CH₄) at −0.6 V vs. RHE. A higher turnover frequency (TOF) value was observed in CuInS₂ compared to those in the other catalysts. CuInS₂ demonstrated remarkable stability, with neither an obvious current drop nor large FE fluctuation for 20 h during electrochemical CO₂ reduction into CH₄, indicating a superior electrocatalytic performance. The higher electrochemical performance of CuInS₂ is associated with a larger BET surface area/electrochemical surface area, rich structural design, and abundant active sites. This work indicates a promising strategy for developing a ternary electrocatalyst for highly selective electrochemical reduction of CO₂ to CH₄.