Nanosheet Assembled Microspheres 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 by 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 others. The lowest Tafel plot of CuInS2 (189.15 mV/dec) suggested the improvement of electrocatalytic activity than ZnIn2S4, (282.53 mV/dec) and NiIn2S4 (247.32 mV/dec). 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. Higher Faraday efficiencies (FEs) were observed in CuInS2 (80.11%) than ZnIn2S4 (67.78%), NiIn2S4 (75.31%) towards the electrocatalytic reduction of CO2 into methane (CH4) at -0.6 V vs RHE. CuInS2 demonstrated remarkable stability, with neither an obvious current drop nor large FEs fluctuation for 20 h during electrochemical CO2 reduction into CH4, indicating a superior electrocatalytic performance. The higher electrochemical performance of CuInS2 is associated with highly active 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 electroreduction of CO2 into CH4.