Oxidation-induced restructuring of copper sulfides for enhanced performance in CO2 electroreduction

•Cu1.81S@WMCNT catalysts are prepared through a facile in-situ crystallization strategy.•Cu1.81S@WMCNT-600 shows moderate activity of CO2 reduction to formate.•Mild oxidation assisted further enhanced catalytic performance of copper sulfides.•Cu1.81S@MWCNT-600-OD shows high selectivity in the formation of formate, making the faradaic efficiency raised to 82 %.•Cu1.81S@MWCNT-600-OD restructures to needle-like dendritic shape with a better catalytic performance.