硫含量对CuS催化剂CO2电催化还原性能的影响

Sulfur content effect on CuS catalysts for electrochemical CO2 reduction

摘要:

铜基催化剂在CO2电催化还原制增值产品中极具潜力，但其面临着还原电位高和产物选择性差等挑战。采用水热合成法制备了不同铜硫比的CuS催化剂，采用XRD、FESEM和XPS对催化剂的形貌、结构进行了表征，探究硫含量对催化剂CO2电催化还原“构效关系”的影响机制。结果表明，硫含量影响CuS晶体成核与生长，进而影响催化剂的形貌特征和硫空位缺陷。随着铜硫比在2:1~1:4范围内变化，CuS催化剂的形貌由荷花状演化为花球状，硫空位浓度由20.66%提高至63.37%，CO2电催化还原活性和目标产物CO选择性明显提升。最佳铜硫比为1:4，对应CuS-1:4催化剂在0.1 M KHCO3电解液中，在-0.51 V (可逆氢电极RHE)的温和电势下CO选择性达72.67%。样品优异的CO2还原性能得益于花球状形貌提供的拓展表面积和气体扩散通道及硫空位缺陷对电子传递和*COOH中间体在催化剂表面吸附的强化作用。

Abstract:

Copper-based catalysts are highly promising for electrochemical CO2 reduction to value-added products, but they face the challenges of high potential and low products selectivity. Herein, CuS catalysts with different Cu/S ratios were prepared via the hydrothermal synthesis method, and the morphology and structure of the catalysts were characterized by XRD, FESEM, and XPS, to investigate the effect of sulfur content on their “structure-reactivity” relationships in CO2 reduction. Results indicated that sulfur content affected the nucleation and growth of CuS crystals, which in turn exerted impacts on the morphology and sulfur vacancy defects of the catalysts. As the Cu/S ratio varied from 2:1 to 1:4, surface morphology of the catalysts changed from the lotus shape to ball-flower structure, and the concentration of sulfur vacancies increased from 20.66% to 63.37%, which resulted in the significant enhancement of CO2 reduction activity and CO selectivity. The optimum Cu/S ratio was 1:4, and the desired CuS-1:4 catalyst exhibited a high CO selectivity of 72.67% under a mild potential of -0.51 V (reversible hydrogen electrode RHE) in 0.1 M KHCO3 electrolyte. The excellent CO2 reduction performance was associated with the expanded surface area and extended gas diffusion channels provided by the ball-flower structure and the facilitated electron transfer and strengthened adsorption of the *COOH intermediates on the catalyst surface contributed by the abundant sulfur vacancy defects.