CoAg共负载的氮碳电催化还原CO_(2)的研究

Study on electrocatalytic reduction of CO_(2)by CoAg co-loaded nitrogen-carbon materials

电催化CO_(2)还原转变成合成气是一种有前途的解决CO_(2)污染的方法.本工作在合成钴基金属有机框架材料ZIF-67的过程中引入Ag+,通过调控Co/Ag物质的量的比和煅烧温度合成一系列的CoAg共负载的氮碳材料(CoAg(a:b)-N-C),并进行电催化还原CO_(2)的性能研究.X射线衍射仪(XRD)和X射线光电子能谱分析(XPS)测试表明,金属Co和Ag主要以单质的形式负载在碳基质上,部分以金属氮键(M-N)的形式存在.透射电子显微镜(TEM)表明,部分金属单质被碳材料包裹,从而有效防止金属颗粒在使用过程中发生团聚.线性扫描伏安法(LSV)测试表明CoAg(a:b)-N-C呈现出高于Co负载氮碳材料(Co-N-C)的电催化还原CO_(2)的活性,其中CoAg(1∶1)-N-C-900在-0.53 V(vs.RHE)下产物CO的法拉第效率(FE)为45%,H2的FE为26%,此时CO/H2比例也达到1.73;产物的FE表明Co/Ag物质的量的比、煅烧温度和还原电位等都会对CO/H2比例产生影响,其中Co/Ag对CO/H2比例的调控范围更大,可达0.43~1.73.机理分析表明,Ag的引入提高了CoAg(1∶1)-N-C-900的导电性和对CO_(2)及中间体CO*的吸附能力,因而最终提高了材料的电催化还原CO_(2)的活性.本研究表明,CoAg(a:b)-N-C是一种有潜力的电催化CO_(2)转化为合成气的材料.

Electrocatalytic CO_(2)reduction to syngas is a promising method for solving the problem of CO_(2)pollution.In this work,Ag+was introduced during the synthesis of cobalt-based metal-organic frameworks ZIF-67 used as precursors,and a series of CoAg co-loaded nitrogen-carbon materials(CoAg(a:b)-N-C)were synthesized by adjusting the Co/Ag molar ratio and calcination temperature.X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)characterizations indicated that the Co and Ag nanoparticles were mainly loaded on the carbon matrix in the form of elementary substances,and some metal element existed by forming chemical bonds between transition metal and N elements(M-N).Transmission electron microscopy(TEM)further verified that some metal nanoparticles were wrapped by the carbon material,thereby effectively preventing the metal nanoparticles from agglomerating during use.Linear sweep voltammetry(LSV)tests indicated that CoAg(a:b)-N-C exhibited higher electrocatalytic CO_(2)reduction activity than Co-N-C.The Faraday efficiencies(FE)of CO and H2 for CoAg(1∶1)-N-C-900 at-0.53 V(vs.RHE)were 45%and 26%,respectively,and the CO/H2 ratio was 1.73.The FE indicated that the Co/Ag molar ratio,calcination temperature and reduction potential could affect the CO/H2 ratio and the CO/H2 ratio was 0.43~1.73 by adjusting the Co/Ag ratio.The mechanism analysis revealed that the introduction of Ag facilitated the electron transport and improved the adsorption ability towards CO_(2)and intermediate CO*,ultimately improving the electrocatalytic reduction activity of CoAg(1∶1)-N-C-900 towards CO_(2).This work indicates that CoAg(a:b)-N-C is a promising material for electrocatalytic CO_(2)reduction into syngas.