超细氧化铜纳米颗粒修饰二维金属有机框架协同增强二氧化碳电化学还原生成乙烯

Integration of ultrafine CuO nanoparticles with two‐dimensional MOFs for enhanced electrochemicgal CO_(2) reduction to ethylene

为了促进CO_(2)电化学还原(ECR)制备燃料和高值化学品,开发高活性、低成本和高选择性催化剂至关重要.本文通过简单的溶剂热法一步合成超细氧化铜(CuO)纳米颗粒修饰的二维Cu基金属有机框架(CuO/Cu-MOF)复合催化剂.并采用X射线衍射、X射线光电子能谱、傅里叶变换红外光谱、高角环形暗场像-扫描透射电镜、N_(2)吸附/脱附、元素分析谱、CO_(2)吸附等方法进行表征,对CuO/Cu-MOF复合材料的组成、形貌和孔结构等进行了系统研究.结果表明,超细CuO纳米粒子的尺寸为1.4到3.3 nm,均匀修饰在二维Cu-BDC MOF表面.由于其结构中丰富的孔道结构,CuO/Cu-MOF在常压下的CO_(2)吸附量可达5.0 mg_(CO2) g_(cat).^(–1),明显优于商业CuO纳米颗粒.进一步在H型电解池、0.1 mol/L KHCO_(3)电解质溶液中研究了CuO/Cu-MOF的ECR性能;结果表明,在CO_(2)饱和的0.1 mol/L KHCO_(3)电解质溶液中,反应产物包括CO,H_(2),HCOOH和C_(2)H_(4).在-1.0至-1.2 V(相对于可逆氢电极,下同)电势范围内,ECR占主导地位;生成C_(2)H_(4)的起始电位为-0.85 V,在-0.9至-1.2 V电势范围内,C_(2)H_(4)是主要产物;电势高于-0.9 V时,CO和HCOOH是主要产物;电势低于-0.9 V时,开始生成CH_(4),且其含量随过电势增加而增加.通过改变材料合成时的前驱体配比、配体种类和反应温度等可调节CuO/Cu-MOF催化剂对ECR产物的活性和选择性,当对苯二甲酸:硝酸铜摩尔比为3:1、温度为100°C时,制得的CuO/Cu-MOF可在-1.1 V电势下将CO_(2)还原为C_(2)H_(4),其法拉第效率可达50.0%,显著优于许多文献报道的Cu基电催化剂以及所合成的纯Cu-MOF和纯CuO,其在相同电解条件下生成C_(2)H_(4)的法拉第效率分别为37.6%和25.5%.此外,生成C_(2)H_(4)的几何分电流密度约为7.0 mA cm^(-2),生成速率为21.0μmol mg_(cat).^(–1) h^(–1),阴极能量效率达到27.7%.催化剂的稳定性测试结果表明,在连续电解10 h后,C_(2)H_(4)的法拉第效率仍保持在45.0%以上.进一步的机理研究表明,CuO/Cu-MOF复合材料中二维金属铜有机框架主体和超细CuO纳米颗粒在ECR反应过程中可协同实现对CO_(2)的吸附和活化,促进C-C耦合,从而高选择性生成C_(2)H_(4).本文为提高ECR生成C_(2)H_(4)的选择性和活性提供了有效策略.

To facilitate the electrochemical CO_(2) reduction(ECR)to fuels and valuable chemicals,the development of active,low cost,and selective catalysts is crucial.We report a novel ECR catalyst consisting of CuO nanoparticles with sizes ranging from 1.4 to 3.3 nm anchored on Cu metal‐organic framework(Cu‐MOF)nanosheets obtained through a one‐step facile solvothermal method.The nanocomposites provide multiple sites for efficient ambient ECR,delivering an average C_(2)H_(4) faradaic efficiency(FE)of~50.0%at–1.1 V(referred to the reversible hydrogen electrode)in 0.1 mol/L aqueous KHCO_(3) using a two‐compartment cell,in stark contrast to a C_(2)H_(4) FE of 25.5%and 37.6%over individual CuO and Cu‐MOF respectively,also surpassing most newly reported Cu‐based materials under similar cathodic voltages.The C_(2)H_(4) FE remains at over 45.0%even after 10.0 h of successive polarization.Also,a~7.0 mA cm^(–2) C_(2)H_(4) partial geometric current density and 27.7%half‐cell C_(2)H_(4) power conversion efficiency are achieved.The good electrocatalytic performance can be attributed to the interface between CuO and Cu‐MOF,with accessible metallic moieties and the unique two‐dimensional structure of the Cu‐MOF enhancing the adsorption and activation of CO_(2) molecules.This finding offers a simple avenue to upgrading CO_(2) to value‐added hydrocarbons by rational design of MOF‐based composites.