Pd/C Catalysts for CO2 Electroreduction to CO:Pd Loading Effect
- 2018年第24卷 
CO2电化学还原反应可以将CO2转化为燃料并同时实现再生能源的有效存储. 目前纳米结构的多相催化剂已经广泛应用于此反应，其中碳负载钯纳米粒子（Pd/C）表现出优异的CO2电化学还原性能. 本工作研究了钯载量对于Pd/C催化剂结构以及其催化CO2还原生成CO反应活性和选择性的影响. 不同载量的Pd/C催化剂通过液相还原方法制备，钯纳米粒子均匀地分散在碳载体上，载量并没有明显改变对纳米粒子的粒径. 在优选的电解质（0.1 mol·L-1 KHCO3）中，CO法拉第效率与载量呈现火山型曲线关系，-0.89 V时载量为20wt%的Pd/C催化剂达到最高的CO法拉第效率(91.2%). 生成CO的几何电流密度随着钯载量的增加而增加，但CO转换频率具有相反的趋势，载量为2.5wt%的Pd/C催化剂具有最高的转换频率. 这种载量对CO2电化学还原反应活性和选择性的影响主要由活性位的数量、反应动力学、中间物种的稳定性以及反应物、中间物种和产物的传质过程等共同决定.Nanostructured heterogeneous catalysts have been widely used in the electrochemical carbon dioxide (CO2) reduction reaction (CO2RR), which can simultaneously achieve the electrocatalytic conversion of CO2 to fuels and the storage of renewable energy sources. Carbon supported palladium nanoparticles (Pd/C) catalysts have been previously reported to show excellent CO2RR performance. However, the crucial role of the metal loading in supported electrocatalysts has been rarely reported. In this work, we study the Pd loading effect on the structure of Pd/C catalysts as well as their activity and selectivity of CO2RR to CO. The Pd loadings in Pd/C catalysts were well controlled by an effective liquid synthesis method. The Pd nanoparticles were homogeneously dispersed on the carbon support, and the Pd loading played a minor role in the particle size. The as-prepared Pd/C catalysts were studied in an optimized electrolyte, 0.1 mmol·L-1 KHCO3. It shows a volcano relationship between CO Faradaic efficiency (FE) and the Pd loading, with the highest CO FE of 91.2% over the 20wt% Pd/C catalyst at -0.89 V versus the reversible hydrogen electrode (vs. RHE). The geometric CO partial current density had a positive correlation with the Pd loading, while the highest turnover frequency for CO production was observed over the 2.5wt% Pd/C catalyst (~ 918 h-1 at -0.89 V vs. RHE). The Pd loading effects on the activity and selectivity of CO2RR to CO could be attributed to the number of active sites, reaction kinetics, and the stabilization of key intermediates, as well as the mass transport of reactants, intermediates and products. This work provides new insight into the loading effect, an important reactivity descriptor determining the CO2RR performance.