钯基纳米材料电化学还原二氧化碳研究进展

电化学二氧化碳还原是利用电能驱动将CO_2高效转化为小分子碳基燃料的新方法,被认为是目前最具应用潜力的碳资源转化技术之一。然而,CO_2还原反应仍面临着诸多挑战,如反应过电位高,产物选择性低以及析氢反应的竞争等。因此,开发高效的电催化剂是发展CO_2还原技术的核心关键。近年来,Pd基材料在CO_2还原反应中表现出独特的催化性能优势:它不仅可以在接近平衡电位下高选择性地还原CO_2生成甲酸/甲酸盐,还能够在一定的负电位区间高效地还原CO_2生成CO。尽管如此,Pd基材料目前仍存在着成本较高、活性不理想以及稳定性差等问题,严重制约了其进一步应用与发展。对此,本文首先简单介绍了CO_2RR的基本原理,并综述了近年来Pd基催化剂电还原CO_2的应用研究及发展现状。重点探讨了尺寸效应、形貌效应、合金效应、核壳效应及载体效应等对Pd基催化剂性能的影响。最后针对这类材料的问题挑战及其未来发展方向进行了探讨与展望。

Recent Progress on Pd-based Nanomaterials for Electrochemical CO2 Reduction

The process that converts CO₂ to value-added chemical fuels or industrial feedstocks is called the electrochemical carbon dioxide reduction reaction (CO₂RR). When used in combination with renewable energy resources such as solar or wind, it represents one of the most promising strategies for transforming the intermittent renewable energy to chemical energy. However, because CO₂ molecules are thermodynamically stable, their electrochemical reduction is kinetically challenging. CO₂RR also has several different reaction pathways with a large spectrum of reduction products, making its selectivity problematic. It often requires the assistance of highly effective electrocatalysts with excellent activity, selectivity, and durability. Recently, palladium (Pd)-based nanomaterials have attracted considerable attention for CO₂RR. They can enable the selective production of formic acid or formate (HCOOH or HCOO^-) at near the theoretical equilibrium, as well as CO at a more negative potential. Unfortunately, the strong surface affinity of Pd toward CO often results in the deactivation of catalytic activity in the electrocatalytic process, in particular for formate production. Over recent years, extensive research effort has been invested into enhancing the electrochemical performances of Pd-based electrocatalysts. By controlling the size, morphology, and crystal surfaces of Pd nanocrystals, the distribution and structure of the atoms on the catalyst surface can be carefully engineered. For example, reducing the size of Pd nanoparticles has been found to significantly enhance the reaction activity and selectivity for the production of both CO and formate. The high-index crystal surfaces of Pd nanocrystals with low coordination numbers also generally show higher electrocatalytic activities. The design of Pd-based alloy nanostructures with tunable electronic structures represents another effective way to improve the electrochemical performance. Incorporation of non-precious metals can not only reduce the cost, but also effectively weaken the surface binding of CO. In addition, dispersing Pd nanoparticles on high-surface-area supports can increase the surface exposure of active sites and facilitate the formation of the electrochemical active phase. In this perspective, we provide an overview of the recent progress on nanostructured Pd-based catalysts for electrochemical CO₂ reduction. First, we briefly introduce the CO₂RR fundamentals as well as the reaction mechanism on Pd-based nanostructures. We then review a number of strategies to promote CO₂RR performance, including utilizing the size effect, morphology effect, alloy effect, core-shell effect, and support effect. Finally, we conclude with a perspective on the future prospects of Pd-based CO₂RR electrocatalysts, providing readers a snapshot of this rapidly evolving field.