Abstract:

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.

Key words: Carbon dioxide reduction, Electrocatalysis, Palladium-based nanomaterials, Carbon monoxide, Formic acid, Stability