The Relationships among Hydrogen Adsorption, CO Stripping, and Selectivity of CO2 Reduction on Pd Nanoparticles

Abstract

The low formation overpotential and strong adsorption ability of CO on palladium surface sites constrain the lower potential limit and current density of the electrochemical reduction of CO2 (CO2ER) to formate on Pd although this reaction has been considered one of the most effective methods for CO2 recycling. Among various factors, the participation of adsorbed hydrogen atoms seems to be a key factor affecting the selectivity of CO2ER on Pd. This article discusses the relationship between the selectivity and hydrogen adsorption on the Pd nanoparticles/carbon (Pd/XC72) catalyst through two kinds of systems: gas diffusion electrode (GDE) and rotating ring disk electrode (RRDE). The main product of the CO2ER on Pd/XC72 is changed from formate to CO when both the terrace and step sites of Pd particles are under a low coverage of adsorbed H atoms. In addition, the progress of CO self-poisoning on the Pd/XC72 catalyst and the peak corresponding to the oxidation of COOH* on the Pt ring electrode are clearly observed by the electrochemical analysis methods. The high selectivity of CO generation from the CO2ER on the Pd/XC72 catalyst is attributed to the progressive adsorption of CO which inhibits the participation of Hads during the CO2ER.