Chemical Modifications of Ag Catalyst Surfaces with Imidazolium Ionomers Modulate H₂ Evolution Rates during Electrochemical CO₂ Reduction

Abstract

Bridging polymer design with catalyst surface science is a promising direction for tuning and optimizing electrochemical reactors that could impact long-term goals in energy and sustainability. Particularly, the interaction between inorganic catalyst surfaces and organic-based ionomers provides an avenue to both steer reaction selectivity and promote activity. Here, we studied the role of imidazolium-based ionomers for electrocatalytic CO 2 reduction to CO (CO 2 R) on Ag surfaces and found that they produce no effect on CO 2 R activity yet strongly promote the competing hydrogen evolution reaction (HER). By examining the dependence of HER and CO 2 R rates on concentrations of CO 2 and HCO 3 − , we developed a kinetic model that attributes HER promotion to intrinsic promotion of HCO 3 − reduction by imidazolium ionomers. We also show that varying the ionomer structure by changing substituents on the imidazolium ring modulates the HER promotion. This ionomerstructure dependence was analyzed via Taft steric parameters and density functional theory calculations, which suggest that steric bulk from functionalities on the imidazolium ring reduces access of the ionomer to both HCO 3 − and the Ag surface, thus limiting the promotional effect. Our results help develop design rules for ionomer−catalyst interactions in CO 2 R and motivate further work into precisely uncovering the interplay between primary and secondary coordination in determining electrocatalytic behavior.

Engineering Catalyst–Electrolyte Microenvironments to Optimize the Activity and Selectivity for the Electrochemical Reduction of CO2 on Cu and Ag

“…50 Similarly, Koshy et al noted that imidazolium-based ionomer coatings have no effect on CO 2 R activity but are able to modulate the activity for HER on Ag. 51 These studies suggest that while some of the ionomer effects we have observed are transferable to Ag, the details of these effects may be chemistrydependent. Further work is needed to explore how ionomers can affect the CO 2 R electrocatalyst microenvironment.…”

Design strategies for markedly enhancing energy efficiency in the electrocatalytic CO2 reduction reaction

“…69 As the most frequently used anions, HCO 3 − can serve as the supplementary proton donor for the reduction reaction beyond protons or water, in which the undesired HER could be promoted. 88,89 In some cases, HCO 3 − also provided the carbon reactant for the CO 2 RR when it is close to the reaction interface. 90 Moreover, halide anions abundant in sea water (environmentally friendly electrolyte) have also demonstrated their functions in adjusting the activity and selectivity of the CO 2 RR on account of their strong interaction with the metal surface.…”

From Stochastic Self‐Assembly of Nanoparticles to Nanostructured (Photo)Electrocatalysts for Renewable Power‐to‐X Applications via Scalable Flame Synthesis

“…Novel materials/properties/phenomena are assessed with respect to the contemporary literature, and a new theory is then proposed. [10,[28][29][30][31] Nowadays, combining experimental and theoretical studies has proven successful in elucidating reaction mechanisms of some electrochemical transformations (e.g., water to hydrogen and oxygen, carbon dioxide to valuable carbon-based products, or nitrogen to ammonia), which provide rational guidance toward the development of application-driven catalysts. [27,[32][33][34][35] For both design approaches, building a novel material is a must-do step, and a suitable synthesis method is one of the pivotal elements to dictate the output properties of the most promising catalyst with respect to an intrinsic activity or long-term stability.…”