posted on 2021-09-02, 10:12authored byDavid
M. Koshy, Sneha A. Akhade, Adam Shugar, Kabir Abiose, Jingwei Shi, Siwei Liang, James S. Oakdale, Stephen E. Weitzner, Joel B. Varley, Eric B. Duoss, Sarah E. Baker, Christopher Hahn, Zhenan Bao, Thomas F. Jaramillo
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 CO2 reduction to CO (CO2R) on Ag surfaces and found that they produce no effect on CO2R activity yet strongly promote the competing hydrogen evolution
reaction (HER). By examining the dependence of HER and CO2R rates on concentrations of CO2 and HCO3–, we developed a kinetic model that attributes HER
promotion to intrinsic promotion of HCO3– reduction by imidazolium ionomers. We also show that varying the
ionomer structure by changing substituents on the imidazolium ring
modulates the HER promotion. This ionomer-structure 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 HCO3– and the Ag surface, thus limiting the
promotional effect. Our results help develop design rules for ionomer–catalyst
interactions in CO2R and motivate further work into precisely
uncovering the interplay between primary and secondary coordination
in determining electrocatalytic behavior.