Phenyl-Free Polynorbornenes for Potential Anion Exchange Ionomers for Fuel Cells and Electrolyzers

Ionomers in the catalyst layer play a critical role in the performance of fuel cells and electrolyzers. Phenyl adsorption on hydrogen oxidation catalysts and electrochemical oxidation of phenyl moieties on oxygen evolution catalysts are detrimental to the alkaline devices' performance. Here the adsorption energy of phenyl-containing ionomers is compared to provide the rationale for implementing phenyl-free ionomers. Density functional theory calculations indicated that the norbornane fragment has minimal adsorption energy on Pt(111) due to the absence of aromatic pi electrons. A soluble quaternized polynorbornene ionomer is prepared by vinyl addition polymerization, and it exhibits high performance in both fuel cells and electrolyzers, proving the advantage of the phenyl-free structure. This study establishes the phenyl adsorption energy-electrode performance relationship, highlighting the importance of material interactions between the catalysts and ionomers.