Studying Molecularly Doped Metals As Catalyst for Alkaline Fuel Cells and Electrolysis

Abstract

The study of molecularly doped metals is a relatively new area of materials science, where metals may be used to entrap soft matter, such as polymers. During the preparation of molecularly doped metals, metal ions in an appropriate solvent interact with the dopant material, then chemically reduce on the surface of the dopant, encapsulating the dopant. Molecular doping shares similar attributes to adsorption phenomena; while adsorption is a 2-dimensional process, molecular doping is a 3-dimensional process, resulting in stronger interactions between the dopant and metal. During molecular doping, molecules may be encapsulated within a metal, creating a dopant-metal structure with far stronger interactions than metal with adsorbed polymer. In particular, entrapment of molecules such as ionomers are of interest for creating electrode materials that synergistically combine ionic conductivity, electronic conductivity, and electrocatalytic activity. This makes molecularly doped metals especially appealing for alkaline fuel cell applications, where catalytically active metals such as silver or nickel may be reduced in solution to entrap anion exchange ionomers. In this work, the formation of an ionomer-Ag composite is studied using polyisoprene-ran-poly(vinylbenzylmethylpiperidinium chloride) (PI-ran-P[VBMPRD]Cl-) to investigate their efficacy for the oxygen reduction reaction (ORR). The parameters governing the encapsulation are studied to prepare composites with tunable ionomer:Ag ratios. Next, the composite materials are prepared on gas diffusion electrodes in a half-cell configuration to evaluate electrocatalytic activity towards the ORR. Ultimately, this work will enhance non-precious metal catalysts by leveraging the molecular doping of metals for enhanced ORR kinetics in alkaline exchange membrane fuel cells.