Wednesday, 1 June 2022: 14:40
West Meeting Room 218 (Vancouver Convention Center)
A. M. Herring, N. C. Buggy, M. C. Kuo, and M. Ezell (Colorado School of Mines)
From fundamental studies of cationic membranes we were able to show that very high anionic conductivities could be achieved in thin robust membranes with controlled water contents. Over the last several years we have further developed these advanced anion exchange membranes (AEMSs) to improve both their chemical and mechanical stability. One of these polymers is being commercialized as the TuffBrane® material and we are now deploying this membrane in devices for electrochemical energy conversion or water purification. While there has been a large amount of work to develop electrocatalysts for fuel cells, much of this was optimized using rotating disk electrodes in aqueous solvents. In solid state electrochemical energy conversion devices using polymer electrolytes, the electrolyte is a polymer with a local morphology and chemistry. This has led us to conclude that it is the polymer/catalyst interfaces that must be understood and improved to achieve the maximum performance in these devices. We have used a toolbox of random, di-block, and triblock polymers where the hydrophobic component or block is polycyclooctene, poly isoprene, or their hydrogenated analogues, polyethylene or polymethylbutylene. The hydrophilic component or block is derived from polychloromethylstyrene via quaternization with trimethylamine or methyl pyrrolidine to give the more stable MPRD cation.
We have began our studies using Ag as a model system although our plans are to extend these studies to other non PGM catalysts. Our first studies used commercial Ag colloids as catalyst particles; these studies showed that we could actually change the degree of crystallinity of the polyethylene block in triblock anion exchange polymers and so alter the polymers water uptake. We then extended this work to spin coated thin films on atomically flat silicon wafers or the same substrate with a Ag coating, and where able to show a number of these polymers had very strong vertical alignment using grazing Incident Small Angle X-Ray Scattering. On-going work on Ni foams in separated anode experiments is showing that the same polymers can also dramatically affect the onset potential and Tafel slope for the oxygen evolution reaction in carbonate electrolyte with or without the addition of the Ag colloids. We have further refined this system by using the Ni support to act as a catalyst to hydrogenate the ionomer in situ so that the middle block is polyethylene. The saturated ionomers show advantages in both performance and stability. Current work with cobalt oxide and high IEC ionomers that shows much promise will be described in this talk. Our eventual goal is to develop polymer system that will self-template catalyst particles for eventual roll to roll processing of device components.
