Ion-conducting membranes
An anion-conducting polymeric membrane comprises a terpolymer of styrene, vinylbenzyl-R s and vinylbenzyl-R x . R s is a positively charged cyclic amine group. R x is at least one constituent selected from the group consisting Cl, OH and a reaction product between an OH or Cl and a species other than a simple amine or a cyclic amine. The total weight of the vinylbenzyl-R x groups is greater than 0.3% of the total weight of the membrane. In a preferred embodiment, the membrane is a Helper Membrane that increases the faradaic efficiency of an electrochemical cell into which the membrane is incorporated, and also allows product formation at lower voltages than in cells without the Helper Membrane.
1. An anion-conducting polymeric membrane comprising a terpolymer of styrene, vinylbenzyl-R s and vinylbenzyl-R x ,
wherein R s is a positively charged cyclic amine group,
wherein R x is at least one constituent selected from the group consisting of Cl, OH and a reaction product between an OH or Cl and an inorganic species or an organic species other than an amine;
wherein the total weight of the vinylbenzyl-R s groups is between 15% and 90% of the total weight of the terpolymer; and
wherein the total weight of the vinylbenzyl-R x groups is between 1% and 25% of the total weight of the terpolymer.
2. The polymeric membrane of claim 1 , wherein said membrane has a thickness of 10-300 micrometers.
3. The polymeric membrane of claim 1 wherein said membrane is a Helper Membrane identifiable by applying a test comprising:
(1) preparing a cathode comprising 6 mg/cm 2 of silver nanoparticles on a carbon fiber paper gas diffusion layer;
(2) preparing an anode comprising 3 mg/cm 2 of RuO 2 on a carbon fiber paper gas diffusion layer;
(3) preparing a polymeric membrane test material;
(4) interposing the membrane test material between the anode and the cathode, the side of the cathode having the silver nanoparticles disposed thereon facing one side of the membrane and the side of the anode having RuO 2 disposed thereon facing the other side of the membrane, thereby forming a membrane electrode assembly;
(5) mounting the membrane electrode assembly in a fuel cell hardware assembly;
(6) directing a stream of CO 2 humidified at 50° C. into the cathode reactant flow channels while the fuel cell hardware assembly is at room temperature and atmospheric pressure, with the anode reactant flow channels left open to the atmosphere at room temperature and pressure;
(7) applying a cell voltage of 3.0 V via an electrical connection between the anode and the cathode;
(8) measuring the current across the cell and the concentration of CO and H 2 at the exit of the cathode flow channel;
(9) calculating the CO selectivity as follows:
Selectivity
=
(
CO
production
rate
)
(
CO
production
rate
+
H
2
production
rate
)
;
and
(10) identifying the membrane as a Helper Membrane if the average current density at the membrane is at least 20 mA/cm 2 , where the cm 2 is measured as the area of the cathode gas diffusion layer that is covered by catalyst particles, and CO selectivity is at least 50% at a cell voltage of 3.0 V.
4. The polymeric membrane of claim 1 , wherein said positively charged cyclic amine group is an imidazolium or a pyridinium.
5. The polymeric membrane of claim 4 , wherein said positively charged cyclic amine group is an alkylpyridinium.
6. The polymeric membrane of claim 4 , wherein said positively charged cyclic amine group is tetramethylimidazolium.