Membrane electrode assembly for CO
Provided herein are membrane electrode assemblies (MEAs) for CO x reduction. According to various embodiments, the MEAs are configured to address challenges particular to CO x including managing water in the MEA. Bipolar and anion-exchange membrane (AEM)-only MEAs are described along with components thereof and related methods of fabrication.
1. A membrane electrode assembly (MEA) for CO 2 electrolysis comprising:
a cathode catalyst layer comprising a catalyst configured to reduce CO 2 ;
an anode catalyst layer; and
a bipolar membrane disposed between the cathode catalyst layer and the anode catalyst layer, wherein the bipolar membrane comprises an anion-conducting polymer layer, a cation-conducting polymer layer, and a bipolar interface between the anion-conducting polymer layer and the cation-conducting polymer layer, wherein the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer, wherein the MEA is configured such that water and carbon dioxide are generated at the bipolar interface and the anion-conducting polymer layer is configured to allow CO 2 and water transport through pores in the anion-conducting polymer layer and away from the bipolar interface, and wherein the bipolar interface is characterized by or comprises one or more of:
covalent cross-linking of the cation-conducting polymer layer with the anion-conducting polymer layer; and
interpenetration of the anion-conducting polymer layer and the cation-conducting polymer layer.
2. The membrane electrode assembly of claim 1 , wherein the bipolar interface is characterized by interpenetration of the anion-conducting polymer layer and the cation-conducting polymer layer and wherein the bipolar interface comprises protrusions having a dimension of between 10 μm-1 mm in a plane parallel to the anion-conducting polymer layer (the in-plane dimension).
3. The membrane electrode assembly of claim 1 , wherein the bipolar interface is characterized by interpenetration of the anion-conducting polymer layer and the cation-conducting polymer layer and wherein the bipolar interface comprises protrusions each having a thickness of between 10% to 75% of the total thickness of the anion-conducting polymer layer.
4. The membrane electrode assembly of claim 1 , wherein the bipolar interface is characterized by interpenetration of the anion-conducting polymer layer and the cation-conducting polymer layer and wherein the bipolar interface comprises a gradient of the anion-conducting polymer and/or the cation-conducting polymer.
5. The membrane electrode assembly of claim 1 , wherein the bipolar interface is characterized by interpenetration of the anion-conducting polymer layer and the cation-conducting polymer layer and wherein the bipolar interface comprises a mixture of the anion-conducting polymer and/or the cation-conducting polymer.
6. The membrane electrode assembly of claim 1 , wherein the bipolar interface comprises covalent crosslinking of the cation-conducting polymer layer and the anion-conducting polymer layer and wherein the covalent crosslinking comprises a material comprising a structure of one of formulas (I)-(V):
or a salt thereof,
wherein:
each of R 7 , R 8 , R 9 , and R 10 is, independently, an electron-withdrawing moiety, H, optionally substituted aliphatic, alkyl, heteroaliphatic, heteroalkylene, aromatic, aryl, or arylalkylene, wherein at least one of R 7 or R 8 can include the electron-withdrawing moiety or wherein a combination of R 7 and R 8 or R 9 and R 10 can be taken together to form an optionally substituted cyclic group;
Ar comprises or is an optionally substituted aromatic or arylene;
each of n is, independently, an integer of 1 or more;
each of rings a-c can be optionally substituted; and
rings a-c, R 7 , R 8 , R 9 , and R 10 can optionally comprise an ionizable or ionic moiety.
7. The membrane electrode assembly of claim 6 , wherein R 7 or R 8 comprises the electron-withdrawing moiety selected from the group consisting of an optionally substituted haloalkyl, cyano, phosphate, sulfate, sulfonic acid, sulfonyl, difluoroboranyl, borono, thiocyanato, and piperidinium.
8. The membrane electrode assembly of claim 6 , wherein the covalent crosslinking comprises a material comprising one or more ionizable or ionic moieties selected from the group consisting of -L A -X A , -L A -(L A′ -X A ) L2 , -L A -(X A -L A′ -X A′ ) L2 , and -L A -X A -L A′ -X A′ -L A″ -X A″ ; wherein:
each L A , L A′ , and L A″ is, independently, a linking moiety;
each X A , X A′ , and X A″ comprises, independently, an acidic moiety, a basic moiety, a multi-ionic moiety, a cationic moiety, or an anionic moiety; and
L2 is an integer of 1 or more.
9. The membrane electrode assembly of claim 8 , wherein each X A , X A′ , and X A″ comprises, independently, carboxy, carboxylate anion, guanidinium cation, sulfo, sulfonate anion, sulfonium cation, sulfate, sulfate anion, phosphono, phosphonate anion, phosphate, phosphate anion, phosphonium cation, phosphazenium cation, amino, ammonium cation, heterocyclic cation, or a salt form thereof.
10. The membrane electrode assembly of claim 1 , wherein the bipolar interface comprises covalent crosslinking of the cation-conducting polymer layer and the anion-conducting polymer layer and wherein the covalent crosslinking comprises a material comprising a structure of one of the following formulas:
or a salt thereof, wherein:
Ar is or comprises an optionally substituted arylene or aromatic;
Ak is or comprises an optionally substituted alkylene, haloalkylene, aliphatic, heteroalkylene, or heteroaliphatic; and
L is a linking moiety, and
wherein one or Ar, Ak, and/or L is optionally substituted with one or more ionizable or ionic moieties.
11. The membrane electrode assembly of claim 10 , wherein the linking moiety comprises a covalent bond, spirocyclic bond, —O—, —NR N1 —, —C(O)—, —C(O)O—, —OC(O)—, —SO 2 —, optionally substituted aliphatic, alkylene, alkyleneoxy, haloalkylene, hydroxyalkylene, heteroaliphatic, heteroalkylene, aromatic, arylene, aryleneoxy, heteroaromatic, heterocycle, or heterocyclyldiyl.
12. The membrane electrode assembly of claim 1 , wherein the bipolar interface comprises covalent crosslinking of the cation-conducting polymer layer and the anion-conducting polymer layer and wherein the covalent crosslinking comprises a crosslinker comprising a structure of one of the following formulas:
wherein:
Ak is an optionally substituted aliphatic or an optionally substituted alkylene;
Ar is an optionally substituted aromatic or an optionally substituted arylene;
L is a linking moiety;
L3 is an integer that is 2 or more; and
X′ is absent, —O—, —NR N1 , —C(O)—, or -Ak-, in which R N1 is H or optionally substituted alkyl, and Ak is optionally substituted alkylene, optionally substituted heteroalkylene, optionally substituted aliphatic, or optionally substituted heteroaliphatic.
13. The membrane electrode assembly of claim 1 , wherein the bipolar interface comprises covalent crosslinking of the cation-conducting polymer layer with the anion-conducting polymer layer.
14. A membrane electrode assembly comprising:
a cathode catalyst layer;
an anode catalyst layer; and
a bipolar membrane disposed between the cathode catalyst layer and the anode catalyst layer, wherein the bipolar membrane comprises an anion-conducting polymer layer, a cation-conducting polymer layer, and a bipolar interface between the anion-conducting polymer layer and the cation-conducting polymer layer, wherein the cation-conducting polymer layer is disposed between the anode catalyst layer and the anion-conducting polymer layer, and wherein the bipolar interface comprises a layer of a second anion-conducting polymer and wherein the second anion-conducting polymer has a lower water uptake than that of the anion-conducting polymer of the anion-conducting polymer layer.
15. The membrane electrode assembly of claim 14 , wherein the thickness of the layer of the second anion-conducting polymer is between 0.1% and 10% of the thickness of the anion-conducting polymer layer.
16. The membrane electrode assembly of claim 14 , wherein the second anion-conducting polymer has an ion exchange capacity (IEC) of between 2.5 and 3.0 mmol/g.
17. The membrane electrode assembly of claim 16 , wherein the anion-conducting polymer of the anion-conducting polymer layer has an IEC of between 1.5 and 2.5 mmol/g.
18. The membrane electrode assembly of claim 14 , wherein the second anion-conducting polymer has a higher molecular weight than that of the anion-conducting polymer of the anion-conducting polymer layer.
19. The membrane electrode assembly of claim 14 , wherein the cathode catalyst layer comprises a catalyst configured to reduce CO 2 .