Introducing six-methoxys and nine-methoxys phosphonium-based ionomers in alkaline-membrane electrolysis for renewable hydrogen production

Abstract

Alkaline membrane-based electrolysis has the great potential to becoming the nextgeneration manufacturing technology for distributed and inexpensive chemical productions exemplified by renewable hydrogen generation. As a key component, alkaline ionomer is critically used in electrodes as an electrochemical binder gluing metallic catalysts and polymeric membrane, largely controlling the cell performance of alkaline-membrane electrolysis. This research program explores a new family of ionomers based on two phosphonium cationic groups into alkaline-membrane electrolysis. In this program, the following research activities have been carried out: 1) performing the chloromethylation reaction on polysulfone, followed by purification, and confirmation by NMR spectroscopy; 2) performing the quaternization reaction with two different tertiary phosphines (9-methoxys and 6-methoxys) onto chloromethylated polysulfone; 3) characterizing the two groups of phosphonium-functionalized polymers including conductivity evaluation and hydration behavior; and 4) preparing ionomer solution using the synthesized phosphonium-functionalized polymers for electrode fabrication; and 5) conducting in-situ hydrogen production with the prepared ionomer solutions, compared with commercial alkaline ionomer. Examined as alkaline ionomer at the cathode of the in-situ alkaline-membrane electrolysis, both 9-methoxys and 6-methoxys phosphonium-based polymers exhibited very effective ionomer function for efficient hydrogen production. Both phosphonium ionomers exhibited much higher cell performance than the commercial ammonium ionomer at all cell temperatures, strongly suggesting the great potential of utilizing phosphonium-functionalized ionomers for alkaline-membrane electrolysis.