Anion-conductive membranes based on 2-mesityl-benzimidazolium functionalised poly(2,6-dimethyl-1,4-phenylene oxide) and their use in alkaline water electrolysis

• Published in: Polymer (Guilford) Vol. 145; pp. 242 - 251
• Main Authors: Marinkas, Angela, Struźyńska-Piron, Izabela, Lee, Yona, Lim, Ahyoun, Park, Hyun S., Jang, Jong Hyun, Kim, Hyoung-Juhn, Kim, Jihyun, Maljusch, Artjom, Conradi, Oliver, Henkensmeier, Dirk
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 06.06.2018; Elsevier BV
• Subjects: 2-Mesityl-benzimidazole; Alkaline electrolysis; Alkaline stability; Alkaline water; Anion exchange; Anion exchange membrane; Anion exchanging; Benzimidazoles; Bromination; Chemical synthesis; Conductivity; Degree of crystallinity; Electrodes; Electrolysis; Infrared spectroscopy; Mechanical properties; Membranes; Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO); Polydimethyl phenylene oxide; Polymers; Polyphenols; Spectroscopy; Thermal stability; Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO); Alkaline electrolysis; Anion exchange membrane; Alkaline stability; 2-Mesityl-benzimidazole
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2018.05.008

For development of anion exchange membrane (AEM) water electrolysis systems, a series of polymers was synthesised by reacting 2-mesityl-benzimidazole (BIM) and brominated poly-(2,6-dimethyl-1,4-phenylene oxide) (Br-PPO) in a Menshutkin reaction, and permethylating the attached BIM groups. The degree of bromination of Br-PPO can be easily monitored by IR spectroscopy: A correlation with the shift of the band around 1190 cm−1 was found. The IEC values of the prepared materials ranged between 1.6 and 2.9 mmol OH− g−1. Only materials with an IEC value of 1.9 (PPO24-BIM) reproducibly formed self-supporting membranes. This may be related to the degree of crystallinity, which decreased from 14 to 3% when the IEC increased from 1.6 to 3 mmol OH− g−1. Materials with IEC values of 1.6 and 2.2 can form self-supporting membranes, but not reproducibly. PPO24-BIM showed a conductivity of 8 mS cm-1 at room temperature, a thermal stability well above 200 °C, and mechanical properties similar to those of commercial FAA3-30 membranes. During water electrolysis, a current density of 300 mA cm-2 at 1.8 V was obtained. At 80 °C in 1 M KOH, degradation of BIM and the PPO backbone were observed by IR spectroscopy and monitoring conductivity and weight loss. [Display omitted] •2-Mesityl-1-methyl-benzimidazolium (BIM) functionalised PPO membranes were prepared.•Shift of IR band at 1190 cm−1 correlates with degree of bromination of PPO.•Due to BIM's bulkiness and PPO's brittleness, only some ratios give stable membranes.•Alkaline water electrolysis at 1.8 V gave a current density of 300 mA cm−2.•Water vapour permeability of several membranes was measured.