Understanding the Effect of Triazole on Crosslinked PPO–SEBS-Based Anion Exchange Membranes for Water Electrolysis

Abstract

For anion exchange membrane water electrolysis (AEMWE), two types of anion exchange membranes (AEMs) containing crosslinked poly(phenylene oxide) (PPO) and poly(styrene ethylene butylene styrene) (SEBS) were prepared with and without triazole. The impact of triazole was carefully examined. In this work, the PPO was crosslinked with the non-aryl ether-type SEBS to take advantage of its enhanced chemical stability and phase separation under alkaline conditions. Compared to their triazole-free counterpart, the crosslinked membranes made with triazole had better hydroxide-ion conductivity because of the increased phase separation, which was confirmed by X-ray diffraction (XRD) and atomic force microscopy (AFM). Moreover, they displayed improved mechanical and alkaline stability. Under water electrolysis (WE) conditions, a triazole-containing crosslinked PPO–SEBS membrane electrode assembly (MEA) was created using IrO2 as the anode and a Pt/C catalyst as the cathode. This MEA displayed a current density of 0.7 A/cm2 at 1.8 V, which was higher than that of the MEA created with the triazole-free counterpart. Our study indicated that the crosslinked PPO–SEBS membrane containing triazoles had improved chemo-physical and electrical capabilities for WE because of the strong hydrogen bonding between triazole and water/OH−.

Development of highly conductive anion exchange membranes based on crosslinked PIM-SEBS with high free volume

“…7c, Tables S4 and S5†). 12,20,21,51,56,64–74 An absolute comparison of their AEMWE cell performance and durability may not be appropriate because the test conditions vary widely. Nevertheless, 30x-PIM-SEBS has a comparable or better performance (1.905 A cm −2 at 2.0 V) and durability (∼65 h, 0.2 A cm −2 ) than many other AEMs.…”

“…Poly(ether ketone), poly(ether sulfone), and poly(ethylene oxide) have been mainly used as aryl ether-type polymer backbones; their synthesis is relatively simple, where oligomers consisting of hydrophilic and hydrophobic units of specific lengths are synthesized and then polymerized into multi-block copolymers. 21–25 This process is advantageous because microphase separation can be simply controlled. However, these aryl ether-type polymers are susceptible to backbone degradation by OH − ions.…”

“…Examples of such polymers include polystyrene, polyethylene, polynorbornene, poly(arylene alkylene), poly(benzimidazole), and poly(styrene- b -ethylene- co -butylene- b -styrene). 10,11,20–23,26 Polyarylene-type AEMs, in particular, demonstrate remarkable alkaline and thermal stability, excellent mechanical properties, and improved IEC and ionic conductivity due to the ion-conducting head groups contained in their polymer backbone structure. In comparison, the side chains of typical existing polymers are grafted with ion-conducting head groups in most cases.…”

“…Thus, suppressing excessive WU and simultaneously achieving high ionic conductivity in polyarylene-type AEMs requires either inducing a structural modification – by introducing, grafting, or hyperbranching spacer-type multi-cation conducting head groups, for example – or adding physical or chemical crosslinkers. 20–22,31–35…”

Recent progress in anion exchange membranes (AEMs) in water electrolysis: synthesis, physio-chemical analysis, properties, and applications

“…Accordingly, PPO-SEBS with triazole crosslinking (such as TriPPO-50SEBS) was found to have a high current density (0.71 A cm −2 ) compared to PPO-SEBS without crosslinking (such as PPO-50SEBS), which had a low current density of 0.42 A cm −2 . 347 Ionic conductivities of high (77.3 mS cm −2 ) and low (66.0 mS cm −2 ) values may be caused by larger and lower current densities by the membranes. Triazole may, thus, increase the membrane conductivity and hence increase the current density.…”