## 2 Hot Topics  
### Membrane Development  
The AEM, comprising an anion exchange cationic group linked to a polymer backbone, is a key constituent that determines the AEMWEs' performance and lifetime. The mechanical and thermal stability is related to the polymer backbone chemistry, whereas the ionic conductivity is influenced by the cationic functional groups. The chemical stability is influenced by both the polymer backbone and the functional groups [7]. There are several AEMs commercially available, and others developed \"in-house\", reported in the literature. The polymer backbone is frequently a polysulfone, crosslinked polystyrene with divinyl benzene (DVB), or polyaromatics [7]. For example, poly(fluoreyn aryl piperidinium)-, polycarbazole-, and polyphenylene-based AEMs were tested in cells attaining current densities as 2.3, 2.57, and 5.3 Acm\({}^{-2}\), respectively, measured at 1.8 V, presenting good durability [4]. The cationic functional groups are generally quaternary ammonium (QA) or imidazolium (IM). Some suppliers commercialize AEMs, such as: Tokuyama (A201) (discontinued production), Fumatech (FumasepR), Ionomer (AemionTM), Dioxide Materials (Sustainion(r), and Orion Polymer (OrionTM). There are research-based membranes, e.g., Versogen (PiperION) and Xergy (XIONTM Ion Exchange Membranes), which are promising alternatives to overtake commercial membranes. Nevertheless, they are offered on the market, although they are costly due to their small production scale and are not cost-competitive with commercial ones. In addition, more studies regarding durability under severe conditions are needed [4]. [PERSON] et al. [14] tested the performance of an AEMWE at 60 \({}^{\circ}\)C with different commercial membranes: Sustainion(r) 37-50, Fumasep FAS-50, Fumasep FAPQ, Neospetta ACM, AMI 7001, Nafion(r) 115, and Celazole(r) PBI. Better results were found using Sustainion(r) 37-50 membranes, operating at 1 Acm\({}^{-2}\) at about 1.9 V for 2000 h. The other membranes presented a high area-specific resistance (ASR) or a higher degradation rate under the tested conditions. [PERSON] et al. [11] published a very interesting paper, giving an overview of the commercial AEMs (Fumatech Fumasep(r) FAA3, Tokuyama A201, Ionomer AemionTM,Dioxide Materials Sustainion(r), and membranes commercialized by Orion Polymer, Cohoes, NY, USA), and reviewed their properties and performances in AEMWE. The authors concluded that all materials (membrane, ionomer, catalyst, cell design, etc.) must be optimized together. Consequently, it is difficult to precisely rank the commercial membranes by analyzing the available literature data, limiting an experimental rank to a system. As an overall tendency, however, the membranes FAA3 and A201 presented a lower ion conductivity than the novel membranes Aemion and Sustainion(r). [PERSON] et al. [15] tested Aemion(tm) AEMs (all-hydrocarbon) with several ion-exchange capacities and thicknesses. The authors reported that better results were obtained using the AEM AF1-HNN8-50, with a thickness of 50 \(\upmu\)m, achieving current densities of 2 Acm\({}^{-2}\) at a potential of 1.82 V using 1 M KOH at 60 \({}^{\circ}\)C.  
[PERSON] et al. [16] used an AEM without an aryl-ether backbone structure (Orion-TM1 TM). The authors reported that this membrane contains quaternary ammonium as a functional group and polyphenylene as the backbone, presenting a high ionic conductivity and stability, performing better and being more durable than the conventional AEM (FAA-3). Additionally, it showed high efficiency using pure water as a feed solution. The optimized TM1-MEA attained a current density of 2.75 Acm\({}^{-2}\) at 1.9 V with great stability of 55 mV h\({}^{-1}\), benefiting from the superior structural advantages of the Orion-TM1 TM membrane. The aryl-ether-free structure and hydrophobic properties inhibited decomposition by ether hydrolysis and prevented the attack of hydrophilic hydroxide ions. [PERSON] et al.