## 2 Topical Research Areas Related to Ionic Liquids and the Contribution of Spiroammonium Compounds
### Green Hydrogen Production and Consumption
#### 2.4.1 The State of the Art
Table 1 presents a comparison of the current state of the main types of electrolyzers: A-WE, PEM-WE, and AEM-WE; the advantages and disadvantages of the most common types of water electrolysis for hydrogen production have been clearly demonstrated [127]. \begin{table}
\begin{tabular}{c c c c} \hline
**Parameters** & **A-WE** & **PEM-WE** & **AEM-WE** \\ \hline Separation & Diaphragm & PEM & AEM \\ Cathode & Nickelpolhedum alloys & Pt group metals & Transition metals \\ Anode & Nickelpolabit alloys & RuOx, IrOx & Transition metals \\ Current collector plate & Nickel & Copper & Copper \\ Bipolar plate & — & Graphite and Ti & Ni or SS \\ Electrolyte & KOH & Pure water & Alkali solution, pure water \\ Current density & \textless{}0.5 A cm\({}^{-2}\) & 1–2 A cm\({}^{-2}\) & 1–2 A cm\({}^{-2}\) \\ Operating temperature & 60–90 \({}^{\circ}\)C & 50–90 \({}^{\circ}\)C & 40–80 \({}^{\circ}\)C \\ Gas purity & \textgreater{}99.5\% & \textgreater{}99.99\% & \textgreater{}99.99\% \\ Lifetime & \textasci{}100\) kh & \textless{}10 kh & \textless{}2 kh \\ Estimated cost & Low & High & — \\ Technology status & Mature & Commercial for small scale & Research and Development \\ \hline \end{tabular}
\end{table} 
Table 1: The comparative illustration of the practical constraints of A-WE, PEM-WE, and AEM-WE [127]. One of the biggest advantages of AEM-WE is the use of low-cost transition metal catalysts instead of traditional noble metal electrocatalysts. AEM-WE is still in its infancy despite irregular research on catalysts and membranes. In order to generate commercially viable hydrogen, AEM-WE technology must be further developed in terms of energy efficiency, membrane stability, stack feasibility, robustness, ion conductivity, and cost reduction. Anion exchange membrane water electrolyzers (AEM-WEs) and fuel cells (AEM-FCs) are technologies that can transform and utilize renewable resources in the form of green hydrogen (H\({}_{2}\)) energy. This aspect has significantly reduced the costs of the key components (membranes, electrocatalysts, bipolar plates, etc. ), as well as offering fast reaction kinetics and fewer corrosion problems. The growing interest in anion exchange membrane fuel cells (AEM-FCs) has led to the subsequent development of hydroxide ion-stable cationic polymer anion exchange membranes for water electrolysis [128]. In general, ion exchange membranes (IEM) are semi-permeable membranes composed of ionic head groups attached to the polymer matrices [129]. They can be broadly classified as anion exchange membranes (AEMs) and proton exchange membranes (PEMs) depending on the type of ion, which is permitted to cross the membrane layer [130]. By exploiting the selective nature of IEMs, a variety of applications exist both for AEMs and PEMs. Specific to AEMs, research is focused on developing AEMs for high-pH and high-temperature applications such as anion exchange membrane fuel cells (AEM-FCs) and anion exchange membrane water electrolysis (AEM-WE). AEM head groups have traditionally been quaternary ammonium (QA) ions; however, current research is also investigating other head groups, such as tertiary diamines, phosphonium, sulphonium, and metal cations (Table 2) [131]. 4.2 Azoniaspiro Compounds Used as Anion Exchange Membrane Components for Water Electrolysis (AEM-WE) and Fuel Cells (AEM-FC)  
AEMs with QA can be formed by reacting a polymer containing a benzyl halide (e.g., chlorine) with an amine (e.g., triethylamine) to add an ammonia group and then treating it with alkaline (e.g., potassium hydroxide) to convert the ammonia group to the salt form, which can participate in anion exchange [132; 133]. Among the requirements of AEMs, alkaline stability is considered one of the major challenges, limiting the practical applications of AEM-FCs. AEMs based on the use of quaternary alkylammonium (QA) cation have been extensively studied due to their relatively high hydroxide ion conductivity, easy functionalization, and adequate alkaline stability over short-time scales [134].