**3. Electrolyzer technologies**

groups of the PBI backbone during polymerization in poly (phosphoric acid) in the crosslinking process. However, the increase in proton conductivity is not translated into better performance of fuel cell. Instead, Pt alloy that has been used as catalysts turned out to give better

[22, 26, 42, 59]

[60, 61] Nanoscale ZrO<sup>2</sup>

precipitation [62]

[60] Development of pyridine-polybenzimidazole

at 0.6 V and 0.69 V at 0.2 A/cm<sup>2</sup>

/air environment [66].

Today, Victrex is the leading manufacturer of PEEK polymer in the world. The sulfonation

or polymerization of sulfonated monomers onto the backbone structure of the polymer. The hydrophilic nature of the PEEK polymer is developed from the accumulation of sulfonic acid groups. It has been reported that the membranes developed the carrier for proton charge as the consequences of the segregation of the sulfonic acid groups and proton conductivity with the help of water movement in PEEK hydrated state [27]. This is supported by the fact that polymer with aromatic rings like polyether ether ketone (PEEK), polybenzimidazoles (PBI), polyoxadiazole, polysulfone (PSf), and polyimides can contribute to cheaper production cost

To date, previous studies have shown that alteration of PEEK polymer properties can replace Nafion membrane in PEM-FC and DEMFC systems. Significant mechanisms are critically used to prepare the PEM from PEEK like PEEK electrophilic sulfonation (S-PEEK), S-PEEK and nonfunctional polymers blending, and S-PEEK heteropolycompounds with polyetherimide doping with organic acids [27]. Therefore, it is crucial to regulate the degree of sulfonation (DS) as it is affecting the thermochemical stability of PEEK membranes by keeping the DS low [68]. It has been reported that the workability of proton exchange membranes

process for its PEEK membrane is introduced using sulfonic acid groups (SO3

and deliver sufficient physicochemical properties [67].

**No. Methods References Remarks**

term [50] 2. Crosslinking of polymer backbone [51–55]

1. Optimization of membrane fabrication

28 Advances In Hydrogen Generation Technologies

4. Forming a composite structure by incorporation of various inorganic

5. Designing composite PA doped

6. Adding more nitrogen atoms to the polymer molecule structure to enhance

Titania and Zirconia

acid retention.

PBI-based membranes using ceramic nanoscale and mesoscale fillers such as

**Table 2.** Summary of PBI improvement techniques.

3. Blending with other polymers [56–58]

techniques

acids

with operation temperatures at

filler and the accompanied membrane

[35, 49] Improvements were found limited demonstrating

weakness in mechanical strength when highly loaded with acid and poor endurance when tested for a long

casting is challenged by agglomeration and

(Py-PBI), which provides an additional pyridine ring capable of boosting the interaction with PA [60, 63–65]

H) via alteration

results, which was 0.49 A/cm<sup>2</sup>

*2.1.1.3. Polyether ether ketone*

180°C and pressure of 1 atm in H<sup>2</sup>

The chemical reaction equation for an electrolyzer is presented in Eq. (1):

$$\text{2CuCl(s)} + \text{2HCl(aq)} \rightarrow \text{H}\_2\text{(g)} + \text{2CuCl}\_2\text{(aq)}\tag{1}$$

The Atomic Energy of Canada Limited (AECL) has succeeded in generating hydrogen from the above step using CuCl/HCl electrolyzer and suggesting an alteration to the existing CuCl cycle [70, 71]. The operating parameters, appropriate membrane selection, and electrochemical cell's scheme are important factors to be tackled in order to have a functional electrolyzer. AECL has tested and determined that the CuCl electrolyzer needs to have these characteristics [72]:


Research conducted by Naterer et al. confirmed that the CuCl/HCl electrolysis reaction rate enhances with the increment of reaction temperature and the concentration of CuCl [72] and greater current density at 80°C when compared to 25°C for the same cell voltage [17]. The schematic diagram of proton exchange membrane (PEM) water electrolysis cells is presented in **Figure 3**. The solid polymer electrolyte that conducts proton ion is sandwiched between two electrodes to construct a membrane electrode assembly (MEA). The MEA is submerged in pure water (18 μ cm) and the proton movement stays within the membrane's boundary.

**Figure 3.** Schematic diagram of PEM electrolysis cell [33].

The efficiency of a PEM cell is dependent on the current density during operation. While a higher current density is crucial to cut down the start-up cost, a lower current density is needed to cut down the cost of operation. Both factors have to be taken into consideration [33]. Different types of electrolytes can be deployed in an EL cell: an alkaline electrolysis (AEL) cell works with a basic liquid electrolyte. In a proton exchange membrane (PEM) EL cell, an acidic ionomer—a process often called solid polymer electrolysis (SPE)—is used, and a high-temperature (HT) EL cell has a solid oxide as the electrolyte. The schematic diagram of the alkaline electrolysis cell is presented in **Figure 4**.

> To ensure a sufficiently high ionic conductivity, every electrolyte requires minimum temperatures. The upper temperature limit is determined mostly by the stability of the cell materials

> Currently, three most used electrolysis technologies are being used. A comparison between

In this chapter, hydrogen production from membrane electrolysis is discussed in detail. Hydrogen production from membrane water splitting technologies possesses great potential as a sustainable hydrogen source. Previous research focused mainly on Nafion-based membrane, but with the advancement in the research, a better and cheaper membrane can be used without compromising on the output of hydrogen production. Composite membrane provides better performance in terms of durability, heat resistance, hydrogen production, and purity.

and components. More details are provided in later in this chapter.

**Table 3.** A comparison between alkaline, PEM, and high-temperature electrolysis [73–75].

**Technology Advantages Disadvantages**

Cost: cheapest and effective Catalyst type: Noble Durability: Long term Stacks: MW range Efficiency: 70% Commercialized

Voltage efficiency: high

System design: compact

Efficiency: 100%

Catalyst: Nonnoble

hot steam

Load range: Good partial load range

Thermal neutral efficiency >100% with

Pressure: High-pressure operation

Degree of purity: high gas purity Dynamics: high dynamics operation Response: rapid system response

Current density: low

Hydrogen Production by Membrane Water Splitting Technologies

Degree of purity: low (crossover of gases)

http://dx.doi.org/10.5772/intechopen.76727

31

Technology: new and partially establish

Cost: high cost of components Catalyst: noble catalyst Corrosion: acidic environment Durability: comparatively low Stack: Below MW range Membrane: limited and costly Commercialization in near term

Technology: in laboratory phase

Durability: low due to high heat, ceramics System design: bulk system design

Electrolyte: liquid and corrosive Dynamics: low dynamic operation Load range: low for partial load Pressure: Low operational pressure

Alkaline electrolysis Technology: oldest and well established

PEM electrolysis Current density: high

**4. Conclusion**

High-temperature steam

electrolysis

alkaline, PEM, and high-temperature electrolysis is presented in **Table 3**.

**Figure 4.** Schematic diagram of the alkaline electrolysis cell [34].


**Table 3.** A comparison between alkaline, PEM, and high-temperature electrolysis [73–75].

To ensure a sufficiently high ionic conductivity, every electrolyte requires minimum temperatures. The upper temperature limit is determined mostly by the stability of the cell materials and components. More details are provided in later in this chapter.

Currently, three most used electrolysis technologies are being used. A comparison between alkaline, PEM, and high-temperature electrolysis is presented in **Table 3**.
