4. Proton exchange membrane fuel cell

ions, following the equations represented in reaction (5), more complex kinetically and ther-

Inert anodes are also applied on water oxidation, usually coated by a catalyst. One example is the use of ITO or FTO electrodes, coated by a self-assembled amorphous film, generated by electrodeposition of cobalt salts into phosphate, methyl phosphonate or borate electrolytes [18]. That approach has as a characteristic the need of an electrolyte medium that is a key factor for activity, selectivity and formation of the self-assembled amorphous film. The selection for cobalt resides on the fact that its tetranuclear oxo core mimics the natural oxygenevolving complex (OEC) of PSII [23]. Regarding cobalt, thin films of Co-Pi (cobalt-phosphate) are deposited on Fe2O3, WO3 and ZnO electrodes, focusing on reducing the onset potential for water oxidation leading to performing the process in neutral pH conditions. A posterior approach deposits Co-Pi thin films on the ITO film attached to an np-Si solar cell, directing

Cobalt is also reported to be associated with molybdenum-based polyoxometalates with the

[23] presents a new class of isostructural cubane-shape catalysts Cobalt-based, Hydrogen substituted by Me, t-Bu, OMe, Br, COOMe and CN, capable to water oxidation under dark or illuminated conditions, unfortunately again under highly basic conditions (pH = 8.0) in the

2+) as photosensitizer and sodium persulfate (S2O8

best quantum efficiency (QE) decrescent substituent order is determined as OMe > COOMe > Me ≈ H ≈ Br ≈ CN > t-Bu. In conclusion, the combination of semiconductor-electrocatalyst-

Yellow scheelite monoclinic BiVO4 is also used as a photocatalyst for O2 evolution under visible light, in the presence of an appropriate electron acceptor. But due to its conduction band bottom limit is located on a more positive potential than the potential of water reduction; it is incapable of evolving into hydrogen [25]. However, BiVO4 doped with In and Mo produces a Bi(1-X)In(X)V(1-X)Mo(X)O4 catalyst, with a more negative conduction band than H+

making it capable of water splitting at neutral pH-evolving hydrogen with no use of any

Following additional layers' approach, Si electrodes gain focus again in 2014, with Kaiser and Jaegermann's [12] work. The electrochemical properties of single-crystalline p-type 3C-SiC films on p-Si and n-Si substrates are investigated as electrodes in H2SO4 aqueous solutions, under dark and light conditions. The photoelectrochemical measurements on different wavelengths indicate the p-SiC film on p-Si substrate which can generate a cathodic photocurrent, corresponding with hydrogen production, and can also generate an anodic photocurrent, for oxygen evolution. Iron nickel oxide (FeNiOx) is also used for water splitting. One remarkable example is reported by Morales et al. on which an amorphous layer of the oxide is oxidatively

the voltage produced by the solar cell to reduce the cited over-potential [15].

electrolyte interfaces is mandatory on water-splitting photocatalysis.

limitations that this system must contain tris(2,2<sup>0</sup>

sodium persulfate (S2O8

presence of (Ru(bpy)3

sacrificial agent [25].

2H2O þ 4H<sup>þ</sup> ➔ O2 þ 4H<sup>þ</sup> (5)


<sup>2</sup>�) in an aqueous borate buffer solution at pH 8.0 [24]. Berardi et al.

2+) and

/H2,

<sup>2</sup>�) as electrolyte. The

modynamically less favorable [22].

70 Advances In Hydrogen Generation Technologies

The proton exchange membrane fuel cell (PEMFC) is a device that converts chemical energy into electrical energy through an electrochemical reaction [29]. At the anode, the hydrogen or other fuel that may produce pure hydrogen like the ethanol-steam reforming process is oxidized and releases protons and electrons. The protons are carried out to the cathode side through electrolyte and the electrons produce electrical current in an external circuit. At the cathode, the electrons and the protons are associated with oxygen (often from atmospheric air) producing water and energy as a final product from PEMFC; thus, the fuel cell system does not produce pollutants and is ambient compatible.

The chemical reactions are:

$$\text{Anode}: \text{H}\_2(\text{g}) \xrightarrow{} \text{2H}^+ + 2\text{e}^- \tag{6}$$

For ethanol-steam reforming reaction the chemical reactions are:

in more than 50% of loss of efficiency due to electrode poisoning effect [37].

C2H5OH þ 3H2O ➔ 2CO2 þ 6H2 (9)

Production of Hydrogen and their Use in Proton Exchange Membrane Fuel Cells

http://dx.doi.org/10.5772/intechopen.76663

73

The PEMFC works at low temperature due to electrolyte that is hydrated (lower than 100�C), which is an advantage, as well as other new materials that enable the cell to work at high temperature [35]. At low temperatures, the catalytic material that presents high efficiency is platinum, for both anode and cathode electrodes. But, as demonstrated previously, hydrogen obtained from steam presents low-content CO, which adsorbs strongly on platinum surface and poisons the electrode. To outline this problem, a second metal is included into the electrode. This second metal often is a transition and not a noble metal which dissociated in water at low potential and provides oxygenated species to oxidize the adsorbed CO at a lower potential. This pathway is known as the Langmuir-Hinshewood mechanism [36], where two adsorbed species react and form a final product; some studies show that PtRu is the more efficient electrocatalyst [37–39]. The use of pure Pt as anode of PEMFC fed with H2 , presenting 100 ppm of CO, results

The research of PEMFC focuses on minimizing the amount of Pt used in the electrodes, due to high cost of this material; moreover, the oxygen reduction reaction which happens at the cathode electrode presents low kinetic and parallel pathways producing H2O2, resulting in loss of power density output. The use of the different cathode material improves the performance of the fuel cell. The development of a membrane working at high temperatures can improve the kinetics of chemical reactions also and results in better fuel cell performance.

The main advantage of the fuel cell system, notably PEMFC, is the efficiency in energy conversion, once the efficiency of electrochemical systems is above the other converter; however, the source of hydrogen is important [40, 41]. The hydrogen obtained from water electrolysis is very pure, but it results in energy deficit [42]; the H2 from steam hydrocarbons contains CO. Thus, the tendency is an aggregate of the system to convert energy. Solar photovoltaic can be used to produce highly

Solar energy is a renewable source that can fulfill the world's needs for the future. The direct conversion of solar energy into renewable hydrogen fuel is done basically by two methods: photocatalysis and photoelectrochemical processes. The hydrogen obtained from photocatalysis and/or photoelectrochemical process can feed PEMFCs to convert chemical energy into electrical energy with high efficiency and without degradation of the ambient. PEMFC fed with H2 obtained from ethanol-steam reforming reaction (which contains CO) must use Pt-based alloy

pure H2 for PEMFC and moreover, solar energy can charge batteries [43] for later use.

catalysts to increase the poisoning tolerance and improve the lifetime of the PEMFC.

5. Conclusions

CO þ H2O \$ CO2 þ H2 (10)

CO þ ½O2 ➔ CO2 (11)

$$\text{Cathode}: \text{O}\_2(\text{g}) + 2\text{e}^- + 4\text{H}^+ \blackrightarrow \text{H}\_2\text{O} \tag{7}$$

The global reaction of the fuel cell system can be written as Eq. (8). The theoretical potential (E) of this reaction is 1.23 V, but at the operational condition the potential is around 0.7 V. This potential result at the maximum output power density is about 1 W cm2 [30, 31].

$$\text{PEMFC}: \text{H}\_2(\text{g}) \left(\text{at anode}\right) + \text{O}\_2(\text{g}) \left(\text{at cathode}\right) \blackrightarrow \text{H}\_2\text{O}(\text{l}) + \text{energy} \tag{8}$$

Figure 4 shows a representative schema of the PEMFC operation. The fuel is fed at the anode site and the oxygen is fed at the cathode side. The electrons from anode to cathode are used in an external electrical circuit to produce electrical work.

An alternative source of hydrogen can be the steam reformation of liquid substances like alcohols of small chairs. Ethanol, for example, is low density and nontoxic alcohol obtained from fermentation of renewable resources like sugarcane. This has been studied as a possible fuel in direct alcohol fuel cell (DAFC) systems [32]. However, its direct use is difficult due to the rupture of CdC bond on platinum or platinum alloy electrodes. The ethanol-steam reforming reactions take place in different steps with endothermic/exothermic reactions [33, 34].

Figure 4. Proton exchange membrane fuel cell (PEMFC), anode fed with H2 and cathode fed with O2. Protons are carried out from anode to cathode through membrane electrolyte and the electrons produce working in an external circuit.

For ethanol-steam reforming reaction the chemical reactions are:

$$\mathrm{C\_2H\_5OH} + 3\mathrm{H\_2O} \bullet 2\mathrm{CO\_2} + 6\mathrm{H\_2} \tag{9}$$

$$\text{CO} + \text{H}\_2\text{O} \leftrightarrow \text{CO}\_2 + \text{H}\_2\tag{10}$$

$$\text{CO} + \mathbb{W}\text{O}\_2 \blackrightarrow \text{CO}\_2\tag{11}$$

The PEMFC works at low temperature due to electrolyte that is hydrated (lower than 100�C), which is an advantage, as well as other new materials that enable the cell to work at high temperature [35]. At low temperatures, the catalytic material that presents high efficiency is platinum, for both anode and cathode electrodes. But, as demonstrated previously, hydrogen obtained from steam presents low-content CO, which adsorbs strongly on platinum surface and poisons the electrode. To outline this problem, a second metal is included into the electrode. This second metal often is a transition and not a noble metal which dissociated in water at low potential and provides oxygenated species to oxidize the adsorbed CO at a lower potential. This pathway is known as the Langmuir-Hinshewood mechanism [36], where two adsorbed species react and form a final product; some studies show that PtRu is the more efficient electrocatalyst [37–39]. The use of pure Pt as anode of PEMFC fed with H2 , presenting 100 ppm of CO, results in more than 50% of loss of efficiency due to electrode poisoning effect [37].

The research of PEMFC focuses on minimizing the amount of Pt used in the electrodes, due to high cost of this material; moreover, the oxygen reduction reaction which happens at the cathode electrode presents low kinetic and parallel pathways producing H2O2, resulting in loss of power density output. The use of the different cathode material improves the performance of the fuel cell. The development of a membrane working at high temperatures can improve the kinetics of chemical reactions also and results in better fuel cell performance.

The main advantage of the fuel cell system, notably PEMFC, is the efficiency in energy conversion, once the efficiency of electrochemical systems is above the other converter; however, the source of hydrogen is important [40, 41]. The hydrogen obtained from water electrolysis is very pure, but it results in energy deficit [42]; the H2 from steam hydrocarbons contains CO. Thus, the tendency is an aggregate of the system to convert energy. Solar photovoltaic can be used to produce highly pure H2 for PEMFC and moreover, solar energy can charge batteries [43] for later use.

### 5. Conclusions

The chemical reactions are:

72 Advances In Hydrogen Generation Technologies

Anode : H2ð Þ g ➔ 2H<sup>þ</sup> þ 2e� (6)

Cathode : O2ð Þþ g 2e� þ 4H<sup>þ</sup> ➔ H2O (7)

The global reaction of the fuel cell system can be written as Eq. (8). The theoretical potential (E) of this reaction is 1.23 V, but at the operational condition the potential is around 0.7 V. This

Figure 4 shows a representative schema of the PEMFC operation. The fuel is fed at the anode site and the oxygen is fed at the cathode side. The electrons from anode to cathode are used in

An alternative source of hydrogen can be the steam reformation of liquid substances like alcohols of small chairs. Ethanol, for example, is low density and nontoxic alcohol obtained from fermentation of renewable resources like sugarcane. This has been studied as a possible fuel in direct alcohol fuel cell (DAFC) systems [32]. However, its direct use is difficult due to the rupture of CdC bond on platinum or platinum alloy electrodes. The ethanol-steam reforming reactions

Figure 4. Proton exchange membrane fuel cell (PEMFC), anode fed with H2 and cathode fed with O2. Protons are carried out from anode to cathode through membrane electrolyte and the electrons produce working in an external circuit.

PEMFC : H2ð Þ g ð Þþ at anode O2ð Þ g ð Þ at cathode ➔ H2O lðÞþ energy (8)

potential result at the maximum output power density is about 1 W cm2 [30, 31].

take place in different steps with endothermic/exothermic reactions [33, 34].

an external electrical circuit to produce electrical work.

Solar energy is a renewable source that can fulfill the world's needs for the future. The direct conversion of solar energy into renewable hydrogen fuel is done basically by two methods: photocatalysis and photoelectrochemical processes. The hydrogen obtained from photocatalysis and/or photoelectrochemical process can feed PEMFCs to convert chemical energy into electrical energy with high efficiency and without degradation of the ambient. PEMFC fed with H2 obtained from ethanol-steam reforming reaction (which contains CO) must use Pt-based alloy catalysts to increase the poisoning tolerance and improve the lifetime of the PEMFC.
