2. Hydrogen production from ethanol-steam reformation

The development of efficient technologies for the production and use of hydrogen, an alternative source for clean energy generation from the conversion of renewable biomass, has been presented as one of the most attractive possibilities for the gradual adaptation of the energy matrix to the global management policies of air pollutant emissions and to the sustainable use of natural resources.

The use of hydrogen in fuel cells, a clean and energy-efficient technology, has been promoted throughout the twenty-first century for the improvement of hydrogen production processes with low levels of carbon monoxide (CO). In particular, the ethanol-steam reforming reaction, a biomass-derived renewable product, has been considered extremely important for the advancement of PEM non-stationary fuel cell technology. The coupling of an ethanol reformer system to PEMFC results in a significant environmental advantage since it promotes a cycle of zero carbon emission when considering the fixation of CO2 in the growth and development of sugarcane crops, feedstock for ethanol production [1].

The ethanol-steam reforming reaction is ideally characterized by the stoichiometric vaporphase feed of 1 mole of ethanol and 3 moles of water in a catalytic reactor. The reaction produces 6 moles of H2 and 2 moles of CO2. This reaction is fundamentally endothermic and thus requires a source of energy external to the system for its realization. In addition, the process hardly occurs without the formation of byproducts and intermediates by the means of parallel reactions on the catalytic surface.

In a thermodynamic study via the minimization of Gibbs free energy using a non-stoichiometric method, Rossi et al. [2] verified that temperatures lower than 700 K do not favor the formation of CO; however, the maximum production of hydrogen notably occurs at higher temperatures. This result exposes the complexity of the process and the necessity to develop new highly selective catalysts to H2 and CO2 leading to the minimization of CO concentration via shift reaction. In general, according to Furtado et al. [3], the ethanol-steam reforming reaction involves numerous steps and usually competes with various reactions, which generate byproducts resulting in a lower H2 yield. The breakdown of the carbon-carbon bond of ethanol multiplies the possible paths in the reaction network represented in Table 1, which requires higher temperatures, typically in the range from 623 to 923 K [4]. Although thermodynamic predictions indicate that it is possible to carry out the steam reforming reaction of ethanol at temperatures in the order of 523 K, the development of catalysts for the technological establishment of the process involves the understanding of many variables that can influence directly or indirectly in its viability. According to these studies, the temperature, pressure, composition and flow of reagents are variables that have a direct influence on the catalytic performance of the process. On the other hand, the use of different catalysts leads to different reaction paths so that the catalyst is a direct process variable and its composition (active phase, support), precursors and method of preparation are considered indirect variables but essentially important.

Keywords: production of hydrogen, ethanol steam reforming, PEMFC, electrochemical

This chapter shows the hydrogen production from ethanol-steam reformation and from photocatalysis and photoelectrochemical processes and the use of the hydrogen in a proton exchange membrane fuel cell (PEMFC) to convert chemical energy into electrical energy. The photocatalysis and photoelectrochemical processes use the solar energy for direct conversion of solar energy into renewable hydrogen fuel; moreover, solar energy is the unique renewable source that can fulfill the world's needs for the future to produce hydrogen fuel and generate the electricity. Hydrogen production can feed a PEMFC which converts chemical energy into electric energy by an electrochemical reaction. H2 is oxidized at the anode and O2 (often in the form of air) is reduced at the cathode, which results in electrical work. This system presents the advantage that it can be used in remote place to convert electrical energy without ambient

The development of efficient technologies for the production and use of hydrogen, an alternative source for clean energy generation from the conversion of renewable biomass, has been presented as one of the most attractive possibilities for the gradual adaptation of the energy matrix to the global management policies of air pollutant emissions and to the sustainable use

The use of hydrogen in fuel cells, a clean and energy-efficient technology, has been promoted throughout the twenty-first century for the improvement of hydrogen production processes with low levels of carbon monoxide (CO). In particular, the ethanol-steam reforming reaction, a biomass-derived renewable product, has been considered extremely important for the advancement of PEM non-stationary fuel cell technology. The coupling of an ethanol reformer system to PEMFC results in a significant environmental advantage since it promotes a cycle of zero carbon emission when considering the fixation of CO2 in the growth and development of

The ethanol-steam reforming reaction is ideally characterized by the stoichiometric vaporphase feed of 1 mole of ethanol and 3 moles of water in a catalytic reactor. The reaction produces 6 moles of H2 and 2 moles of CO2. This reaction is fundamentally endothermic and thus requires a source of energy external to the system for its realization. In addition, the process hardly occurs without the formation of byproducts and intermediates by the means

2. Hydrogen production from ethanol-steam reformation

sugarcane crops, feedstock for ethanol production [1].

of parallel reactions on the catalytic surface.

energy, electrocatalysts

64 Advances In Hydrogen Generation Technologies

1. Introduction

degradation.

of natural resources.


Table 1. Thermodynamically possible reactions in the steam reforming process.

Alternatives for purification of the reformate for the removal of CO and feed in PEMFC have been proposed by several researchers [3–10]. According to Rosseti et al. [5, 6], there are wellestablished routes, such as high- and low-temperature water-gas shift (WGS) and methanation, which can be integrated into the hydrogen production unit. Chen et al. [8] experimentally investigated a reaction system composed of two stages, an ethanol vapor reforming reactor (Ni/Al2O3 catalyst) followed by a water-gas shift reactor (Fe/Cr2O3 catalyst) to purify the hydrogen stream. In this study, four operational parameters including liquid flow, H2O/C molar ratio, reactor temperature and water-gas shift (WGS) reactor temperature were evaluated. The results indicated that the molar ratio H2O/C is the factor that most influences the performance of the system, which can be optimized to minimize CO formation.

efficiency of the process and the possibility of operating with diluted bioethanol feed, reducing the cost with the purification step. The system consisted of six reactors connected in series for production and purification of hydrogen, containing a fuel processor, which includes a steam reformer, two water-heating gases and a serial methanation reactor, in addition to the fuel cell. The heat was generated by burning part of the reformate. During the process, it was verified that the change in water/ethanol ratio in the feed of the reactor had a direct impact on the

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

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In view of the earlier information, it can be concluded that the ethanol-vapor reforming process combined with PEMFC is undefined between the two technological options presented, namely: reforming reactor and WGS systems in contrast to the use of membranes in the ethanol-steam reforming process. Finally, the technological development of the PEMFCs will

3. The role of photophysics and photochemistry on water split process

Solar energy is the unique renewable source that can fulfill the world's needs for the future [12]. The direct conversion of solar energy into renewable hydrogen fuel is done basically by two methods, photocatalysis and photoelectrochemical (PEC) water splitting. The first method relies on photocatalytically active particles suspended in aqueous electrolyte solutions, where one or both water-splitting half reactions take place. The second method uses photocata-

Photocatalysis involves photophysical processes, initiated by photon absorption, followed by the generation of excited states and finalized as a photochemical or electrochemical redox reaction. These excited states permit that a prohibitive reaction under certain conditions can occur by the use of a photocatalyst, and this reason makes photocatalysis interesting for solar

On search (and development) of new materials/catalysts for water-splitting processes, a common approach is to mimic natural processes and/or analogue materials. In case of water splitting, the natural process is photosynthesis. Under this point of view, the central role of natural water-splitting process is occupied by an enzyme complex, known as photosystem II

Photons absorbed by this enzymatic complex are transferred to the catalyst core, where a single charge separation takes place [4]. This catalyst core in PS II is a Mn4CaO5 oxo-bridged complex, represented by two similar models in Figure 2, but its exact reaction mechanism is still obscure [16]. Chlorophyll fluorescence is used to provide information on many aspects of photosynthesis. There are two different quenching mechanisms for chlorophyll fluorescence, a photochemical and a non-photochemical quenching. The first one is caused by charge separation at PS II reaction centers and can be considered a reliable measure of the PS II charge separation rate.

production of H2, that is, the increase in the ratio also increased the H2 yield.

possibly define the commercial choice for one of the two technologies.

lytically active particles or thin films deposited on electrodes [13].

energy conversion technologies [14].

(PS II), capable to split water using sunlight [15].

3.1. Principles

Another alternative widely evaluated in the available literature [9, 10] considers the use of reactive systems of hydrogen-permeable catalytic membranes, which can lead to the production of highly pure hydrogen and therefore enable direct integration between the reformer unit and PEMFC. Koch et al. [11] studied the ethanol-steam reforming process aiming to feed a PEM fuel cell to produce clean energy. The process consists of two stages as shown in Figure 1; the first stage produces a high hydrogen content gas via ethanol steam reformation. The second stage, a palladium-based membrane, separates the hydrogen from the rest of the reformed gas, producing high-purity hydrogen (>99.9999%), which prevents poisoning produced by impurities or fuel shortage. Koch et al. concluded that ethanol-steam reformer process was able to generate a pure hydrogen stream of up to 100 mm/min to feed the PEM fuel cell [11].

Based on the feasibility of energy cogeneration through fuel cells from biomasses such as ethanol, Rossetti et al. [6] performed the simulation and optimization of the H2 production process from the ethanol reformation with water vapor. The layout of the system was inspired by an existing unit in combined heat and power generation, with the purpose of evaluating the

Figure 1. Simplified scheme of the reformer processes [11].

efficiency of the process and the possibility of operating with diluted bioethanol feed, reducing the cost with the purification step. The system consisted of six reactors connected in series for production and purification of hydrogen, containing a fuel processor, which includes a steam reformer, two water-heating gases and a serial methanation reactor, in addition to the fuel cell. The heat was generated by burning part of the reformate. During the process, it was verified that the change in water/ethanol ratio in the feed of the reactor had a direct impact on the production of H2, that is, the increase in the ratio also increased the H2 yield.

In view of the earlier information, it can be concluded that the ethanol-vapor reforming process combined with PEMFC is undefined between the two technological options presented, namely: reforming reactor and WGS systems in contrast to the use of membranes in the ethanol-steam reforming process. Finally, the technological development of the PEMFCs will possibly define the commercial choice for one of the two technologies.
