2. Hydrogen and the environment

significant advantages as an energy transporter, a hydrogen-based economy has been emerg-

Hydrogen is not easily available in nature like fossil fuels. Though it might be obtained from any main energy source, it can be then employed as a straight fuel to the internal combustion engine in a fuel cell. The by-product of hydrogen is the water by-product [8–12]. The crucial trouble challenged by the modern world is the shortage of fossil. Therefore, it is indispensable to work out an alternative fuel that can substitute non-renewable fossil fuels. Hydrogen gas is one of the extremely versatile, efficient and sustainable clean energy carriers that may be used to substitute the fossil fuels due to its high energy yield when compared to conventional hydrocarbon fuels [13, 14]. The energy storage capacity of hydrogen is superb because a unit weight of it can generate nearly 33 kWh of energy [15]. Substituting hydrogen for fossil fuels in ultimate energy uses could bring this key environmental welfare [16] into accordance with the technical, green and cost challenges, and it is easy to overcome the difficulties in, for instance, production, storage and transport of hydrogen [17–19]. Hydrogen can be considered to be a secondary energy source since it can be converted to energy in the form of heat or electricity through either combustion or electrochemical reactions. The chief problem in using hydrogen fuel roots from its absence in nature and the requirement of cheap production systems [20, 21]. Extensive processes exist for H2 production which depends on the kind of the raw materials considered. The processes could be separated into two main classes viz., traditional and technology that can be renewed. Class one process is the fossil fuels and comprises the techniques of pyrolysis and hydrocarbon reforming. In the latter process, hydrocarbon reforming process, involve the chemical methods of reforming: steam, dry, partial

The former class includes the techniques that bring hydrogen from biomass and water. The primary feeds of biomass are partitioned into two biological and thermochemical processes.

ing as a clean, efficient, zero-carbon alternative to current energy structures [8].

40 Advances In Hydrogen Generation Technologies

oxidation, autothermal steam and hydrocarbon decomposition.

Figure 1. Hydrogen production methods.

Hydrogen is regarded as a renewable and sustainable solution for mitigating global fossil fuel utilization and destroying the global warming [22]. The purpose of producing hydrogen as "Green Hydrogen" is to cause zero or low environmental impact. For this purpose all CO2 and other pollutants must be removed when hydrogen is extracted from fossil fuels. Not only the environmental concern, but also the increase in energy demand inclines the researchers to develop new and current techniques and seek new energy sources. However, to ensure the sustainability of modern societies, hydrogen is a promising future energy carrier since it is a very important and environment friendly substitute to fossil fuels [23]. Hydrogen is counted as a green fuel since it is carbon-free henceforth CO2 emission free. However, it can be generated from an extensive collection of fossil fuel and viable energy origin, so the type of hydrogen production process determines the emissions that will occur. Besides being abundance in the universe, hydrogen is not consumed like hydrocarbons; because it changes state from water to hydrogen back and forth when used as a fuel. However, production of hydrogen is not always CO2 free. There exist various production methods such as gasification, electrolysis, and biological routes while these production methods can be performed using different feedstocks like water, biomass, or coal [24]. Some of these routes use non-renewable sources, some use extreme chemicals, and others have unknown life cycles. For the purpose of finding a clean energy route from the beginning of the circle to the end, a systematic approach to analysis is essential. This analysis should assess the whole production in such terms: terminating the dependency on non-renewable resources, reducing wastes, increasing efficiency or implementation of renewable sources to the systems.
