A Brief Overview of Hydrogen Production
Hydrogen can be an ideal sustainable energy carrier, due to the very low level of emissions related to its use and its vast sources and if it is produced from renewable vast resources and at low costs, then the hydrogen economy will be fully advantageous.
The global demand for environmental concerns and energy production, due to rising standards of living and increasing population are very sensitive and significant issues in the 21st century (Dudley, 2016; Nikolaidis & Poullikkas, 2017; Sunita & Ghoshal, 2015).
For instance, in 2015, the world total primary energy supply (TPES) reached 13,423 Mtoe (1 Mtoe = 11.63 TWh), of which 81% came from fossil fuels and 27% were consumed by transportation sector. 23,816 TWh of electricity were generated in 2014, of which 66% came from fossil fuels (Dupont, 2007; Conti, et al., 2016). The increase in world oil consumption was predicted to rise from 82 to 121 million barrels per day between 2006 and 2030 (Dupont, 2007). While for the year 2040, the energy consumption is estimated to be 20,533 Mtoe (Conti, et al., 2016). The CO2 emissions as a result of fossil fuel utilization, in 2014 were 32,381 Mt (Birol, 2016) (Meyer & Pachauri, 2014). The instability in the crude oil price, the limited reserve of fossil fuels, the increased environmental worries related to greenhouse gas (GHG) emissions and global warming, the overall human health and safety considerations will gradually decrease the fossil fuel production over time, and motivate the research for alternative non-fossil fuel energy sources, that could greatly reduce the CO2-related emissions and their adverse effect on global warming (Muradov & Veziroğlu, 2008; Balat & Balat, 2009; Birol, 2016). An estimated 30–40% of the carbon dioxide from human activity released into the atmosphere dissolves into oceans, rivers and lakes. The uptake of carbon dioxide (CO2) from the atmosphere causes the ocean acidification (decrease in natural ocean alkalinity). Part of the CO2 absorbed by the ocean reacts with the water to form carbonic acid, some of these extra carbonic acid molecules react with a water molecule to give a bi-carbonate ion and a hydronium ion, thus decreasing ocean natural alkalinity by increasing H+ ion concentration.
Renewable energy is the world’s fastest-growing source of energy, at an average rate of 2.6%/year compared to 2.3%/year of nuclear energy, 1.9%/year for natural gas, coal growing at an average rate of 0.6%/year and with an average increase of 1.4%/year in total world energy demand (Conti, et al., 2016). According to the latest Eurostat statistics, the share of renewable energy in gross final energy consumption in the European Union (EU) reached 16.7% in 2015, which nearly doubles the 2004 level of 8.5%. The EU aims to reach a 20% share by 2020 and at least 27% by 2030. Eleven countries have already reached the level required to meet their national 2020 targets: Sweden (53.9% vs. 49%), Finland (39.3% vs. 38%), Denmark (30.8% vs 30%), Croatia (29% vs. 20%), Estonia (28.6% vs 25%), Lithuania (25.8% vs. 23%), Romania (24.8% vs. 24%), Bulgaria (18.2% versus a 16% target), Italy (17.5% vs. 17%), the Czech Republic (15.1% vs. 13%) and Hungary (14.5% vs. 13%) (Dupont, 2007).
Hydrogen is considered an important future alternative source for sustainable energy systems in the stationary power, transportation, industrial and residential sectors (GII, 2014; Serfass, 2011; Edwards, et al., 2008; Riis, et al., 2006) as it can be safely transported through conventional means (GII, 2014; Serfass, 2011; Pasman & Rogers, 2010; Zhou, 2005). Hydrogen can be stored as compressed gas, cryogenic liquid or solid hydride (Zheng, et al., 2012; Lipman, 2011; Sakintuna, et al., 2007; Riis, et al., 2006; Züttel, 2004; Züttel, 2003). Hydrogen can be used as the fuel either for direct combustion in an internal combustion engine or in a fuel cell device, producing only water as a byproduct (Lipman, 2011; Serfass, 2011; Marbán & Valdés-Solís, 2007; Granovskii, et al., 2006; Van Mierlo, et al., 2006; Shinnar, 2003).
There are no natural hydrogen deposits, and for this reason the production of hydrogen plays a key role in modern society (Sitzer, et al., 2008). Hydrogen can be produced from any primary energy source (Milbrandt & Margaret, 2009). Hydrogen is currently accepted as an environmentally benign secondary form of renewable energy, as a carbon-free alternative to fossil fuels, that possess the highest energy content as compared to any known fuel, see Table 1 (Ibrahim & Canan, 2015).
Table 1. Higher and lower heating values (HHV and LHV, MJ/kg) for various fuels at ambient temperature and pressure
| Fuel | State Physical | HHV (MJ/kg) | LHV (MJ/kg) |
| Hydrogen | Gas | 141.9 | 119.9 |
| Methane | Gas | 55.5 | 50 |
| Ethane | Gas | 51.9 | 47.8 |
| Gasoline | Liquid | 47.5 | 44.5 |
| Diesel | Liquid | 44.8 | 42.5 |
| Methanol | Liquid | 20 | 18.1 |
Adapted from (Ibrahim & Canan, 2015).
It has been predicted that the world’s hydrogen and fuel cell market will grow to $26 billion by 2020 and $180 billion by 2050 (Serfass, 2011). Today, hydrogen and fuel cells are responsible for up to 40,000 jobs, by 2019, there may be as many as 700,000 jobs worldwide employed by the hydrogen and fuel cell industry worldwide when taking into account direct and indirect jobs created by the industry (Serfass, 2011). Hydrogen and fuel cell-powered vehicles (FCV) progress has gained sufficient viability that 31 automakers are currently designing and manufacturing hydrogen fuel cell vehicles across the globe (Serfass, 2011). Global consumption of merchant and captive hydrogen is forecast to increase 3.5%/year through 2018 to 290 billion cubic meters (bcm), driven by strong growth in petroleum hydrotreating and hydrocracking refining operations (GII, 2014). A small fraction is already used to fuel driving cars while in the near future applications including power generation and heating in residential and industrial sectors are expected (GII, 2014; Lipman, 2011; Serfass, 2011).
A wide variety of processes are available for H2 production, which according to the raw materials used could be divided into two major categories namely, conventional (fossil fuels) and renewable technologies. The first category includes the processing of fossil fuels by reforming and pyrolysis. In hydrocarbon reforming, the participating processes are steam reforming, partial oxidation and autothermal steam reforming. The second category (i.e., renewable technologies) involves the methods that produce hydrogen from either water or biomass (renewable resources).
The H2 production from water-splitting processes includes electrolysis, thermolysis and photo-electrolysis. The utilization of biomass as a feedstock involves two general subcategories namely, thermo-chemical and biological processes. Thermo chemical technology mainly involves pyrolysis, gasification, combustion and liquefaction, whereas the major biological processes are direct and indirect bio-photolysis, dark fermentation, photo-fermentation and sequential dark.