Is the H2 economy realizable in the foreseeable future? Part I: H2 production methods

Depósito de Investigación de la Universidad de Sevilla https://idus.us.es This is an Accepted Manuscript of an article published by Elsevier in International Journal of Hydrogen Energy, Vol.45, on May 2020 available at: https://doi.org/10.1016/j.ijhydene.2020.03.092 Copyright 2020 Elsevier. En idUS Licencia Creative Commons CC BY-NC-ND 1 Is the H2 Economy realizable in the foreseeable future? Part I: H2 Production Methods Hassan Nazir1, Cindrella Luis2, Sujin Jose3, Jyoti Prakash4, Navaneethan Muthuswamy5,6, Marthe Buan6, Cristina Flox6, Sai Chavan4, Xuan Shi4, Pertti Kauranen6, Tanja Kallio6, Gilberto Maia7, Kaido Tammeveski8, Nikolaos Lymperopoulos9, Elena Carcadea10, Emre Veziroglu11, Alfredo Iranzo12* and Arunachala Kannan4* 1US-Pakistan Center for Advanced Studies in Energy (USPCAS-E), National University of Sciences and Technology, Islamabad 44000, Pakistan 2Department of Chemistry, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu, India 3School of Physics, Madurai Kamaraj University, Palkalai Nagar, Madurai 625021, Tamil Nadu, India 4The Polytechnic School, Ira A. Fulton Schools of Engineering, Arizona State University, Mesa, AZ 85212, USA 5Department of Chemical Engineering, Norwegian University of Science and Technology, Sem Sælands vei 4, N-7491 Trondheim, Norway 6Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, FI-00076 Espoo, Finland 7Institute of Chemistry, Federal University of Mato Grosso do Sul, University City, Senador Filinto Müller Avenue no. 1555, 79074-460 Campo Grande-MS, Brazil 8Institute of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia 9Fuel Cells and Hydrogen Joint Undertaking, Avenue de la Toison d'Or 56-60, B-1060 Brussels, Belgium 10National Center for Hydrogen and Fuel Cells, National R&D Institute for Cryogenics and Isotopic Technologies – ICSI Ramnicu Valcea, 4 Uzinei Street, 240050, Romania 11Editor-in-Chief, International Journal of Hydrogen Energy, USA 12School of Engineering, Universidad de Sevilla, Camino de los Descubrimientos, s/n, 41092, Sevilla, Spain Abstract The efforts on energy system decarbonization and improved sustainable energy efficiency in the developed countries led energy enthusiasts to explore alternative highly effective pathways in accomplishing these goals. Specifically, the transition from hydrocarbon to H2 economy using fuel cells and H2 technologies is a sustainable and favorable approach forward in meeting stationary, transportation, industrial, residential, and commercial sectors. This review in three Parts brings out the capability of H2 for enabling an energy revolution through much-needed flexibility in renewable energy resources. The review identifies the developments and challenges within the H2 generation, storage, transportation, distribution, and usage - as well as applications along with national and international initiatives in the field, all of which suggest a pathway for a greener H2 society. The review also highlights the opportunities and challenges in major energy sectors for H2 technologies. Part I of the series highlights the importance of H2 economy and initiatives from various agencies, and presents several H2 generation methods. Keywords: H2 Generation; Storage; Distribution; Economy * Corresponding Authors: [email protected] and [email protected] *Manuscript (Revised, clean, unmarked, FINAL version) 2 Table of Contents 1. Introduction ............................................................................................................................. 3 2. Initiatives in different regions (USA, Canada, Europe, Asia, Africa and Australia) .............. 8 3. H2 production methods ......................................................................................................... 12 3.1 From fossil fuels ............................................................................................................. 17 3.1.1 Hydrocarbon reforming .......................................................................................... 17 (i) Steam methane reforming ............................................................................................ 17 (ii) Partial oxidation .......................................................................................................... 18 (iii) Auto thermal reforming ............................................................................................. 18 3.1.2 Hydrocarbon pyrolysis ............................................................................................ 19 3.2 From renewable sources ................................................................................................. 19 3.2.1 Biomass process ...................................................................................................... 20 (i) Thermochemical ........................................................................................................... 20 (ii) Biological .................................................................................................................... 21 3.2.2 Water splitting ......................................................................................................... 22 (i) Electrolysis ................................................................................................................... 22 (ii) Thermolysis ................................................................................................................. 23 (iii) Photo-electrolysis ....................................................................................................... 23 4. Conclusion ............................................................................................................................ 23 References ..................................................................................................................................... 25 3 1. Introduction Energy demands for almost all countries are contingent on the so-called fossil fuel economy. The majority of the transportation sector (planes, trains, and automobiles) around the world is fueled exclusively through petroleum products such as gasoline, diesel and kerosene. In addition, a huge percentage of power plants use fossil fuels such as oil, natural gas, and coal as feedstock. Even though fossil fuels have played a critical role in societal development, they have created problems such as air pollution, environmental pollution, global warming, and economic dependence. Hydrogen (Greek: water former) is an odorless, tasteless, colorless and very reactive element in Group 1 of the Periodic Table and is the only truly clean chemical fuel. The H2 economy has a promise to eliminate all the above issues associated with fossil fuel economy. The H2 enthusiasts recognize it as a key component in a clean, sustainable energy system, or H2 economy. The H2 economy will feature H2 as an energy carrier in the stationary power, transportation, industrial, residential, and commercial sectors. While H2 is most abundant element on Earth and also a rich source of energy, it does not occur naturally as a gas. It exists naturally combined with other elements and, once separated, H2 can be converted into electricity or burned as a fuel. In particular, H2 is compatible with high-efficiency fuel cells, reciprocating engine or combustion turbines for power generation with zero emissions of greenhouse gases. H2 can serve all sectors of the economy (transportation, power, industrial, and buildings). The H2 economy could help significantly reduce greenhouse gas emissions, especially if H2 is produced from renewable sources, nuclear energy or fossil fuel-based systems with carbon sequestration. H2 is an energy carrier that can be stored, transported by truck or pipeline, and used for power generation on-demand, with water as the sole byproduct. 4 It is worth noting that the gravimetric energy density of H2 is three times higher than gasoline and other fossil-based sources of fuel. Since it is extremely light in mass compared to gasoline, H2 needs to be stored and transported under high pressure. In order to understand the benefits of H2, it is important to address a few concerns in the context of the current energy economy. The following major realities lead us to believe that the current hydrocarbon economy is not sustainable: (a) depleting raw materials for the fossil fuel economy with an ever-increasing demand for energy in developing countries, (b) with fossil fuels extracted in very few countries, there is always economic motivation leading to enormous political conflicts, and (c) poor air quality due to the emissions from fossil fuel usage leads to health and climate impacts throughout the world. Introducing and implementing H2 economy would lead to eliminating pollution caused by fossil fuels, greenhouse gases, and economic dependence. H2 can be produced from water by electrolysis using renewable energy sources such as wind, hydro, solar, and tidal energy leading to a sustainable system without any pollution. Figure 1 provides the solar H2 cycle along with possible efficiency in each conversion step. In fact, the H2 economy could also lead to a distributed generation. H2 can be produced wherever there is access to electricity and water, ultimately leading to energy security. 5 Figure 1. Solar H2 Cycle with the typical efficiency values. However, there are also hurdles for the successful implementation of the H2 economy and they are H2 generation, transportation, distribution, and storage. Once these are resolved at an affordable cost, the H2 economy will be commercially viable. The major advantages, challenges, and opportunities towards the H2 economy will be discussed in detail in the following sections. The scientific community across the globe is actively working to figure out the measures to successfully implement the H2 economy. Numerous research activities are being conducted, and certain measures are already underway demonstrating the potential of H2 economy. A thorough literature survey on the H2 economy from the year 2010 onwards using Web of Science; Core Collection led to more than 124500 research publications on the fundamental science/chemistry of the materials for H2 storage and production, components and systems for H2 distribution and applications, developments in the H2 economy and so on. As shown in Figure 2a, number of 6 publications and on H2 economy and Figure 2b, number of publications country-wise, H2 economy-related research activities increased significantly in the recent past. It is very interesting that among various countries, China stands first with more than 37000 research publications followed by USA (22000), Japan (7880), Germany (7670), South Korea (6720), India (6680), France (5480), and England (5190), since 2010. Figure 2. (a) Number of publications and on H2 economy, and (b) number of publications country-wise. 7 Figure 3. Schematic representation of the overall H2 economy, showing the scope of the review. Scope of this review can be visualized through the configuration shown in Figure 3. The feasibility of H2 economy is building on the research and development outcomes of H2 production, storage, transportation/storage/distribution, and conversion for realizing a sustainable energy economy in the foreseeable future, for various applications. In the H2 production process, the electricity cost for the electrochemical water splitting process is one of the major barriers for a sustainable energy system and/or economy. However, there are opportunities for large-scale H2 generation using wind, solar, tidal and hydro as renewable energy sources. H2 can be compressed or liquefied and stored for small and medium scale applications or transported through pipelines for large-scale applications. In general, the technologies related to H2 storage, transportation and distribution are well developed. Through large-scale H2 production, distribution and transportation would become affordable for various applications [1]. Through concerted efforts 8 by the energy industries, local and federal governments, educational institutions and non-profit H2 advocates/organizations, the establishment of a secure and sustainable energy economy is possible to achieve in the foreseeable future. Part I of the review is focusing on H2 production methods, whereas Part II will bring out the current status on H2 storage, transportation and distribution. H2 usage, applications, challenges and opportunities for realizing H2 economy will be provided in Part III of the review. 2. Initiatives in different regions (USA, Canada, Europe, Asia, Africa and Australia) In terms of global initiatives, it is worth to mention the International Partnership for H2 and Fuel Cells in the Economy (IPHE), whose mission is to facilitate and accelerate the transition to clean and efficient energy and mobility systems using H2 and fuel cell technologies across applications and sectors [2]. It is an international governmental partnership to advance H2 and fuel cells, formed in 2003 by 19 Member Countries and the European Commission. The IPHE members comprise 2/3 of the world’s GDP and invest nearly $1 Billion annually on H2 and fuel cells. The main initiatives are focusing on Regulations, Codes, Standards and Safety (Foster harmonization across countries and share safety information, best practices, lessons learned) and on Education and Outreach (Create unbiased factual materials, increase stakeholder engagement through workshops, policy forum events, education events, share information on status, gaps, analysis, opportunities, etc.) In order to establish H2 economy in the USA, the Department of Energy has formed a concept called H2@Scale (Figure 4a) for exploring wide-scale H2 production and utilization in making the power generation and transmission sectors highly resilient. The Fuel Cell Technologies Office hosted an H2@Scale Consortium (Figure 4b) Kick-Off Meeting in August 2018, in 15 Figure 6. Various H2 production methods based on fossil fuel and renewable energy sources. H2 in molecular form can be produced from many different sources, and in many different ways [21] as shown in Figure 6. Among different production methods (Figure 6), currently the most widely used is fossil fuel/natural gas steam reforming [22], whereas electrolysis and byproduct of chlor-alkali industry [23] provide secondary source of H2. The current and future H2 production technologies focus on using diverse, domestic resources including fossil fuels, such as natural gas and coal (with carbon sequestration); nuclear energy; and renewable energy sources, such as biomass, wind, solar, geothermal, and hydro-electric power using a wide range of processes [24– 27]. DOE is focused on developing technologies that can produce H2 at a target cost of < $4/kg (delivered and dispensed). To reach these goals, the program looks at a wide portfolio of processes over a range of time frames and production scales as depicted in Figure 7. 16 Figure 7. DOE plan for H2 production targeting near, mid and long-term application. Currently, more than 90 % H2 is produced by large-scale natural gas reforming process in the USA [20]. This established technology has been shown to be able to reach the cost targets in the near-term, as H2 dispensing stations are being built. To produce H2 economically in environmentally friendly ways in the future, DOE supports the research and development of a wide range of technologies. In the mid-term, technologies based on renewable resources, such as biomass and wind-generated electricity, are anticipated to begin reaching the cost targets. In the longer term, technology pathways with near-net zero carbon emissions, such as those based on solar energy, are expected to become viable. A brief overview of different H2 production methods is presented in the following sub-sections. 17 3.1 From fossil fuels Currently, fossil fuels (natural gas: 48 %, heavy oils and naphtha: 30 %, and coal: 18 % [28]) are the primary source for H2 production due to acceptable price levels. The two major techniques namely, hydrocarbon reforming and pyrolysis methods have been discussed here. 3.1.1 Hydrocarbon reforming Hydrocarbon reforming is the process by which the fuel is converted into H2 through some reforming techniques [29]. In addition to the hydrocarbon, the other reactant can be either steam (steam reforming) or oxygen (partial oxidation) or both (auto-thermal reaction). (i) Steam methane reforming In the steam reforming process, hydrocarbon and steam are catalytically converted to H2 and CO2. The whole process involves the following major steps: generation of reforming or synthesis gas (syngas), water-gas shift, and methanation or gas purification. The raw materials involved in this process consist of methane, natural gas, and other methane containing gases through various combinations of light hydrocarbons including ethane, propane, butane, pentane, light, heavy naphtha and bio-methanol or bio-ethanol [29,30]. SMR process is the most developed, efficient (up to 85 %) and widely being used for large-scale H2 production [31]. In a typical process, the steam and natural gas are reacted together at 850–900 °C in the presence of a nickel-based catalyst to produce syngas. The syngas is treated using a pressure swing adsorption process to separate near 100 % H2 [32]. The projected costs of each component in a SMR process-based H2 production are: 60.7 % feedstock, 29.1 % capital investment and 10.2 % O&M [33]. The H2 production cost for plant with a design capacity of 380,000 kg/day, at 90 % capacity factor and a natural gas cost of $ 10 per MMBtu, are estimated to be $ 2.27 and 2.08 per kg with and without carbon capture and sequestration, respectively [34]. 18 (ii) Partial oxidation In the partial oxidation (POX) process, hydrocarbon feedstock reacts with steam and is converted to H2 and CO2 in the presence of O2 gas. The POX process can occur at ~950 °C (feedstock: methane to naphtha) in the presence of a catalyst and ~1300 °C (feedstock: methane, heavy oil and coal) without using any catalyst [33]. After the reforming step, sulfur is removed to obtain pure O2, which is recirculated to partially oxidize hydrocarbon feedstock. This process is extremely capital intensive due to O2 recirculation and desulphurization steps. However, POX is the most appropriate technology to produce H2 from heavier feedstock such as heavy oil residues and coal [35]. In another process, coal is used as feedstock and the process is called coal gasification [36]. The coal gasification followed the same mechanism as POX, however, it becomes more expensive due to additional handling of un-reacted solid feedstock and a large amount of byproduct ash. In a typical coal gasification case study, the H2 cost of $ 1.63 and 1.34 per kg, respectively are reported for plants with and without carbon capture and sequestration [34]. (iii) Auto thermal reforming In an auto thermal reforming (ATR) process, partial exothermic oxidation provides the heat during endothermic steam reforming, and this leads to increased H2 production. Typically, steam with O2 or air, is injected into the reformer chamber for simultaneous occurrence of reforming and oxidation reactions [37]. The present process involves lower investment costs of about ~25 and ~50 % than the SMR and coal gasification methods, respectively. Advanced large-scale ATR plants with ~90 % CO2 capture at an efficiency of ~73 % enable H2 production cost of $1.48 per kg [38]. 19 3.1.2 Hydrocarbon pyrolysis Hydrocarbon pyrolysis involves the thermal decomposition under specific conditions for H2 production. The thermo-catalytic decomposition of light liquid hydrocarbons (boiling point: 50 to 200 °C) produces elemental carbon and H2, whereas heavy residual hydrocarbon fractions (boiling point: >350 °C) would lead to H2 through two steps (hydrogasification and methane cracking) [39,40]. The energy required for H2 production by methane decomposition in inert environment at ~ 980 °C is significantly lower (37.6 kJ/mol) than that by the SMR method (63.3 kJ/mol) and could be easily met by combustion of ~ 15-20 % of H2 produced in the process. In addition, pyrolysis does not require any waste gas sequestration or CO2 removal steps. Hence, capital costs for large-scale H2 productions plants are lower compared to SMR and POX methods, leading to ~ 30 % lower in H2 cost [41] and the cost can be lowered further by using the carbon byproduct in other industries. From environmental point of view, it would be more advantageous to produce both H2 and carbon by the catalytic decomposition of natural gas compared to H2 production by SMR coupled with CO2 sequestration. The major drawbacks of this technology are related to the H2 separation due to the low H2 partial pressures in the reaction mixture and membrane durability at high temperature required for decarbonization equilibrium. As an alternative, a low-temperature plasma process has been proposed for CH4 decomposition with proper utilization for carbon byproduct [42]. 3.2 From renewable sources The continuous rapid rise in atmospheric CO2, with ~ 414.7 ppm for May 2019 at NOAA’s Mauna Loa Atmospheric Baseline Observatory [43], clearly necessitates the need to shift towards carbon free technology. With the depletion of fossil fuel and the increase of the 20 greenhouse effect, the use of renewable resources is expected to dominate the energy mix. The following sub-sections consolidate H2 production methods using renewable sources. 3.2.1 Biomass process Biomass is renewable and can be obtained from an array of sources such as energy crops and crop residues, wood and wood residue, grass, industrial organic residues, animal and municipal wastes. Biomass can used for producing H2 by thermochemical and biological processes. (i) Thermochemical H2 and H2 rich gases can be produced from biomass in the thermochemical process either by pyrolysis and gasification [44]. In this process, CH4 and CO with other gaseous products can be processed for more H2 production through steam reforming and water-gas-shift reactions [45,46]. Another part of the thermochemical process is the biomass pyrolysis and it is usually carried out at ~850 K in inert atmosphere [47]. The efficiency of the biomass pyrolysis depends on feedstock type, catalyst employed and the operating temperature and duration. The H2 production cost projected is the range of 1.25 to $2.2 per kg, depending on the biomass type and batch size [48]. In the biomass gasification method, the biomass is converted to into a syngas at ~500-1400 °C in a gasification medium such as air, O2 and/or steam. The syngas produced is treated as in the pyrolysis process and critical factors affecting the yield are the same [49]. It is reported that a typical biomass gasification-steam-reforming-pressure-swing-adsorption requires 2.4 TJ of primary energy input per TJ of H2 [50]. For a plant with 139700 kg H2 per day using biomass (cost: $ 46-80 per ton), the H2 production cost is expected to be $ 1.77 to 2.05 per kg [34]. 21 (ii) Biological The major biological processes employed for H2 production are direct and indirect biophotolysis, photo and dark fermentation due to its low energy-intensive and normal operating conditions [16]. The bio-H2 process involves the bacteria/algae assisted photolysis of water through hydrogenase or nitrogenase enzyme system, and biomass for fermentative processes where the carbohydrate-containing materials are converted to organic acids and then to H2 gas by bioprocessing technologies [51,52]. The absence of H2 catalyzing enzymes in the natural plant is the reason for the green plants to take part in the only CO2 reduction process, whereas algae contain H2-producing enzymes and can produce H2 under certain conditions [53]. The projected H2 production cost from photo-bioreactor (capacity: $50 per m2; 10 % solar conversion efficiency) is $2.13 per kg [54]. In the case of indirect bio-photolysis, H2 production rate using both hydrogenase and nitrogenase enzymes is comparable to the direct bio-photolysis process. This process is still in a conceptual stage and the projected H2 production cost is about $1.42 per kg assuming the total capital cost of $135 per m2 [54]. The algae based H2 production is a promising process since it utilizes renewable fuel sources and CO2. However, the process is limited due to certain drawbacks such as low H2 production potential and the requirement of large surface area to collect sufficient light. Another bio-photolysis process is fermentation and it involves the microbial conversion of organic feedstock in the presence or absence of oxygen to alcohols, acetone, etc. [51,55]. These processes are promising for bio-H2 production as they utilize waste materials and provide inexpensive energy generation with simultaneous waste treatment. However, low solar energy conversion efficiency and demand for elaborate anaerobic photo-bioreactors covering large areas, as well as the limited availability of organic acids, are the 22 key barriers restricting these processes [56–58]. In fact, the thermochemical process is superior compared to biological process due to faster kinetics and environmentally friendlier nature. 3.2.2 Water splitting The H2 production by the splitting of most abundant water using electrolysis, thermolysis, and photo-electrolysis techniques is the most promising approach and it is a clear and environmentally benign [11,59,60]. (i) Electrolysis The H2 production by water electrolysis using electrical energy is a well establish endothermic process [12]. The most developed and commonly used electrolysis techniques are alkaline [61], proton exchange membrane (PEM) [12] and solid oxide electrolysis cells (SOEC) [62]. In the electrolysis processes, pure H2 is produced at the cathode following different mechanisms and is separated from water and O2. The water electrolysis process for large-scale H2 production cannot compete with the other techniques due to extensive electrical energy requirement (~40 kWh per kg of H2). Commercialized alkaline electrolyzers (efficiency ~ 73 %) can reach 380000 kg H2 annual production rates with a system energy consumption of 53.4 kWh per kg H2 $3.2 per kg [63]. It must be noted that electrolyzers will play a fundamental role in the transition towards the H2 economy with electricity generated from renewable sources. This implies the integration of renewables into the grid, where H2 is considered to be the only energy vector. Electrolyzers can convert renewable electricity into a H2 that can be stored, transported and distributed to the endusers for various applications. Electrolyzers are currently available at small scale (< 5 MW) production, although demonstration projects up to 10 MW are already being considered. 23 (ii) Thermolysis Thermolysis (or thermochemical) process involves the water splitting at high temperature i.e. ~2500 °C due to its high Gibbs free energy. To make this process more sustainable, several thermochemical water-splitting cycles have been proposed using Cu-Cl or SnO2 based catalysts using solar flux or nuclear energy, with the future interest be focused to the progress on solar collectors [64]. The H2 production cost depends on the cost of component materials, corrosion issues and overall system efficiency [65]. (iii) Photo-electrolysis The photo-electrolysis process involves the splitting of water by the charge generated in a semiconductor electrode by absorbing visible light [66]. The photo-catalyst semiconductor materials generate electron-hole pair with the absorption of photons (bandgap), and under applied bias potential the separated electrons flow through an external circuit to the cathode to couple with H+ for H2 production, whereas holes present at the anode react with water to generate H+ and O2. This process is mainly limited by the charge transport and visible light absorption efficiency of the semiconductor electrode [67]. A recent study projected a cost of $10.36 per kg H2 [68]. 4. Conclusion Part I of the series on H2 economy examined various H2 production methods from fossil fuels and renewable energy resources in terms of process as well as economy. Large scale centralized H2 production from fossil fuels by auto-thermal reforming and steam methane reforming are currently the most economically viable methods and will continue to be significant, although carbon capture and sequestration will need to be integrated for progressing towards zero carbon footprint. Distributed H2 production by water electrolysis is the most promising approach by 24 using renewable energy. Mid-term large-scale commercialization of electrolyzers is possible by developing cost effective and durable components with improved system efficiency. In addition, H2 production by electrolysis will need to be complemented by the available SMR technology enabling low-cost and large-scale H2 production, coupled with carbon capture and sequestration. In the long term, medium scale H2 production methods using photosynthetic microbial systems would become sustainable with breakthroughs in molecular, genomic, and bioengineering research. In the long term, green H2 production using renewable energy resources is expected to increasingly penetrate the market with research, development and demonstration in various geographical regions (USA, Canada, Europe, Asia, Africa and Australia) with government support for realizing H2 economy. Acknowledgment AMK would like to thank The J. William Fulbright Foreign Scholarship Board and The Bureau of Educational and Cultural Affairs of the US Department of State for the “Distinguished Chair Award” as well as Aalto University, Espoo, Finland for financial support. 31 Hydrogen Energy 2002;27:1185–1193. 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H2@Scale (a) vision with H2 as an energy carrier, and (b) Consortium R&D Pillars. 5. H2 (a) production cost by methods, and production capacity in the (b) world, (c) Asia, (d) Europe, (e) America and (f) Rest of the world in million cubic meters per day. 6. Various H2 production methods based on fossil fuel and renewable energy sources. 7. DOE plan for H2 production targeting near, mid and long-term application.