Is the H2 economy realizable in the foreseeable future? Part III: H2 usage technologies, applications, and challenges and opportunities

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 (50), on October 2020, , available at: https://doi.org/10.1016/j.ijhydene.2020.07.256 © 2020 Elsevier. En idUS Licencia Creative Commons CC BY-NC-ND 1 Is the H2 Economy realizable in the foreseeable future? Part III: H2 Usage Technologies, Applications, and Challenges and Opportunities Hassan Nazir1, Navaneethan Muthuswamy2,3, Cindrella Louis4, Sujin Jose5, Jyoti Prakash6, Marthe E.M. Buan3, Cristina Flox3, Sai Chavan6, Xuan Shi6, Pertti Kauranen3, Tanja Kallio3, Gilberto Maia7, Kaido Tammeveski8, Nikolaos Lymperopoulos9, Elena Carcadea10, Emre Veziroglu11, Alfredo Iranzo12* and Arunachala Kannan6* 1US-Pakistan Center for Advanced Studies in Energy (USPCAS-E), National University of Sciences and Technology, Islamabad 44000, Pakistan 2Department of Chemical Engineering, Norwegian University of Science and Technology, Sem Sælands vei 4, N-7491 Trondheim, Norway 3Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, FI-00076 Espoo, Finland 4Department of Chemistry, National Institute of Technology, Tiruchirappalli 620015, TN, India 5School of Physics, Madurai Kamaraj University, Palkalai Nagar, Madurai 625021, TN, India 6The Polytechnic School, Ira A. Fulton Schools of Engineering, Arizona State University, Mesa, AZ 85212, USA 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, International Association for Hydrogen Energy, USA 12School of Engineering, Universidad de Sevilla, Camino de Los Descubrimientos, s/n, 41092, Sevilla, Spain Abstract Energy enthusiasts in developed countries explore sustainable and efficient pathways for accomplishing zero carbon footprint through the H2 economy. The major objective of the H2 economy review series is to bring out the status, major issues, and opportunities associated with the key components such as H2 production, storage, transportation, distribution, and applications in various energy sectors. Specifically, Part I discussed H2 production methods including the futuristic ones such as photoelectrochemical for small, medium, and large-scale applications, while Part II dealt with the challenges and developments in H2 storage, transportation, and distribution with national and international initiatives. Part III of the H2 economy review discusses the developments and challenges in the areas of H2 application in chemical/metallurgical industries, combustion, and fuel cells. Currently, the majority of H2 is being utilized by a few chemical industries with > 60 % in the oil refineries sector, by producing grey H2 by steam methane reforming on a large scale. In addition, the review also presents the challenges in various technologies for establishing greener and sustainable H2 society. ______________________________________________________________________________ Keywords: H2 application; Combustion; Industrial; Fuel Cells; H2 Society * Corresponding Authors: [email protected] and [email protected] *Revised Manuscript (Clean, unmarked, FINAL version) Click here to view linked References 2 1. Introduction ........................................................................................................................... 3 2. Industrial uses of H2.............................................................................................................. 5 2.1. Ammonia production ......................................................................................................... 6 2.2. Oil refining .......................................................................................................................... 7 2.3. Methanol production ......................................................................................................... 7 2.4. DME and other Renewable Fuels to H2 Supplement ...................................................... 8 2.5. H2 reduction/hydrogenation .............................................................................................. 9 3. Fuel Cells................................................................................................................................ 9 3.1. Transportation applications types .................................................................................. 10 3.1.1. Fuel cell electric vehicles .......................................................................................... 10 3.1.2. Buses, coaches and trucks ........................................................................................ 12 3.1.3. Trains and trams ....................................................................................................... 14 3.1.4. Material handling equipment .................................................................................. 15 3.1.5. Maritime applications ............................................................................................... 16 3.1.6. Aerospace applications ............................................................................................. 18 3.1.7. Refueling infrastructure ........................................................................................... 19 3.2. Stationary applications .................................................................................................... 20 3.2.1. Micro-CHP ................................................................................................................ 20 3.2.2. Backup power ............................................................................................................ 22 3.2.3. Prime power .............................................................................................................. 22 4. H2 combustion ..................................................................................................................... 23 4.1. Internal combustion engines ........................................................................................... 24 4.2. Gas turbines ...................................................................................................................... 26 4.3. Thermal energy ................................................................................................................ 28 5. The market potential for green H2 .................................................................................... 30 6. Challenges and Opportunities ........................................................................................... 34 7. Summary ............................................................................................................................... 43 References .................................................................................................................................... 46 3 1. Introduction All major sectors in the hydrocarbon economy can progress towards decarbonization with a deployment of H2 technologies. H2 economy can be attained through the large-scale integration of renewable energies and intermittent power generation with the production of green H2 as described in Part I of this review series [1]. Once the cleaner H2 production technologies mature in the near future with commercial viability ($1.5 to 3 per kg H2), most likely through water electrolysis and/or steam methane reforming (SMR) with carbon capture and storage (CCS), a significant deployment into mass markets is very likely to occur [2]. H2 also enables the distribution of energy not only to end-users such as refueling stations but also to various industrial sectors by road, pipelines, and ocean in solid, compressed, or liquid forms, as detailed in Part II of the review series [3]. The role of stored H2 at large scale (underground or in the gas grids blended with natural gas) to increase the energy system resilience is expected to evolve together with the penetration of renewable energies in the power generation mix. The major goal of Part III of the H2 economy series is to review how H2 will contribute to achieve the zerocarbon footprint of sectors such as transportation (light and heavy-duty on-road, rail, and ship), industry, and buildings (heat and power), as well as its use as feedstock in industries such chemicals, refineries, or steel. Fuel cell stacks are matured enough for commercialization and durability has been generally proved such as in London’s buses with over 25,000 h operation. Thus, the most significant challenge for a massive deployment is to reduce stack and system costs, which will require both economies of scale (increased productions) and further technology developments to reduce material costs, typically the load of catalyst precious metals. The use of fuel cell stacks in heavy-duty applications is promising a vast market in the next decade, not only in road transport but also in trains (such as the recent Alstom iLint FCH train with 400 kW FC) 4 and ships. Moreover, green H2 from large-scale renewable electrolysis and SMR/CCS will play an essential role to decarbonize industry, replacing the grey H2 currently used in the refining and ammonia production industry. Clean H2 is also expected to replace fossil feedstock such as coke in steel manufacturing, and to progressively replace natural gas for heat and power generation. Figure 1. Schematic representation showing the scope of Part III of the review including H2 usage, applications, challenges and opportunities. The scope of Part III of the review series is shown in Figure 1, where the realization of H2 economy in a sustainable manner in the foreseeable future for various applications is presented. As seen on the left-hand side of Figure 1, H2 can be effectively utilized for applications comprising industrial processes as a hydrogenating agent, fuel cells (FC) as a direct anode fuel as well as in the combustion process as a feedstock. Major H2 consumers are the industrial processes related to ammonia production and oil refineries where H2 is produced by steam methane reforming in large-scale. As the cleanest energy conversion devices, low-temperature FCs use relatively pure H2 as fuel, being utilized for transportation and stationary applications. With its high gravimetric energy content, H2 is also being considered as a cleaner fuel for gas 5 turbines, internal combustion engines, and as a direct fuel for thermal energy applications. As shown in Figure 1 (right-hand side), the review also brings out the major issues associated with large-scale H2 production and distribution along with market potentials and opportunities for commercialization with the aim of developing a sustainable and secure H2 society [4,5]. 2. Industrial uses of H2 H2 is widely used in industry, with consumption of ~70 million tons per year in 2019 in pure form (about 6 % of the natural gas use) and another 45 million tons as syngas, according to the International Energy Agency (IEA) [6], as shown in Figure 2(a-d). It is, therefore, an established industrial gas being part of the global industrial business. The production market of H2 for industrial uses was valued at $115 billion in 2017 and is expected to grow to $155 billion in 2022 [7,8]. The H2 production market is typically divided into “merchant” H2 for delivery to customers (central generation of H2 to be sold/distributed by tanks, trucks or pipeline), and “captive” H2 (on-site H2 generation at a given facility to be consumed for internal uses). Focusing on the chemical and process industry [9], H2 is a fundamental reactant in the refining industry and for ammonia production, and therefore fertilizers. Over 27 % of the H2 produced globally is used for ammonia synthesis, refineries use ~33 %, methanol producers use ~10 %, and over 6 % are used by other industries [6]. It is worth mentioning that other chemical industries such as chlor-alkali are producing large quantities of H2 as a by-product, and the potential for integrating a FC based power generation plant to reduce the industry’s electrical consumption has been proven to be a reality [5,10–12]. 6 Figure 2. (a) Global H2 production per year as pure H2 and as syngas, (b) global usage of H2 as syngas, (c) global usage of pure H2, and (d) sector-wise usage of H2 [6]. 2.1. Ammonia production Ammonia is industrially produced by combining H2 and N2 by the reaction of N2+3H2⇋2NH3, with the rate-determining step of dissociative chemisorption of N2 on the iron catalyst surface (Fe2N and γ-Fe4N), through the Haber-Bosch process. In general, both reactants are produced onsite: N2 by low-temperature separation of air, and H2 mainly from natural gas steam reforming (thus “captive” H2). The industrial process conditions are 250 - 350 bar and 450 - 550 °C with αFe (ferrite) as a catalyst. Overall, 90 % of the ammonia production is used for the fertilizer industry, although it is also used as a refrigerant in refrigeration plants (R-717). In the early 20th century, large hydropower driven alkaline electrolyzers were used to produce H2 for ammonia synthesis. For example, a 165 MW electrolyzer with 37000 m³ H2/h was operated at Aswan in Egypt [13]. 7 2.2. Oil refining Oil refineries are the largest consumer of H2, which is produced on-site mainly from natural gas reforming as “captive” H2, with over 33 % share of the global H2 production [6]. H2 is used for the processing of intermediate oil products by hydrogenation reactions usually using nickel, palladium or platinum catalysts, as well as for the processing of crude oil into refined fuels (diesel, gasoline, and jet fuel) by hydrocracking and hydro-desulfurization [14,15]. Hydrocracking takes place at 70 – 150 bar and 400 – 800 ºC depending on the nature of the feedstock. Strict regulations requiring low sulfur in diesel together with the increase in the feedstock containing lower-quality heavy crude oil has increased the H2 use in refineries. Recent efforts are being carried out to introduce clean H2 generation into refineries. The FCH-JU has funded the REFHYNE project to supply clean refinery H2, operating the world’s largest H2 electrolyzer (10 MW, producing 1300 -t of H2/year) in the Shell Rhineland Refinery in Wesseling, Germany and design studies are underway to scale up to 100 MW level [16]. 2.3. Methanol production The production of methanol, mainly by the catalytic hydrogenation of carbon monoxide (CO + 2H2  CH3OH; H = -90.7 (kJ/mole)), accounts for 10 % of the global H2 use. The industrial process conditions are 50 – 100 bar and 250 ºC. Renewable methanol as a liquid fuel has been proposed as another carbon-neutral energy vector in parallel to H2 [17]. Other industrial-scale methanol production methods (synthesis, gasification, reforming), can be used to cover the rising demand of this fuel. Methanol can be used in transportation applications, directly in internal combustion engines or by blending with gasoline and diesel to reduce emissions. It must be mentioned that methanol has proved its applicability in transportation being used directly as a 8 fuel in methanol fuel cells (DMFC) or after on-board reforming in proton exchange membrane fuel cells. Also, methanol is a raw material used to synthesize formaldehyde (CH2O), acetic acid (CH3COOH), dimethyl ether (DME, CH3OCH3), and other chemicals. Several projects have tried to find the best production method for methanol or to demonstrate its suitability for various applications. Obtaining green methanol is a subject of many projects, such as Power2Me [18,19], MefCO2 [20], and Djewels projects [21]. The last-mentioned project started in January 2020 with the main goal to demonstrate the operational readiness of a 20 MW electrolyzer for the production of green fuels (green methanol). It will bring the technology close to the commercial stage (TRL 8) and will be the basis for scaling up the system to 100 MW. Several applications are expected at the end of the projects that deal with methanol usage, i.e. a small scale H2 generator (NEMESIS2 project) [22], an auxiliary power unit (METAPU project) [23] or light transport vehicles [24,25]. 2.4. DME and other Renewable Fuels to H2 Supplement DME can be synthesized from syngas (2CO+4H2 CH3OCH3+2H2O) or dehydration of methanol (2CH3OH  CH3OCH3 + H2O). In addition to being a cleaner and efficient fuel in diesel engines, DME also has multiple uses as refrigerant, a propellant for spray cans, household fuel, solvent, and methylation agent in the chemical industry. In the past 15 years, there has been a huge demand for DME, from 150k T/year worldwide to more than 2000k T/year only in China [26]. When DME is obtained from methanol, it can be used successfully in diesel engines for trucks and heavy-duty applications due to water removal. In the BioDME project [27,28], Volvo used DME fuel in diesel trucks for driving more than 1,500,000 km, so the project has been considered a success story. DME can be used in stationary applications, and has been used as 15 2035 and 2040 in France and the UK, respectively [59]. Inlandsbanan (a Swedish train operator) and Statkraft (energy utility company) [70], and Pesa Bydgoszcz SA (a Polish rail vehicle manufacturer) and PKN Orlen (state-owned oil refinery) [71] have signed Letters of Intent to develop FC powered freight trains in their respective countries. Stadler Rail Group, Switzerland will supply the first FC powered train to California in the USA [72]. FC trams are tested in St. Petersburg (Russia), and Foshan (China) [59,73,74]. It is expected that in St. Petersburg the H2 FC trams will get on the line in 2022/2023. A prototype of these next-generation trains powered by a 400 kW PEMFC is being tested in South Korea, for further commercialization [75]. East Japan Railway Company is utilizing Toyota FC technology to develop a FC powered (180 kW PEMFC) train between Yokohama and Kawasaki, that can operate at ~60 mph [76]. The state-ofthe-art and future targets for FC electric trains are summarized in Table S5 [41]. 3.1.4. Material handling equipment Material handling equipment (MHE) is considered as a promising niche market for FC deployment. This category comprises forklift trucks in warehouses and specialty vehicles in airports and harbors. FC powered forklift trucks offer better availability over battery-powered units due to fast refueling and they can be used indoors in contrast to diesel-powered units. Plug Power as the market leader has proven the commercial viability and sold over 20000 FC forklifts with refueling systems [59]. Plug Power has joined hands with Amazon and Walmart to deploy FC powered forklifts in their fulfilment centers in the USA. While in Europe, Carrefour (leading food retail) has deployed 137 units in northeastern France [77]. Theinterest in the deployment of FC based MHE by leading companies such as Toyota Motor Corporation, BMW Manufacturing Co., Coca-Cola, FedEx Freight, Mercedes, Procter and Gamble, IKEA, Sysco, and others, indicate that the number of activities for deployment of FCEVs continues to grow in the global 16 market [78,79]. This promises a transition from diesel-powered material handling systems towards H2 FC based MHE [59]. Moreover, South Korea is also developing the world’s first FC powered construction equipment, where Hyundai Motor Group in partnership with their construction wing aims to produce FC powered excavators at mass scale by 2023 [80]. In Table S6, the state-of-the-art and future targets for forklifts are summarized [41]. 3.1.5. Maritime applications FCs have been used for submarine propulsion for a long time. In 2019 TKMS (Germany) unveiled a 4th generation FC system for submarine applications with tested operational capability of 70000 hours [81] and Navantia is finalizing the construction of the first S80-class submarine with 300 kW FC stacks for the Spanish Navy. More recently, after demonstrations such as the Nemo H2 passenger boat operating in Amsterdam channels, and the Energy Observer Yacht [82] promoting renewable energy over a seven-year world tour, FCs are considered as auxiliary power units (APU) to support the onboard electric loads (hotel loads) and for the propulsion of all types of marine vessels [83]. The EU through the Horizon2020 program and the FCH JU is supporting maritime FC deployment for prime propulsion or auxiliary loads with 150 to 600 kW as can be seen in Figure 4 [58]. Evidently, PEMFC is the most preferred power system for promoting zero carbon footprint, by using pure H2. 17 Figure 4. Horizon2020 and FCH JU supported projects in H2-FC propulsion in the maritime sector. In several countries actions have been undertaken to build H2-fueled ships and boats [59]. Powercell Sweden AB and Havyard Group (a Norwegian ship technology company) signed a contract to design and develop a FC system comprising of multiple 200 kW FC stacks (collective output 3.2 MW) for installation in one of Havila Kystruten's maritime vessel to be operated in Norwegian waters [84]. In Norway, fuel-cell vessels for 200 passengers and 60 cars are under construction. FC boats for inland waterways are planned in France. Bloom Energy and Samsung Heavy Industries intend to build solid oxide fuell cell (SOFC) powered ships. Hyundai is building FC powered fishing boats. ABB in collaboration with Hydrogène de France planned to develop megawatt-scale FC powered ships in order to curb the global GHG emissions since shipping constitutes 2.5% of the GHG emissions [85]. Toshiba Energy Systems supplied compact 30 kW FC systems (with increased 18 volumetric power density, ~three times to the stationary model) for powering Japanese maritime vessels [86]. 3.1.6. Aerospace applications FCs are being used to produce space power since the Gemini earth-orbiting mission in 1960s. The Gemini FC was an early version of the PEMFC technology. However, alkaline fuel cells (AFC) were selected for the Apollo program and the following space mission for several decades including the space shuttles [87,88]. However, NASA is considering PEMFC and SOFC technologies for future missions [89]. The space FCs are supplied with cryogenic H2 and O2, and the water produced is used by the crew on manned flights. FCs are also studied as a power source for small electric aircraft and as APUs for full-size jet planes. The most recent advances in the technology have been piloted in the HY4, a four-passenger concept plane by the German Aerospace Research Institute DLR [90]. However, the first commercial aerospace application of FCs appears to be drones and UAVs where the flying time and range can be extended over Liion batteries. Doosan Mobility Innovation (South Korea) signed agreements with Microsoft, ReadyH2, and SkyFire Consulting (USA) to develop advanced FC powered drones for various applications [91]. HES Energy Systems (Singapore), Hy-Hybrid Energy (Scotland), and Goldi Mobility (Hungary) signed MoU to develop H2 powered drones [92]. Leading FC companies such as Ballard, Hydrogenics, etc. are developing their offering for this market [93]. The stateof-the-art and future targets for FC electric aircraft are summarized in Table S7. Preliminary findings by the FCH JU and the Clean Sky JU [94] to be published in summer 2020 have shown that H2 propulsion is the most promising solution for shortto medium-range aircraft in the next 15-20 years [58]. 19 3.1.7. Refueling infrastructure As a clean energy carrier, H2 is primarily an alternative fuel in the transportation sector, which accounts for nearly 25 % of the global primary energy consumptions. The transportation sector faces two major challenges: (i) implementation of infrastructures for H2 production, storage, transportation/distribution, and (ii) refueling, as well as the development of affordable fuel cell electric vehicles (FCEV). Customers will have no incentive to buy FCEV until a convenient H2 refueling station network is established, yet it is not commercially viable to construct a large number of HRS without adequate FCEVs, a chicken-and-egg dilemma [95,96]. Therefore, fleet operators (buses, taxies, delivery vans) would be a more natural starting point for infrastructure development rather than FCEVs for private use. H2 cannot use the existing distribution network for liquid fuels and requires new propulsion systems and technologies. However, the installation of new H2 refueling infrastructure involves high investment risks and uncertainties, especially at the early stage of FCEV penetration. In order to overcome this challenge, a collaborative consortium involving infrastructure companies, car manufacturers, and the government can help to share the risks. R&D collaborations between the infrastructure and automotive companies are critical to ensure the simultaneous increase of the HRS and FCEV. Government policies such as subsidies or tax breaks are also necessary to alleviate the high capital cost and long payback period. H2 infrastructure establishment initiatives are taking place in the USA (California), Europe (Germany) and Asia (Japan). The German H2 Mobility program has announced investment plans to build 1000 HRS by 2030 [97] and the Japan FC Commercialization Conference planned to build 1000 H2 HRS by 2025 [98]. Even though the FCEVs have a higher retail price than internal combustion engine vehicles, both the 20 fuel (because of higher efficiency) and maintenance costs (with lesser number of rotating parts) are lower. The safety of H2 refueling infrastructures also plays a critical role in customer acceptance for FCEVs. As of now, standards for connections, safety aspects, and performance requirements for H2 refueling and FCEVs have been established through ISO and SAE standards [99]. The stateof-the-art and future targets for HRS are summarized in Table S8 [41]. 3.2. Stationary applications Stationary FC applications range from sub kilowatt backup power units to multi-megawatt power stations. As the large units typically use fossil fuels as the primary fuel in combination with hightemperature FC technology (SOFC, molten carbonate fuel cell (MCFC)), they are not discussed in detail here. 3.2.1. Micro-CHP The most wide-spread FC application is domestic combined heat and power (CHP) units or better known as micro-CHP systems. In 2014, the Japanese (m-CHP) ENE-FARM project passed 100000 sold systems, with roughly 300000-350000 cumulative installations by 2019 [59,100]. The ambitious goal is to install 5.3 million systems by 2030 covering 10 % of Japanese homes [100,101]. In Europe, the targets are less ambitious. The target is to install more than 2500 systems by 2021 and deploy 10000 systems annually thereafter [102,103]. The state-of-the-art and future targets for m-CHP, 0.3-5 kW system, are summarized in Table S9 [41]. 21 The South-Korean government has set a target of 100000 m-CHP systems by 2020 [104]. In Japan, 93 % of the systems installed are based on PEMFC technology. The systems have reached the target price of ¥800,000 (US$7,350) per unit (≤1 kW), and no more subsidies are given. The price for a SOFC system (≤1 kW) is ¥1,230,000 (US$11,300). The micro-CHP systems use methane or LPG as a primary fuel, and a fuel processor is needed to produce H2 to be fed to the FC module. No fuel processor is needed when H2 is used as the primary fuel, which would simplify the micro-CHP system and decrease its cost. A micro-CHP system using green H2 produced by wind power has been demonstrated in Lolland island, Denmark in collaboration with IRD fuel cells and local authorities [105]. A special case of the micro-CHP is an off-grid system where electrolytic H2 is produced for on-site storage and reuse. Typically, such hybrid systems have been designed for residential applications (see Figure 5), integrating photovoltaic panels for the production of electricity, short-term battery storage, electrolysis systems to provide the H2 for long-term storage, and FCs to supply the electricity [106]. Although not economically feasible yet, commercialization efforts have started in Germany [107]. 22 Figure 5. Hybrid system designed for residential applications. 3.2.2. Backup power Backup power (BUP) for telecom towers is another early niche market for PEMFC and DMFC [108]. The number of units supplied by different suppliers are listed in Table S10. The average system size is 5 kW like for the MHE. Larger units are supplied to data centers and hospitals. However, as they mostly use natural gas as the primary fuel, they are not further discussed here. 3.2.3. Prime power A large FC system typically uses natural gas or biogas as the primary fuel. South-Korea is the leading market for MW-scale prime FC power. MCFC used to be the leading technology choice. However, phosphoric acid fuel cell (PAFC) and SOFC technologies are gaining ground, and the 23 leading technology providers Doosan (PAFC) and Bloom Energy (SOFC) are showing increasing interest in pure H2 as the fuel for their systems [59]. Industrial by-product H2 from processes like dehydrogenation and chlorine production offers here a niche application. Apart from being produced for on-site industrial usage, it must be considered that H2 is also produced as a side stream or by-product. A few pilot plants where by-product H2 is used for electricity generation in a PEMFC stack are known. The installation at the Akzo Nobel chlor-alkali plant (Delfzijl, the Netherlands) is one of the most representative, with a 70 kW FC starting in 2007 and having over 30000 h of operation [10]. A scale-up of the technology has been demonstrated with the 1 MW PEMFC power plant in service at the SolVin chlorine plant in Antwerp-Lillo (Belgium) since 2012, and later being transported to Martinique for further operation [109]. The world´s first 2 MW PEMFC power plant (with combined heat and power) is already operating in a chlor-alkali plant (Ynnovate Sanzheng Fine Chemicals Co Ltd) in Yingkou, China [110]. Based on such examples, it is foreseen that many opportunities (and challenges) are available for the chemical industry, in terms of introducing large‐scale production of renewable H2. 4. H2 combustion H2 is considered one of the most prominent fuels due to it being clean (no emissions of COX and soot) and its extremely high gravimetric energy density compared to fossil fuels. Due to its good flammability, H2 can be employed as a combustion fuel in different types of burners, internal combustion engines, and turbines. The adiabatic flame temperature for H2 (2045 °C) in comparison with acetylene (2400 °C), propane (1980 °C) and methane (1957 °C) in air, qualifies H2 as an effective combustion fuel also for high-grade heat. A comparison of the combustion properties of H2 with other fuels is provided in Table S11. In addition, the amount of energy liberated for H2 combustion (LHV: 120 kJ.g-1) is ~ 2.5 times the heat of combustion of typical 24 hydrocarbon fuels (gasoline (45 kJ.g-1), diesel (43 kJ.g-1), methane (50 kJ.g-1), propane (46 kJ.g1), etc.). Hence, the H2 mass required is ~ one third that of a typical hydrocarbon, for any specific load. However, the drawback of employing H2 for combustion is due to the very low density of H2 (i.e., the low volumetric energy density of ~ 10 MJ.m-3) - an order of magnitude lower than that of the natural gas at STP, due to the very low molecular weight of H2. The flashpoint of H2 is also extremely low (< –253 ºC) making it the most flammable among various fuels such as methane (–188 ºC), propane (–104 ºC), gasoline (–43 ºC) and methanol (11 ºC). In particular, 4 to 75 % of H2 is flammable in air and 15 to 59 % is explosive at ambient temperature. The octane number, one of the key characteristics for combustion is also highly favorable for H2 (130) compared to methane (125), propane (105), octane (100), gasoline (87) and diesel (30). This section reviews the status of the H2 usage in an internal combustion engine (ICE), gas turbines, and other heating systems [111]. 4.1. Internal combustion engines H2 internal combustion engine (H2ICE) technology can be divided into port fuel injection (PFI) and direct injection (DI) methods using spark discharge, dual-fuel operation with pilot diesel, respectively. In the spark ignition (SI) ICEs, PFI based engine combustion mode using H2 will have pre-ignition, knock, and backfiring issues due to lower ignition energy and quenching distance of H2, leading to lower power output along with efficiency degradation of engines. It has been demonstrated that the ignition energy of H2-air mixtures at ambient pressure increases exponentially with a decreased stoichiometry, solving the pre-ignition issue [112]. In particular, turbocharging along with H2 DI is proposed to solve the disadvantages of the H2 PFI SI engine [113]. Several configurations such as liquid H2 injection system, direct injection H2, pressureboosted H2ICE or hybrid-electric H2ICE have been explored for performance improvement and 31 directly or through P2P storage. However, producing H2 using the excessive electricity by water electrolysis and use of this H2 in the gas grid (P2G), mobility (P2H), or industry (P2Industry), contributes to the indirect electrification and decarbonization of these sectors. Installed electrolyzer capacity to be in hundreds of GWs in Europe by 2050, and several TWs globally. Key regulatory obstacles identified were (i) lack of clarity on the rules under which storage can access markets, (ii) application of final consumption fees to storage, and (iii) payments for curtailment to RES producers. Further, the FCH JU supported a study in 2017 to identify profitable H2 energy storage applications for Europe [141]. The analysis undertaken was at mesoscale, meaning detailed power system modelling by considering their expected grid reinforcements, with the goal to identify potential issues due to over-injection of RES in the network or by high local peak demand. The proximity to the natural gas network was also taken into consideration in identifying suitable locations. Moving to the monetization of P2H systems, different value streams were considered for industrial and transport applications to provide electricity grid services and lastly to inject H2 into the gas grid. Three case studies were selected: a case of semicentralized (SC) production for mobility application (1 MW scale), a light industry case (5 MW scale), and an oil refinery case (20 MW scale). The assumptions on performance and costs for alkaline and PEM electrolyser technologies were given for 2017 and 2025 for the three electrolyser capacities, as shown in Table 3. The profitability of a P2H project is determined by the H2 selling price, the electricity cost (including grid fees, taxes, etc), and the system cost, as determined by the system size. Table 3 summarises the results of the analysis, where all business cases were profitable, with the exception of the refinery case in 2017. Payback time is reduced by up to 50 %, when revenues from grid services and H2 injection to the natural gas grid are 32 taken into consideration – stacking up of revenues. To build a profitable business case, electricity price and H2 gas grid injection tariff should not exceed 40-50 and 90 €/MWh, respectively. Table 3. Summary of profitability of three business cases in Europe [141]. Parameter SC Mobility (Albi, France) Light Industry (Trige, Denmark) Large Industry (Lubeck, Germany) 2017 2025 2017 2025 2017 2025 Primary market H2 (Ton/year) 270 950 900 900 3230 3230 Average total electricity price (€/MWh) 44 45 38 47 17 26 Nominal Size (MW) 2 12 6 6 40 40 CAPEX (1000*€/MW) 3600 1900 1760 1400 1480 960 H2 cost (€/kg) 6.7 4.1 3.5 3.4 2.4 2.3 H2 price (€/kg H2) 7 6 5 5 1.8 2.6 Net margin per kg H2 (€/kgH2) 0.3 1.9 1.5 1.6 -0.6 0.3 Share of grid services in net margin (%) 75 72 39 37 - 85 Net margin without grid services (k€/MW/year) 39 71 228 248 -146 30 Net margin with grid services (k€/MW/year) 159 256 373 393 -13 195 Payback Period without grid services (years) 11 9 4.6 3.7 - 8.4 Payback Period with grid services (years) 8 4.5 3.4 2.7 - 3.5 Key risk factors Taxes and Grid fees, H2 price, Fleet Size, Injection tariff, etc. Taxes and Grid fees, H2 price, etc. Taxes and Grid fees, Carbon price, etc. In early 2020, H2 Europe (Industry Grouping of the FCH JU) released a document on a “Green Hydrogen for a European Green Deal Initiative by 2030” [142]. The analysis calls for a 40 GW electrolyzer capacity to be installed in Europe, 6 GW captive market close to the demand locations, and 34 GW close to the resource. Similarly, another 40 GW of electrolyzer capacity can be installed in North Africa, with 7.5 GW for the domestic market and 32.5 GW of H2 production capacity for exporting H2 to Europe using the existing natural gas pipeline network [142]. The total investments in electrolyzer capacity are estimated at € 25-30 billion, creating 33 140,000 – 170,000 jobs in manufacturing and maintaining 2x40 GW of electrolyzers, in Europe and Africa. The installation of this electrolyzer capacity along with the solar plants and wind parks for feeding them with green electricity would lead to 82 million tons of CO2 reductions per year. The renewable H2 cost would be competitive with low carbon H2 (SMR+CCS) by 2025 at 1.5-2 €/kg and with grey H2 (SMR) by 2030 at 1-1.5 €/kg. The global market potential by 2050 as estimated by IRENA, BNEF, Fraunhofer, and H2 Council are 5280, 7380, 9000, and 21700 TWh, corresponding to 134, 187, 228, and 549 million tons H2, respectively [143]. The FCH JU has estimated € 430 billion, (with a necessary support of € 145 billion as a COVID-19 economic recovery plan for the efforts towards realizable H2 economy) the total investment required to achieve the targets for transition towards H2 economy up to 2030 [144]. These estimates form the base for the new EU H2 strategy launched in July 2020 [145]. Such investments not only contribute to progress towards a clean energy system, but also would dramatically scale-up the H2-related industry creating and securing highly-specialized jobs and economic growth. The market for PEMFC is expected to grow at a compound annual growth rate (CAGR) of 15.28 % during the period 2019-2024 [146]. The main reason is based on the improvements in R&D activities in this field, making PEMFC technology competitive with other alternatives, such as Li-ion batteries, leading to a greater penetration on the vehicle market. Nowadays, the cost of these technologies along with the lack of refuelling infrastructure are some of the main barriers for their commercialization for stationary and transportation applications. Several studies on system cost analysis for automotive FCs also show that the total system costs are approaching the DOE targets with over 100000 units per year. Trucks and other heavy vehicles have been the main sector adopting FC technologies since 2017. The “Fuel Cell Industry Review” published yearly, showed in its 2019 report that a total yearly FC shipment 34 exceeding 1 GW was achieved in 2019 for the first time [59]. An increasing trend is clearly observed as only 300 MW were shipped in 2015. A combination of new innovative technologies, government policies, and infrastructure is rapidly emerging as several countries (Table 4) prioritize green H2 for their energy future and build the practicalities in establishing H2 societies with widespread applications. Table 4. Strategies adapted in decarbonizing transport and energy production sectors, by a few leading countries. Countries Major Activities USA California is aiming for 1,000 H2 fueling stations and one million FCEVs, by 2030. Argentina Signed an Agreement with Japan for producing green H2 from wind power, in 2019. Netherlands Successfully tested a turbine using a blend of 30% H2 and 70% natural gas and aims to employ 100% H2, by 2025. Austria Operating world’s largest green H2 production plant, since 2019. South Korea Plans to build three H2 powered cities by 2023 and powering 10% of the countries need by H2, by 2030. Japan Leading the world in building H2 Society with 100+ H2 fueling stations. 6. Challenges and Opportunities The realization of the H2 economy depends on major challenges being solved but leads to great opportunities for business development and benefits for society. One of the main challenges is the need for a green H2 generation, replacing the current main route for producing H2 which is steam reforming of fuels such as natural gas, thus producing grey H2. A decarbonized H2 economy with zero-carbon footprint will require green sources of H2 [147,148], such as water electrolysis coupled to renewable energy sources (PV and wind) or solar thermochemical H2 production [149]. The technology for electrolysis is sufficiently developed to allow for its integration with renewables such as PV and wind, and several pilot and large-scale demonstration projects are in progress. Anyhow, a major scale-up from 10-100 MW units today 35 to GW scale units is still needed to reach the TW level deployment targets by 2050. The cost of the technology is however still too high for such large scale deployment, although substantial cost reductions are expected in the near future [150,151]. The cost of H2 production from renewable electricity could fall 30 % by 2030 as a result of declining costs of renewables and the scaling up of H2 production. The potential of H2 to further foster the deployment and penetration of renewables such as solar PV and the wind is unquestionable when it comes to store surplus energy in situations with lower demands. The need for large scale and safe H2 storage methods with a high storage density is currently also a major challenge [147,152]. A H2 economy will not be realizable without appropriate storage systems, which must be covering not only small scale storage intended for local usage and applications [153], but also large scale storage of H2 including even seasonal storage. The storage of H2 is linked to another subsequent challenge, which is finding efficient means for H2 transportation and distribution to the point of use (end-users). Although there are initiatives ongoing such as distribution along the natural gas grid [154] and transportation in H2 carriers including organic hydrides, MOFs, or ammonia, a major challenge remains to make H2 distribution work in a real-life scenario within a H2 economy. The first MW-scale Power-to-Gas project was demonstrated at Falkenhagen (Germany) in 2013, in a demonstration project run by Uniper Energy Storage [154,155]. The plant aimed to store wind energy in the natural gas grid, generating around 360 Nm³/h of H2 through electrolysis, and feeding it into the gas grid. In the USA, a major initiative is in progress in Utah, with plans to store renewable H2 to reach an impressive 1000 MW energy storage plant in a salt dome. The company MHPS Americas is planning to produce electricity by gas turbines run on natural gas and H2 mixtures, significantly 36 lowering carbon emissions. In a later stage, a transition to fully H2-powered turbines would be developed. Finally, the challenges associated with the efficient usage of H2 are still to be solved. The final efficiency of the conversion of electricity to H2 via electrolysis and the subsequent H2 conversion to electricity in FC systems is still rather low. Further technology developments will be required to ensure that H2 energy is efficiently used within a H2 economy. This involves not only electrolysis and FC systems, but also any other zero carbon footprint systems based on H2. Despite the high H2 penetration potential in the medium and long terms, further technology developments are highly required as the transition towards a H2 economy based on current technology would require significant costs [156]. In parallel to the technology development and demonstration, preparation for the hydrogen economy should become an integral part of the infrastructure planning comprising transmission and distribution networks and storage facilities. Harmonized regulations and transparent market rules should be estabilished in order for the industry to commit for the long-term investments [145]. As a cross-cutting issue, the societal acceptance of a transition towards a H2 economy and a H2 society is also expected to be a significant challenge, depending on local traditions, culture, and technology acceptance [157–161]. The transition towards H2 should be in line with customer convenience and preferences in order to avoid adoption difficulties. As an example, it is an advantage that H2 can provide the same refueling speed and range as existing combustion-engine vehicles. Indeed, Human Sciences will need to be significantly considered for achieving deep decarbonization and deployment of H2 technologies, as many issues are involved such as consumer behavior and lifestyle or market design and circular economy. 37 In most cases, however, the challenge itself is backing a subsequent opportunity. This is particularly true in the transition towards a H2 economy, wherefrom a general point of view, the challenge of the transition is providing the opportunity to progressively developing an energy system towards the zero-carbon concept, lessening the current global warming issues (see as an example the “A Clean Planet for all” EU vision [162]). The technology development requirements and the technology commercialization is a major opportunity for new business development and growth, green H2 production from renewables will change energy and fuel markets [163]. This leads to opportunities for the potential creation of millions of high-quality jobs worldwide, as much as 30 M jobs according to the H2 Council. The H2 Council, launched at the World Economic Forum 2017 [164,165] believes that by 2030, H2 will already be a significant energy carrier with several millions of H2-powered vehicles and an increasingly expanding infrastructure. The Council believes that the H2 sector has the potential to involve a financial weight similar to the current hydrocarbons industry, expecting to involve annual revenues worth around $2.5 trillion by 2050. There are interesting initiatives led both by governments and private companies aimed at fostering the H2 economy, mostly starting from a local point of view. It is worth mentioning Masdar City in the United Arab Emirates, and countries such as Iceland, Norway, and Japan. The fully sustainable Masdar City, outside of Abu Dhabi, is intended to host up to 50000 people and 1500 businesses related to green technologies, where the city is planned to fully rely on solar and other renewable energies aiming at achieving a zero-carbon footprint. The government of UAE is committed to further develop its green energy economy and has worked with major companies such as Air Liquide and Toyota to derive strategies to strengthen the H2 industry. In 2019, a major solar-driven H2 electrolysis facility was inaugurated in Dubai, which is the first in the Middle East and North Africa (MENA) region. 38 Japan is probably the world leader in the progression towards a H2 economy, being significantly supported by the government and with the involvement of major companies. Japan's “Basic H2 Strategy” [166] was released in December 2017 with a commitment to become the first H2 society, by achieving cost parity of H2 with traditional fossil fuel. The future H2-based energy system of Japan, consistent with the layout shown in Figure 3 of Part 1 of the H2 economy review series [1], is depicted in the H2 Strategy (Japan METI-Ministry of Economy, Trade and Industry) [166,167] and relies on large amounts of H2 imports from locations within the “sunbelt” in Australia and other countries. Japan intends to start the importing of liquefied H2 by 2030 and has recently revealed the world`s first ship exclusively designed for H2 transport [3]. This strategy results in major opportunities for business growth and companies such as Kawasaki Heavy Industries are getting significantly involved. Kawasaki has started the construction of pilot H2 liquefaction facilities in Victoria State, Australia, worth $355 million, to ship H2 to Japan and aims to start exporting trials by the end of 2020. According to Australia’s CSIRO, technology costs for green H2 production are starting to significantly fall, and thus green H2 costs are approaching the cost of fossil fuels so that Australia can soon export renewable H2 to Japan and South Korea. Opportunities for the automotive industry are also opening as the H2 economy develops. The FCEV Mirai was released in 2016 by Toyota, with several thousands of units sold in Japan and the USA, and the Hyundai Nexo was released in 2019 with also over 3000 units sold in one year. Other initiatives such as the one by South Korea also represents major opportunities for industry and business development, as the government intends to carry out a major investment plan to 39 increase the number of FC vehicles to over 6 million by 2040, raising in parallel the H2 refueling infrastructure up to 1200 stations. The government estimates a creation of over 400000 jobs because of such measures and over $35 billion per year in value-added to the economy by 2040. The opportunities for a H2 economy development in China are also huge. China is currently investing about 100 billion yuan per year in H2 energy, and major Chinese vehicle manufacturers such as Great Wall Motors are about to release FC vehicles as early as 2022, with an overall estimated production capacity about 170000 FCEVs per year. The opportunities for business growth and job creation are therefore enormous. The IEA [6] highlights some near-term opportunities to widespread H2 penetration in the energy system, such as making industrial ports key locations for scaling up the use of clean H2. As described in Part 1 of this review series [1], a majority of H2 is being produced by steam methane reforming for oil refineries and chemical industries concentrated in coastal regions in Europe, North America, and China. Encouraging these key players to progressively move towards greener H2 production would result in the drive down of the overall costs, further boosting clean H2 generation, for example by fueling trucks and ships and powering other nearby industrial facilities. Additional opportunities according to IEA [6] are to introduce clean H2 in the already existing natural gas pipeline infrastructure (Power-to-Gas), boosting the demand for H2 and thus reducing costs, or favoring H2 in larger trucks, buses and trains for making the FC vehicles more competitive. Launching international shipping routes, as with the existing LNG market, would also contribute to the successful deployment of H2 in the global energy system. Figure 10 illustrates various opportunities of the H2 economy. Several industrial processes are using H2 [168,169]. One of the most important sectors is the Chemical and Process Industry as discussed in Section 2, which is the largest producer and consumer, H2 is also widely used in the 40 metallurgical industry as a reducing agent, for metal alloying, and the production of carbon steels and special metals. The semiconductor and electronics industry are also using H2 as a reducing agent and as a carrier gas. The production of flat glass, where H2 is used as an inert and protective gas, or as a coolant for generators are other examples of industrial uses of H2. Figure 10. H2 economy: Various opportunities. In line with the Paris Agreement (2015), the intergovernmental panel on climate change (IPCC 2018) urges to reduce the GHG emissions by 45 % by 2030 (compared to 2010) and then to net zero by 2050 [37,170,171]. In this massive transition, the H2 economy will play a major role in achieving decarbonization [171]. 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(a) Global H2 production per year as pure H2 and as syngas, (b) global usage of H2 as syngas, (c) global usage of pure H2, and (d) sector-wise usage of H2. 3. Reduction of cost and increase in number of FC buses in Europe. 4. Horizon2020 and FCH JU supported projects in H2-FC propulsion in the maritime sector. 5. Hybrid system designed for residential applications. 6. Schematic representation of (a) liquid H2 storage and injection system, (b) injector used for DI-H2ICE, (c) pressure-boosted H2ICE, and (d) a hybrid-electric version of an H2ICE. 7. A schematic of a gas turbine showing fuel flexibility. 8. Comparison of (a) natural gas, (b) H2 enriched natural gas, and (c) H2 flames for thermal energy applications. 9. Comparison of natural gas and low-carbon heating technologies for large-scale retrofit deployment to domestic buildings. 10. H2 economy: Various opportunities. 11. Transition from hydrocarbon to H2 economy, related to H2 production, transportation and utilization along with barriers. 12. H2 usage: realizable in the coming decades.