The Potential of Hydrogen Technologies for Low-Carbon Mobility in the Urban-Industrial Symbiosis Approach

According to the International Energy Agency (IEA) [1], transport accounts globally for 37% of CO2 emissions from end-use sectors; moreover, it significantly contributes to air pollution, mainly through the release of particulate matter (PM), nitrogen oxides (NOx), and sulphur oxides (SOx), impacting urban air quality and communities’ health [2, 3].

These issues require a shift to zero-emissions vehicles to reduce the environmental impacts of the transportation sector, as recognized by European [4] and global climate change mitiga tion strategies [5, 6]. In this effort towards a low-carbon mobility, hydrogen fuel vehicles (Fuel Cell Electric Vehicles – FCEVs) can be complementary to battery electric vehicles, opting for the most appropriate technology for each application and market segment [7, 8]. Also, the local railway sector, where diesel trains are mostly employed, can switch to hydro gen trains, supporting the sector’s decarbonisation [9]. In fact, when used in fuel cells, hydrogen produces only water as a by-product and can be considered an alternative to fossil fuels [10].

Hydrogen is conventionally produced by fossil fuels using technologies like hydrocarbon reforming and hydrocarbon pyrolysis for industrial applications; to reduce the impacts of the production processes, many processes to obtain hydrogen from renewable resources are available, such as biomass-based technologies and approaches using water splitting [11]. Biomass-based technologies are thermochemical and biological methodologies that both release less CO2 than conventional processes, producing the so-called “low-carbon” hydrogen [10]. The power to hydrogen process uses electrolysis to convert surplus electricity into hydrogen, splitting water molecules into dioxygen (O2) and dihydrogen (H2). When the employed electricity is only of renewable origin, e.g., produced by photovoltaic or wind sys tems, the produced hydrogen can be considered clean and is conventionally qualified as “green hydrogen” [5].

The deployment of renewable power-to-mobility hydrogen applications requires the devel opment of hydrogen generation plants, distribution infrastructure, as well as refuelling and charging stations, posing techno-economic, security, and public acceptance issues [5]. On the contrary, the existing industrial areas can represent for the local communities a familiar industrial structure where facilities giving rise to perceived risks or disadvantages can be confined [12]. Thus, the industrial parks (IP) can create synergies with the adjacent urban areas, providing a suitable location for renewable power plants [13] to produce green hydro gen, for hydrogen storing and distribution facilities, and for exchange parking as a last-mile solution. In this approach, implementing the urban-industrial symbiosis model, the industries contribute to reduce both the emissions of the trucks, vans, and car traffic serving the com mercial area and the environmental impact of the urban mobility. The urban-industrial symbiosis extends the industrial symbiosis concept to urban-industrial synergies, represent ing an integrated approach to the urban regeneration strategies that links the urban metabolism research field and the sustainable city planning [14]. The main advantages for the involved industries are related to eco-innovation, while the local communities benefit from the envi ronmental restoration and improved well-being [15].

This paper aims at reviewing the scientific literature in order to analyse the green hydrogen solutions suitable to support local low-carbon mobility through the urban-industrial approach. The sustainability issues related to the adoption of this strategy are discussed to support future research applications and decision-making processes.

The more recent scientific literatures have been reviewed focusing on three main topics: the green and low-carbon hydrogen technologies, the low-carbon mobility solutions using hydro gen, and the hydrogen technologies employed in the energy hub context, suitable for the UIS context. The thematic analysis follows the outline illustrated in Figure 1.

From the reviewed literature, the power-to-mobility applications of hydrogen suitable for the UIS context have been extracted and discussed.

Green hydrogen is a power-to-hydrogen application, and it is obtained via electrolysis using renewable electric power; this is the lower emission process to generate hydrogen, producing high purity hydrogen [16]. Thus, green hydrogen is used when high purity hydrogen is requested or to reduce the peak loads on the grid and to stabilize the intermittent power sup ply from renewables [17], as hydrogen storage has proven to be an achievable option to support the increasing integration of power generation by renewable energy sources (RES) into the electricity grid [18].

Water electrolysis is a well-known endothermic process using electrical energy input to split water molecules into hydrogen and oxygen molecules. The typical electrolysis unit is the elec trolyser, consisting of an electrolyte where a cathode and an anode are immersed. Three types of electrolysers are currently available commercially, each using different electrolytes and working under different conditions: alkaline water electrolyser (AEL), proton-exchange mem brane electrolyser (PEM), and solid oxide electrolysis cells (SOEC) [5, 19]. The different technologies show different stages of development, performance, and cost [20].

The IRENA compared the key performance indicators for the different technologies in 2020 with 2050 projections, showing their large-scale applicability potential (Table 1).

Considering only the stack, PEM electrolysers have the smallest footprint, with an esti mated footprint of 8 to 13 × 104 m2 for a 1 GW PEM facility, compared to an estimated footprint of 10 to 17 × 104 m2 for a 1 GW AEL facility [21].

The main renewable technologies employed or modelled for green hydrogen production are solar technologies, mainly photovoltaic (PV) systems [22]. Solar and wind-hydrogen coupling have been widely studied using case studies analysis, techno-economic assessment, and simulations [23–27], showing good economic potential depending on both local wind or PV electricity cost and the electrolysers technology maturity [16, 28].

Three are the main approaches to store hydrogen: it can be stored physically as a gas or liq uid, or by adsorption and absorption on the surface or within solid materials, with different volumes, temperature, pressure, and storage duration characteristics.

The high-pressure gaseous hydrogen storage is the most common and mature technology; since the energy density of hydrogen by volume is low, it is necessary to compress it at up to 77 MPa to reduce the size of the storage tanks. Another way to increase the hydrogen density is to store it as a liquid at atmospheric pressure but at a very low temperature, about –253°C. Finally, solid-state storage, involving the combination of hydrogen with materials through physisorption or chemisorption, allows storing hydrogen at moderate temperatures and pres sures [5, 10].

Besides the green hydrogen, the so-called “low-carbon hydrogen” can also support the low-carbon mobility. The low-carbon hydrogen can be produced using biomass which, under some conditions [29], is considered a renewable source of energy. On the contrary, the GHG accounting of hydrogen is recognized as a possible indicator for a general definition of clean hydrogen [30]. Biomass can be used to produce hydrogen, along with other byproducts, by thermochemical processes, namely, gasification and pyrolysis. In both technologies, the yield of hydrogen production depends on parameters such as the type of feedstock, the tempera ture, and the type of catalysts used [10].

According to the scenarios designed by IRENA [31], the transport sector could be the second largest user of renewable hydrogen by 2050. In the transport sector, hydrogen can be used in fuel cell electric vehicles (FCEVs). The use of clean hydrogen as a low-carbon transport fuel is going to take off as cars, buses, and commercial vehicles (trucks and vans) become availa ble. The power-to-mobility configuration includes renewable electricity production, green hydrogen production, and the hydrogen supply network, including the refilling stations.

The hydrogen can be used as fuel in internal combustion engines (slightly modified gasoline engines), but they have low efficiency and emit dangerous nitrogen mixtures [61]. Currently, the most efficient power-to-mobility hydrogen applications are the FCEVs, since they gener ate electricity by chemically combining the hydrogen and the oxygen from air into nonpolluting water. FCEVs were first introduced by car brands, like Honda, Toyota, and Hyundai, and are now being followed by other brands; in 2018, the market value of FCEVs was $651.9 million, with a 66.9% increase predicted to 2026 [32]. Moreover, about 25,000 forklifts powered by hydrogen fuel cells are already in use worldwide, as well as more than 500 buses, 400 trucks, and 100 vans [33].

Due to the low-operating temperature (about 80°C), the most suitable fuel cells for FECVs are the proton exchange membrane (PEM) fuel cells, which include a solid polymer mem brane electrolyte and carbon electrodes, with platinum used as a catalyst [3].

According to the LCA comparative study of Candelaresi et al., a medium driving range of 600 km can be assumed for the FCEVs (0.76 kg of H2 every 100 km) and they show an excel lent transport decarbonization potential [34]. Moreover, when compared to battery-powered electric vehicles, FCEVs have a shorter refueling time and longer driving range [35]. Ian nuzzi et al. [36] compared the conventional buses used in the city of Rosario (Argentina) and equivalent fuel cell electric buses by means of LCA analysis, finding that the logistics of raw materials and transport of hydrogen in a radius of 50 km from the use place are not relevant in terms of energy and greenhouse gas emissions.

Regarding the economic barriers to the FCEVs’ deployment, the analysis performed by Ajanovic and Haas [33] based on the technological learning shows that the cost of the FCEVs is expected to reduce more faster than that of conventional fueled vehicles, making FCEVs competitive in the market.

The need for expensive infrastructure, requiring common standards and regulations for safety and maintenance management, is considered an important barrier to the power-to-mobility application [35].

The hydrogen refueling stations (HRS) have different configurations depending on where hydrogen is produced. In the case of on-site production, HRS includes the hydrogen produc tion unit, the compression system, storage tanks, the gas booster to regulate pressure during the refueling procedure, a cooling unit to guarantee safety during the fast vehicle’s tank refill, other safety equipment (relief valves, sensors, and waterless fire suppression), mechanical and electrical components, and the dispensers. For off-site production, the hydrogen must be delivered from a central production unit (or a local storage hub) by road transportation or dedicated pipelines. Heavy-duty trucks transport hydrogen by means of tube trailers contain ing compressed (more than 180 bar) or liquefied gas (at a temperature –253°C); the pipeline transportation is a low-cost solution if existing ones can be used, since this kind of transporta tion does not require energy for compression or liquefaction nor the use of vehicles, but it must include a receiving station. On-site production requests a higher investment: HRSs with on-site water electrolysers can request an investment 1.5 times higher than a same capacity off-site station [37]. As far as concern, the cost of hydrogen distribution and dispensing into FCEVs, the use of on-board metal hydride storage tanks reduces the fueling costs with respect to the use of 700 bar tanks because of lower compression costs [38].

The refilling station network should be located through geo-optimization tools after accu rately mapping the hydrogen consumption needs for light and heavy vehicles, considering urban areas and logistic centers, industries, and transport fleets [19].

Both for centralized and distributed hydrogen production, regulatory procedures include, among others, the environmental impact assessments and the urban planning acts’ compli ance. The HyLaw project, funded under the Horizon 2020 Programme, provides an online database including the applicable regulations in 23 European countries, while calling the attention of policymakers on legal barriers to be removed for the deployment of hydrogen applications [39].

Although the economic, safety, and regulatory concerns are addressed, the green hydro gen-to-mobility applications show great potential with the technological advancements. Robinius et al. [40] present a model for the analysis of the power-to-mobility application of the green hydrogen in Germany in 2050, considering the national renewable energy sources (RES) poten tial and the hypothesis of using the surplus renewable energy to produce hydrogen. The simulated scenarios include a distributed production that requires minimal hydrogen infrastructure, which is more cost-effective; a transmission network to connect the electrolysers to a number of sec ondary sources (hubs); and a distribution network connecting the hubs to the hydrogen fuelling stations located along the freeways. The economic analysis of the scenarios shows the cost- competitive potential of such a solution. The model applied by Fragiacomo and Genovese to a regional project deploying the power-to-mobility green hydrogen in Southern Italy demonstrates both financial performance and health-related economic positive impacts due to the reduction of carbon dioxide emissions [41]. Schitea et al. consider The development of the hydrogen mobility in Romania starting with urban agglomeration to be a reasonable choice to justify the initial investments, hypothesizing to revamp the available refuelling infrastructure [42].

The creation of a green hydrogen value-chain for the urban public transport (fuel cell buses) in Germany is proposed by Coleman et al. [43], considering near-site hydrogen production and short-distance pipeline infrastructure. Indeed, in the ramp-up phase of hydrogen infrastructure development, small-scale transportation strategies could be economically viable [44].

Beside the techno-economic and regulatory issues related to the implementation of the hydrogen distribution networks already mentioned, other main barriers to the large-scale deployment of green hydrogen applications can be the availability of water supply for elec trolysis and the safety and public acceptance issues [17].

The main hydrogen safety research streams include three topics: storage and detection, combustion and explosion, and ignition and propagation [45]. In China, hydrogen is consid ered a dangerous chemical, making the installation of HRS possible only in chemical plant areas or far away from urban areas [17]. On the contrary, the EU-funded project Hydrogen Mobility Europe [46] reported, by March 2021, the monitoring data of 330 FCEVs, made by Daimler, Honda, Hyundai, and Toyota, 237 fuel cell range-extended electric vans, made by Symbio, and 39 hydrogen refuelling stations located in 8 EU countries; among other results, the FCEV have proven to be reliable, and there have been no vehicle or HRS safety issues. However, regarding the public’s acceptance of HRS safety concerns, surveys show that there are high percentages of opponents to the building of stations near their residences, requiring more communication efforts and risk information to improve acceptance [47, 48].

According to the review by Emodi et al., the engagement of local communities and local authorities in hydrogen projects, providing benefits and supporting infrastructure, promotes the social acceptance of the hydrogen industry [49].

The smart multi-energy systems (MES) combine different and complementary energy con version technologies [50], including a share of renewable; when arranged as energy hubs [51], they support the energy-based industrial symbiosis, promoting the urban-industrial symbiosis approach [14].

Many studies have been conducted on the hydrogen technologies used in multi-energy and distributed energy systems [52], where hydrogen storage enables the coupling of different energy forms [53]. The analysis is performed at different scales (household, buildings, and current power plants) considering the hydrogen support to the high penetration of renewable sources (mainly sun and wind); with respect to end-use, the hydrogen used as fuel in vehicles, boilers, or CHP units, as a raw material for the industry are considered, and as a renewable energy storage medium [54]. In stationary applications, hydrogen energy storage systems can provide higher energy storage density and a longer life cycle compared to lead-acid or lithium ion batteries [53, 55]. Moreover, it reduces the lifecycle carbon emissions of energy storage [56]. Fang et al. modelled the microgrid of an industrial park, showing that hydrogen-based energy storage can better achieve peak shaving and reduce grid connection fluctuations, as well as reduce the electricity cost of industrial parks, compared to conventional batteries [57].

Maroufmashat et al. [58] reviewed the common applications of energy hubs, including the use of hydrogen as an energy vector for storage and FCEV fuelling; they found that the dis tributed generation and delivery of hydrogen is more sustainable both from an environmental and economic point of view than centralized delivery. Moreover, Edwards et al. [44] observe that industrial clusters include suitable transmission and distribution infrastructure that can reduce the initial investment costs. Erikson and Gray [59] investigated the challenges of inte grating hydrogen production, storage, and use into microgrid configurations with the aim of optimizing the hydrogen deployment within local hybrid renewable energy systems; their optimization model considers techno-economic, environmental and socio-political objec tives, to allow a socially responsible evaluation of the hydrogen application to off-site or on-site FCEV filling stations. Bartolucci et al. [60] show that, though still not viable from an economic point of view, a significant penetration of hydrogen into the MES allows us to achieve a reduction of fossil primary energy up to 80%, implying a carbon footprint reduc tion, and higher levels of flexibility and resilience of the energy hubs. A trade-off between the high installation cost of small distributed hydrogen generation plants and the reduced cost of a local distribution network must be reached, taking into account the better coverage of the territory and the potential for higher emissions reduction [61].

The Hydrogen Valleys platform [62], promoted by the European Union, collects more than 30 hydrogen-based projects to be used as best practices for the deployment of hydrogen applications, including production, transportation, and various end uses such as mobility or industrial feedstock. A feasibility analysis for the implementation of the green hydrogen val ley in the industrial area of Ravenna (Italy) has been performed by Guzzini et al. [63] showing that the design optimization is not sufficient to make the project economically competitive, so it is also necessary to design financial instruments to support the adoption of green hydro gen in local clusters. On the other hand, Mayyas et al. [64] demonstrated that renewable energy from large scale power hubs serving industrial consumers can be stored in the form of hydrogen with a competitive levelized cost of hydrogen production and levelized cost of energy storage in the United States, to be sold later as a fuel for FCEVs or converted back into electricity. As far as energy communities are concerned, Caramanico et al. [65] performed a life cycle assessment of the application of a fuel cell/photovoltaic hybrid micro-cogeneration heat and power system for a residential building with a detailed economic analysis, showing that annual savings can be obtained, but due to the high capital costs, some kind of incentives are needed to foster the deployment of such technologies. Liu et al. [66] modelled the plan ning of a distributed hydrogen-based MES and applied it to twelve typical cities around the world with different energy demand profiles and solar radiation, finding that this application can significantly reduce the operation cost of the energy system, except in high cooling demand and low solar radiation regions.

Zhang et al. [67] demonstrated the viability of a solar and biomass polygeneration system to satisfy cooling, heating, electricity, and hydrogen demand for vehicle fuelling in an urban con text. Xu et al. [35] proposed a framework for electricity and hydrogen supply integrated with a PV power system at a local community level, considering both residential and non- residential vehicles; the numerical application of the model showed the feasibility of the proposed frame work that ensures the power balance of the residential area and reduces its operational cost.

Genovese and Fragiacomo [68] presented a smart energy conversion system where the produced hydrogen is used both for the mobility and heat and power applications needed near the station; the analysis includes a fuel cell hydrogen fleet of 41 vehicles, 43 bicycles, and 28 fuel cell forklifts, as well as a cogeneration unit using a hydrogen 50 kWe PEM. This multi service facility configuration allows us to distribute the on-site produced green hydrogen to serve the local economy.

Liu et al. [69] developed a hybrid renewable energy system combining stationary battery and mobile hydrogen vehicle storage for a campus, office, and residential buildings; their comprehensive techno-economic-environmental feasibility study shows the viability of this application for achieving zero-energy buildings and communities in urban areas. The integra tion of FCEVs into the local electricity network has been demonstrated to be technically and economically feasible; additionally, FCEVs can provide a flexible energy buffer to the local system: when parked, they can provide backup power and grid balancing [70]. Maroufmashat et al. [71] modelled and optimized a system including four interacting energy hubs in an urban context, where one acts as an HRS for forklifts and vehicles, and the others serve a food dis tribution center, a residential complex, and a school, considering that the hubs can exchange surplus energy. The results of the study showed that distributed hydrogen production is more preferable in environmental and economic terms than the hydrogen distribution infrastructure.

As highlighted by the performed literature review, the most recent advances in fuel cell elec tric vehicle technologies and demonstration projects show the viability of adopting this low carbon mobility solution, once the economic barriers are overcome. Moreover, this solution contributes to provide storage systems suitable to support the increasing integration of power generation by RES into the electricity grid at the industrial park level and to recover heat for industrial applications.

Though the recovered literature does not specifically mention their use in the urban- industrial symbiosis, the benefits of such an approach are obvious from the prior research review.

The sustainability-related basis of adopting the green hydrogen power-to-mobility strategy in the UIS context and the advantages for the local communities are summarized and pre sented in Table 2.

The discussed issues demonstrate that the opportunities offered by the creation of syner gies between industrial clusters and the nearby urban areas in an integrated urban planning perspective can allow us to fully exploit the sustainability potential of low-carbon mobility solutions using green hydrogen.