“In these periods of major change, the established points of reference are being swept away, even in so-called traditional industries” (2).

Sustainable mobility is already on the agenda of every government in the world. The concept of sustainable development, defined by the Brundtland Commission as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs” (3) has permeated and is now a standard objective in all spheres of life and at government level. It is also at the core of the Sustainable Development Goals (4), recently launched by the United Nations as global objectives for 2030.

Transport plays a fundamental role for economic development and social welfare of a country. The movement of individuals and goods facilitates production and trade, enhances labour mobility and provides customers with access to goods. Transport externalities jeopardise sustainability. Transport externalities include environmental externalities (mainly climate change, air pollution and noise), but also extend to accident externalities and congestion externalities (5–7). The environmental impact of transport is substantial and ”based on continuing current rates of growth for passengers and freight, and if no mitigation options are implemented to overcome the barriers, the current transport sector’s GHG emissions could increase by up to 50% by 2035 at continued current rates of growth and almost double by 2050” (8).

Most policies in place and most proposed policies by design focus on existing externalities. However, the transport externalities we know today may be replaced by other problems. The world is being shaken up by new technologies and the speed of change is unprecedented. The term ‘disruptive technologies’ is becoming widespread, as shown by recent reports produced by McKinsey and Company, USA (9) and Deloitte LLP, UK (10). With the help of a comprehensive literature review, the aim of this paper is to understand the impact that current and proposed policy could have on the technological change in the road transport sector and how this will change the nature of the problems encountered and the sustainability.

The paper is organised as follows. Section 2 concentrates on alternative energy vehicles, with particular attention to electric and fuel cell vehicles based on their likely preponderance in the vehicle fleet by 2050. Section 3 concentrates on the UK policy in supporting the development and manufacture of electric vehicles (EVs) and Section 4 on the sustainability considerations resulting from current policy measures. Section 5 brings together the key findings and Section 6 concludes with final thoughts and direction for policy recommendations.

In terms of sustainability and emissions in particular, the transport sector is coming under increasing scrutiny. The ‘Paris Agreement’ of 2015 aims to hold the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognising that this would significantly reduce the risks and impacts of climate change (11). Transport, as the source of nearly a quarter of all Europe’s greenhouse gas (GHG) emissions (Figure 1), has become one of the focal points. This section focuses on technological improvements that are possible for passenger cars up to 2050 rather than on behavioural change or significant modal shift. The basis for this is that although their modal share would decrease by about 7% between 2010 and 2050, passenger cars will still represent about 67% of total passenger transport activity in 2050 based on European Union (EU) projections (13), whilst a UK study predicted a growth in overall road traffic demand of between 37% and 61% by 2050 (14).

Fig. 1.

In looking to reduce emissions from the road transport sector, the EU has taken regulatory action, which commits the automotive industry to reach a fleet average of 95 g CO₂ km^–1 by 2020 (15). Whilst the 2020 target can still be achieved without a radical industrial transformation, the 10 g CO₂ km^–1, calculated as the tolerable maximum in 2050 to stay below 2°C global warming (16), will require a much more radical departure from current technological trajectories. Technological innovation will play a major role in taking on this challenge.

Beyond 2020 and towards 2050, road transport vehicles are very likely to be propelled by a range of low-carbon technologies: battery electric and fuel cell electric propulsion; and varying degrees of hybridisation. Electromobility, either battery or fuel cell electric, will increasingly challenge the paradigm of internal combustion engine (ICE)‐based mobility, simply because it is technically impossible to increase the efficiency of ICEs to the levels needed to achieve the emissions requirements (17). However, due to the various political and technological uncertainties, it is far from clear how fast and how radical the market penetration of these alternative energy vehicles will be, even though most predictions and forecasts give them a preponderant role in 2050 (18).

2.1 Vehicle Penetration by 2050

2.2 Electricity Generation and Supply

2.3 Hydrogen as an Option?

The UK Climate Change Act, which became legislative in 2008, aims to reduce the emissions of all GHGs by 80% by the year 2050 (from a 1990 baseline). The importance of the transport sector in achieving this target is illustrated (Table II), with transport contributing one third of all UK CO₂ emissions in 2018 compared to just over one fifth in 1990.

To reduce transport related CO₂ emissions, the UK Government plans to phase out ICEs from new vehicle sales by 2040 and “has set ambitions to ensure that almost every car and van in the UK is a zero-emission vehicle by 2050” (37). However, these ambitions come with much uncertainty and the feasibility has been questioned.

Several risk factors will determine how quickly and deeply alternative energy vehicles will penetrate the UK vehicle mix and whether it will become a sustainable market segment. It is of strategic importance that industry understands these risks that can inform their research and development (R&D) investments. Alternative energy vehicles are a new product in a new industry and their radically different composition potentially means substantial change to production systems and value chains. The risk for industry in investing in the nascent value chain is compounded by competing alternative-vehicle technologies. Even though in the UK the government stance is to be technology neutral, government policies play a key role in how new technologies are supported by the wider stakeholder community (38). This will affect the quantitative nature of the risk and its perception in a significant way.

3.1 Creating a Competitive Electric Vehicle Manufacturing Sector

3.2 UK Government Policy in Support of Battery Development

The highly developed car industry is capable of producing sophisticated cars at low production costs. To reach the targets required to meet the Paris Agreement will require alternative drivetrain technology and for the industry the BEV is at present the most market viable solution. However, it takes courage to start the production of large numbers of EVs and the decision is not purely a technical one. It is a combination of science, technology, engineering and public policy that defines the type of EV that will be successful in the marketplace.

The current policy framework allows for a number of potentially divergent pathways. The one discussed in the previous section focused on improving the value proposition by reducing the cost of the high value components, in this case the battery, with the objective of aligning the cost of the EV to the present combustion engine incumbent. Examples of original equipment manufacturers (OEMs) that have adopted this pathway include Jaguar, UK, with its I-PACE, Tesla, USA, with the Model S, Model X and Model 3 and Chevrolet, USA, with the Bolt. Each combines existing approach to vehicle manufacture (materials and processes), hence realising a low-cost base vehicle platform, combined with a battery that has a high energy capacity and relative low cost (achieved through economies of scale associated with the battery manufacture). A further approach, exemplified by BMW, Germany, with its i3, is to increase the overall efficiency by reducing the vehicle weight through innovative manufacturing methods and material choices. This approach recognises that the customer requirement of increasing range and reducing cost can potentially be achieved by focusing on reducing the size of the battery: a lightweight vehicle can cover longer distances with the same battery capacity. A further, and more extreme approach to lightweighting, is the Ped-elec (Coventry University, UK). The dichotomy is that mobility concepts used in urban areas are, at present, extensions of those used outside of the urban environment. They are inherently less efficient. Ped-elec responds to a call for new personal mobility based on energy used per unit mass moved (50).

Based on adoption rate (sales of each vehicle type) it is clear that the industry is gravitating to one particular pathway, reducing the cost of the high value battery whilst retaining the existing approach to manufacture of the vehicle (materials and processes). The option of weight reduction (focusing on energy used per unit mass moved) is a higher cost approach relative to providing additional battery capacity to overcome the lower vehicle efficiencies. Indeed, the need to realise increasing economies of scales in the area of battery manufacture are worrying national governments (UK included) concerned that the battery manufacture will act as the nucleus around which the rest of the industry gravitates; presently the industry gravitates around the location where final assembly of the vehicle takes place. However, whilst this is the preferred option, is it the most sustainable?

EV manufacturing requires more energy and results in more carbon emissions than manufacturing a conventional car (51). A study conducted by the American Chemical Society (ACS) estimated that the Ford Focus EV (Ford Motor Company, USA) has 39% higher ‘cradle to gate’ emissions then a conventional Ford Focus (52). In fact, Ellingsen et al. stated that EVs of all sizes may require 70,000 km to become cleaner than conventional vehicles to make up the manufacturing debt (53).

Various studies on the growth in EV and hence the demand for raw materials required in battery manufacture highlight that certain key materials (such as cobalt, nickel and copper) are at risk from supply constraints. In response, development has begun looking at materials such as iron to replace the cobalt commonly found in batteries (54) whilst research activity into the recycling of battery packs is also a priority area of research. At present there are no facilities for recycling EV batteries in the UK. Processes such as hydrometallurgical recycling and leaching are currently seen as energy efficient methods of recovering spent battery materials, aiming to reduce the cost of recycled batteries metals. Currently research is being undertaken to recycle larger percentages of battery material, with some promising results. Natarajan reports that 99.9% of lithium, 98.7% cobalt and 99.5% of magnesium were leached out of a cathode with a purity of between 98.7% and 99.4% (55). Another study, related to lithium-ion phone batteries, saw 90.02% of cobalt and 86.04% of lithium restored to maximum concentration (56). These tests are currently resigned to laboratories and not available in the UK on a commercial scale. Whilst the metals recycled from EV batteries are deemed to be of sufficient quality to be used in new EV batteries with no performance issues, due to issues of cost, recycled lithium costing three times that of new lithium, and the individual material compositions of each EV battery, bulk battery recycling on a commercial scale is currently not considered economically viable.

Achieving the Sustainability Goal

In Section 2, the case for alternative energy vehicles as a response to meeting policy objectives was made. Although there is some uncertainty of the share of each technology in the powertrain portfolio, it is clear going forward that ICEs will represent only a small percentage of the total vehicle fleet or disappear altogether. It is further evident that there are multiple interest groups in the alternative energy vehicle market and that in preparation for the new mobility paradigm envisaged for 2050 investments will need to be made in new infrastructure and connectivity. Hence, there needs to be an orchestration of policy intervention to integrate issues of energy policy, transport policy and social policy.

In Section 3, there was a discussion around the policy support that the UK Government has in place to realise its ambition of a world leading UK alternative energy vehicle sector. It is clear that the industry, in transitioning to electrification, faces considerable risk. The industry chooses to leverage existing competencies in vehicle design and manufacture, and to achieve cost reduction and range improvements through a focus on the battery. In response the UK Government has put in place support for battery development, leveraging existing research competencies in this area by coordinating activities, and for battery manufacture by looking to attract inward investment and securing the future of automotive manufacturing in the UK.

In Section 4, the policies in support of transitioning to an alternative energy vehicle fleet on the one side and supporting the development of the UK capability in response were brought together in order to explore sustainability. The issue is that the way in which the industry responds to the challenge of emissions reduction creates a cleaner vehicle fleet, but does not necessarily consider optimising the efficiency or sustainability. The problem is that to square the circle – to meet the customer demand of increased range at reduced cost – the industry has looked to economies of scale at the manufacturing level and at the same time look for incremental improvements in the batteries. This enables vehicles to utilise larger batteries at less cost, but at the same time leads to heavier vehicles that fail to optimise efficiency and with increased energy demand can lead to stressing of the energy grid. A further problem is that larger batteries consume more materials and there is risk that certain material supply chains are being stressed and may not be able to respond to future demand, posing critical challenges regarding sustainability and security of supply chain. Whilst interventions, for example greater recycling and the retention of previously processed materials in the value chain, could influence this, the costs associated with these interventions would go counter to the objective of reducing the cost of the battery through economies of scale. Whilst lighter vehicles would be a move in the right direction, and a pathway exists for such vehicles within existing policy framework, the existing requirements for measuring the environmental performance of vehicles focus on emissions at the tailpipe and the move to electric drive removes a check on vehicle weight. Policy intervention is required to correct the above. This policy can target control of vehicle mass directly or can influence it indirectly through a move towards life cycle analysis of CO₂, each approach having its merits and challenges.

The transition to electrification of the vehicle drivetrain represents a considerable risk to the vehicle manufacturing sector. The UK has put in place policies to support both the production and research parts of the equation, but at the same time there is potential mismatch between the direction that is set by these policies and creating a sustainable road transport sector. New policies are required that orchestrate closer coordination across the separate policy areas: promoting lighter vehicles will reduce the stress on raw material supply chains; development of recharging networks will reduce range anxiety and align with the drive to reduce mass through enabling smaller batteries; and improvements in connectivity will lead to greater leverage of both vehicle and energy network capability.

The world is at the start of an energy revolution: the biggest energy transformation since the Industrial Revolution, during which the use of fossil fuels drove growth and prosperity, with global temperature increase implications that we have only started to understand relatively recently. This energy revolution will drive the world towards a lower carbon, more sustainable future, with major implications for energy and electricity generation, heating, industrial power and transportation. Governments, states and regions are proposing, and in some cases (such as the UK) committing to, net zero greenhouse gas (GHG) or carbon dioxide emission targets over the coming years. To date, 15 countries have set defined targets to become net zero economies by 2050 or earlier, with over 50 others, including Germany and Canada, discussing when to implement such a target. Perhaps most significantly, the European Union (EU) intends to be net zero by 2050: this objective is at the heart of the European Green Deal and in line with the EU’s commitment to global climate action under the Paris Agreement.

Interestingly, at the time of writing, around 49% of global gross domestic product (GDP) derives from nations and regions discussing, or with legislated, net zero emissions targets to be achieved by 2050 at the latest (1). Significantly, eight months previously this figure was only 16%, demonstrating the rapid rate at which such commitments are being made. Companies are also making net zero commitments, and this pace is accelerating too: in 2017, 87 companies made such commitments, in 2018 this rose to 174, and in 2019 398 companies announced net zero targets.

Figure 1 summarises the proportion of global fossil-derived CO₂ from each of the major sectors. While electricity generation is the largest contributor, the transportation sector comes second, accounting for around 23% of global CO₂ emissions.

Fig. 1.

Figure 2 looks into the transport sector in a little more detail, revealing that passenger road vehicles contribute almost half (45%) of transport CO₂, with freight vehicles accounting for another 30%, so road transport accounts for almost 75% of the emissions. The aviation and shipping industries also release large levels of CO₂, each at around 11% of global transport-derived emissions, with rail being a relatively minor contributor, at 1%. But to add a little context, these rail CO₂ emissions are around 0.1 billion tonnes per year, the same level as those of Belgium or Austria. Therefore, it is clear that transport has a critical role to play in the global decarbonisation agenda.

Fig. 2.

This special edition of the Johnson Matthey Technology Review looks at the challenges faced in the decarbonisation of the transport sector, and highlights the likely solutions that will be implemented to enable this transition. The articles consider the regulatory frameworks already in place, and those likely to come in the near future, to accelerate the moves to net zero across the transport ecosystem. The current status of the technologies that will play a key role in this transition is discussed, along with expected future developments and performance targets. It is clear that both battery-based and hydrogen fuel cell-based electric vehicles will make major contributions to the decarbonisation of ground transportation, across cars, vans, buses and trucks, and these technologies are discussed in detail. Challenges with the roll-out of the infrastructure for these new vehicles are also assessed, and the likely paths forward are presented.

Battery and fuel cell technologies are unlikely to see large scale uptake in the marine and aviation sectors in the foreseeable future, so here the focus is on the development and deployment of alternative, sustainable, lower carbon fuels which will replace the existing heavy fuel oil and aviation fuels, to mitigate carbon emissions from these two very large sectors.

Meeting net zero GHG emission targets within the transportation sector can only be achieved alongside clean generation of electricity and hydrogen, since these will be the fuels for the highest volume future transport modes (cars and trucks). Therefore, articles in this special edition also look at the changes required in electricity and hydrogen generation to enable the move to clean transport. Recall that electricity generation currently accounts for around 38% of global CO₂ emissions, so increasing the use of renewables and nuclear power are an essential piece of the net zero jigsaw puzzle.

This brings me to the final message: reducing transport CO₂ or GHG emissions to zero is not in itself enough to stabilise earth’s climate. It is a critical step, but needs to take place alongside the decarbonisation of the other major sectors: power generation, industry and building heating and cooling. There is a need for a cross-sector, systems-based approach, rather than looking at individual large emitters in isolation. The article on hydrogen looks at the role that it can play as an energy vector, enabling cross-sector coupling to facilitate the decarbonisation of transport, as well as other key areas such as domestic heating, industrial processes, and as a feedstock for low or zero carbon chemicals and fuels. It also discusses hydrogen’s use as a source of low carbon dispatchable power, as well as how it is a key enabler of significant increases in renewable energy or electricity generation. To reach net zero GHG emissions all the key sectors need to work together, and this special edition, though focused on transport, considers the other changes in the future energy ecosystem that link to, and in some cases enable, clean mobility.

For the past few decades, energy demand in the world has been rising considerably due to an increase in global population and demands for industrial production. The world has been undergoing a massive shift away from fossil fuels towards cleaner energy sources and hydrogen could be an excellent alternative for this purpose (1–3). PEMFCs powered by hydrogen have attracted much attention as a promising candidate for eco-friendly vehicles, i.e. FCEVs, owing to their high power density, high efficiency and zero emission features (4–10).

Since the world’s first mass production of Tucson ix35 FCEV by Hyundai Motor Company (hereinafter abbreviated as Hyundai) in February 2013, global automotive OEMs have also focused on commercialising FCEVs (11–15), including the latest manufacturing of the second generation FCEV (i.e. Nexo) by Hyundai in March 2018 (2). Specifically, Toyota Motor Corporation, Japan, unveiled a mass-produced FCEV, i.e. Mirai, in December 2014 (11, 12). The Mirai FCEV with a seating capacity of four persons employed two hydrogen storage tanks and hydrogen compression pressure of 70 MPa. To reduce contact resistance and improve water management in fuel cells, Mirai adopted three-dimensional fine mesh flow fields which were different from conventional flow fields composed of ribs and channels. In 2016, Honda Motor Company, Japan, also deployed a mass-produced FCEV, i.e. Clarity (13). The Clarity FCEV offered a seating capacity of five persons, two hydrogen storage tanks and hydrogen compression pressure of 70 MPa. In 2017, Daimler, Germany, launched a new generation of FCEV, i.e. Mercedes-Benz GLC F-CELL, with a hydrogen storage system similar to that of other automotive OEMs (14). In June 2018, Audi, Germany, teamed up with Hyundai to share intellectual property and components of fuel cells, with the aim of accelerating the commercialisation of FCEVs and expanding the global market (15). Accordingly, the global market for PEMFCs has been expanding to a broad range of applications including not only for vehicles such as passenger (i.e. sport utility vehicles (SUVs) and sedans) and commercial vehicles (i.e. buses and trucks) but also for trains, trams, forklifts, power generators and vessels. To meet the needs and requirements for these various applications, it is essential to develop more durable and cost-effective materials, components and systems for PEMFCs. Here we present the recent advances in hydrogen and PEMFCs technologies and address remaining technical challenges and barriers to be resolved, which are critical to commercialise next-generation PEMFCs and thus power the future society.

Hydrogen has been regarded as a promising candidate for alternative energy to fossil fuels because it is versatile and can be used in a broad range of applications such as transportation, chemicals, synthetic fuels and metals processing (16–30). Figure 1 shows the concept of wide-scale hydrogen production and utilisation suggested by the US Department of Energy (DOE) (21).

Fig. 1.

In addition, hydrogen is abundant in that approximately 70 million tonne-H₂ year^–1 is used today in pure form, mostly for oil refining and ammonia manufacture for fertilisers. A further 45 million tonne-H₂ year^–1 is used in industry without prior separation from other gases (22). One of the key features of hydrogen production is its diversity. Hydrogen can be produced by a variety of resources including fossil fuels such as natural gas and coal (with carbon capture and storage (CCS)), nuclear energy and renewable energy sources such as wind, solar, biomass, geothermal and hydroelectric power (16–30). Figure 2 shows an illustration of hydrogen production technologies suggested by the US DOE (25, 26). Most hydrogen is currently being produced by conventional ways based on fossil fuels (i.e. steam methane reforming (SMR) or natural gas reforming) which generate a significant amount of carbon dioxide emissions, resulting in ‘brown’ or ‘grey’ hydrogen. However, if the carbon dioxide emitted from the conventional SMR process can be captured and stored, or reused, the hydrogen produced is cleaner than grey hydrogen, which is often referred to as ‘blue’ hydrogen. The cleanest version of all is ‘green’ hydrogen which is produced by renewable energy sources such as wind or solar power, without generating carbon dioxide emissions (23–26). Although the share of green hydrogen produced by clean technologies is now relatively low, the production amount of green hydrogen is expected to increase considerably through water electrolysis powered by renewable energies, photoelectrochemical (PEC) and solar thermochemical hydrogen (STCH) techniques in the future as the hydrogen economy grows (3, 16–20, 23–26).

Fig. 2.

Hydrogen can serve as a versatile energy carrier and plays an essential role in decarbonising major sectors of the economy (27–29). In the power sector, the timing of variable electricity supply and demand is not well matched over the day nor between seasons, which increases the need for operational flexibility. For instance, the production amounts of renewables vary considerably between seasons. Solar generation in Europe is approximately 60% lower in winter than in summer, which coincides with higher electricity demand of about 40% as days become shorter and colder in winter than in summer (27, 28). Therefore long-term energy storage is necessary for large-scale renewable power integration and in this context hydrogen enables large-scale and efficient renewable energy integration through cost-effective long-term storage capability. Figure 3 shows the electricity supply and demand simulation results for Germany in 2050 (27). In this scenario of 90% renewables in Germany, curtailment of more than 170 TWh year^–1 is predicted for 2050, which is equivalent to approximately half the energy needed to fuel the German passenger vehicles with hydrogen. As shown in Figure 3, summer has curtailed periods of electricity oversupply, whereas winter has periods of electricity deficits, indicating strong mismatch between supply and demand of electricity produced by renewable energy sources (RES). Therefore, if we use water electrolysis to convert excess renewable electricity into hydrogen during times of power oversupply, the produced hydrogen can be used to provide back-up power during power deficits or can be used in other sectors such as transport based on fuel cells, industry or residential applications (21, 22, 27–29). In this way, hydrogen can bridge gaps in supply and demand of power and thus can serve as a long-term carbon-free seasonable energy storage medium (27, 28).

Fig. 3.

Hydrogen enables international energy distribution, linking renewable energy-abundant regions (for example, Australia or Norway) with those being deficient in renewable energies and thus requiring energy imports (for example, Japan or South Korea) since hydrogen can store and transport renewable electricity efficiently over long periods of time (27–33). For instance, Japan plans to launch the first technical demonstration of a liquefied hydrogen carrier ship to enter international trade in the near future (27–33). To date, hydrogen pipelines and gaseous or liquefied tube trailers are the most common ways of transport. As the distribution of hydrogen increases, the costs for liquefaction and transport are expected to drop by 30–40% by 2032 (27).

Here we address the recent paradigm shift of global automotive industry before going deep into the details of FCEVs powered by PEMFCs. Recently, while hydrogen has been receiving great attention worldwide and facilitating the energy transition from fossil fuels to renewable energies, the global automotive industry has been experiencing a paradigm shift from traditional internal combustion engine vehicles (i.e. gasoline- and diesel-powered vehicles) to next-generation vehicles based on future mobility concepts such as connected, autonomous, shared and electric (CASE) vehicles (also called autonomous, connected, electric and shared (ACES) vehicles) (34–36). Figure 4 represents an illustration of future mobility concept of Hyundai which is intended to provide ‘connected mobility’, ‘clean mobility’ and ‘freedom in mobility’ for customers.

Fig. 4.

The CASE technologies are closely interlinked with each other and to implement the future mobility concept, in particular, the combination of both autonomous and electric vehicles should be inevitable. The level of autonomy ranges from level-0 (i.e. no automation) to level-5 (i.e. full automation) (37–39). The electric vehicles powered by either batteries or fuel cells are generally well suited to autonomous vehicles. However, as the autonomous vehicles encounter the need for a higher level of autonomous driving technologies which normally require a rapid energy consumption of electric vehicles, the vehicles need more frequent electricity-charging for battery electric vehicles (BEVs) or hydrogen-refueling for FCEVs. In this case, FCEVs could be a better candidate for the platform of autonomous vehicles owing to their longer driving range: over 600 km (i.e. Nexo FCEV) and shorter refueling time, usually less than 5 min (40, 41).

To meet various demands and requirements for customers in the world, as shown in Figure 5, Hyundai has been developing a variety of clean and eco-friendly vehicles over the last decade, i.e. gasoline- and diesel-powered vehicles with improved fuel economy, hybrid electric vehicles (HEVs), plug-in HEVs and pure electric vehicles such as BEVs and FCEVs. And Hyundai has been increasing the share of electrification of the vehicles. In general, BEVs and FCEVs have different strengths that complement each other in that BEVs are more adequate to shorter driving range applications, while FCEVs have a more competitive edge in heavier and longer driving range applications such as buses and trucks.

Fig. 5.

Recently, Hyundai has been actively increasing its commitment to commercialising FCEVs due to their versatile potential in the future power systems, which will be discussed in detail in the following section.

Figure 6 shows the history of FCEV development of Hyundai since 1998. Hyundai developed a proprietary in-house 80 kW stack system in 2004 and since then Hyundai has achieved significant advancements in FCEV commercialisation technologies, finally launching the world’s first mass-produced FCEV (i.e. Tucson ix35: the first generation FCEV) in February 2013, followed by the manufacturing of the second generation FCEV (i.e. Nexo) in March 2018, whose features will be discussed later in more detail.

Fig. 6.

Figure 7 shows a photo and a package layout of the world’s first mass-produced Tucson FCEV of Hyundai. The Tucson FCEV employed an existing internal combustion engine vehicle’s platform. A 100 kW fuel cell stack was located in the engine bay. The vehicle adopted a battery system with 24 kW and two hydrogen storage tanks with a capacity of 5.64 kg-H₂, leading to a driving range of 415 km according to fuel economy tests in Korea. The Tucson FCEVs were deployed in 18 countries worldwide.

Fig. 7.

Through the technical expertise for manufacturing Tucson FCEV since 2013, Hyundai had improved significantly the PEMFC technologies and finally commercialised the second generation of the mass-produced Nexo FCEV in March 2018, with improved performances and durability compared with its predecessor. Figure 8 shows an overview and general features of the Nexo FCEV. In contrast to the Tucson FCEV which had to use an existing internal combustion engine vehicle’s platform, the Nexo FCEV was built on a newly developed and fully dedicated vehicle platform, which renders it higher power and improved driving dynamics than the Tucson FCEV. Figure 8(a) shows the new design of Nexo which was optimised to reduce the drag coefficient from 0.35 (Tucson) to 0.33 (Nexo). Multiple aerodynamic features were discreetly integrated into the front, side and rear areas of the Nexo. As shown in Figure 8(b), the Nexo also performs a remote smart parking assist function which allows the vehicle to autonomously park or retrieve itself from a parking lot.

Fig. 8.

On top of that, a variety of advanced driver assistance system technologies such as the blind-spot view monitor, the lane-following assist and the highway driving assist systems were implemented into the Nexo FCEV to facilitate safe driving. As shown in Figures 8(c) and 8(d), the interior of Nexo features the wide black dashboard that houses two large liquid-crystal displays to hold the digital instrument cluster (left) and the navigation system (right). Figure 8(e) shows the overall package layout of the Nexo FCEV. It primarily consists of an integrated power module with a fuel cell stack and a balance of plant (BOP) system, a motor with maximum torque of 395 N m, three hydrogen storage tanks with a capacity of 156.6 l and 6.33 kg-H₂ and a battery system with a power of 40 kW and an energy capacity of 1.56 kWh.

Figure 9 shows an enlarged view of the integrated power module of the Nexo FCEV. The integrated power module is mainly composed of a 95 kW fuel cell stack and a BOP system consisting of fuel (hydrogen) processing, thermal management and air processing systems. The fuel cells in the Nexo’s stack employ advanced membrane-electrode assemblies (MEAs) with perfluorinated sulfonic acid ionomer-based reinforced membranes and platinum-based electrodes, carbon fibre paper-based gas diffusion layers (GDLs) with microporous layers, metallic bipolar plates and elastomeric sealing gaskets. The BOP system is also of great importance to achieve improved performances, enhanced durability and reduced cost of the Nexo FCEV. The fuel processing system mainly consists of hydrogen supply lines and hydrogen-related sensors, and the air processing system is primarily composed of air humidifier, air compressor and other components. The thermal management system includes cooling-related valves and sensors.

Fig. 9.

Table I summarises key features between Tucson and Nexo FCEVs of Hyundai. Both FCEVs placed their stacks in the front engine bay instead of under the floor and employed hydrogen compression pressure of 70 MPa, hydrogen refuelling time of less than 5 min and a seating capacity of five persons. The Nexo FCEV adopts a variety of proprietary fuel cell components and systems as well as advanced vehicle operation technologies as summarised in Table I. In comparison with its predecessor Tucson FCEV, as listed in Table I, the motor power of the Nexo FCEV increased significantly from 100 kW to 120 kW. Most importantly, the durability of the Nexo FCEV approximately doubled from 4 years/80,000 km to 10 years/160,000 km and the driving range on a single charge increased considerably from 415 km to 609 km, to the authors’ best knowledge, which should be unprecedented among all mass-produced electric vehicles commercially available to date. The cold start-up capability in wintertime had been limited due to the freezing of water produced intrinsically during the oxygen reduction reaction (ORR) at the cathode of PEMFCs and thus challenging to a wide adoption of FCEVs on the real road worldwide. As for the Nexo FCEV, however, the cold start-up capability was greatly improved from −20°C to −30°C, facilitating the vehicle’s market penetration in the world. The system efficiency of the Nexo improved from 55% to 60% as a result of enhanced performances of fuel cell components and systems. The acceleration time from 0 to 100 km h^–1 of the Nexo decreased by 3.3 s, i.e. from 12.5 s to 9.2 s and the maximum vehicle speed increased from 160 km h^–1 to 177 km h^–1. Thanks to the newly developed and fully dedicated vehicle platform, the Nexo FCEV can adopt three hydrogen storage tanks, which enable a larger internal volume of hydrogen tanks from 140 l to 156.6 l and a higher hydrogen storage capacity from 5.64 kg to 6.33 kg, which has contributed to the long driving range of Nexo.

One of the biggest obstacles standing in the way of wider adoption of FCEVs worldwide is the safety concern about hydrogen. Therefore it is of paramount importance to verify the safety of hydrogen storage system in FCEVs. For the past two decades, Hyundai has done a lot of front, rear and side crashworthiness tests on FCEVs as shown in Figure 10. Figures 10(a), 10(b) and 10(c), 10(d) represent the front and rear collision tests of the Nexo FCEV, respectively. In the rear collision or crash test, the vehicle was placed on the transparent test plate underneath which a camera was located. A mobile barrier crashed against the FCEV at the rear end, which caused damage and deformations of hydrogen storage system in the FCEV. Despite the deformations after the collision test, there was no leakage out of the tanks, verifying the safety of the hydrogen storage system. In 2018, the Nexo FCEV was awarded the highest rating in safety from the European crashworthiness test, i.e. European New Car Assessment Programme (Euro NCAP).

Fig. 10.

To date the global markets for PEMFCs for a variety of FCEV applications have been growing very rapidly in terms of both passenger vehicles and medium- and heavy-duty vehicles such as buses and trucks, which require much higher durability than passenger vehicles, i.e. 5000 h for passenger vehicles vs. 25,000 h for heavy-duty vehicles (21, 42, 43). In addition to automotive applications, the PEMFCs are also in demand for other applications such as fuel cell electric trains. Figure 11 shows transportation applications of BEVs, FCEVs, biofuels and synthetic fuels-powered vehicles suggested by Hydrogen Council (27). The FCEVs are expected to occupy the markets of medium- to large-sized passenger vehicles, commercial vehicles including buses and trucks, and even trains.

Fig. 11.

Recently, the concept of commercialising fuel cell electric trains and trams has been materialising in the world. For instance, as an alternative to diesel-powered trains, Alstom Company, France, launched the world’s first passenger train powered by hydrogen fuel cells, i.e. Coradia iLint^TM, to offer commercial passenger service in Germany in September 2018 (44, 45). The Coradia iLint^TM fuel cell electric train was specially designed for operation on non-electrified lines, enabling clean and sustainable train operation while ensuring high performances with a maximum speed of 140 km h^–1. Another commercialisation project of eco-friendly trams powered by PEMFCs has been underway by Hyundai Rotem Company in collaboration with Hyundai Motor Company in South Korea since June 2019 (46). The project plans to develop a low-floor fuel cell electric tram which can travel up to 200 km at a maximum speed of 70 km h^–1 on a single charge by late 2020.

In addition to the role of PEMFCs for transportation applications, another interesting potential of PEMFCs is their capability to produce electricity as a power generator using hydrogen energy. Accordingly, over the last few years, the potential of PEMFCs in FCEVs as distributed power suppliers has received great attention worldwide. Figure 12 shows an illustration of the distributed power generation concept by PEMFCs in FCEVs. The FCEVs can produce approximately 10 kW under idling conditions, which can be used to provide electricity for houses and buildings.

Fig. 12.

To validate and demonstrate extensively the distributed power generation concept by PEMFCs in FCEVs and thus increase public awareness on this aspect, a vehicle-to-grid (V2G) demonstration project (i.e. Hydrogen Electric House project) using Hyundai’s Tucson and Nexo FCEVs has been progressing in South Korea since August 2017. Figure 13 shows the Hydrogen Electric House project in South Korea. The FCEVs can supply electricity, heat and water for the Hydrogen Electric House.

Fig. 13.

The FCEVs also can provide back-up power for people in emergency regions such as earthquake and typhoon disaster areas. In addition it can be used as an electricity charger for BEVs and plug-in HEVs.

Recently, a similar demonstration project showing the V2G technology through integrating an FCEV with photovoltaic power and a residential building was reported in the Netherlands to implement a net zero-energy residential building concept (47). This project showed that utilising an FCEV working in V2G mode could reduce the annually imported electricity from the grid by approximately 71% over one year and aid the buildings in the microgrid to implement the net zero-energy building target.

Another feature of interest of FCEVs differentiating themselves from other types of vehicles is their capability to clean the outside air and thus mitigate air pollution in society (2). Similar to BEVs, the FCEVs do not emit any air pollutants and particulate matter (PM) out of the vehicles while driving on the road. Unlike the BEVs, however, the Nexo FCEV of Hyundai employs an advanced air filter to filter out most of the fine dusts and micro-sized PM in the outside air, enabling to provide purified oxygen from air for the cathode in fuel cells.

On a basis of this positive perspective on hydrogen and PEMFCs, Hyundai announced its investment plan for PEMFCs and FCEVs to the public as the ‘FCEV Vision 2030’ in December 2018. According to this plan, Hyundai will invest US$6.9 billion and produce 700,000 PEMFC systems by 2030: specifically, 500,000 PEMFC systems for automobiles and 200,000 PEMFC systems for other applications such as forklifts, trams, trains, power generators and vessels, as shown in Figure 14.

Fig. 14.

To realise the vision for hydrogen economy through hydrogen and PEMFCs, the fuel cell industry, investors and governments in the world will need to ramp up and coordinate their efforts (27–29). And in order to facilitate the commercialisation of next-generation PEMFCs for a broad range of applications, from the technical point of view, it is of paramount importance to develop more durable and cost-effective fuel cell materials, components and systems as well as advanced fuel cell operation techniques. Here we address several key challenges to be overcome in the future.

Even though there have been extensive efforts to increase hydrogen refuelling infrastructure worldwide over the last decade, the infrastructure is still scarce to deploy the FCEVs, in particular passenger vehicles, sufficiently on the real road. Therefore, to reduce the dependence on the hydrogen refuelling infrastructure, it is necessary to turn our attention to other applications that are less dependent on the number of hydrogen refuelling stations (HRSs). These applications include trams, trains and medium- to heavy-duty commercial vehicles such as fuel cell electric buses (FCEBs) and trucks. For instance, the ideal locations for HRSs of FCEBs are regarded as the bus depot, which allows to estimate the HRS location precisely and thus minimise the cost for HRS construction, indicating no infrastructure requirements on the operation routes (23, 48–50). Fuel cell electric trucks, trains and trams appear to be in a similar condition. For an FCEB to become commercially competitive, however, it is of great importance to develop highly durable fuel cell materials, components and systems first, followed by a drastic reduction of cost, since the durability requirements for FCEBs are much higher than those of passenger vehicles such as SUVs and sedans. It was reported that ultimate lifetimes of an FCEB and its power plant should be approximately 800,000 km and 25,000 h, respectively (42, 43, 48–50), which are five times longer than that of ordinary passenger vehicles. Among core components of PEMFCs for FCEBs, the membrane failure due to pinhole formation seemed to be critical to the lifetime of FCEBs (42), requiring highly durable membranes in terms of both chemical and mechanical durability.

In the case of cathode catalysts for PEMFCs, over the last two decades, extensive research works have been performed to develop durable and cost-effective ORR catalysts with lower Pt loadings (4–6), i.e. highly active Pt-based core-shell catalysts. As pointed out clearly in the literature (5), however, intensive research efforts on developing more durable and reliable electrodes using these novel catalysts should be further exerted, since not all promising ORR activity of catalysts based on typical rotating-disk electrode (RDE) test results have translated into real-world MEA performance, causing a great mismatch between RDE and fuel cell data.

As for the anode catalysts for PEMFCs, it is necessary to develop more effective cell voltage reversal-tolerant anode (RTA) based on oxygen evolution reaction (OER) catalysts. Figure 15 shows a schematic illustration of PEMFC operation under normal conditions with sufficient hydrogen supply for the anode and abnormal conditions of hydrogen starvation at the anode (52).

Fig. 15.

As reported in the literature (51–59), the durability of FCEVs can be significantly reduced by insufficient hydrogen oxidation reaction due to hydrogen starvation at the anode at both normal (i.e. 60~90°C) and subfreezing operation temperatures, which would eventually cause cell voltage-reversal problems. To mitigate the cell voltage-reversal degradation, a variety of system and operation control strategies, i.e. gas purging of anode compartment to remove accumulated nitrogen or water at the anode (60, 61), have been developed over the past decades. However, these techniques could limit the vehicle performance and make the vehicle system and operation more complicated. Therefore, as an alternative, material-based approaches have been suggested through adding OER catalysts to the anode, leading to an RTA (51–59). However, despite the recent progress on reducing cell voltage-reversal degradation through various techniques described above, it is not still sufficient to guarantee long-term reversal-tolerant durability and thus requires more robust and stable RTAs under acidic operation conditions of PEMFCs as well as much simpler and more effective system control technologies.

It is also critical to understand better the difference between the pristine and aged structures of fuel cell materials and components, i.e. membranes and electrodes in MEAs, GDLs and bipolar plates, on both micro- and nanoscales since the performance and durability of PEMFCs are closely related with these structural features. Therefore it is essential to develop more advanced imaging techniques, i.e. three-dimensional nanoscale X-ray computed tomography (62–64) and electron tomography performed in a high-angle annular dark-field scanning transmission electron microscope (65, 66) and correlate the imaging results with the performances and durability of actual fuel cells.

PEMFCs powered by hydrogen have received much attention as a promising candidate for FCEVs owing to their high power density, high efficiency and zero emission features. Hyundai commercialised the world’s first mass-produced Tucson ix35 FCEV in 2013, followed by the manufacturing of the second generation Nexo FCEV in 2018. To date, other global automotive OEMs, i.e. Toyota, Honda, Daimler and Audi, have also focused on commercialising FCEVs, which leads to an expansion of the global market of PEMFCs for a broad range of applications. Hydrogen is regarded as an excellent alternative to fossil fuels. In comparison with the existing grey hydrogen produced by conventional fossil fuels, the share of green hydrogen produced by excess renewable energies is expected to increase considerably in the future. Hydrogen can serve as a versatile energy carrier and plays an essential role in decarbonising major sectors of the economy.

Recently the global automotive industry has been experiencing a paradigm shift from traditional internal combustion engine vehicles to next-generation vehicles based on future mobility concepts such as CASE. These technologies are closely interlinked with each other. The FCEVs could be a strong candidate for the platform of autonomous vehicles owing to their longer driving range over 600 km and shorter refueling time usually less than 5 min.

Over the last decade, Hyundai has been actively increasing the commitment to commercialising FCEVs due to their versatile potential in the future power systems. In comparison with its predecessor Tucson ix35 FCEV, the durability of the Nexo FCEV approximately doubled from 4 years/80,000 km to 10 years/160,000 km and the driving range on a single charge increased considerably from 415 km to 609 km. The cold start-up capability of the Nexo FCEV was greatly improved from −20°C to −30°C. The Nexo FCEV was also awarded the highest rating in safety from the European crashworthiness test.

The global markets for PEMFCs have been growing very rapidly in terms of both passenger vehicles and medium- and heavy-duty vehicles such as buses and trucks, which require much higher durability than passenger vehicles. The PEMFCs are also in demand for other applications such as trains, trams, power generators and vessels. Hyundai will produce 700,000 PEMFC systems by 2030. To realise this vision, it is of paramount importance to develop more durable and cost-effective fuel cell materials, components and systems as well as advanced fuel cell operation techniques. It includes the development of highly durable membrane, more cost-effective cathode catalysts, RTA and advanced imaging techniques.