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1 Introduction

Looking back at the last decade, the automotive industry is under increasing pressure to develop innovative and environmentally friendly drive technologies. In order to realize the ambitious and regulatory framework conditions of carbon dioxide reduction (CO2) by the year 2030, research is being conducted into electrifying drive solutions. The future viability of fuel technology is controversially discussed in this context [1].

When comparing the sustainability of different drive technologies, life cycle analyses are carried out in which the occurring CO2 emissions are considered along the manufacturing, utilization and recycling phases. With regard to the utilization phase, battery- and hydrogen-powered electric vehicles do not emit any direct emissions [2].

In this context, the sustainability of passenger cars and light commercial vehicles is measured on the basis of the CO2 emissions emitted during the utility phase in grams per kilometer, with high penalties having to be paid if set limit values are exceeded [3]. On July 14, 2021, the EU Commission presented a ban on the sale of new cars with internal combustion engines from 2035 in its climate plans.

In order to maintain competitive in drive technologies, the field of future Fuel Cell (FC) technology must be caught up. Existing obstacles along the lifecycle must be analyzed and proposals for action must be made. In order to be able to use FC technology sustainably and comprehensively and thus contribute to more climate-friendly mobility, the potential for optimization along the FC life cycle must be continuously analyzed. With the help of questions on the weaknesses of the technology with interview partners from research, industry and politics, concrete measures for action are to be developed within the framework of a strategy paper. Within the framework of this paper, a sustainability strategy is developed, in which proposals for action are listed for achieving the selected milestones for increasing the sustainability of FCs. These proposals for action are primarily intended to answer the research questions of CO2 emission reduction and the sensible use of automobiles powered by hydrogen. The strategy paper results from the knowledge gained from the life cycle meta-study as well as the analyzed interview responses from FC experts. The strategy paper is intended to provide an overview of the aspects of sustainability enhancement along the FC life cycle.

2 Life Cycle Analysis on Fuel Cells

Life cycle analysis is used to record and assess the environmental impact from cradle to grave, i.e. from the extraction of raw materials to the manufacture, use and disposal of the product. The method of life cycle analysis aims to provide information on resource consumption and emerging pollutant emissions from product manufacture, usage and disposal. Life cycle analysis consider possible environmental damage over the entire product life cycle and are used for decision-making. The standardization of the LCA methodology was recorded by the International Organization for Standardization within the framework of the ISO 14040 (ISO 2006a) and ISO 14044 (ISO 2006b) standards. In the following, 13 life cycle analyses that are relevant for FCs are further analysed. Studies with life cycle analyses published in the period 2015–2021 are examined. In addition to fuel cell drives, the life cycle analyses examined other drive technologies in order to make a comparison with conventional or purely electric drives. A further meta-analysis is necessary since no life cycle analysis covers the emissions of all five life cycle phases of an automobile with PEM fuel cell drive.

According to an analysis by SIMONS, achieving large reductions in the life cycle emissions of FC vehicles (FCVs) requires that the environmental impacts are consistently lower than for internal combustion vehicles (ICVs). The analysis shows very clearly that powering FCVs with hydrogen produced from fossil resources (directly or indirectly via electrolysis) offers no environmental benefits compared to gasoline vehicles from a life cycle perspective [4].

Platinum and carbon fibers were identified by MIOTTI et al. as the most important sources of environmental impact in FCVs. For platinum, a combined effort to reduce pollution and increase recycling rates can significantly reduce these impacts. For carbon fibers, recycling becomes more problematic. Therefore, a reduction in material use and a simultaneous increase in production efficiency will have to occur [5].

According to LI et al., the well-to-wheel (WTW) energy efficiency of FCVs using hydrogen from solar solid oxide electrolysis cell (SOEC), solar thermochemical, and nuclear SOEC systems is comparable to that of Battery electric vehicles BEVs [6].

Favorable results were calculated by AHMADI et al. for switching from conventional gasoline vehicles to hydrogen FCVs, based on a significant reduction in greenhouse gas emissions (72%), complemented by significantly reduced life-cycle fuel costs. In addition, FCVs have no harmful emissions during vehicle operation, which could contribute to a noticeable improvement in air quality in urban areas. The estimated life-cycle energy consumption of the hydrogen FCV was 21% higher than that of the gasoline vehicle due to the higher energy required for hydrogen production, distribution, and delivery, as well as for the vehicle's material production [7].

The results of a study by PREVEDEOUROS reinforce the position that transportation policy should be dynamic to reflect changes in vehicle fleet and regional data, to support clean technologies and renewable energies, and to complement existing transportation regulations. FCVs have the lowest CO2 emissions at 260 g per passenger-mile [8].

The environmental benefits of using hydrogen in the use phase of the FCV were highlighted by EVANGELISTI et al. The FCV shows significant advantage in the utility phase compared to the other technologies. However, the reduction of environmental impact in the production of FCVs is necessary. It is still an important challenge that needs to be addressed in the coming years [9].

In 2030, according to MEYER et al. the platinum demand for the FCVs and the catalytic converters is ca. 110 tons. Platinum is already very well recycled today. Global platinum demand is covered to 23% from secondary material. The end-of-life recycling rate for platinum in the vehicle sector is over 50%. The use of recycled material originating from the mobility sector significantly dampens the demand for primary material [10].

The hydrogen FCV selected for the study by KARAASLAN et al. did not show any promising advantages over combustion engine propulsion, either in terms of emissions or consumption. This is due to the fact that the process of hydrogen production emits a considerable amount of greenhouse gases even when using the energy path of electrolysis as opposed to the combustion of natural gas. In addition, the electricity used in this pathway is converted to hydrogen and then back to electricity within the fuel stacks, making this energy pathway much less efficient than that for electric vehicles [11].

An analysis by ZAPF et al. shows that, except for THG emissions, there has already been a significant reduction in passenger-mile or specific car emissions in Germany in the past. The CO2 emission reduction of about 15% was cancelled out by 2017 by an increase in passenger car traffic in Germany, so that total CO2 emissions from passenger car traffic increased by 0.5% between 1995 and 2017 [13].

The study by the Fraunhofer Institute for Solar Energy Systems ISE identified in its life cycle analysis that FC cars are the most climate-friendly. Here, the emissions for passenger vehicles of different drives were compared over a mileage of 150,000  km [12].

The more the share of renewable energy increases, the production costs of FCVs decrease, and the required range of BEVs increases, the more the competitiveness of FCVs increases compared to BEVs in terms of cost and environmental impact. Provided that the electricity mix has a low CO2 intensity, it is recommended to promote BEVs for short-distance and delivery transport (e.g. parcel services) and FCVs for long-distance passenger and freight transport [13].

According to COX et al., only in areas with very clean electricity (below 200 g CO2eq/kWh) do FCVs powered by hydrogen from electrolysis offer climate benefits compared to ICVs [14].

Based on the assumption that there will be 100% renewable energy generated by today's plants in 2050, according to LOZANOVSKI et al. the Catenary electric vehicle has the lowest greenhouse gas emissions, followed by the BEV. The FCEV is in the middle range and the internal combustion vehicles have the highest GHG values [15].

3 Hypotheses for Sustainability Optimization

Based on the state of the art and the comparison of the life cycle analyses, three hypotheses are established for each life cycle step. The selected hypotheses are discussed with experts through directed questions. In case of validation, strategy points can be drawn inferentially from the hypothesis. In Table 1, three potential hypotheses per life cycle phase are explained. The prioritization (1–3) is based on a qualitative literature analysis and serves to focus a hypothesis and thus strategy approach. Regards to the extensive subject area and the diverse backgrounds of the experts and stakeholders, a draft strategy for increasing the sustainability of the entire life cycle can be defined in a targeted and comprehensible manner. This minimizes the risk of deviation from the overall topic and a one-sided focus on certain phases. The hypotheses that have not been prioritized can be scientifically processed by means of an empirical investigation and a selection of further experts.

Table 1. Hypotheses for each life cycle step.
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4 Expert Interviews and Strategies on Fuel Cells

As part of the expert selection process, a total of 54 potential interview partners were contacted and requested for an interview with a brief introduction to the research project. Thirteen experts agreed to an interview (Table 2). In selecting the individual experts, attention was paid to the diversity of the fields of action of the various players.

Various hypotheses for increasing the sustainability of the PEM FC life cycle emerged from the state of the art and the comparison of the life cycle analyses (Table 1). The interview questionnaires developed and interviews conducted serve to collect internal knowledge from the experts with regard to the hypotheses established. The interview questions were adapted to the expertise of the respective expert.

The statements of the interview partners are assigned to the categories of production, hydrogen production, hydrogen infrastructure, utilization and end-of-life. In a qualitative content analysis, an evaluation of expert statements is carried out and measured on the basis of internal and external quality criteria. The internal quality criteria include intersubjective comprehensibility, credibility, regularity, and auditability. External quality is measured by the possibility of generalization and transferability.

The composition of the elements from the state of the art, the meta-study of the life cycle analyses and the expert interview statements results in strategy points and milestones. In terms of a holistic approach, the areas of production, hydrogen generation and infrastructure, utilization and end-of-life are considered for strategy points and milestones (Fig. 1). For the elaboration of the strategy points, the knowledge gained from the state of the art, the meta-study of the life cycle analyses as well as the interviews were used. The goal of the strategy is to increase the sustainability of hydrogen-powered vehicles during market entry and expansion. The advantages of the emission-free tank-to-wheel balance when using green hydrogen must be weighed against the CO2 emissions of the infrastructure expansion. The critical components are the remaining CO2 budget to achieve the 1.5 ℃ climate target and the short time period to undercut total emissions compared to maintaining conventional vehicle powertrains. To achieve the best “operating point”, a milestone to be reached is defined for each life sector.

Table 2. Interviewed Experts
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An iterative process would be necessary to check the progress and practicability of the sustainability strategy. In analogous sustainability strategies, the developed points are evaluated in various constellations of actors and stakeholders from politics, research, industry and citizens’ initiatives. The preparation of an independent preliminary, targeted study appears reasonable, in order to obtain a broad view of the existing conditions and possible problem areas. The regulatory, financial or idealistic obstacles should be openly discussed in order to be able to initiate improvements. In practice, it has been shown that constant evaluation and regular adaptation of a strategy are useful for achieving milestones in terms of content and in a timely manner. There is no guarantee for the success of sustainability strategies due to the complex and multi-layered nature of the topic regarding the desired change in transport and the current inertia of established structures.

Fig. 1.
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Strategy points and milestones for fuel cell vehicles

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5 Summary

From the state of the art as well as the comparison of the life cycle analyses, hypotheses can be derived for the sustainability increase of the PEM fuel cell life cycle. Complemented by the knowledge gained from interviews with experts, the hypotheses can be used to establish 5 strategy points and milestones. These are based on production, hydrogen generation, hydrogen infrastructure, utilization, and end-of-life.

Major progress has already been made in production by fully automating the series production of a PEM FC system. A remaining challenge is the investment security, that must be created in order to enable large-scale production of PEM FCs. For hydrogen generation, as a result of the increased use of renewable energies for power generation, the electricity peaks that occur could be used to generate green hydrogen from the electrolysis of water. In the interviews, it is regretted, that one hundred percent green hydrogen cannot be distributed at the hydrogen fuel stations due to a lack of supply. The construction of the existing hydrogen infrastructure resulted in emissions that must be deducted from the remaining CO2 budget of the energy sector. When the sustainability of the PEM FC life is considered holistically, there is the potential of emission savings. The sustainability enhancement of the transport sector by 2050 is predominantly focused on the use of battery electric vehicles, although municipalities could convert their commercial vehicle fleets to PEM fuel cells in sensible business cases. The lack of a foreign purchase market requires necessary investments in local recycling structures in case of increasing return rates or creative leasing systems of the PEM fuel cells at end-of-life.

In summary, the sustainability strategy includes the promotion of knowledge transfer regarding the manufacturing processes as well as an investment security, sector coupling projects in the field of hydrogen production, an expansion stop of the refueling station infrastructure, the focus on the use in public transport and finally a leasing and tracking system of the PEM fuel cells.