Life Cycle Assessment of the Domestic Micro Heat and Power Generation Proton Exchange Membrane Fuel Cell in Comparison with the Gas Condensing Boiler Plus Electricity from the Grid

Electricity and heat generation are the largest sources of global greenhouse gas emissions worldwide, accounting for about 55% [1,2]. The residential sector accounts for 39% of global final energy consumption in buildings and industry [3]. The majority (82%) of the total primary energy demand in the EU residential sector is consumed for space heating and hot water supply [4,5]. In line with the goals of the European Union of “improving energy efficiency” by 27% in 2030 and “reducing greenhouse gas emissions” by 40% in 2030 compared to 1991, the minimum efficiency requirements within the Ecodesign legislative framework and the EU Energy Label [6,7,8] have proven to be effective. Another effective tool of eco-design, which has been gaining importance in recent years, is life cycle assessment (LCA), which allows for the quantitative assessment of the life cycle environmental performance of products and can be used by manufacturers and developers to design more sustainable and energy-efficient products, as well as by the government to support decision-making for legislation [9].

In addition to energy efficiency, increasing the share of low-emission energy technologies is another way to optimize the environmental impact of the energy sector [10]. However, the market for heating appliances continues to be dominated by fossil fuel-based appliances and less efficient conventional electric heating technologies, which account for almost 80% of new sales [11]. Sales of heat pumps and renewable heating devices such as solar hot water systems have nevertheless increased, accounting for more than 10% of total sales in 2019. To be in line with the International Energy Agency’s (IEA) sustainable development scenario (SDS), the share of low-emission heating technologies, such as heat pumps, district heating, and renewable and hydrogen-based heat, must increase to 50% of sales by 2030 [11,12]. Among various clean energy supply technologies, fuel cells (FC) seem to be a promising alternative to conventional energy supply systems because of relatively high energy efficiency and low emissions [13,14,15,16]. Several support packages were developed in Europe, generally, and especially in Germany to encourage the residential use of fuel cell technology. Consequently, more than 1000 systems have been built in 10 countries, with the largest number of installed units in Germany [6].

Bachmann et al., 2019 conducted the LCA of residential fuel cell micro heat and power cogeneration (FC-µCHPs) and compared it with a stand-alone gas condensing boiler (GCB) and a heat pump (HP) [17]. For the assumed full loading hours (FLHs), relevant environmental impacts, including global warming potential, were generally smaller for the FC-µCHPs than for the HP and the stand-alone GCB [17]. Notter et al., 2015 conducted a comparative cradle-to-grave LCA of two types of Proton-exchange membrane fuel cell (PEMFC) applications: PEMFC µCHP (with carbon black (CB) and multiwalled carbon nanotubes (MWCNTs)) and Stirling engine. Their findings are that platinum is the key material in HT-PEMFCs, whereby the benefits from platinum savings outperform the burdens from MWCNT production. Furthermore, they found out that both µCHP plants (PEMFC and Stirling engine) have comparable environmental impacts. However, the PEFMC produces more electricity and less heat as compared to the Stirling engine. System expansion in the way that both plants produce an equal amount of electricity and heat resulted in an advantage of 20%. Points ReCiPe for the PEMFC [18]. Other LCA studies show that FCs are only more environmentally friendly and efficient in comparison to conventional systems if the operation or use phase is considered [19,20]. The main role here is fuel sourcing, where hydrogen production causes environmental impacts. Concerning the manufacturing phase, the same applies to electrode materials, where, in many cases, either a noble metal such as platinum or other precious metals or costly materials are used [19,20]. Stack optimization and research for eco-friendly materials are important steps to achieve this goal [21]. Furthermore, the results of Lotrič et al., 2021 and Mori et al., 2021 show that the environmental impacts of the manufacturing phase could be substantially reduced by recycling the used device components and materials [22,23]. The authors pointed out the importance of critical materials—in this case, the platinum-group metals (PGMs) by comparing the end-of-life phase with and without the recycling of PGMs. The comparative LCA results showed that the environmental impacts increase in the case of both systems (alkaline water electrolyzer (AWE) and proton-exchange-membrane water electrolyzer (PEMWE)) because of the larger quantity of PGMs compared to the scenario without the recycling of PGMs [22]. Also, Riemer et al., 2023 [24] conducted a comparative LCA study on commercial state-of-the-art PEMFC with high and low platinum content and a novel technology called anion exchange membrane fuel cell (AEMFC) regarding PGM loading, cell performance, and lifetime. The authors’ findings were that the PEMFC outperforms the AEMFC from an environmental point of view despite the lower PGM loading of the AEMFC. Increasing the performance and lifetime of AEMFC resulted in a lower or comparable environmental impact than a PEMFC in 17 out of 27 of impact categories, including climate change. The main contributors to the environmental impact of both systems are platinum in the electrodes, chromium steel in the bipolar plates, and polytetrafluoroethylene (PTFE) in the gas diffusion layer [24]. Parise et al., 2005 conclude that there is still a long way to go for the widespread use of fuel cells, which depends on cost, efficiency, and life expectancy [15,21,25]. According to the reviewed literature, the durability of the PEMFC for stationary application may vary between ca. 40,000 and 80,000 h [3,26]. As stated in the literature cited by Dhimish et al., 2021, there could be a linkage between the degradation rate due to low voltage produced by the fuel cell and the membrane temperature [25]. As stated by Yan et al., 2023, the large-scale commercialization of PEMFCs requires higher power and current densities; however, at high operating current densities, the massive accumulation of liquid water will lead to flooding and impede the gas diffusion, resulting in rapid degradation of cell performance. Accordingly, improving the water management ability is imperative for pursuing better cell output performance [27]. Furthermore, the operational strategy (electricity- vs. thermal-led strategy) could impact the performance, economic aspects, and environmental profile of the PEMFC-based CHP system [15]. From the environmental point of view, the thermal-led strategy, which was investigated in their current work, proved to be more advantageous compared to other alternatives [15].

In summary, proton exchange membrane fuel cell (PEMFC) systems are considered promising solutions for producing clean energy [19,28,29,30]. However, only a few comparative LCA studies have been conducted that show significant reductions in CO₂ emissions compared to conventional and other alternative energy supply technologies [3,18,31,32,33]. Therefore, our LCA study focused on the global warming potential as well as on the other environmental aspects regarding critical raw materials and recyclability. In contrast to the mentioned LCA studies [3,18,31,32,33], we have analyzed a semi-self-sufficient system (PEMFC with the integrated lead battery as an intermediate storage) that is suitable under certain circumstances to cover the entire energy demand of a single-family house. This comparative LCA was conducted for the case of German households to identify environmental hotspots and gain information for decision-makers such as developers and manufacturers of PEMFC systems, consumers, or authorities.