The 25th edition of the European Electrolyser & Fuel cell Forum (EFCF 2021) in Lucerne, Switzerland, focusing on low temperature electrolyzers, fuel cells, and H2 processing, has taken place under unusual circumstances. On the one hand, the urgency to fight climate change has finally reached the decision makers at the highest level of the European Union, putting in place the so-called “Green Deal” under Mrs. Ursula von der Leyen, the President of the European Commission. Hydrogen and related technologies are finally understood as enabler of a decarbonized economy and recognized as strategic field for the creation of a new industry and the associated jobs in Europe. On the other hand, COVID19 pandemic has strongly affected the daily work of researchers and engineers, as well as the pace of progress due to practical reasons. The challenges of the pandemic situation and the restrictions applied due to this have obliged the organizers to keep the EFCF 2021 edition as a fully virtual event. The EFCF conference series is well known as more than a mere scientific and technical exchange on the latest results. Therefore, one of the main challenges was to facilitate direct interaction between peers. To accomplish this, a dedicated virtual meeting place was offered to allow people to exchange casually. Up to 80 conference participants simultaneously used the opportunity of this side-offering, and we are confident that this has led to new ideas and joint projects, as would have been the case physically in Lucerne. Challenged by the political changes and the increased interest, EFCF2021 decided not to broaden the scope of topics but to focus on fundamental understanding of electrocatalyst materials and reaction kinetics, as well as progresses and current issues for fuel cell and electrolyzer systems, respectively. Furthermore, contributions related to advanced characterization and diagnostic methods as well as system modeling have been featured during the conference, and a session was dedicated to hydrogen processing including H2 purification, compression, storage, and distribution. In total, 157 papers were presented at EFCF2021, of which more than 100 were presented in live-streamed sessions. The poster presentations were freely accessible during the conference on EFCF's website in the form of pdf files or MP4 presentations. Finally, a limited number of scientific papers have been selected to become part of this special issue. Many thanks are due to the Editor-in-Chief Prof. Ulrich Stimming and Associate Editor Dr. Petra Bele of the journal Fuel Cells – From Fundamentals to Applied Systems for their great support on publishing this topical issue in this esteemed journal.

Surface modification of metallic bipolar plates is a crucial subject for the performance elevation of proton exchange membrane fuel cells (PEMFCs). In this work, a series of NbC/а-C:H films with different Nb/C ratios are prepared by arc ion plating. Film microstructure, composition, mechanical properties, hydrophobility, interfacial contact resistance (ICR), and corrosion resistance in the simulated cathode environment of PEMFCs are systematically studied. The results show that within the experiment conditions, higher NbC content helps to promote the film hardness and adhesion strength as well as the interfacial conductivity. While higher а-C:H content attributes to a more compact microstructure thus improving the anti-corrosion performance. The best corrosion resistance and conductivity come with the lowest corrosion current density of 0.09 µA/cm2 and ICR of 0.77 mΩ cm2, respectively. Based on the result of this research, to further improve the comprehensive performance of NbC/а-C:H film, strategies for increasing the metal carbide content and preventing surface metal oxidation while keeping a dense and fine microstructure need to be considered.

A high-rate oxygen reduction reaction (ORR) is necessary for polymer electrolyte membrane fuel cells (PEMFC). In this work, by using a solution plasma technique, Pt catalytic particles coated with N-doped graphene (Pt-NG) were effectively produced at 25°C. According to transmission electron microscope images, the average diameter of Pt particles was 4 nm, while the graphene layer thickness was less than 1 nm. A catalytic layer of Pt-NG supported on single-walled carbon nanotubes (Pt-NG/SWCNT) was synthesized. Cyclic voltammetry was used to assess the ORR characteristics of Pt-NG/SWCNT catalytic layers. Only at a density of SWCNT to solvent ratio of 0.75 mg ml−1 were the ORR peaks clearly visible. Because of the high resistivity of SWCNT layers, the ORR peaks in other ranges, 0.4 mg ml−1 to 2.0 mg ml−1, were not clearly observed. The effect of SWCNT concentration on conductivity was proven to follow the basic concept of the percolation threshold.

A comprehensive multiphysics 3D model of an anode-supported planar reversible solid oxide cell (rSOC) with a half-channel-unit-cell geometry is created and validated. The physical phenomena that are modeled include reversible electrochemistry/charge transport, coupled with momentum/mass/heat transport. Several electrode microstructures comprising the homogeneous and functionally graded porosity distributions are applied to the validated model, to evaluate and compare the current-voltage (j-V) performance in both fuel cell mode and electrolysis mode. The results indicate that increasing the porosity in a homogeneous porous electrode does not always promote the cell's j-V performance. An optimal porosity emerges where the effect of porosity on the mass transport is maximized, which ranges between 0.5 and 0.7 in the working conditions of the present study. Compared with homogeneous porous electrodes, the heterogeneous porous electrode design with a functionally graded porosity distribution is found to be a potential option to better the overall j-V performance of the rSOC. Furthermore, it is discovered that theoretically grading the porosity in the width direction (i.e., increasing porosity from the center of each gas channel to the center of each adjacent rib) brings an outsize benefit on the cell's performance, compared to the traditional way of improving the porosity along the cell thickness direction.

Fuel Cells – From Fundamentals to Systems publishes on all aspects of fuel cells, ranging from their molecular basis including theory and with molecular processes at catalyst surfaces and microscopic processes in membranes to their application in systems such as power plants, road vehicles and power sources in portables. It includes electrochemical energy technology as in energy conversion and storage with batteries, supercapacitors and electrolytic processes. Fuel Cells is a platform for scientific exchange in a diverse interdisciplinary field. All related work in chemistry, physics, materials science, chemical engineering, electrical engineering, and mechanical engineering is included.

Metal-supported solid oxide cells with Yttria-stabilized zirconia (YSZ) electrolytes fabricated by atmospheric plasma spraying are routinely found to have open-circuit voltages (OCVs) below the Nernst potential due to gas crossover and combustion resulting from electrolyte defects. To improve splat bonding and reduce coating defects, YSZ electrolytes were fabricated here at >800°C substrate temperatures and torch-substrate relative velocities of 4 and 12 m/s by atmospheric suspension plasma spraying. Electrolyte microstructures appeared dense, with porosities estimated to be approximately 2.2–3.5 vol%. Minimal segmentation cracking was observed on samples fabricated at 12 m/s. The full cells that were electrochemically tested had permeabilities in the range of 4–6 × 10−19 m2, and the maximum recorded OCV was ∼26 mV below the Nernst potential for 750°C. Potential performance gains from YSZ deposition at substrate temperatures >800°C may have been masked by poor substrate-fuel electrode contact. Using electrochemical impedance spectroscopy, it was found that the ohmic and polarization resistances decreased and increased, respectively, over time. The calculated distribution of relaxation times of the tested cells, together with observations from the literature, were employed to identify possible cell degradation mechanisms observed during short-term durability testing.

Fuel Cells – From Fundamentals to Systems publishes on all aspects of fuel cells, ranging from their molecular basis including theory and with molecular processes at catalyst surfaces and microscopic processes in membranes to their application in systems such as power plants, road vehicles and power sources in portables. It includes electrochemical energy technology as in energy conversion and storage with batteries, supercapacitors and electrolytic processes. Fuel Cells is a platform for scientific exchange in a diverse interdisciplinary field. All related work in chemistry, physics, materials science, chemical engineering, electrical engineering, and mechanical engineering is included.

Fuel Cells – From Fundamentals to Systems publishes on all aspects of fuel cells, ranging from their molecular basis including theory and with molecular processes at catalyst surfaces and microscopic processes in membranes to their application in systems such as power plants, road vehicles and power sources in portables. It includes electrochemical energy technology as in energy conversion and storage with batteries, supercapacitors and electrolytic processes. Fuel Cells is a platform for scientific exchange in a diverse interdisciplinary field. All related work in chemistry, physics, materials science, chemical engineering, electrical engineering, and mechanical engineering is included.

The combined influence of factors, that is, operating cell temperature, humidification temperature (HT) (indirectly relative humidity), and reactant gas inlet-line temperature on the performance of proton exchange membrane fuel cell was experimentally and statistically studied. A catalyst-coated membrane, membrane electrode assembly, of 6.25 cm2 active area and 0.29 mgpt cm–2 catalyst loading was used in the study. Experimentally, the effect of individual factors and their combinations on cell performance was studied. Statistical analyses were carried out to find the main and interaction effects of different factors. Analysis of variance (ANOVA, 5% significance level, 95% confidence level) analysis, which was validated for homoscedasticity, was used to evaluate the significance of the main and interaction effects of factors. From the study, it was observed that the HT had a significant main effect (988 W m–2). Both interaction plots and ANOVA results revealed that the combination of operating cell and HT was the most significant. The study showed a very interesting observation that the statistical interaction effect (545 W m–2) was half of the experimental deviation value (1090 W m–2) between the summation of independent effects and the combined effect.

Preferential oxidation of CO (CO-PROX) in the hydrogen-rich stream has been carried out over Pt-NaY catalysts containing various Pt loadings along with Fe, Co, and Au. Catalysts have been characterized with inductively coupled plasma-atomic emission spectroscopy, Brunauer, Emmett, and Teller surface area, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature programmed reduction, and Pt dispersion. CO-PROX activities and CO oxidation selectivities are observed to increase with an increase in Pt content. Pt-NaY catalyst with 0.75 wt.% Pt loading shows maximum CO-PROX activity at low temperatures. An increase in space velocity decreases the CO and O2 conversions, but CO oxidation selectivity increases. A decrease in activity is observed when reformat gas contains around 20% H2O. During the stability test, no change in CO and O2 conversions is observed, but a small increase in the CO oxidation selectivity is noticed after 10 h indicating that the Pt-NaY catalyst is a promising candidate for CO-PROX reaction in a hydrogen-rich stream. The Pt-Fe-NaY catalyst shows better activity than the Pt-NaY catalyst but starts deactivating after 10 h. However, activity is observed to decrease over Pt-Co-NaY and Pt-Au-NaY catalysts. Pt-Fe-NaY catalyst with 0.75 and 0.35 wt.% Pt and Fe, respectively, shows better CO-PROX activity at a temperature of 75°C.

The EFCF conference series still continued the strong tradition as one of the leading international meetings in the field of low temparature fuel cells, providing an excellent opportunity to present recent technical progress, establish new contacts, and to exchange technical, industrial and busin.ess information. This conference series takes normally place in Lucerne, Switzerland, but due to the ongoing COVID-19 pandemic took place again as a virtual event.

Fuel Cells – From Fundamentals to Systems publishes on all aspects of fuel cells, ranging from their molecular basis including theory and with molecular processes at catalyst surfaces and microscopic processes in membranes to their application in systems such as power plants, road vehicles and power sources in portables. It includes electrochemical energy technology as in energy conversion and storage with batteries, supercapacitors and electrolytic processes. Fuel Cells is a platform for scientific exchange in a diverse interdisciplinary field. All related work in chemistry, physics, materials science, chemical engineering, electrical engineering, and mechanical engineering is included.

Analysis of buoyancy effect on the evaluation of carbon dioxide gas from passive direct methanol fuel cell current collectors’ (CCs’) openings is carried out. Two types of setups are chosen for the analysis, one with taper cylindrical openings and the other with uniform cylindrical openings. The analysis shows that buoyancy is more effective in taper cylindrical openings due to the accommodation of a larger bubble volume compared to that bubble volume in a uniform cylindrical opening. In this experimental study, SS-316L has been selected as the CC material. During the experiment, it is observed that the CO2 is getting expelled more easily. The best power density (PD) obtained using taper cylindrical openings at a methanol concentration of 3 M is 7.056 mW cm−2, whereas it is 5.219 mW cm−2 in the case of uniform cylindrical openings at the same 3-M methanol concentration. Hence, the taper cylindrical openings are found to perform better at 3-M concentration than cylindrical openings by 35.19% at its best PD point and further, the weight of the CCs is also reduced leading to gravitational PD improvement. Analysis of charge density over the tapered surface is also carried out.

The high global demand for fossil fuels and resulting climate-change effects due to air pollution have led to the rapid development of renewable energy sources. Battery and proton exchange membrane fuel cells have high power densities and high energy, and supercapacitors can provide peak power. These devices have the advantages of high thermal efficiencies and no carbon emissions during use, which have far-reaching applications in the fields of hybrid vehicles and ships. To compensate for the slow dynamic response of fuel cells, batteries or supercapacitors are often used as auxiliary power sources to form hybrid powertrains in practice. Therefore, to take full advantage of the hybrid system, energy coordination between multiple energy sources using an energy management strategy is important. The equivalent consumption minimization strategy has been widely investigated due to its simplicity, small operation, good control, and real-time optimization. In this paper, the topologies of fuel cell hybrid power systems are first systematically classified and characterized. Then, the calculation of equivalent hydrogen consumption for a battery, fuel cell, and supercapacitor is reviewed. To reduce overall hydrogen consumption and extend the life of fuel cells and batteries, an equivalent hydrogen consumption minimization strategy is applied to the energy management of hydrogen fuel power systems.

This study deals with the fabrication of a low-cost ceramic anode made by blending the rice husk and mild steel dust with soil (RMS anode) for its application in plant microbial fuel cells (PMFCs). The high cost of electrode material has been a major concern in practical applications of the PMFC technology, but the present composition of waste materials such as rice husk, mild steel dust along with soil has served as an alternative low-cost electrode material. Tagetes erecta plant has been used to produce clean and continuous electrical energy in the PMFC. The blending of rice husk has improved the porosity of the ceramic anode. The maximum power density recorded in PMFC with 50% rice husk anode was 1.4 mW/m2 as against 0.26 mW/m2 with the anode without rice husk. High biomass growth in terms of better plant height and higher chlorophyll content was also detected in the PMFC system within 60 working days.

In this research, the performance of a tubular fuel cell based on a nickel oxide–yttria-stabilized zirconia (Ni-YSZ) anode support containing 90 wt% NiO ≈ 82 vol.% of Ni (Ni82) is compared with a cell containing the conventional Ni-YSZ support with 50 vol.% Ni. A Ni-YSZ buffer layer with a tailored microstructure was added to the Ni82 support layer to provide intermediate porosity and to reduce the thermal expansion mismatch with the anode functional layer. Both cells were tested using infiltrated Nd2NiO4+δ cathodes. High peak power densities of 790 and 478 mW/cm2 were achieved at 600 and 550°C, respectively, for the Ni82 cell which was 25% and 87% higher than the performances for the conventional cell at respective temperatures. In addition, no degradation was found during four redox cycles at 550°C, making this support an attractive candidate for low-temperature solid oxide fuel cell applications.

Green hydrogen can be produced by integrating water electrolyzers to renewable energy sources. The integration confronts the problem of renewable power volatility that requires advanced control strategies. There are three main electrolyzer control approaches, which are: battery hysteresis cycle, model-based scheduling, and frequency response. These approaches do not fully solve the problem of electrolyzer operation under power fluctuating conditions. This study introduces a novel integration and control approach for water electrolyzers based on model predictive control algorithm. The algorithm controls electrolyzer load so that steering the system into a breakeven energy balance across the main DC busbar that links generation and demand sides. However, the energy balance is subject to power conditioning losses and capacity constraints of electrolyzer. The novel approach uses simplified prediction models for the generation and demand and introduces a compensator for model uncertainty based on a novel role to the battery as a sensor of energy imbalance. The approach is tested on a 5 kW polymer electrolyte membrane electrolyzer and showed that fully automated energy balancing is achievable for grid connected and stand-alone systems. Also, the electrolyzer can operate at partial capacity with improved efficiency and hydrogen yield, and it is applicable to any mix of renewables.

In proton exchange membrane fuel cells (PEMFCs), the avoidance and detection of failures such as flooding and dry-out are crucial. Non-destructive measurement approaches using magnetic sensors have been developed for this purpose. To reduce the number of sensors required to be installed in a PEMFC system for evaluation, we propose a control method for PEMFCs using the magnetic flux density as an index. The proposed method determines the failure conditions by calculating a simple current mapping with a reduced number of sensors. The results of four-point magnetic flux densities under failure conditions and stable control using two-point measurement indices are presented.

Fuel cells for mobile applications obtain their oxygen from the ambient air in road traffic. This air has contaminations of various impurities that can have negative effects on the lifetime of fuel cell systems in vehicles. The identified most relevant contaminants are toluene, nitrogen dioxide, ammonia, and sulfur dioxide. A modified test bench enables different dosages of the above-mentioned pollutant gas concentrations on the cathode side. We examined influences both in static cycles for quasi-steady states and in dynamic cycles for rapid load changes to examine reversible and irreversible degradation effects. We showed that the harmful cathode gases examined could lead to a shortening of the service life of fuel cells. Whereas this is well known for higher concentrations of pollutants, this contribution provides data in the sub-ppm range – including the effects of gas mixtures – for which literature data is still limited.

A voltage decrease in the long-term operation of hydrogen fuel cell (FC) electric cars under steady settings under constant load and dynamic operating conditions is a performance constraint of concern. Although accelerated stress test (AST) procedures have been sought to diagnose degradation, the AST results of FC stacks have not been reported extensively. The purpose of this article is to discuss the generation of AST of FC stacks based on real load profiles and the consequences of load changes and start-stop circumstances, which are mostly generated by common driven cycles in urban regions with high driving speeds and traffic jams. The highlight of this study is to analyze the effects of cycle repetition on the aging FC stack, especially the voltage degradation factor, degradation kinetics, and energy consumption. The relation between actual system temperatures in side cells assembled in the FC stacks and material degradation was also analyzed. The results presented high heat accumulation, related to chemical degradation, that occurred during load cycling and may result in membrane thinning and pinholes in the membrane. Temperature cycling corresponded to mechanical degradation generated during the start-stop cycling test, which may lead to membrane degradations—cracking, tearing, and pinholes.