Reformate hydrogen from biogas is an attractive fuel alternative for energy conversion in PEM fuel cells. However, in the reformate traces of ammonia may be found, e.g. if the biogas is produced from agricultural resources. In this investigation the effect of ammonia in the fuel gas, on each part of the fuel cell, is studied by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), symmetrical hydrogen cell (H2|H2)- and real fuel cell operation. A considerable degradation in performance is observed by introducing 200 ppm ammonia. The results show that ammonia not only affects the polymer electrolyte membrane but also the oxygen reduction reaction (ORR) and catalyst ionomer in both electrodes, whereas the hydrogen oxidation reaction (HOR) is the worst affected. In the short-term, the performance is reversible if running the cell on neat hydrogen after ammonia exposure, but this does not apply for long-term exposure. A mitigation method with air bleed is tested but gives no improvement of the performance.

Sinusoidal ripple-current charging has previously been reported to increase both charging efficiency and energy efficiency and decrease charging time when used to charge lithium-ion battery cells. In this paper, we show that no such effect exists in lithium-ion battery cells, based on an experimental study of large-size prismatic cells. Additionally, we use a physics-based model to show that no such effect should exist, based on the underlying electrochemical principles.

The effects of external compression on the performance and ageing of NMC(1/3)/Graphite single-layer Li-ion pouch cells are investigated using a spring-loaded fixture. The influence of pressure (0.66, 0.99, 1.32, and 1.98 MPa) on impedance is characterized in fresh cells that are subsequently cycled at the given pressure levels. The aged cells are analyzed for capacity fade and impedance rise at the cell and electrode level. The effect of pressure distribution that may occur in large-format cells or in a battery pack is simulated using parallel connected cells. The results show that the kinetic and mass transport resistance increases with pressure in a fresh cell. An optimum pressure around 1.3 MPa is shown to be beneficial to reduce cyclable-lithium loss during cycling. The minor active mass losses observed in the electrodes are independent of the ageing pressure, whereas ageing pressure affects the charge transfer resistance of both NMC and graphite electrodes and the ohmic resistance of the cell. Pressure distribution induces current distribution but the enhanced current throughput at lower pressures cell does not accelerate its ageing. Conclusions from this work can explain some of the discrepancies in non-uniform ageing reported in the literature and indicate coupling between electrochemistry and mechanics.

A deeper understanding of porous electrode preparation and performance losses is necessary to advance the anion exchange membrane fuel cell (AEMFC) technology. This study has investigated the performance losses at 50 °C for varied: Tokuyama AS-4 ionomer content in the catalyst layer, Pt/C loading and catalyst layer thickness at the anode and cathode, relative humidity, and anode catalyst. The prepared gas diffusion electrodes in the interval of ionomer-to-Pt/C weight ratio of 0.4–0.8 or 29–44 wt% ionomer content show the highest performance. Varying the loading and catalyst layer thickness simultaneously shows that both the cathode and the anode influence the cell performance. The effects of the two electrodes are shown to vary with current density and this is assumed to be due to non-uniform current distribution throughout the electrodes. Further, lowering the relative humidity at the anode and cathode separately shows small performance losses for both electrodes that could be related to lowered ionomer conductivity. Continued studies are needed to optimize, and understand limitations of, each of the two electrodes to obtain improved cell performance.

Flexible, low-weight electrodes with integrated current collectors based on chopped polyacrylonitrile carbon fibers (CF) were produced using an easy, aqueous fabrication process, where only 4 wt% of TEMPO-oxidized cellulose nanofibrils (CNF) were used as the binder. A flexible full cell was assembled based on a LiFePO4 (LFP) positive electrode with a CF current collector and a current collector-free CF negative electrode. The cell exhibited a stable specific capacity of 121 mAh g(-1) based on the LFP weight. The CF in the negative electrode acted simultaneously as active material and current collector, which has a significant positive impact on energy density. Stable specific capacities of the CF/CNF negative electrode of 267 mAh g(-1) at 0.1 C and 150 mAh g(-1) at 1 C are demonstrated. The LFP/CNF with CF/CNF, as the current collector positive electrode (LFP-CF), exhibited a good rate performance with a capacity of -150 mAh g(-1) at 0.1 C and 133 mAh g(-1) at 1 C. The polarization of the LFP-CF electrode was similar to that of a commercial Quallion LFP electrode, while much lower compared to a flexible LFP/CNF electrode with Al foil as the current collector. This is ascribed to good contact between the CF and the active material.

Fuel cells are foreseen to have an important role in sustainable energy systems, provided that catalysts with higher activity and stability are developed. In this study, highly active sputtered thin films of platinum alloyed with yttrium (Pt3Y) are deposited on commercial gas diffusion layers and their performance in a proton exchange membrane fuel cell is measured. After acid pretreatment, the alloy is found to have up to 2.5 times higher specific activity than pure platinum. The performance of Pt3Y is much higher than that of pure Pt, even if all of the alloying element was leached out from parts of the thin metal film on the porous support. This indicates that an even higher performance is expected if the structure of the Pt3Y catalyst or the support could be further improved. The results show that platinum alloyed with rare earth metals can be used as highly active cathode catalyst materials, and significantly reduce the amount of platinum needed, in real fuel cells.

For the promising Li-O-2 battery to be commercialized, further understanding of its constituents is needed. This study deals with the role of O-2 in Li-O-2 batteries, both its influence on electrochemical performance and its solubility in lithium-salt-containing dimethyl sulfoxide (DMSO) electrolytes. Experimentally, the electrochemical performance was evaluated using cylindrical ultramicroelectrodes. Two independent techniques, using a mass spectrometer and an optical sensor, were used to evaluate the O-2 solubility, expressed as Henry's constant. Furthermore, the ionic conductivity, dynamic viscosity, and density were also measured. Density functional theory calculations were made of the interaction energy between O-2 and the different species in the electrolytes. When varying O-2 partial pressure, the current was larger at high pressures confirming that the O-2 concentration is of key importance when studying the kinetics of this system. Compared with neat DMSO, the O-2 solubility increased with addition of LiTFSI and decreased with addition of LiClO4, indicating that the salt influences the solubility. This solubility trend is best explained in terms of apparent molar volume and interaction energy between O-2 and the salt anion. In conclusion, this study shows the importance of O-2 concentration, not just its partial pressure, and that the choice of Li salt can make this concentration increase or decrease.

Lignin-based carbon fibers (LCFs) from the renewable resource softwood kraft lignin were synthesized via oxidative thermostabilization of pure melt-spun lignin and carbonization at different temperatures from 1000 degrees C to 1700 degrees C. The resulting LCFs were characterized by tensile testing, scanning electron microscopy (SEM), X-ray diffraction (XRD) and confocal Raman spectroscopy. The microstructure is mainly amorphous carbon with some nanocrystalline domains. The strength and stiffness are inversely proportional to the carbonization temperature, while the LCFs carbonized at 1000 degrees C exhibit a strength of 628 MPa and a stiffness of 37 GPa. Furthermore, the application potential of LCFs was evaluated as negative electrodes in a lithium-ion battery (LIB) by electrochemical cycling at different current rates in a half-cell setup. The capacity drops with the carbonization temperature and the LCFs carbonized at 1000 degrees C have a capacity of 335 mAh g(-1). All LCFs showed good cycling stability. Because of the mechanical integrity and conductivity of the LCFs, there is no need to apply current collectors, conductive additives or binders. The advantage is an increased gravimetric energy density compared to graphite, which is the most common negative electrode material. LCFs show a promising multifunctional behavior, including good mechanical integrity, conductivity and an ability to intercalate lithium for LIBs.

A structural lithium ion battery is a material that can carry load and simultaneously be used to store electrical energy. We describe a path to manufacture structural positive electrodes via electrophoretic deposition (EPD) of LiFePO₄ (LFP), carbon black and polyvinylidene fluoride (PVDF) onto carbon fibers. The carbon fibers act as load-bearers as well as current collectors. The quality of the coating was studied using scanning electron microscopy and energy dispersive X-ray spectroscopy. The active electrode material (LFP particles), conductive additive (carbon black) and binder (PVDF) were found to be well dispersed on the surface of the carbon fibers. Electrochemical characterization revealed a specific capacity of around 60–110 mAh g⁻¹ with good rate performance and high coulombic efficiency. The cell was stable during cycling, with a capacity retention of around 0.5 after 1000 cycles, which indicates that the coating remained well adhered to the fibers. To investigate the adhesion of the coating, the carbon fibers were made into composite laminae in epoxy resin, and then tested using 3-point bending and double cantilever beam (DCB) tests. The former showed a small difference between coated and uncoated carbon fibers, suggesting good adhesion. The latter showed a critical strain energy release rate of ∼200–600 J m⁻² for coated carbon fibers and ∼500 J m⁻² for uncoated fibers, which also indicates good adhesion. This study shows that EPD can be used to produce viable structural positive electrodes.

State-of-health estimates of batteries are essential for onboard electric vehicles in order to provide safe, reliable, and cost-effective battery operation. This paper suggests a method to estimate the 10-s discharge resistance, which is an established battery figure of merit from laboratory testing, without performing the laboratory test. Instead, a state-of-health estimate of batteries is obtained using data directly from their operational use, e.g., onboard electric vehicles. It is shown that simple dynamical battery models, based on a current input and a voltage output, with model parameters dependent on temperature and state of charge, can be derived using AutoRegressive with eXogenous input models, whose order can be adjusted to describe the complex battery behavior. Then, the 10-s discharge resistance can be conveniently computed from the identified model parameters. Moreover, the uncertainty of the estimated resistance values is provided by the method. The suggested method is validated with usage data from emulated electric vehicle operation of an automotive lithium-ion battery cell. The resistance values are estimated accurately for a state-of-charge and temperature range spanning typical electric vehicle operating conditions. The identification of the model parameters and the resistance computation are very fast, rendering the method suitable for onboard application.