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Abstract Extensive models have been developed to study the performance of aqueous redox flow batteries, especially for all-vanadium flow battery. Nevertheless, there are few established models to study the non-aqueous deep eutectic solvent (DES)-based flow batteries, which have wider electrochemical window and higher energy density than do the aqueous redox flow batteries. In this study, a stationary two-dimensional model is set up to study the performance of iron-vanadium redox flow battery using DES as electrolyte, in which the property parameters of the DES are experimentally determined. The effects of temperature on the over-potentials, pump power loss, distribution of ions concentration and local current density are studied. The simulation results show that with the increase of temperature, the over-potentials decrease mildly; the electrochemical reactions inside the DES-electrolyte redox flow battery mainly happen in the area close to the membrane, which is different from the aqueous one, and the rise of temperature also leads to an improvement of electrode utilization. For the DES electrolyte with higher viscosity, the pump power loss could not be neglected. It is found that the pumping loss of the entire porous electrode largely decreases from 0.138 W at 25 °C to 0.022 W at 55 °C (with 84.05% reduction). These results are in good agreement with the experimental outcomes. Therefore, this model can be applied to predict the performance of DES based battery and further to develop new kinds of non-aqueous flow batteries.

Abstract To improve the cold start performance of polymer electrolyte fuel cells (PEFCs), a novel microporous layer (MPL) with planar-distributed wettability, in which hydrophilic and hydrophobic rows are arrayed alternately in the in-plane direction, is proposed and examined. Since freezing occurs near the MPL and catalyst layer (CL) interface, which inhibits continued power generation, the reduction of water on the CL is important. Based on liquid exclusion of the hydrophobic area, liquid movement toward and absorption into the hydrophilic area should occur. As a result, extension of the temperature range for continuous operation at lower temperature and improvement of operational time of the PEFC at sub-freezing temperature (−4.2 °C to −10.0 °C) are achieved and no performance degradation occurs at 60–80 °C.

Abstract To take the advantage chemical-looping combustion (CLC) process for CO 2 sequestration, carbon-air fuel cell (CAFC) and conventional solid oxide fuel cell (SOFC) are prepared for high-efficiency series power generation. The tubular CAFC (Cell-I) consisting of Sb anode, (Y 2 O 3 ) 0.08 (ZrO 2 ) 0.92 (YSZ) electrolyte and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ -Gd 0.1 Ce 0.9 O 3-δ (LSCF-GDC) cathode has achieved peak power densities of 117, 186 and 295 mW cm −2 at 700, 750 and 800 °C, respectively. Fueled by repeatedly added 3 g of coconut-derived activated charcoal, Cell-I has operated stably at 800 °C for 21 h under the condition of 0.4 A cm −2 and 0.502 V, with an electrical efficiency of 30.8%. The tubular conventional SOFC (Cell-II) is designed with Ni-YSZ as anode, YSZ electrolyte as electrolyte and (La 0.8 Sr 0.2 ) 0.95 MnO 3-δ -YSZ (LSM-YSZ) as cathode. The anode exhaust gas of Cell-I, which is operated at temperatures from 750 to 850 °C, contains CO and CO 2 . Using this exhaust gas as fuel, Cell-II has demonstrated peak power densities between 87 and 133 mW cm −2 at 750 °C, and performed stably for 6 h at 0.1 A cm −2 and 0.720 V during which 69.6% of CO in the exhaust gas is consumed. Cell-II has achieved an extra electrical efficiency of 11.0%, giving a total electrical efficiency of 41.8% for the series power generation.

Abstract In this work, a lightweight, ultrathin and flexible paper-based gel electrolyte is developed for liquid-free Al-air batteries, which employs a natural cellulose paper to store an alkaline gel. The as-fabricated electrolyte can be applied in either mechanical-rechargeable or single-use Al-air batteries, providing an open-circuit voltage (OCV) of 1.5 V and a peak power density around 3.5 mW cm−2. In addition, the battery discharge specific capacity is as high as 900 mA h g−1 even with low-purity Al. Moreover, a flexible Al-air battery can be obtained, which exhibits a stable performance under different bending angles. By optimizing the electrolyte properties including polymer concentration, gel loading and solution casting time, the battery power output can be further improved to 6.4 mW cm−2. Finally, two stacking strategies are investigated for developing Al-air battery packs, including both vertical stacking and planar stacking. Benefited from the complete ionic isolation among the single cells, both stacking strategies are demonstrated viable, with a normal OCV of 5.6 V for a 4-cell stack and a stacking efficiency as high as 87.5%. Such kind of liquid-free Al-air batteries are especially suitable for powering portable electronic devices with small rated power.

Abstract Polyacenic semiconductor (PAS), heat-treated at 700°C, has a lithium intercalation capacity as high as 438 mAh g −1 which is higher than the theoretical capacity of 372 mAh g −1 for graphite. The electrochemical behaviour of PAS is examined by studying Li/PAS and Li/graphite cells. In a PAS or graphite anode, three reactions are distinguished: (i) reaction of lithium with the Teflon binder; (ii) decomposition of electrolyte, and (iii) intercalation of Li + ions. Two laboratory cells with liquid organic electrolyte or polymer electrolyte and PAS as the anode demonstrate that PAS is a promising anode material for lithium-ion batteries.

Abstract Local compression distribution in the gas diffusion layer (GDL) of a polymer electrolyte membrane fuel cell (PEMFC) and the associated effect on electrical material resistance are examined. For this purpose a macroscopic structural material model is developed based on the assumption of orthotropic mechanical material behaviour for the fibrous paper and non-woven GDLs. The required structural material parameters are measured using depicted measurement methods. The influence of GDL compression on electrical properties and contact effects is also determined using specially developed testing tools. All material properties are used for a coupled 2D finite element simulation approach, capturing structural as well as electrical simulation in combination. The ohmic voltage losses are evaluated assuming constant current density at the catalyst layer and results are compared to cell polarisation measurements for different materials. The results show that the largest part of the polarisation difference found between roll-good and batch type materials with wide channel flowfields is well captured by the simulation and is due to additional electrical losses in the locally low compressed GDL. Thus, for the first time a broader understanding of the significant performance impact of diffusion layer mechanical properties is generated. However, at higher loads an interaction of compression with electrical and additional heat and mass transport effects occurs, which will be included in the next part of the study. This part is limited to structural mechanics and coupled electrical transport effects.

Abstract During cycling, mechanical stresses can occur in the composite electrode, inside the active material, but also in the solid electrolyte interphase layer. A mechanical model is proposed based on a system made of a spherical graphite particle surrounded by the solid electrolyte interphase layer. During lithium intercalation or de-intercalation, stresses in the graphite are produced, governed by the diffusion induced stress phenomena and in the solid electrolyte interphase, driven by the graphite expansion. The stresses in both materials were simulated and a sensitivity analysis was performed to clarify the influence of principal parameters on both processes. Finally, assuming that the solid electrolyte interphase is the weakest material and therefore more prone to fracture than graphite, the experimental capacity fade during cycling was modeled based on its break and repair effect rather than on the fracture of the active material. The mechanical model of the solid electrolyte interphase was implemented in a single particle lithium ion battery model in order to reproduce capacity fade during battery lifetime. The model results were compared against cycle life aging experimental data, reproducing accurately the influence of the depth of discharge as well as the average state of charge on the capacity fade.

Abstract In this work, a high-performance porous electrode, made of KOH-activated carbon-cloth, is developed for vanadium redox flow batteries (VRFBs). The macro-scale porous structure in the carbon cloth formed by weaving the carbon fibers in an ordered manner offers a low tortuosity (∼1.1) and a broad pore distribution from 5 μm to 100 μm, rendering the electrode a high hydraulic permeability and high effective ionic conductivity, which are beneficial for the electrolyte flow and ion transport through the porous electrode. The use of KOH activation method to create nano-scale pores on the carbon-fiber surfaces leads to a significant increase in the surface area for redox reactions from 2.39 m 2 g −1 to 15.4 m 2 g −1 . The battery assembled with the present electrode delivers an energy efficiency of 80.1% and an electrolyte utilization of 74.6% at a current density of 400 mA cm −2 , as opposed to an electrolyte utilization of 61.1% achieved by using a conventional carbon-paper electrode. Such a high performance is mainly attributed to the combination of the excellent mass/ion transport properties and the high surface area rendered by the present electrode. It is suggested that the KOH-activated carbon-cloth electrode is a promising candidate in redox flow batteries.

Abstract A detailed two-dimensional model of direct flame fuel cell (DFFC) was developed by considering the coupling effects of heterogeneous chemical and electrochemical reactions, electrode microstructure, transport processes of mass, charge and energy, as well as the thermal mechanical stress. The stress distribution was simulated at different heat-up rates which represent the typical DFFC and the common solid oxide fuel cell (SOFC) operation. Transient temperature field and associated thermal stress distributions are determined and analyzed for two different cell structures. The failure probability of the fuel cell is defined and estimated by employing the Weibull statistic. The model is demonstrated to be a useful tool for understanding the mechanical stress distribution within a DFFC cell and for the cell structure design and optimization. The results reveal that the failure probability of an SOFC cell plate working in flame conditions may be 6 orders higher than that in the common SOFC operation conditions. The anode-supported SOFC shows better thermal shock resistance compared with the electrolyte-supported SOFC. The uniformity of the flame temperature is vital in the DFFC system since the non-uniform distribution of the flame temperature greatly increases the failure probability.