• Energy Research
• 3. Good health close
• CN close
• DE close
• KR close
• Journal of Power Sources close

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.

Retaining optimum acid-contents in membranes and electrodes is critical to maintaining the performance and durability of acid-doped high-temperature (HT) polymer-electrolyte-membrane fuel cells (PEMFCs). Since the distribution of acids is influenced by the operating and compression conditions of the stack, there is great demand for understanding the behavior of individual membrane-electrode-assemblies (MEAs) while operating the cells in a stack. In this study, an in-situ diagnosis method using electrochemical impedance spectroscopy (EIS) is implemented during the durability test of an HT-PEMFC stack. Adopting a lumped equivalent-circuit model, the specific parameters are obtained from EIS results, and the changes of the values are compared with the performance loss of individual MEA. From this analysis it can be concluded that the main cause of performance degradation of the stack is due to the loss of electrolytes in the cathode, which leads to an increase in the proton transport resistance of cathode catalyst layers. In addition to the proton transport loss in the cathode, the charge transfer resistance of the oxygen reduction reaction has contributed to the performance decay of the stack. The causes of the increase in the cathode charge transfer resistance for each cell of the stack are discussed.

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.

The anodic performance enhancement of solid oxide fuel cells (SOFCs) by introducing penetrating electrolyte structures was investigated using a random resistor network model considering the transport of electrons and ions, and the electrochemical reaction in composite anodes. The composite anode was modeled as a mixture of ionic and electronic particles, randomly distributed at simple cubic lattice points. The dependence of the anodic polarization resistances on the volume fraction of the electronic phase, the thickness of the anode, and the insertion of various penetrating electrolyte structures were explored to obtain design criteria for best performing composite anodes. The network simulation showed that the penetrating electrolyte structures are advantageous over flat electrolytes by enabling more efficient use of electrochemical reaction sites, and thereby reducing the polarization resistances.

Abstract Regarding the reliability of the polymer electrolyte membrane (PEM) fuel cell, the advancement of fuel, thermal and water management techniques of the system have been critically investigated. In this study, a 1 kW class PEM fuel cell stack is built with an Aciplex-S™ membrane, which is integrated to be automatically controlled in a hydrogen-fueled power generation system of a 80 cm ×70 cm ×120 cm single unit with a dc/ac inverter which produces 220 VAC power. Intensive and systematic care should be taken especially with the longer cell stack which is being operated under repeated current load change. The automatically controlled fuel-feed and thermal management system achieved in this study can markedly enhance the fuel efficiency and the reliability of the cell stack. The devices in the sub-systems are all electrically controlled versions to be manipulated on a touch screen via a PLC unit. The thermal and fuel-feed control logic are pre-built-in the CPU of the PLC unit based on an early study of cell stack evaluation. In addition, the power inverting and dummy load unit is coupled to the power generation system, and an additional data acquisition system has been constructed.

Abstract Sodium borohydride (NaBH 4 ) in the presence of sodium hydroxide as a stabilizer is a hydrogen generation source with high hydrogen storage efficiency and stability. It generates hydrogen by self-hydrolysis in aqueous solution. In this work, a Co–B catalyst is prepared on a porous nickel foam support and a system is assembled that can uniformly supply hydrogen at >6.5 L min −1 for 120 min for driving 400-W polymer electrolyte membrane fuel cells (PEMFCs). For optimization of the system, several experimental conditions were changed and their effect investigated. If the concentration of NaBH 4 in aqueous solution is increased, the hydrogen generation rate increases, but a high concentration of NaBH 4 causes the hydrogen generation rate to decrease because of increased solution viscosity. The hydrogen generation rate is also enhanced when the flow rate of the solution is increased. An integrated system is used to supply hydrogen to a PEMFCs stack, and about 465 W power is produced at a constant loading of 30 A.

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.