In this study, the change of electrochemical parameters during the gradual water accumulation of a polymer electrolyte fuel cell (PEFC) are estimated using electrochemical impedance spectroscopy ...(EIS) measurements and an impedance model based on electrode theory during a two‐step oxygen reduction reaction (ORR). EIS measurements were carried out in a 5 cm2 H2/O2 PEFC operated under a dead‐ended configuration of the gas reactants and during gradual accumulation of water. Kramers‐Kronig evaluation demonstrated that the EIS measurements comply with stability and linearity properties and the inductive loops featured at low frequencies are attributed to electrochemical mechanisms within the PEFC and not to instability during gradual water accumulation. The impedance model has been reported in a previous study and simulates inductive loops at low frequencies which are attributed to platinum oxide formation during the ORR. The estimated parameters obtained from this EIS‐modeling analysis can provide an insight into the decrease in PEFC performance during flooding conditions. A further qualitative analysis considering the effect of long‐term water accumulation on the oxygen‐reduction charge transfer resistance is discussed. It is possible to have an insight into the physical mechanisms of the PEFC, by combining different experimental techniques and fundamental theory in a complimentary manner.
The demand of new and environmentally friendly energy sources has induced the research and development of technologies for the energy generation from organic compounds. Among these strategies of ...energy production by bioelectrochemical systems the enzymatic fuel cells show several potential applications including as power suppliers for non-invasive and implantable medical devices. In this work, a new membrane-less enzymatic biofuel cell based on mediated electron transfer glucose oxidase-anode and direct electron transfer laccase-cathode operated in acidic conditions has been designed and characterized. Both, glucose oxidase/hydroquinone anode and laccase cathode were obtained by enzyme covering on gold electrodes modified with single-walled carbon nanotubes. The maximal current density generated was 3.87 and 2.36 mA cm−2 for the anode and cathode, respectively. The glucose/O2 biofuel cell showed an OCV of 0.52 V and delivered a maximum power density of 0.24 mW cm−2 at 0.27 V in acidic pH conditions. This performance is the higher reported so far without added cofactor to the electrolyte in acidic conditions.
•Glucose oxidase/laccase enzymatic fuel cell efficiently works at low pH.•Immobilized hydroquinone is an effective redox mediator for anode.•The enzymatic fuel cell showed a maximal current density of 0.79 mA/cm2.•The enzymatic fuel cell showed a maximal power density of 0.24 mW/cm2.•This performance is the higher reported so far in acidic conditions.
Impedance spectroscopy is a very useful technique as a testing method in analysis of electrochemical systems, material studies, corrosion systems, batteries, etc. However its use in fuel cells has ...been relatively limited. This work presents impedance results during MEA’s evaluation, when testing conditions are varied in single cells. Contributions of different processes effects on complex plane results are discussed.
ABSTRACTDegradation suffered by metallic materials of boilers, gas turbines, and furnaces is caused mainly by molten salts as thin salt films. Molten salts are formed by combustion of residual fuel ...oils, and they are deposited on metal surfaces of boiler equipment such as superheater and reheater, which can be at temperatures from 650°C to 900°C. These temperatures correspond to the liquids of many combustion products from residual fuel oils, which include compounds of vanadium, sulfur, and oxygen, such as sodium sulfate-vanadium pentoxide (Na2SO4-V2O5) mixture solution. Control of high-temperature molten salts corrosion by materials selection has been partially successful through the use of heat-resistant iron and nickel-based alloys with high chromium content. A significant amount of research has been conducted on the molten salt corrosion of many types of alloys with these characteristics, applying weight-loss and electrochemical methods. Nevertheless, scarce information can be found for corrosion of Alloy 800 (UNS N08800) under the experimental conditions considered in this work, using electrochemical techniques. In this paper, corrosion performance of Alloy 800 exposed by immersion in deep crucible melts of two solutions of Na2SO4-V2O5 at 700°C and 900°C is evaluated by electrochemical techniques and compared to the weight-loss method. The results obtained provide information on the kinetics and mode of corrosion attack for material evaluation and performance under these experimental conditions.
This work presents a methodology for the design of a hydrogen fuel cell-based hybrid electric power plant for hybrid electric vehicles (HEV), where a battery bank and ultracapacitors are also ...considered as components of the hybrid power plant. The methodology considers the design features of an electric vehicle and evaluates its energy and power requirements as to fulfil a driving cycle. The work starts by weight minimizing a fuel cell taking into consideration its physical and electrochemical characteristics. Batteries and ultracapacitors are then sized according to their dynamic response features and considering specifications from commercial candidate cells, to propose an electric configuration and specify the baseline for a hybrid power plant. In order to illustrate the methodology, a crossover utility electric vehicle and a WLTC class I drive cycle are used. This work shows that by reducing the power plant size, power and energy requirements can also be minimized and the overall performance can be increased promoting fuel and costs savings. For comparison and to show the impact of weight minimization on the energy on board and cost, this work presents the energy and power required by different power plant configurations. Results showed that including ultracapacitors to the power plant offers more benefits, such as less stress on batteries, at a marginal initial cost compared to a case without ultracapacitors, where batteries should attend transients with a limited capability for energy recovery from regenerative breaking. The methodology is easily implemented and does not large computational resources providing with a power plant baseline for further design stages, such as particular energy management approaches depending on particular priorities for the developer, such as range, productivity and performance, economy and others.
•A fuel cell design as the main energy source of a hybrid electric vehicle.•Sizing method of energy sources independent of associated energy management strategy.•Sizing aiming at minimizing hybrid electric power plant weight.•Sources size reference values for any energy management strategy.
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