Michael Fowler

Performance comparison of Fick’s, dusty-gas and Stefan–Maxwell models to predict the concentration overpotential of a SOFC anode

Models for mass transport inside a porous SOFC anode were developed based on Fick’s model (FM), the dusty-gas model (DGM) and the Stefan–Maxwell model (SMM) to predict the concentration overpotential. All models were validated with experimental data for H2–H2O–Ar and CO–CO2 systems. The effect of pore size on all model predictions was discussed. It was concluded that the dusty-gas model is the most appropriate model to simulate gas transport phenomena inside a SOFC anode. However, this model requires numerical solution, whereas Fick’s and Stefan–Maxwell’s do not. It was found that the SMM, rather than the FM, is a good approximation of the dusty-gas model for H2–H2O system, except in the case of high current density, low H2 concentration and low porosity, where only the DGM is recommended. For the CO–CO2 system, there is no simple rule for selecting an alternate model to DGM. Depending on the CO concentration, porosity and current density, the FM or the SMM could be used. The only restriction is for small porosities where only the DGM should be used. This paper also demonstrated that only the DGM is recommended for a multicomponent system (H2–H2O–CO–CO2).

Optimal Transition to Plug-In Hybrid Electric Vehicles in Ontario, Canada, Considering the Electricity-Grid Limitations

This paper analyzes the feasibility of optimally utilizing Ontarios grid potential for charging plug-in hybrid electric vehicles (PHEVs) during off-peak periods. Based on a simplified zonal model of Ontarios electricity-transmission network and a zonal pattern of base-load generation capacity from 2009 to 2025, an optimization model is developed to find the optimal, as well as maximum, penetrations of PHEVs into Ontarios transport sector. The results of this paper demonstrate that the present and projected electricity grid in Ontario can be optimally exploited for charging almost 6% of the total vehicles in Ontario or 12.5% of the vehicles in Torontos transport sector by 2025; this corresponds to approximately 500 000 PHEVs that can be charged from the grid without any additional transmission or power-generation investments beyond those currently planned.

Electrically Rechargeable Zinc–Air Batteries: Progress, Challenges, and Perspectives

Zinc-air batteries have attracted much attention and received revived research efforts recently due to their high energy density, which makes them a promising candidate for emerging mobile and electronic applications. Besides their high energy density, they also demonstrate other desirable characteristics, such as abundant raw materials, environmental friendliness, safety, and low cost. Here, the reaction mechanism of electrically rechargeable zinc-air batteries is discussed, different battery configurations are compared, and an in depth discussion is offered of the major issues that affect individual cellular components, along with respective strategies to alleviate these issues to enhance battery performance. Additionally, a section dedicated to battery-testing techniques and corresponding recommendations for best practices are included. Finally, a general perspective on the current limitations, recent application-targeted developments, and recommended future research directions to prolong the lifespan of electrically rechargeable zinc-air batteries is provided.

Graphene-wrapped hierarchical TiO2 nanoflower composites with enhanced photocatalytic performance

Graphene-wrapped titanium dioxide nanoflower composites (G–TiO2) consisting of nanosheets and nanoparticles were synthesized using a two-step solvo/hydrothermal process. Materials were characterized using SEM, TEM, high-resolution TEM (HRTEM), XRD, Raman spectroscopy, and FTIR. Further analysis was performed using Branauer–Emmett–Teller (BET) specific surface area analysis, electrochemical impedance spectroscopy (EIS), UV-Vis spectroscopy, and diffuse reflectance UV-Vis spectroscopy. Photocatalytic activity was determined by the photo-degradation of methylene blue under UV irradiation. Results show that the TiO2 nanoflower exhibits a higher photocatalytic activity than commercial P25 by a factor of 1.49. This is attributed to the highly crystalline, hierarchical nature of the nanoflower structure, which provides improved charge transport and a reduced recombination rate of photo-generated electron–hole pairs. After wrapping with graphene, the G–TiO2 composite can further improve the photocatalytic performance by providing a planar conjugated surface for dye adsorption, by further reducing recombination through accepting electrons from TiO2, and by causing a red shift in light absorption. The highest photocatalytic performance was found using a graphene loading of 5 wt%, which outperforms commercial P25 by a factor of 3.4.

A Robust Optimization Approach for Planning the Transition to Plug-in Hybrid Electric Vehicles

This paper proposes a new technique to analyze the electricity and transport sectors within a single integrated framework to realize an environmentally and economically sustainable integration of plug-in hybrid electric vehicles (PHEVs) into the electric grid, considering the most relevant planning uncertainties. The method is based on a comprehensive robust optimization planning that considers the constraints of both the electricity grid and the transport sector. The proposed model is justified and described in some detail, applying it to the real case of Ontario, Canada, to determine Ontarios grid potential to support PHEVs for the planning horizon 2008-2025.

Impact of Liquid Water on Reactant Mass Transfer in PEM Fuel Cell Electrodes

The breakthrough conditions (capillary pressure and liquid water saturation) in a fibrous gas diffusion medium (GDM) used in polymer electrolyte membrane (PEM) fuel cell electrodes have been studied experimentally by two independent techniques and numerically by pore network modeling. Experiments show that treatment of the GDMs with a hydrophobic polymer coating reduces the water saturation at a breakthrough by 50%. Invasion percolation modeling is employed to simulate the breakthrough process and to determine mass-transfer rates through the partially saturated network. This model shows that the water saturation at breakthrough is drastically reduced when a microporous layer (MPL) is incorporated into the GDM, agreeing with experiments. However, the simulations yield limiting currents significantly higher than those observed in practice whether or not an MPL is present. Further calculations to include the contribution of condensation to water saturation within the GDM also result in unrealistically high limiting currents and suggest that mass-transfer resistance in the catalyst layer that is not included in the model plays an important role. If condensation is the principal mode for water accumulation within the GDM, simulations show that the MPL has only a small impact on liquid water distribution and does not improve performance, contrary to expectation.

The Feasibility of Hydrogen Storage for Mixed Wind-Nuclear Power Plants

A novel methodology for economic evaluation of hydrogen storage for a mixed wind-nuclear power plant is presented in this article in a context of a ldquohydrogen economyrdquo. The simulation of the operation of the combined nuclear-wind-hydrogen system is discussed first, where the selling and buying of electricity and the selling of excess hydrogen and oxygen is optimized to maximize profits. This simulation is done in two phases: In the pre-dispatch phase, the system operation is optimized according to stochastic wind and price forecasts to obtain optimal hydrogen charge levels for the operational horizon. In the second phase, a real-time dispatch is carried out on an hourly basis to optimize the operation of the system to maximize profits, and to follow the storage levels of the pre-dispatch phase. Based on the operation planning and dispatch results, an economic evaluation is performed to determine the feasibility of the proposed scheme for investment purposes. The results of these studies demonstrate that hydrogen for the sole purpose of storage of electricity is not economically feasible at the current state of hydrogen technology development, unless hydrogen is sold to the market for other purposes such as transportation, as in the case in a hydrogen economy, or in the case of limited electricity transmission capacities, i.e., transmission congestion.

A Technical and Economic Review of Solar Hydrogen Production Technologies

Hydrogen energy systems are being developed to replace fossil fuels–based systems for transportation and stationary application. One of the challenges facing the widespread adoption of hydrogen as an energy vector is the lack of an efficient, economical, and sustainable method of hydrogen production. In the short term, hydrogen produced from fossil fuels will facilitate a transition to the hydrogen economy. In the long term, renewable hydrogen production methods will have to be adopted as resources become scarce, causing the price of fossil fuels to rise. In this work, a number of methods have been considered for the renewable production of solar hydrogen, and thermochemical sulphur-iodine cycles proved to be the most promising. The sulphur-iodine cycles have the highest efficiencies and use widely available reactants with relatively straightforward reaction mechanisms, which make them the most economical and technically feasible option for renewable hydrogen production.

Numerical modeling and experimental investigation of a prismatic battery subjected to water cooling

ABSTRACT In this paper, a numerical model using ANSYS Fluent for a minichannel cold plate is developed for water-cooled LiFePO4 battery. The temperature and velocity distributions are investigated using experimental and computational approach at different C-rates and boundary conditions (BCs). In this regard, a battery thermal management system (BTMS) with water cooling is designed and developed for a pouch-type LiFePO4 battery using dual cold plates placed one on top and the other at the bottom of a battery. For these tasks, the battery is discharged at high discharge rates of 3C (60 A) and 4C (80 A) and with various BCs of 5°C, 15°C, and 25°C with water cooling in order to provide quantitative data regarding the thermal behavior of lithium-ion batteries. Computationally, a high-fidelity computational fluid dynamics (CFD) model was also developed for a minichannel cold plate, and the simulated data are then validated with the experimental data for temperature profiles. The present results show that increased discharge rates (between 3C and 4C) and increased operating temperature or bath temperature (between 5°C, 15°C, and 25°C) result in increased temperature at cold plates as experimentally measured. Furthermore, the sensors nearest the electrodes (anode and cathode) measured the higher temperatures than the sensors located at the center of the battery surface.

Molecular Functionalization of Graphene Oxide for Next-Generation Wearable Electronics

Acquiring reliable and efficient wearable electronics requires the development of flexible electrolyte membranes (EMs) for energy storage systems with high performance and minimum dependency on the operating conditions. Herein, a freestanding graphene oxide (GO) EM is functionalized with 1-hexyl-3-methylimidazolium chloride (HMIM) molecules via both covalent and noncovalent bonds induced by esterification reactions and electrostatic πcation-π stacking, respectively. Compared to the commercial polymeric membrane, the thin HMIM/GO membrane demonstrates not only slightest performance sensitivity to the operating conditions but also a superior hydroxide conductivity of 0.064 ± 0.0021 S cm(-1) at 30% RH and room temperature, which was 3.8 times higher than that of the commercial membrane at the same conditions. To study the practical application of the HMIM/GO membranes in wearable electronics, a fully solid-state, thin, flexible zinc-air battery and supercapacitor are made exhibiting high battery performance and capacitance at low humidified and room temperature environment, respectively, favored by the bonded HMIM molecules on the surface of GO nanosheets. The results of this study disclose the strong potential of manipulating the chemical structure of GO to work as a lightweight membrane in wearable energy storage devices, possessing highly stable performance at different operating conditions, especially at low relative humidity and room temperature.