• Energy Research

Surface irradiation by power ultrasound has proven to offer beneficial effects not only for surface cleaning, but also for the modification of functional properties of metallic or organic coatings. However, the process scale-up has failed to match laboratory observations and data, in particular for the design of industrial sono-reactor systems. To solve this problem, electrochemical systems have been developed and used as effective sensors for ultrasonic activity allowing numerous useful quantitative information to help designing better sono-reactor and process control. Moreover, new types of ultrasonic transducers (e.g., focalised ultrasonic transducers) and new progress in the modulation of ultrasonic transducer excitation have pave the way to industrialization.

The development of highly stable and active electrocatalysts for the oxygen evolution reaction (OER) has attracted significant research interest. IrO2 is known to show good stability during the OER however it is not known to be the most active. Thus, significant research has been dedicated to enhance the activity of IrO2 toward the OER. In this study, IrO2 catalysts were synthesized using a modified Adams fusion method. The Adams fusion method is simple and is shown to directly produce nano-sized metal oxides. The effect of the Ir precursor salt to the NaNO3 ratio and the fusion temperature on the OER activity of the synthesized IrO2 electrocatalysts, was investigated. The OER activity and durability of the IrO2 electrocatalysts were evaluated ex-situ via cyclic voltammetry (CV), chronopotentiometry (CP), electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV). Physical properties of the IrO2 electrocatalysts were evaluated via X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), and energy dispersive spectroscopy (EDS). The results show that the addition of excess NaNO3 during the modified Adams fusion reaction is not a requirement and that higher synthesis temperatures results in IrO2 electrocatalysts with larger particle sizes and reduced electrocatalytic activity.

We show that the coupling effects in non-equilibrium thermodynamics for heat-, mass- and charge- transport in the polymer electrolyte membrane fuel cell (PEMFC) all give significant contributions to local heat effects. The set of equations was solved by modifying an open-source 1D fuel cell algorithm. The entropy balance was used to check for model consistency. The balance was obeyed within 10% error in all PEMFC layers, except for the cathode backing. The Dufour effect/thermal diffusion and the Peltier/Seebeck coefficient are commonly neglected. Here they are included systematically. The model was used to compute heat fluxes out of the cell. A temperature difference of 5 K between the left and right boundary of the system could change the heat fluxes up to 44%. The Dufour effect, for instance, increases the temperature of both anode and cathode, up to 9 K. The possibility to accurately predict local heat effects can be important for the design of fuel cell stacks, where intermediate cooling is central. This work is based on Paper 1484 presented at the Atlanta, Georgia, Meeting of the Society, October 13–17, 2019.

AbstractThis review describes some recent developments in the area of flow field plates (FFPs) for proton exchange membrane fuel cells (PEMFCs). The function, parameters and design of FFPs in PEM fuel cells are outlined and considered in light of their performance. FFP materials and manufacturing methods are discussed and current in situ and ex situ characterisation techniques are described.

Abstract Gas diffusion electrode (GDE) based on a novel dual catalyst layer (CL) structure is designed to enhance the performance of poly(2,5-benzimidazole) (ABPBI)-based high temperature proton exchange membrane fuel cell (PEMFC). Differing from conventional GDE with simplex binder CL, the dual CL GDE is prepared using two different binders, in which a polyvinylidene difluoride (PVDF) CL works as the outer layer to obtain good electrode kinetics by intimately contacting with the electrolyte membrane, while a polytetrafluoroethylene (PTFE) CL works as the inner layer to reduce mass transport limitations. Single cell test and electrochemical analysis on both the dual CL GDE and conventional GDEs are performed to evaluate the effect of the novel CL structure on the fuel cell performance. The results show that significant reductions on both kinetics and mass transfer losses account for the enhanced performance of the novel dual CL structured GDE.

The fractal-type flow-fields for fuel cell (FC) applications are promising, due to their ability to deliver uniformly, with a Peclet number Pe~1, the reactant gases to the catalytic layer. We review fractal designs that have been developed and studied in experimental prototypes and with CFD computations on 1D and 3D flow models for planar, circular, cylindrical and conical FCs. It is shown, that the FC efficiency could be increased by design optimization of the fractal system. The total entropy production (TEP) due to viscous flow was the objective function, and a constant total volume (TV) of the channels was used as constraint in the design optimization. Analytical solutions were used for the TEP, for rectangular channels and a simplified 1D circular tube. Case studies were done varying the equivalent hydraulic diameter (Dh), cross-sectional area (DΣ) and hydraulic resistance (DZ). The analytical expressions allowed us to obtain exact solutions to the optimization problem (TEP→min, TV=const). It was shown that the optimal design corresponds to a non-uniform width and length scaling of consecutive channels that classifies the flow field as a quasi-fractal. The depths of the channels were set equal for manufacturing reasons. Recursive formulae for optimal non-uniform width scaling were obtained for 1D circular Dh -, DΣ -, and DZ -based tubes (Cases 1-3). Appropriate scaling of the fractal system providing uniform entropy production along all the channels have also been computed for Dh -, DΣ -, and DZ -based 1D models (Cases 4-6). As a reference case, Murray’s law was used for circular (Case 7) and rectangular (Case 8) channels. It was shown, that Dh-based models always resulted in smaller cross-sectional areas and, thus, overestimated the hydraulic resistance and TEP. The DΣ -based models gave smaller resistances compared to the original rectangular channels and, therefore, underestimated the TEP. The DZ -based models fitted best to the 3D CFD data. All optimal geometries exhibited larger TEP, but smaller TV than those from Murray’s scaling (reference Cases 7,8). Higher TV with Murray’s scaling leads to lower contact area between the flow-field plate with other FC layers and, therefore, to larger electric resistivity or ohmic losses. We conclude that the most appropriate design can be found from multi-criteria optimization, resulting in a Pareto-frontier on the dependencies of TEP vs TV computed for all studied geometries. The proposed approach helps us to determine a restricted number of geometries for more detailed 3D computations and further experimental validations on prototypes.

The design of a campus mail delivery vehicle powered by 350 bar hydrogen feeding a 1.2 kW PEM fuel cell to charge a lead acid battery pack is described. Five vehicles supplied to the campus at the University of Birmingham to measure the performance and to evaluate relevance to fleet operations are discussed. It is shown that the performance is better than that of a standard diesel van in two drive cycles, one following an academic circuit around the campus, the other doing multiple mail delivery stops. The acceleration and drive cycle compliance are found to be adequate on campus and the efficiency is significantly better than the diesel. The need for extension of range and increase in power and acceleration to meet standard urban drive cycles is clearly demonstrated.