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A H2/Br2 flow battery operating with redox-mediated bromate anions ( BrO 3 − ) has shown several beneficial features induced by the bromate-bromide chemical reaction, particularly in terms of cell performance and safety issues. In this study, a kinetic model of the chemical reaction is developed by thoroughly accounting for detailed reaction steps and by incorporating a three-dimensional, transient H2/Br2 flow battery model. First, the H2/Br2 flow battery model with BrO 3 − is validated against experimental data where cell voltage recovery is observed until the BrO 3 − is completely consumed. The model successfully reproduces the measured voltage evolution data during discharge, thus accurately capturing the transient behavior of an H2/Br2 cell influenced by the bromate-bromide chemical reaction. In addition, H2/Br2 cells are simulated with and without BrO 3 − and model predictions reveal that the reversible voltage, ohmic overpotential in the membrane, and activation overpotential of the Br2 reduction reaction are all improved due to the use of BrO 3 − in the catholyte. The present model for the H 2 - Br 2 - BrO 3 − system enables the quantitative analysis of the beneficial effects for using redox-mediated bromate anion and thus becomes a useful tool for designing and optimization of H2/Br2 cell with BrO 3 − .

In actual PEM fuel cell systems, the coolant flow rate is generally controlled to maintain a preset temperature at the coolant outlet. This implies that a change in coolant supply flow rate is a good early indicator of a malfunctioning PEM fuel cell stack and system components. In this study, various fuel cell malfunctions are simulated based on the practical coolant flow control strategy by using a three-dimensional, two-phase, multiscale PEM fuel cell model developed in our previous studies. The focus is on analysis of the characteristics of coolant flow rate change along with voltage degradation in various fuel cell malfunction cases. The model predictions show that in general, the coolant flow rate tends to increase proportionally with the degree of voltage degradation, but the increase in temperature inside the membrane electrode assembly (MEA) is not always related to the voltage drop and is influenced more directly by local current density distribution. Although the present numerical comparison between the normal and malfunctioning cases is conducted at the low current density of 0.3 A cm−2, the general cell behavior will not be altered at higher current densities due to inverse relationship between cell performance and waste heat generation. The present work elucidates the complex interplay among increase in coolant flow rate, increase in MEA temperature, voltage drop, and change in local current density distribution when a PEM fuel cell malfunctions.

The proton exchange membrane fuel cell (PEMFC) is promising technology for efficient power generation and has wide applications. In PEMFC development, it is important to diagnose malfunctions in a system with defective components and a PEMFC stack can act as an effective sensor to detect the various malfunctioning modes. Hence, the focus of this study is to analyze the response of a PEMFC under various malfunction conditions including humidifier, air blower, and coolant pump, catalyst layer degradation, and membrane aging based on 3D PEMFC simulations. Except for the coolant supply malfunction, other malfunctions exhibit similar behavior in terms of voltage drop and temperature rise, requiring more detailed measurement techniques such as Electrochemical Impedance Spectroscopy to identify the cause of malfunctions. In addition, measuring the relative humidity of the outlet gas may not provide sufficient information to distinguish the malfunction of the anode or cathode humidifier. The results of the study suggest fault detection and isolation methods under these malfunction conditions to prevent more severe failure of the PEMFC stack and system. An extensive multi-dimensional contour comprising temperature, relative humidity, liquid saturation, water content, and current density is also provided for the better analyzation of system malfunctioning behaviors.

This paper reports novel cathode flow-field designs for passive typed air-cooled polymer electrolyte membrane fuel cells (PEMFCs) to help alleviate electrolyte dehydration and performance degradation issues under excess dry air supply conditions. The proposed flow-field designs include 7 three-dimensional (3D) patterned designs in addition to a parallel channel configuration equipped with rectangular baffles to control the airflow for more efficient heat removal. The designs were evaluated numerically using 3D, two-phase PEMFC simulations. Compared to a typical parallel flow channel configuration, the proposed flow-field designs show better heat removal and water retention capability. The improvement in single cell voltage was around 13–75 mV at an operating current density of 0.5 A cm−2, whereas the larger pressure drops around ∆ P = 6.9–317.6 Pa cm−1 were required because of the more complex flow-field configurations compared to the simple straight parallel channel geometry ( ∆ P = 7.4 Pa cm−1). This work presents a comprehensive understanding of air-cooled PEMFC operating characteristics under excessive dry air supply conditions and a new design strategy for cathode flow-fields.

In all-vanadium redox flow battery (VRFB) systems, the electrolyte imbalance between the negative and positive electrodes inevitably occurs and subsequently necessitates costly electrolyte rebalancing procedures for long-term VRFB operation. We propose a new operating strategy for VRFBs that alleviates the electrolyte imbalance issue, which is to employ water and sulfuric acid at different concentrations as initial supporting electrolytes between the negative and positive electrodes. Using a three-dimensional VRFB model that was developed and validated in our previous study, we numerically demonstrate that the degree of electrolyte imbalance can be reduced by using appropriate compositions of the initial anolyte and catholyte. Detailed simulation results reveal that the diffusive water crossover flux between the negative and positive electrodes, which is a main contributor to electrolyte imbalance during charge-discharge cyclic operations, can be effectively suppressed by controlling the initial anolyte and catholyte compositions.