PEM single fuel cell as a dedicated power source for high-inductive superconducting coils

In practice, the voltage of a hydrogen–oxygen fuel cell is around 1 V at open circuit and from 0.6 V to 0.7 V at full rated load and it can be considered as a low-voltage energy source. Moreover, preliminary investigations undertaken on a single proton exchange membrane fuel cell (PEMFC) highlighted its behavior as a DC current source, that can be directly controlled by the H₂ flow rate when the operating point is at very low voltage. In this paper, we present an innovative application of PEMFC that relies on taking advantage of both low voltage level and current source operating mode to feed a high inductive superconducting coil. Such a coil has no resistance and among others, is very sensitive to current ripples. Thus, specific power supplies are designed to feed them but they exhibit in most cases a huge volume and/or a low energy yield. Connecting a superconducting coil to a PEMFC implies to operate in short-circuit, which is an unusual use of PEMFC. To this end, requirements of such an application are defined, by making use of a PEMFC electrical model based on a 1D analog representation of mass transport phenomena. This model, that enables to take into account the influence of gas supply conditions, notably diffusion limit operation, is directly implemented in a standard simulation software used in electrical engineering. Then, simulation results and experimental results obtained by supplying a 10 H superconducting coil cooled by liquid helium by means of a single 100 cm² PEMFC are compared and discussed.     

Online voltage consistency prediction of proton exchange membrane fuel cells using a machine learning method

Widely acknowledged by experts, the inconsistency between the cells of the proton exchange membrane fuel cell stack during operation is an important cause of the fuel cell life decay. Existing studies mainly focus on qualitative analysis of the effects of operating parameters on fuel cell stack consistency. However, there is currently almost no quantitative research on predicting the voltage consistency through operating parameters with machine learning methods. To solve this problem, a three-dimensional model of proton exchange membrane fuel cell stack with five single cells is established in this paper. The Computational Fluid Dynamic (CFD) method is used to provide the source data for prediction model. After predicting the voltage consistency with several machine learning methods and comparing the accuracy through simulation data, the integrated regression method based on Gradient Boosting Decision Tree (GBDT) gets the highest score (0.896) and is proposed for quickly predicting the consistency of cell voltage through operating parameters. After verifying the GBDT method with the experimental data from the fuel cell stack of SUNRISE POWER, in which the accuracy score is 0.910, the universality and accuracy of the method is confirmed. The influencing sensitivity of each operating parameter is evaluated and the current density has the greatest influence on the predicted value, which accounts for 0.40. The prediction of voltage consistency under different combination of operating parameters can guide the optimization of structural parameters in the process of the fuel cell design and operating parameters in the process of fuel cell control.     

Anode bleeding experiments to improve the performance and durability of proton exchange membrane fuel cells

Cost, durability, efficiency and fuel utilization are important issues that remain to be resolved for commercialization of proton exchange membrane fuel cells (PEMFC). Anode flow mode, which includes recirculation, dead-ended and exit bleeding operation, plays an important role in fuel utilization, durability, performance and the overall cost of the fuel cell system. Depending on the flow mode, water and nitrogen accumulation in the anode leads to voltage transients and local fuel starvation, which causes cell potential reversal and carbon corrosion in the cathode catalyst layers. Controlled anode exit bleeding can avoid the accumulation of nitrogen and water and improve fuel utilization. In this study, we present a method to control the bleed rate with high precision in experiments and demonstrate that hydrogen utilization as high as 0.9988 for a 25 cm² single cell and 0.9974 for an 8.17 cm² single cell can be achieved without significant performance loss. In the experiments, anode pressure is kept at 1 bar higher than the cathode pressure to decrease nitrogen crossover from the cathode, decreasing the crossover from the cathode. Moreover, four load cycle profiles are applied to observe the cumulative loss in the electrochemical surface area (ECSA), which are acquired from cyclic voltammetry (CV) analysis. Experiments confirm that the ECSA loss and severe voltage transients are indicative of fuel starvation induced by prolonged dead-ended or low exit-bleed operation modes whereas bleed rates that are larger than the predicted crossover rate are sufficient to operate the fuel cell without voltage transients and detrimental ECSA loss.     

Dynamic characteristics of local current densities and temperatures in proton exchange membrane fuel cells during reactant starvations

Reactant starvation during proton exchange membrane fuel cell (PEMFC) operation can cause serious irreversible damages. In order to study the detailed local characteristics of starvations, simultaneous measurements of the dynamic variation of local current densities and temperatures in an experimental PEMFC with single serpentine flow field have been performed during both air and hydrogen starvations. These studies have been performed under both current controlled and cell voltage controlled operations. It is found that under current controlled operations cell voltage can decrease very quickly during reactant starvation. Besides, even though the average current is kept constant, local current densities as well as local temperatures can change dramatically. Furthermore, the variation characteristics of local current density and temperature strongly depend on the locations along the flow channel. Local current densities and temperatures near the channel inlet can become very high, especially during hydrogen starvation, posing serious threats for the membrane and catalyst layers near the inlet. When operating in a constant voltage mode, no obvious damaging phenomena were observed except very low and unstable current densities and unstable temperatures near the channel outlet during hydrogen starvation. It is demonstrated that measuring local temperatures can be effective in exploring local dynamic performance of PEMFC and the thermal failure mechanism of MEA during reactants starvations.     

An integrated simulation model for PEM fuel cell power systems with a buck DC-DC converter

Fuel cell powered systems generally have a high current and a low voltage. Therefore, the output voltage of the fuel cell must be stepped-down using a DC-DC buck converter. However, since the fuel cell and converter have different dynamics, they must be suitably coordinated in order to satisfy the demanded load. Accordingly, this study commences by constructing a MATLAB/Simulink model of a proton exchange membrane fuel cell (PEMFC) system comprising a PEMFC stack, an air/fuel supply system, and a temperature control system. The validity of the PEMFC model is demonstrated by comparing the simulation results obtained for the polarzation curves of a single fuel cell with the corresponding experimental curves. A model is then constructed of the DC-DC buck converter used to step-down the PEMFC output voltage. In addition, a sliding mode control (SMC) scheme is proposed for the DC-DC buck converter which guarantees a low and stable output voltage given transient variations in the output voltage of the PEMFC. Finally, a model is constructed of a DC-AC inverter with a pulse width modulated (PWM) control scheme which enables the PEMFC stack to supply the grid or power AC applications directly. Overall, the combined PEMFC/DC-DC buck converter/DC-AC inverter model provides a powerful and versatile tool for the design and development of a wide range of PEMFC power systems.     

质子交换膜燃料电池的应用研究

质子交换膜燃料电池（PEMFC）与其它燃料电池一样，是利用氧化、还原反应产生电子流的装置。它以氢为燃料、以氧为氧化剂，把化学能直接转化为电能。由于该电池以氢气为燃料，生成的产物是水，对环境造成的污染少。在化石燃料日益短缺及环境污染日益严峻的条件下，燃料电池倍受关注。而近几年发展起来的质子交换膜燃料电池（PEMFC）由于其无污染、发电效率高等特点正受到各国各部门的重视。主要评述了PEMFC的主要用途、工作原理及其实现商业化所面临的几个主要问题。     

On-line fault diagnostic system for proton exchange membrane fuel cells

In this paper, a supervisor system, able to diagnose different types of faults during the operation of a proton exchange membrane fuel cell is introduced. The diagnosis is developed by applying Bayesian networks, which qualify and quantify the cause–effect relationship among the variables of the process. The fault diagnosis is based on the on-line monitoring of variables easy to measure in the machine such as voltage, electric current, and temperature. The equipment is a fuel cell system which can operate even when a fault occurs. The fault effects are based on experiments on the fault tolerant fuel cell, which are reproduced in a fuel cell model. A database of fault records is constructed from the fuel cell model, improving the generation time and avoiding permanent damage to the equipment.     

A family of high gain fuel cell front-end converters with low input current ripple for PEMFC power conditioning systems

Since the output voltage of the proton exchange membrane fuel cell (PEMFC) is relatively low and load-dependent, a high-performance fuel cell front-end converter is required to achieve boost and power regulation in PEMFC systems. In response, a novel family of high gain fuel cell front-end converters with low input current ripple is proposed. The proposed topologies can substantially improve the voltage gain through the expansion and combination of active switched-inductor networks and passive switched-capacitor units. The introduced interleaved parallel structure is convenient to limit the current ripple on the input side to prevent accelerated aging of fuel cells, which is another prominent advantage. Meanwhile, the converters can achieve the automatic current sharing between parallel inductors and the low voltage stress on active switches and diodes. In this paper, the fuel cell model and topology derivation of the high gain fuel cell front-end converters are first analyzed. Then, it further describes the operating mode and steady-state performance of converters under the inductor current continuous conduction mode. The comparison with other converters shows that this converter is suitable for connecting the PEMFC to the high voltage DC bus. Finally, a 200 W, 20/180 V converter prototype is implemented, and the simulation and experiment prove the theoretical correctness and validate the superior performances of the proposed converters.     

Experimental investigation on voltage response to operation parameters of a unitized regenerative fuel cell during mode switching from fuel cell to electrolysis cell

In this work, a proton exchange membrane unitized regenerative fuel cell with a 25 cm² active area and a transparent window was designed to study the influence of mode switching from the fuel cell mode to the electrolysis cell mode on the cell voltage and the gas‐liquid two‐phase flow behaviors in the oxygen flow channels. Results indicate that: the growth rate of electrolysis cell voltage before the water pumped to the oxygen flow channels decreases with the increase of the fuel cell current density; while the growth rate of electrolysis cell voltage before the water pumped to the oxygen flow channels increases with the cell temperature; the voltage of electrolysis cell mode before the water pumped to the oxygen flow channels decreases with the increase of water flow rate; the different voltage reduction speeds are attributed to the different water flow rates. The water temperature has an obscure influence on the cell voltage of electrolysis cell mode before the water pumped to the oxygen flow channels.     

Numerical analysis of improved water management of open-cathode proton exchange membrane fuel cells with a dead-ended anode by pulsating flow

Anode water management is critical for the efficient operation of proton exchange membrane fuel cells with a dead-ended anode. To clarify the mass transfer phenomenon in the anode flow channel under the dead-ended anode mode, and reveal the influence mechanism of pulsating flow on water management, a three-dimensional, two-phase, non-isothermal transient model is established in this study. The water content and species distribution in different layers are analyzed, and the internal relationship between water transport behavior and output performance of the proton exchange membrane fuel cell under different operating conditions is explored. The simulation results show that the output performance of the proton exchange membrane fuel cell in dead-ended anode mode is directly related to the gas diffusion layer's water saturation and the hydrogen mass transfer. Furthermore, pulsating flow can effectively suppress the back diffusion of water, and improve the mass transfer rate of hydrogen. Consequently, the water management and the operational stability of the proton exchange membrane fuel cell are significantly improved. The research results of this paper have important guiding significance for improving the water and gas management of fuel cells.     

Trace-metal contamination in proton exchange membrane fuel cells caused by laser-cutting stains on carbon-coated metallic bipolar plates

Trace-metal contamination poses a threat to performance and stability of proton exchange membrane fuel cells (PEMFCs). In this study the source of origin and degree of metal dissolution from carbon-coated 316L bipolar plates (BPPs) are evaluated after a long-term PEMFC test run under conditions resembling a real-life automotive application. Despite intact carbon-coating, metal dissolution occurs from uncoated oxycarbide stains on the plates’ surface. Which correlates with post-mortem detection of chromium, iron and nickel in the membrane electrode assembly. The rate of cell voltage decrease throughout the high current operations is found to be twice as high in the presence of metal ions. Metal dissolution can be correlated with transients in cell voltage during dynamic current load cycling as a result of temporary global fuel starvation. The observed difference in metal dissolution on the anode and cathode BPP indicates weak galvanic coupling between the bipolar plate(s) and the electrode layer(s).     

Hydrogen pumping effect induced by fuel starvation in a single cell of a PEM fuel cell stack at galvanostatic operation

In a proton exchange membrane fuel cell stack, a single cell is potentially subjected to voltage reversal under fuel starvation conditions, which is extremely harmful to its durability. In this work, we develop a two-dimensional computational model to investigate the current and potential distributions in a single cell under these voltage reversal conditions. It is found that most of hydrogen under these conditions is oxidized in a narrow region close to the fuel-inlet, and the anode area before hydrogen depletion can be characterized into an activation limited region and a mass-transport limited region. Meanwhile, an unexpected hydrogen evolution phenomenon is discovered in the cathode catalyst layer (CCL) adjacent to the fuel inlet, owing to the imbalance between the localized ultrahigh hydrogen oxidation current density in the anode and the lower limiting current density of oxygen reduction reaction in the adjacent CCL. Furthermore, the evolved hydrogen gas is also found to be oxidized nearby due to the steep variation of electrolyte potential in the CCL, indicating the coexistence of hydrogen evolution, hydrogen oxidation and oxygen reduction within the micron-scale thickness of CCL, which significantly adds to the complexity of the coupled phenomena in the voltage-reversal single cell.     

Maximum power cold start mode of proton exchange membrane fuel cell

Successful and fast cold start is important for proton exchange membrane (PEM) fuel cell in vehicular applications in addition to the desired maximum power in any case. In this study, the maximum power cold start mode is investigated in details and compared with other cold start modes based on a multiphase stack model. It is found that for the maximum power cold start mode, the current density is generally kept at high levels, and the performance improvement caused by the membrane hydration and temperature increment may not be observable. Therefore, before the melting point, the performance drops continuously. The maximum power cold start mode could better balance the heat generation and ice formation, leading to improved cold start survivability than that in the constant voltage and constant current modes, with a fast start-up generally guaranteed. Once the survivability can be ensured, the initial water content needs to be higher for fast cold start, suggesting that over purging should be avoided. The maximum power mode is suggested to be optimal for PEM fuel cell cold start based on the modeling results.     

Modeling and experimental parameterization of an electrically controllable PEM fuel cell

Optimized integration of fuel cells into grids or on-board power supplies is necessary to facilitate replacement of conventional energy producers by a reliable and plannable power generation technology. Due to the interdependency between fuel cell current and voltage, integration of fuel cells requires a power conditioning system, which increases integration weight and cost. For this reason, integration of electric field modifier electrodes into the setup of proton exchange membrane fuel cells is a new approach to control the output voltage in order to minimize the subsequent power conditioning system. This approach considers the physics of proton transport through the electrolyte membrane and could offer a lever to control the ohmic resistance. In this paper, a fuel cell model is implemented in MATLAB and extended by electric field modifier electrodes, allowing control of the ohmic resistance through an externally applied voltage. The concept of boosting and attenuating fuel cell voltage is presented along with different setups to enable this behavior. Furthermore, an electrical equivalent circuit for electrically controllable fuel cells is developed and implemented in MATLAB/Simulink. A method to parameterize the developed MATLAB and Simulink models by first experimental results is presented.     

Mitigating performance deterioration analysis of VC-PEMFC with dead-ended anode by pulsation fuel supplying mode

Hydrogen starvation and water flooding are two principal factors resulting in performance deterioration of the proton exchange membrane fuel cell stack at the dead-end anode. This paper proposes a novel hydrogen supply mode called the pulsation mode aimed at mitigating the problems of performance deterioration in a 10-cell open-cathode vapor chamber proton exchange membrane fuel cell stack to increase the performance. This method does not require complex equipment and structure, only four controllable solenoid valves are sufficient to generate periodic pulsation inside the anode channels. The experiments were used to validate the effectiveness of the new mode and to compare the effects of different pulsation frequencies on the performance of the stack. A series of parameters such as voltage, power growth rate, and voltage stability index are used to analyze the operating characteristics of the stack. The results show that the periodic pulsations generated by the new mode are potent of increasing the species mass transfer rate within the anode channels, and the species mass transfer rate increases with the increase of pulsation frequency. Meanwhile, selection of a suitable pulsation frequency can effectively improve stack water management and reduce the probability of hydrogen starvation. Finally, the new mode is able to enhance the voltage down valley of the stack under large external load variation. The ohmic resistance of the stack in the new mode has proved to be lower by the current interruption method. Furthermore, it is capable of increasing the net power of the stack by up to 7.71%.     

Experimental study and mitigation of abnormal behavior of cell voltage in a proton exchange membrane fuel cell stack

The aim of this study is to investigate the abnormal behavior of cell voltage in a proton exchange membrane fuel cell stack and a mitigation strategy. The proposed strategy is simple and requires only a three‐way solenoid valve to replace the direct way solenoid valve of the original system. It is applied to a proton exchange membrane fuel cell stack with a dead‐ended anode to verify its validity. The behavior of the cell voltages in the stack is discussed in detail, especially the cell reversal process. The results show that the proposed strategy can significantly reduce the severity of hydrogen starvation. And the maximum power of the stack is increased by 10.67%. It is a sudden increase related to cell reversal mitigation. Uneven hydrogen distribution is the cause of low cell voltage and cell reversal. This strategy increases the cell voltage by increasing the hydrogen content in the anode flow channel downstream. It also significantly reduces the fluctuations in cell voltage and improves the uniformity of the cell voltage. This experimental study contributes to mitigate hydrogen starvation in cells of proton exchange membrane fuel cell stacks in application.     

Behavior of PEMFC in starvation

Starvation is a vivid word to describe the operation condition of a fuel cell in sub-stoichiometric reactants feeding. In starvation, a fuel cell could not present its best performance; moreover, there might also be safety issue because of cell reversal. In this paper, current density distributions of proton exchange membrane fuel cell (PEMFC) in hydrogen and air starvation were studied with a segmented single fuel cell. Experimental results show that the polarization curves of the overall cell are different for anode and cathode starvation. And the current density distribution results show that for anode starvation, current density of the starved region drops sharply to zero, while for cathode starvation, there is no zero current density region observed. Numerical simulations give similar results.     

Anionic-cationic bi-cell design for direct methanol fuel cell stack

A new fuel cell stack design is described using an anion exchange membrane (AEM) fuel cell and a proton exchange membrane (PEM) fuel cell in series with a single fuel tank servicing both anodes in a passive direct methanol fuel cell configuration. The anionic-cationic bi-cell stack has alkaline and acid fuel cells in series (twice the voltage), one fuel tank, and simplified water management. The series connection between the two cells involves shorting the cathode of the anionic cell to the anode of the acidic cell. It is shown that these two electrodes are at essentially the same potential which avoids an undesired potential difference and resulting loss in current between the two electrodes. Further, the complimentary direction of water transport in the two kinds of fuel cells simplifies water management at both the anodes and cathodes. The effect of ionomer content on the AEM electrode potential and the activity of methanol oxidation were investigated. The individual performance of AEM and PEM fuel cells were evaluated. The effect of ion-exchange capacity in the alkaline electrodes was studied. A fuel wicking material in the methanol fuel tank was used to provide orientation-independent operation. The open circuit potential of the bi-cell was 1.36 V with 2.0 M methanol fuel and air at room temperature.     

Performance prediction of proton exchange membrane fuel cells using a three-dimensional model

In this study a steady-state three-dimensional computational fluid dynamics (CFD) model of a proton exchange membrane fuel cell is developed and presented for a single cell. A complete set of conservation equations of mass, momentum, species, energy transport, and charge is considered with proper account of electrochemical kinetics based on Butler–Volmer equation. The catalyst layer structure is considered to be agglomerate. This model enables us to investigate the flow field, current distribution, and cell voltage over the fuel cell which includes the anode and cathode collector plates, gas channels, catalyst layers, gas diffusion layers, and the membrane. The numerical solution is based on a finite-volume method in a single solution domain. In this investigation a CFD code was used as the core solver for the transport equations, while mathematical models for the main physical and electrochemical phenomena were devised into the solver using user-developed subroutines. Three-dimensional results of the flow structure, species concentrations and current distribution are presented for bipolar plates with square cross section of straight flow channels. A polarization curve is obtained for the fuel cell under consideration. A comparison between the polarization curves obtained from the current study and the corresponding available experimental data is presented and a reasonable agreement is obtained. Such CFD model can be used as a tool in the development and optimization of PEM fuel cells.     

Dynamic modeling of high temperature PEM fuel cell start-up process

High temperature proton exchange membrane fuel cells (HT-PEMFCs) are considered to be the next generation fuel cells. Compared with standard low temperature proton exchange membrane fuel cells (LT-PEMFCs) the electrochemical kinetics for electrode reactions are enhanced by using a polybenzimidazole based membrane at an operation temperature between 160 °C and 180 °C. However, starting HT-PEMFCs from room temperature to a proper operation temperature is a challenge in application where a fast start of the fuel cell is required such as in uninterruptible power supply systems. There are different methods to start-up HT-PEMFCs. Based on a 3D physical model of a single HT-PEMFC, the start-up process is analyzed by comparing the start-up duration of the different start-up concepts. Furthermore, the temperature distribution in the HT-PEMFC is also analyzed. Finally, an optimal start-up method is proposed for the given cell configuration.