Dead-ended Anode Operation Research Articles

Experimental investigation on operational stability and its influencing mechanisms for PEMFC with dead-ended anode

Proton exchange membrane fuel cell (PEMFC) with dead-ended anode (DEA) suffers from nitrogen diffusion and water accumulation, leading to unstable performance. The core of this paper is to enhance the stability of DEA operation. By coupling the flow field structure with the DEA mode, the factors affecting the stability are explored, the performance degradation mechanism after DEA operation is revealed, and the purging strategy is formulated by combining the energy management with the voltage stability as a prerequisite. The experimental results show that the serpentine flow field is advantageous for maintaining the most stable DEA operation with a minimum voltage recession of 17.01 mV and a voltage undershoot of 11.63 mV. The local current density distribution exhibited a pattern of highest values at anode inlet and lowest at anode outlet, which could be improved by increasing operating pressure and reducing load current density. In this experiment, PCB was innovatively combined to investigate the degradation of each region of PEMFC after 60h of DEA operation. It is found that the most severe performance degradation occurs in anode outlet with a degradation rate exceeding 50%, while the center area has a degradation rate of no more than 20%.

Simultaneous measurement of local current and temperature distributions in proton exchange membrane fuel cells with dead-ended anode

The dead-ended anode (DEA) operation could cause local flooding and local hydrogen starvation in proton exchange membrane fuel cells (PEMFCs), resulting in drastic changes in fuel cell performance. In order to study the detailed local dynamic characteristics of DEA operation, simultaneous measurements of the dynamic variation of local current and local temperature in a PEMFC with DEA have been performed using a local current measurement gasket and micro thermocouples. The results show that the local fuel cell performance distribution gradually becomes uneven during DEA operation and the evolutions of local current and temperature strongly depend on the locations along the flow channel. The highest local current and local temperature are observed near the anode inlet, posing serious threats for the local fuel cell. Furthermore, with anode purging, the current distribution becomes uniform quickly due to the fast mass transfer capacity of hydrogen, but the local temperatures take much longer time to become uniform and stable because of the thermal capacity of fuel cell components. The anode purging also causes local temperature undershoots and the amplitude is over 4℃ in this study. Finally, the effects of operating conditions are discussed. The local current and temperature distributions become more uneven as overall operating current increases and operating temperature decreases. The local temperatures are all reduced as anode inlet pressure and air stoichiometry increase due to the enhanced convection cooling effect. It is demonstrated that measuring local current and temperature is effective in investigating local dynamic performance of PEMFCs with DEA.

A novel CCHP system based on a closed PEMEC-PEMFC loop with water self-supply

Targeting the shortcomings of oxygen waste and reactant supplement of electrolyzer, this paper proposes a novel combined cooling, heating and power (CCHP) system based on proton exchange membrane electrolysis cell (PEMEC) and H2/O2 proton exchange membrane fuel cell (PEMFC) with water self-supply. In this system, H2/O2 PEMFC adopts a dead-ended anode and cathode operation mode to achieve 100 % hydrogen and oxygen utilization and water recovery. For the application scenario of a household in Shanghai, China, the performance of the CCHP system in summer and winter is investigated. When the system gives priority to meeting the electric and cooling load, there will be insufficient heat at the initial stage of operation. The pre-operation model can realize the hourly matching of residential electric, heating and cooling loads. After one day of operation in summer and winter, there are 19.1 kWh and 45.5 kWh electricity surplus, 7.27 × 106 kJ and 1.97 × 106 kJ heat surplus, 1200 mol and 300 mol hydrogen surplus, respectively. Moreover, the estimated payback period for this system is 7.6 years, which will be significantly shortened with the decrease of the cost of photovoltaic panels and PEMEC.

An Artificial Intelligence Solution for Predicting Short-Term Degradation Behaviors of Proton Exchange Membrane Fuel Cell

The dead-ended anode (DEA) and anode recirculation operations are commonly used to improve the hydrogen utilization of automotive proton exchange membrane (PEM) fuel cells. The cell performance will decline over time due to the nitrogen crossover and liquid water accumulation in the anode. Highly efficient prediction of the short-term degradation behaviors of the PEM fuel cell has great significance. In this paper, we propose a data-driven degradation prediction method based on multivariate polynomial regression (MPR) and artificial neural network (ANN). This method first predicts the initial value of cell performance, and then the cell performance variations over time are predicted to describe the degradation behaviors of the PEM fuel cell. Two cases of degradation data, the PEM fuel cell in the DEA and anode recirculation modes, are employed to train the model and demonstrate the validation of the proposed method. The results show that the mean relative errors predicted by the proposed method are much smaller than those by only using the ANN or MPR. The predictive performance of the two-hidden-layer ANN is significantly better than that of the one-hidden-layer ANN. The performance curves predicted by using the sigmoid activation function are smoother and more realistic than that by using rectified linear unit (ReLU) activation function.

Numerical simulation on purge strategy of proton exchange membrane fuel cell with dead-ended anode

Proton exchange membrane fuel cells with dead-ended anode simplify fuel cell system and effectively reduce its volume, weight and cost. In this study, a three-dimensional numerical model of a dead-ended anode PEMFC with single straight channel is developed. The effect of operating conditions, including operating temperature, anode inlet pressure, and cathode relative humidity on operating characteristics of dead-ended anode PEMFC was studied in detail. What's more, the purge cycle, hydrogen utilization and energy efficiency are analyzed and the reasonable purge strategy was optimized. The results indicates that the decrease of anode partial pressure caused by the accumulation of nitrogen and liquid water is the main reason for the voltage decline during dead-ended anode operation. The purge cycle is effectively prolonged by increasing anode pressure and reducing the relative humidity of cathode. The purge cycle is extended from 437s to 562.5s as the anode pressure increased from 50 kPa to 150 kPa. The purpose of optimizing the purge strategy is to fully remove the accumulated water and nitrogen, so as to prolong the purge cycle and improve hydrogen utilization and energy efficiency. From the result, the hydrogen utilization and energy efficiency of the base case are 95.77% and 40.05%.

Numerical modeling of anode-bleeding PEM fuel cells: Effects of operating conditions and flow field design

Operating the PEM fuel cell in the dead-ended anode mode reduces the overall cost and complexity of the system but causes a voltage loss and carbon corrosion in the cathode catalyst layer due to hydrogen starvation in the anode. Whereas allowing an ultra-low flowrate at the anode outlet offers a very high utilization of hydrogen and achieves a stable voltage transient. Here, a time-dependent pseudo-three-dimensional, two-phase, and non-isothermal model is developed to study the optimum bleeding rate, which maximizes the hydrogen utilization, achieves a stable cell voltage and avoids carbon corrosion, which is commonly observed when the bleed rate is set to zero, i.e. the dead-ended mode. The model is validated against the experimental data by comparing the polarization curves and cell voltage transients during the dead-ended anode operation of small experimental cells with serpentine and straight anode flow channels. Moreover, the effects of operating conditions on cell performance during the anode bleeding operation mode are investigated. Results demonstrate that the hydrogen utilization exceeds 99% in the anode-bleeding mode without hydrogen starvation, and the cell performance improves significantly for higher anode pressure, lower cell temperature, and lower relative humidity at the cathode inlet. Lastly, it is found that serpentine channels in the anode improve the uniformity of the distribution of hydrogen compared to straight and interdigitated channels in the anode-bleeding mode while the cathode flow field consists of serpentine channels.

Local degradation in proton exchange membrane fuel cells with dead-ended anode

The dead-ended anode (DEA) configuration can simplify proton exchange membrane fuel cell (PEMFC) systems and reduce system cost. However, the DEA configuration can also accelerate fuel cell degradation during long-term operations. Understanding the degradation mechanisms is crucial to improve fuel cell durability. In this study, experiments are performed to investigate the local degradation phenomena in PEMFCs during DEA operations. The detailed degradation mechanisms are revealed through various electrochemical analysis. The local polarization curves show that the local fuel cell performance decreases are very non-uniform and the inlet area suffers the most severe performance decrease. Electrochemical measurements indicate that the most serious carbon corrosion in catalyst layer occurs near the anode outlet. However, the most severe local membrane degradation is observed near the anode inlet. Furthermore, we observe that the pressure swing anode supply mode can significantly mitigate fuel cell degradation during DEA operation. The water and gas distributions in the anode are much more uniform with the periodical oscillatory flow under pressure swing mode, reducing local membrane dehydration and avoiding local hydrogen starvation. Thus, both the local membrane degradation and local carbon corrosion are significantly mitigated under the pressure swing mode.

A transient Pseudo-3D model of the PEM fuel cell for the analysis of dead-ended anode and anode bleeding operation modes

The high energy density of hydrogen is very advantageous for automotive applications, however the high cost and low durability of proton exchange membrane (PEM) fuel cells limit their commercial use. The anode-bleeding operation mode offers a very high hydrogen utilization and cost reduction by eliminating the components necessary for the recovery of hydrogen in the flow-through mode and avoids the carbon corrosion reaction, which causes degradation of the catalyst layer when the bleeding rate is set to zero in the dead-ended mode. A two-phase, non-isothermal, transient and pseudo-three-dimensional model is developed here to study the cell performance and carbon corrosion during dead-ended and anode bleeding operation modes. The model is validated against the experimental data from the literature and used to investigate the effects of the geometric and operation parameters on the voltage transient during dead-ended anode (DEA) operation mode. Results demonstrate that a lower load-current density, higher anode pressure, lower relative humidity at the cathode inlet, higher stoichiometric flow in the cathode, higher cell temperature, and shorter, deeper and wider channels can improve the cell performance under the DEA operation. The bleeding rate is optimized to sustain a stable transient cell voltage without carbon corrosion in the cathode catalyst layer while the hydrogen utilization is more than 99%.

Examining the effect of the secondary flow-field on polymer electrolyte fuel cells using X-ray computed radiography and computational modelling

Flow-fields are key factors in determining the operation of fuel cells. While extensive work has been conducted to develop and optimise the reactant flow and current collection performance of polymer electrolyte membrane fuel cell (PEMFC) components, there is a factor that remains largely unaccounted for. Depending on how a membrane electrode assembly (MEA) is incorporated into a cell, there will often be a small gap between the edge of the gas diffusion layer (GDL) and the seal or bipolar plate. This gap acts as a ‘secondary flow-field’ (SFF) that can bypass or affect/augment the conventional or ‘primary flow-field’. Understanding how this affects performance (either positively or adversely) is essential for holistic flow-field design. This paper describes the issues associated with the SFF, examines how cell compression affects its width due to lateral expansion of the GDL and discusses the results of a 3-D computational model that investigates the effect of the SFF during dead-ended anode (DEA) operation for a fuel cell without a macroscopic (conventional) anode flow-field.

A quasi-2D transient model of proton exchange membrane fuel cell with anode recirculation

Anode recirculation of proton exchange membrane fuel cell (PEMFC) is considered as an effective way for self-humidification and efficient hydrogen utilization, but nitrogen crossover presents a problem. To investigate the transient characteristics of PEMFC with anode recirculation, a comprehensive quasi-2D non-isothermal transient model is developed. The simulation results show that for a PEMFC initially operated with dry hydrogen, anode recirculation leads to certain level of performance increase in the beginning due to self-humidification effect, and then the performance decreases caused by nitrogen crossover, hydrogen dilution and the increase of anode activation loss. The nitrogen accumulation in anode downstream is severer than upstream, and the performance decline rate decreases with increasing cathode inlet velocity under the simulated operating conditions. The performance and current density distribution uniformity of counter-flow configuration is better than co-flow under low inlet humidity, but the difference becomes smaller with anode recirculation. Anode recirculation and dead-ended anode (DEA) operation both have self-humidification effect, and compared to DEA, the advantages of anode recirculation can be summarized as lower performance decline rate, less chance of local hydrogen starvation and better current density distribution uniformity.

Degradation mitigation effects of pressure swing in proton exchange membrane fuel cells with dead-ended anode

High cost remains to be one of the primary obstacles for the commercialization of proton exchange membrane fuel cells (PEMFCs). To simplify the fuel cell system and reduce cost, dead-ended anode (DEA) is widely used. However, water and nitrogen can accumulate in the dead-ended anode, resulting in cell performance decrease and severe cell degradation. Anode pressure swing supply is a new technology which has been shown to be effective in reducing local water and nitrogen accumulation in the anode channel. In this work, the effects of pressure swing supply on fuel cell degradation have been experimentally studied. Two sets of experiments on the same fuel cell are conducted, one under conventional constant pressure operation and the other under pressure swing operation. Polarization curves show that pressure swing supply can significantly mitigate cell degradation during DEA operations. Electrochemical characterizations are performed to study the mechanisms of mitigations in cell degradation. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results show that pressure swing supply can significantly reduce electrolyte membrane degradation, but has no significant mitigation effect on the cathode catalyst degradation during DEA operation. Further examinations of the membrane-electrode-assembly (MEA) by scanning electron microscope (SEM) confirm the significant difference in membrane degradations since there is a very large difference in average thickness of the membranes after the degradation tests.

Local potential evolutions during proton exchange membrane fuel cell operation with dead-ended anode – Part I: Impact of water diffusion and nitrogen crossover

Abstract Operating a PEMFC with a dead-ended anode may lead to local fuel-starvation because of water and possibly nitrogen accumulation in the anode compartment. In previous works, we used a segmented linear cell with reference electrodes to monitor simultaneously the local potentials and current densities during dead-ended anode operation. The results indicated that water transport as well as nitrogen crossover through the membrane were most probably the two key factors governing fuel starvation. In this first from a set of two papers, we evaluated with more details the contributions of nitrogen crossover and water transport to hydrogen starvation. To assess nitrogen contribution, the fuel cell cathode compartment was first supplied with pure oxygen instead of air. The results showed that in the absence of nitrogen (in the cathode side) the fuel starvation was much slower than with air, suggesting that nitrogen contribution cannot be neglected. On the other hand, the contribution of water flooding to hydrogen starvation was investigated by using different cooling temperature on the cathode and anode sides in order to drive water toward the colder plate. The results showed that with a colder anode side, fuel starvation was faster. In the opposite case of a hotter anode plate, water accumulation in the anode compartment was limited, nitrogen crossover through the membrane was the main reason for hydrogen starvation in this case. To fully assess the impact of the thermal configurations on membrane-electrode assembly (MEA) degradation, aging protocols with a dead-ended anode and a fixed closing time were also performed. The results showed that operation with a hotter anode could help to limit significantly cathode ElectroChemical Surface Area (ECSA) losses along the cell area and performance degradation induced by hydrogen starvation.

Local potential evolutions during proton exchange membrane fuel cell operation with dead-ended anode – Part II: Aging mitigation strategies based on water management and nitrogen crossover

Abstract Proton exchange membrane (PEM) fuel cells operate with dead-ended anode in order to reduce system cost and complexity when compared with hydrogen re-circulation systems. In the first part of this work, we showed that localized fuel starvation events may occur, because of water and nitrogen accumulation in the anode side, which could be particularly damaging to the cell performance. To prevent these degradations, the anode compartment must be purged which may lead to an overall system efficiency decrease because of significant hydrogen waste. In the second part, we present several purge strategies in order to minimize both hydrogen waste and membrane-electrode assembly degradations during dead-ended anode operation. A linear segmented cell with reference electrodes was used to monitor simultaneously the current density distribution along the gas channel and the time evolution of local anode and cathode potentials. To asses MEA damages, Platinum ElectroChemical Surface Area (ECSA) and cell performance were periodically measured. The results showed that dead-end mode operation with an anode plate maintained at a temperature 5 °C hotter than the cathode plate limits water accumulation in the anode side, reducing significantly purge frequency (and thus hydrogen losses) as well as MEA damages. As nitrogen contribution to hydrogen starvation is predominant in this thermal configuration, we also tested a microleakage solution to discharge continuously most the nitrogen accumulating in the anode side while ensuring low hydrogen losses and minimum ECSA losses provided the right microleakage flow rate is chosen.

Nitrogen Blanketing and Hydrogen Starvation in Dead-Ended-Anode Polymer Electrolyte Fuel Cells Revealed by Hydro-Electro-Thermal Analysis

Dead-ended anode operation has a number of practical advantages that simplify system complexity and lower cost for polymer electrolyte fuel cells. However, dead-ended mode leads to performance loss over time which can only be reversed by performing intermittent purge events. This work applies a combined hydro-electro-thermal analysis to an air-cooled open-cathode fuel cell, presenting experimental functional maps of water distribution, current density and temperature. This approach has allowed the identification of a ‘nitrogen blanketing’ effect due to nitrogen cross-over from the cathode and a ‘bypass’ effect where a peripheral gap between the gasket and the GDL offers a hydrogen flow ‘short circuit’ to the border of the electrode. A consequence of high local current density at the margin of the electrode, and resulting high temperatures, may impact the lifetime of the cell in dead-end mode.

Impact of Water Management on Local Potential Evolutions during PEM Fuel Cell Operation with Dead-Ended Anode

Operating a PEMFC with a dead-ended anode may lead to local fuel-starvation because of water and possibly nitrogen accumulation in the anode compartment. In previous works, we used a segmented linear cell with reference electrodes to monitor simultaneously the local potentials and current densities during dead-ended anode operation. The results indicated that water transport as well as nitrogen crossover through the membrane were most probably the two key factors governing fuel starvation. In this work, we evaluated with more details the contributions of nitrogen crossover and water transport to hydrogen starvation by using different cooling temperature on the cathode and anode sides. The results show that with a colder anode side, fuel-starvation was faster. In the opposite case of a hotter anode plate, water accumulation in the anode compartment was limited, suggesting that nitrogen crossover through the membrane was probably the main reason for hydrogen starvation in this case while water it is water in regular operation (i.e., with identical cooling temperature on both sides).

Development of a Pure Oxygen Fuel Cell System for an Autonomous Underwater Vehicle with Focus on Fuel Starvation due to Inert Gas Accumulation on the Anode

In this paper a LT-PEM fuel cell stack is used in an autonomous underwater vehicle (AUV) as a range-extender to increase its mission duration by continuously supplying the AUV with electricity. A battery buffers the difference between generated power from the fuel cell and consumed power of the AUV motor and payload. For fuel cell operation in an AUV different challenges arise linked to the surrounding sea water. These conditions lead to the design of a closed fuel cell system which will be outlined. Additionally measurements concerning a purge free dead-ended anode operation of the fuel cell stack will be presented.

Impact of Water Management on Local Potential Evolutions during PEM Fuel Cell Operation with Dead-Ended Anode

The operation of proton exchange membrane (PEM) with a dead-ended anode may lead to local fuel starvation due to the excessive accumulation of liquid water and possibly nitrogen (due to crossover through the membrane) in the anode compartment. Such fuel-starvation events are localized and may remain undetected in terms of overall cell performance. However, these events can lead to significant rise of the anode (and thus cathode) local potentials and accelerate carbon corrosion and catalyst degradation, which can be particularly damaging to the cell performance [1-3]. In previous works we used a segmented linear cell with reference electrodes to monitor simultaneously the local anode and cathode potentials (i.e. the difference between the metal and electrolyte potential) and current densities during operation while the anode outlet remaining closed between several hundreds and a few thousands of seconds [4]. Apart from the addition of the reference electrodes, this cell is similar to that described in [5]. Such dead-ended anode operation sequences were repeated during 216 hours, which led to non-uniform ElectroChemical Surface Area (ECSA) losses, strong carbon corrosion rates (estimated by measuring CO2 concentration at the cathode exhaust) and performance degradation along the cell area. The damage was more pronounced in the regions suffering the longest from fuel starvation: i.e., close to the anode outlet. In a first step, several parameters like membrane thickness, air relative humidity and average current density were varied and the results indicated that water transport from the cathode to the anode as well as nitrogen crossover through the membrane [6] were most probably the two key factors governing fuel starvation. Then, we evaluated with more details the contributions of nitrogen crossover and water transport to hydrogen starvation. Based on the recent works of Thomas et al. [7, 8], the cell was operated by using three thermal configurations with different cooling temperature on the cathode and anode sides (while the cell average temperature was kept constant) in order to drive water toward the colder side: Tanode = Tcathode = 65°C;Tanode = 62.5°C < Tcathode = 67.5°C;Tanode = 67.5°C > Tcathode = 62.5°C; Figure 1 shows the cathode potential evolutions for the six first cycles of dead-end/purge for each thermal configurations (i), (ii) and (iii). For the second configuration (ii), i.e. Ta < Tc, water accumulation in the anode side was favored. As a consequence, the average closing time was 35% faster than for configuration (i). For the third configuration (iii), Ta > Tc, the average cycle duration was seven times greater than that of configuration (i) and ten times greater than that of configuration (ii). For the third configuration, water accumulation in the anode compartment was limited – in practice, no liquid water can be observed at the anode outlet following the purge –. Nitrogen crossover through the membrane was probably the main reason for hydrogen starvation. In order to assess the impact of the thermal configuration on carbon corrosion and performance decrease, the three aging protocols (for each thermal configuration) were repeated but by setting a fixed time span between two successive purges (and by this way the total number of purges performed in 216 hours). The results allowed us to state that the configuration (iii), Tanode>Tcathode, was less damaging than the two other configurations. Eventually, such results should help optimizing purge protocols of fuel cell stack operated with a dead-end mode. Figure 1

In situ analysis of voltage degradation in a polymer electrolyte membrane fuel cell with a dead-ended anode

In this paper, the impact of dead-ended anode (DEA) operation on the liquid water management of polymer electrolyte membrane fuel cells (PEMFCs) was investigated using X-ray synchrotron radiography. The fuel cell voltage and concurrent through-plane liquid water saturations in anode and cathode gas diffusion layers (GDLs) were measured during DEA and open anode operation. It was observed that DEA operation led to significant increases in liquid water content in both anode and cathode GDLs, along with fuel cell power output degradation. A strong correlation was observed between the buildup of the liquid water in the anode and the cathode, and as a result, the liquid water transport in the cathode was also significantly impacted by this DEA operation.

Dynamic cell performance of kW-grade proton exchange membrane fuel cell stack with dead-ended anode

This paper examines the dynamic cell performance of a kW-grade proton exchange membrane fuel cell stack with anode dead-ended mode fuel supply. A self-made kW-grade 40 cells stack with reaction area of 112.85cm2 has been used in the experiment. A single-chip (DSPIC30F4011) is utilized for establishing a control circuit to monitor the voltage and current with constant-current loading. The stack temperature is controlled at a low-level temperature rise. To enhance the hydrogen utilization and reduce the water flooding in the fuel cell stack, the dead-ended anode operation is accomplished by controlling the open or close of the anode outlet solenoid valve. As the loading is heavy, the anode outlet solenoid valve is purged frequently to force the water to flow out. While a light load, the anode outlet solenoid valve is shut down for a period time for hydrogen saving. The solenoid valve is controlled to be opened, referred as purge interval, reaching the discharge amount for 1000C, 1500C, and 2000C as parameter, respectively. The open period of solenoid valve, referred as purge duration, is set as 1s, 3s, and 5s for this study. Experimental results indicate an optimal purge interval and duration for water management and cell performance of the fuel cell stack.

High Potential Excursions during PEM Fuel Cell Operation with Dead-Ended Anode

Operating a proton exchange membrane (PEM) fuel cell with a dead-ended anode may lead to local fuel starvation due to the excessive accumulation of liquid water and possibly nitrogen (because of membrane crossover) in the anode compartment. In this paper, we present experimental results obtained with a segmented, linear cell with reference electrodes along the gas channels, used to record local anode and cathode potentials. By simultaneously monitoring the local potentials and current densities during operation, we assessed the impact of fuel starvation on local fuel cell performance during aging protocols consisting of repeated dead-ended anode operation sequences (with anode outlet closed longer than in real use conditions). During the aging protocols, we observed strong local cathode potential excursions close to the anode outlet. The cathode showed non-uniform ElectroChemical Surface Area (ECSA) losses and performance degradation along the cell area. The damage was more severe in the regions suffering the longest from fuel starvation. Similar experiments performed in different operating conditions and with different membrane thickness showed that water management impacts significantly the cathode potential variations and thus the MEA degradation. Most of the MEA degradation is attributed to local cathode potential excursions above 1.2 V although potential cycling between 0.5 V and 0.7 V also had an impact in the regions well supplied with hydrogen (hydrogen purges were triggered when the fuel cell voltage dropped from about 0.7 V to 0.5 V). According to our results, localized and transient hydrogen starvation events may be difficult to detect by considering only the overall fuel cell performance.