Hydrogen purge and reactant feeding strategies in self-humidified PEM fuel cell systems

A 6 kW proton exchange membrane fuel cell system, operating in self-humidified conditions, was characterized in two anode operative modes: dead-end and flow through with exhaust recirculation. The anode sub-system was specifically designed in order to adjust the level of recycled anodic stream. The role of anode purge frequency, anode recirculation level and air stoichiometric ratio was analysed in the power range 1–5 kW. The aim of this study was to define management strategies to assure efficient and reliable cell performance during steady-state, warm-up and load variation phases. The results evidenced the combined effect of hydrogen purge, air flow rate impulse, and recycled anodic stream on individual cell performance recovery when unstable working conditions were detected during system start-up and load variations.     

In situ detection of anode flooding of a PEM fuel cell

This paper proposes an early detection scheme of anode flooding in a PEM fuel cell. Through experimental testing of an eight-cell hydrogen-fueled polymer electrolyte stack it is shown that anode flooding can be detected prior to a rapid voltage decline. The proposed detection scheme requires no additional costly instrumentation and uses the existing voltage scan cards.     

Investigation of anode flow field for direct dimethyl ether fuel cell

In this work, we presented the novel anode flow field for direct dimethyl ether fuel cell (DDFC). The anode flow field of the DDFC consisted of hydrophilic, hydrophobic, and diffusion region (with a ratio of region areas of 3:6:1). The maximum power density of the DDFC with novel anode flow field was 67 mW cm⁻², which was higher than that of the cell fed with conventional flow field (60 mW cm⁻²). The electrochemical impedance spectra analyses revealed that the mass transfer resistance of novel anode flow field was lower than that of conventional flow field. The constant current operation curves showed that the performance decay ratio of the novel anode flow field was lower than that of conventional one. It indicated that the novel flow field benefited the long-term operation of DDFC.     

Effectiveness of anode in a solid oxide fuel cell with hydrogen/oxygen mixed gases

A porous Ni/YSZ cermet in mixed hydrogen and oxygen was investigated for its ability to decrease oxygen activity as the anode of a single chamber SOFC. A cell with a dense 300 μm YSZ electrolyte was operated in a double chamber configuration. The Ni–YSZ anode was exposed to a mixture of hydrogen and oxygen of varying compositions while the cathode was exposed to oxygen. Double chamber tests with mixed gas on the anode revealed voltage oscillations linked to lowered power generation and increased resistance. Resistance measurements of the anode during operation revealed a Ni/NiO redox cycle causing the voltage oscillations. The results of these tests, and future tests of similar format, could be useful in the development of single chamber SOFC using hydrogen as fuel.     

Thickness effects of anode catalyst layer on reversal tolerant performance in proton exchange membrane fuel cell

Real-world driving conditions will likely cause hydrogen starvation at the anode chambers of stacks to trigger voltage reversal events, posing a tremendous challenge to the durability of proton exchange membrane fuel cells (PEMFCs). The reversal-tolerant anode (RTA), a material-based solution, that inclusion of oxygen evolution reaction (OER) catalyst into the anode is usually employed to cope with the voltage reversal issue. In this work, we investigate the impact of anode catalyst layer thickness on the voltage reversal performance of the membrane-electrode assemblies (MEAs) with conventional anodes (Pt/C catalyst) and RTAs doped with IrO₂ catalyst, a representative OER catalyst. We find that regardless of how thick the anode catalyst layer is, the conventional MEAs exhibit almost similar voltage reversal behaviors and times, only about 1 min to reach the shutdown voltage (?2.5 V). As for the RTA MEAs, a surprising thickness effect that the thinner RTA with the same IrO₂ loading shows superior voltage reversal tolerance. Notably, an ultra-thin RTA (~2 μm) exhibits the reversal tolerance time of 310 min, which is five times higher reversal tolerance time than most of the reported RTAs. We conclude that this thickness effect mainly results from the ionomer distribution on the OER catalyst. Besides, we observe that the RTA with a higher ionomer content shows the better reversal tolerance performance. Our work highlights the importance of the OER Triple-Phase-Boundary (TPB) and the need for improved electrode designs for robust RTAs.     

The critical pressure drop for the purge process in the anode of a fuel cell

Purge operation is an effective way to remove the accumulated liquid water in the anode of proton exchange membrane fuel cells (PEMFCs). This paper studies the phenomenon of the two-phase flow as well as the pressure drop fluctuation inside the flow field of a single cell during the purge process. The flow patterns are identified as intermittent purge and annular purge, and the two purge processes are contrastively analyzed and discussed. The intermittent purge greatly affects the fuel cell performance and thus it is not suitable for the in situ application. The annular purge process requires a higher pressure drop, and the critical pressure drop is calculated from the annular purge model. Furthermore, this value is quantitatively analyzed and validated by experiments. The results show that the annular purge is appropriate for removing liquid water out of the anode in the fuel cell.     

Analysis of solid oxide fuel cell system concepts with anode recycling

The main drivers for anode recirculation are the increased fuel efficiency and the independence of the external water supply for the fuel pre-reforming process. Different system flow-schemes have been defined and a set of parameters have been elaborated as basis for various calculations. Taking into account the combinations of layout, cell type, fuel utilization, fuel, and recycling ratio the total number of cases modeled was about 220. All calculated SOFC systems are on a high level of electrical net efficiency in the range of 50–66%. The electrical and thermal efficiencies are mainly influenced by the fuel utilization. The layout itself, the choice of fuel gas or the type of cell have minor effects on the system efficiency.     

A gas management strategy for anode recirculation in a proton exchange membrane fuel cell

The anode configuration and gas management strategy are two of factors that affect the energy efficiency of a proton exchange membrane fuel cell. In order to improve the hydrogen utilization, unused hydrogen can be recirculated to the inlet using a pump. However, impurities diffusing from the cathode to the anode may cause the dilution of hydrogen in the anode. As a result, a gas management strategy is required for the anode recirculation configuration. In this preliminary study, a novel configuration for anode recirculation and a gas management strategy are proposed and verified by experiments. Two valves are installed in the recirculation line. The anode is operated in four modes (dead-end, recirculation, compression, and purge), and the real-time local current density (LCD) is monitored for gas management purposes. The results show that the LCD distribution is uniform during the recirculation mode and nonuniform during the dead-end and compression modes. With this configuration and gas management strategy, the cycle duration is increased by a factor of 6.5.     

Electrodeposition of PEM fuel cell catalysts by the use of a hydrogen depolarized anode

Up to 30% of the expensive catalyst metal in conventional fuel cell catalysts is not utilized in fuel cells caused by an absence of contact to either the ion conducting, electron conducting or educt phase. This contact can be improved by in situ electrodeposition with a precursor layer which is mostly done in a galvanostatic mode in the literature. In this paper electrochemical deposition with a hydrogen depolarized anode is described and so a potentiostatic electrodeposition under the control of the working-electrode potential and dry working-electrode conditions is enabled. This potentiostatic electrodeposition with a hydrogen depolarized anode significantly increases the performance of the fuel cell.     

Carbon anode in direct carbon fuel cell

Direct carbon fuel cell (DCFC) is a kind of high temperature fuel cell using carbon materials directly as anode. Electrochemical reactivity and surface property of carbon were taken into account in this paper. Four representative carbon samples were selected. The most suitable ratio of the ternary eutectic mixture Li₂CO₃–K₂CO₃–Al₂O₃ was determined at 1.05:1.2:1(mass ration). Conceptual analysis for electrochemical reactivity of carbon anode shows the importance of (1) reactive characteristics including lattice disorder, edge-carbon ratio and the number of short alkyl side chain of carbon material, which builds the prime foundation of the anodic half-cell reaction; (2) surface wetting ability, which assures the efficient contact of anode surface with electrolyte. It indicates that anode reaction rate and DCFC output can be notably improved if carbon are pre-dispersed into electrolyte before acting as anode, due to the straightway shift from cathode to anode for CO₃²⁻ provided by electrolyte soaked in carbon material.     

Effect of an anode modified with nitrogenous compounds on the performance of a microbial fuel cell

Three kinds of nitrogenous compounds (ammonium peroxydisulfate, ethylenediamine, methylene blue) were applied to modify graphite felt anodes in microbial fuel cells. All of the performances were greatly improved by modifying the anode surface. The maximum power density of the microbial fuel cell with modified anode was 355, 545, and 510 mW/m², respectively, which was larger than the ungroomed control (283 mW/m²). The power density of microbial fuel cell with ethylenediamine-treated electrode was highest among the four microbial fuel cells. The increase of power density was correlated with the changes of N/C and O/C ratios on the anode according to the X-ray photoelectron spectrometry analysis.     

Air-breathing membraneless laminar flow-based fuel cell with flow-through anode

This paper describes a detailed characterization of laminar flow-based fuel cell (LFFC) with air-breathing cathode for performance (fuel utilization and power density). The effect of flow-over and flow-through anode architectures, as well as operating conditions such as different fuel flow rates and concentrations on the performance of LFFCs was investigated. Formic acid with concentrations of 0.5 M and 1 M in a 0.5 M sulfuric acid solution as supporting electrolyte were exploited with varying flow rates of 20, 50, 100 and 200 μl/min. Because of the improved mass transport to catalytic active sites, the flow-through anode showed improved maximum power density and fuel utilization per single pass compared to flow-over planar anode. Running on 200 μl/min of 1 M formic acid, maximum power densities of 26.5 mW/cm² and 19.4 mW/cm² were obtained for the cells with flow-through and flow-over anodes, respectively. In addition, chronoamperometry experiment at flow rate of 100 μl/min with fuel concentrations of 0.5 M and 1 M revealed average current densities of 34.2 mA/cm² and 52.3 mA/cm² with average fuel utilization of 16.3% and 21.4% respectively for flow-through design. The flow-over design had the corresponding values of 25.1 mA/cm² and 35.5 mA/cm² with fuel utilization of 11.1% and 15.7% for the same fuel concentrations and flow rate.     

Experimental analysis of a PEM fuel cell performance at variable load with anodic exhaust management optimization

In this paper an investigation on the performance of a commercial Proton Exchange Membrane (PEM) fuel cell, installed at the laboratory of the University of Bologna, is carried out, taking into account the anodic exhaust management and its effects on the flooding phenomenon.     

Experimental investigation of parameters influencing the freeze start ability of a fuel cell system

To improve the freeze start ability of a fuel cell system some significant influencing parameters are defined and investigated. Experiments with a fuel cell test system are carried out in a climate chamber at various conditions. The time interval until fuel cell stack power equals 50% of its maximum power is defined as an indicator for a successful freeze start as well as a value for comparison and evaluation of the results. The target of this work is the minimization of this freeze start time by avoiding the freezing of process water on the catalyst layer of the Membrane Electrode Assembly (MEA), since this leads to temporary performance losses.The shut down strategy of the fuel cell system is identified to be one of the main parameters influencing the freeze start. It is found that a higher degree of dryness in the stack leads to a significant improvement in the freeze start performance, since the water absorbing capacity of the membrane increases and therefore also the time until its saturation. If this saturation takes place after the temperature of the MEA reached 0 °C, no significant ice-formation occurs. It is shown that by improving the shut down strategy of the fuel cell system at T_Start = −6 °C a start without performance loss can be realized. At temperatures lower than that temporary performance losses occur.Even if a lower voltage leads to a higher current and therefore to a higher water production rate, its effect on the freeze start due to the increased heat of reaction is positive. Further investigated parameters, for example the volume of the coolant loop, also affect the freeze start ability, but it can be concluded that the shut down strategy is of main importance.     

Effects of fuel cell anode recycle on catalytic fuel reforming

The presence of steam in the reactant gas of a catalytic fuel reformer decreases the formation of carbon, minimizing catalyst deactivation. However, the operation of the reformer without supplemental water reduces the size, weight, cost, and overall complexity of the system. The work presented here examines experimentally two options for adding steam to the reformer inlet: (I) recycle of a simulated fuel cell anode exit gas (comprised of mainly CO₂, H₂O, and N₂ and some H₂ and CO) and (II) recycle of the reformate from the reformer exit back to the reformer inlet (mainly comprised of H₂, CO, and N₂ and some H₂O and CO₂). As expected, anode gas recycle reduced the carbon formation and increased the hydrogen concentration in the reformate. However, reformer recycle was not as effective due principally to the lower water content in the reformate compared to the anode gas. In fact, reformate recycle showed slightly increased carbon formation compared to no recycle. In an attempt to understand the effects of individual gases in these recycle streams (H₂, CO, CO₂, N₂, and H₂O), individual gas species were independently introduced to the reformer feed.     

The fuel cell electric vehicles: The highlight review

Transportation sector is the important sector and consumed the most fossil fuel in the world. Since COVID-19 started in 2019, this sector had become the world connector because every country relies on logistics. The transportation sector does not only deal with the human transportation but also relates to logistics. Research in every country has searched for alternative transportation to replace internal combustion engines using fossil fuel, one of the most prominent choices is fuel cells. Fuel cells can use hydrogen as fuel. Hydrogen can be fed to the fuel cells to provide electric power to drive vehicles, no greenhouse gas emission and no direct combustion required. The fuel cells have been developed widely as the 21st century energy-conservation devices for mobile, stationary, and especially vehicles. The fuel cell electric vehicles using hydrogen as fuel were also called hydrogen fuel cell vehicles or hydrogen electric vehicles. The fuel cells were misconceived by several people that they were batteries, but the fuel cells could provide electric power continuously if their fuel was provided continuously. The batteries could provide electric power as their only capacities, when all ions are released, no power could be provided. Because the fuel cell vehicles play important roles for our future transportation, the overall review for these vehicles is significantly interesting. This overall review can provide general and technical information, variety of readers; vehicle users, manufacturers, and scientists, can perceive and understand the fuel cell vehicles within this review. The readers can realize how important the fuel cell technologies are and support research around the world to drive the fuel cell vehicles to be the leading vehicles in our sustainable developing world.     

Characterisation of electrical performance of anode supported micro-tubular solid oxide fuel cell with methane fuel

The reduction and operation of Ni–YSZ anode-supported tubular cells on methane fuel is described. Cells were reduced on pure methane from 650 °C to 850 °C, varying reduction time and methane flow rate. The effect on electrochemical performance with methane fuel was then investigated at 850 °C after which temperature-programmed oxidation (TPO) was employed to measure carbon deposition. Results showed that carbon deposition was minimized after certain reduction conditions. The conclusion was that 30 min reduction at 650 °C with 10 ml min⁻¹ methane reduction flow rate led to the highest current output over 1.2 A cm⁻² at 0.5 V when the cell operated at 850 °C between 10 ml min⁻¹ and 12.5 ml min⁻¹ methane running flow rate. From these results, it is evident that solid oxide fuel cell (SOFC) performance can be substantially improved by optimising preparation, reduction and operating conditions without the need for hydrogen.     

Performance study of a PEM fuel cell

This paper presents the installation, maintenance and the efficiency of a Polymer Electrolyte Membrane (PEM) fuel cell, Ballard Trade Mark that use pure hydrogen as fuel and air as an oxidant. A study of the overall efficiency, considering the co-generation of electrical and thermal energies, is performed. The system consists of the cell, a CC/CC converter, a battery, a DC/AC inverter and the load. The behavior of the system is experimentally analyzed for different load states (cases) by measuring and controlling all the parameters registered by the communication software of the cell. The software can adjust limit values for current intensity, hydrogen flow, pressure and the temperature.     

A numerical investigation of the effects of compression force on PEM fuel cell performance

In the present study we report on numerical investigations into the effects of compression on the performance of a unit cell. The focus of this study is how the transport properties of the gas diffusion layer (GDL) material, specifically porosity and permeability, affect numerical predictions of cell performance. Experimental data of porosity and permeability of uncompressed and compressed GDLs were obtained using a porometer, and used in numerical simulations. A 3D model with two parallel channels and an membrane electrode assembly (MEA) is constructed for the calculations. Three different configurations of transport properties were tested, i.e. uniform uncompressed GDL properties, uniform compressed GDL properties, and non-homogeneous GDL properties. It is found that the non-homogeneous case shows noticeable differences in predicted cell performance. For the non-homogenous case, simulations with a pressure difference between two cathode channels were carried out to gain insight into the effect of cross-channel flow on the overall prediction of cell performance. We found that the cross-channel flow changes local current density distribution primarily on the high-pressure channel. The present study demonstrates the importance of the proper use of transport properties for the compressed portion of the GDL.     

Effect of anode diffusion layer fabricated with mesoporous carbon on the performance of direct dimethyl ether fuel cell

In this study, we present the novel membrane electrode assembly (MEA) for direct dimethyl ether fuel cell (DDFC). The anode gas diffusion layer (AGDL) of the MEA is fabricated with mesoporous carbon to facilitate the anode mass transport and enhance the performance of DDFC. The major differences of mesoporous carbon AGDL (MAGDL) and XC-72 AGDL (XAGDL) are the BET surface, the pore volume, and the pore size distribution. The MAGDL provides many more passageways for mass transport than XAGDL. The MAGDL possesses hydrophilic small and hydrophobic middle pores, which benefit the liquid and gas transport simultaneously. The maximum power density of DDFC increases by 20% when using MAGDL instead of XAGDL at 60 °C. The electrochemical measurements indicate that the promotion of the anode two-phase mass transport is the main reason for the significant improvement of DDFC performance.