Cathode Air Purification in Fuel Cell Systems

Structure simulation design of a cathode air filter for SO2 contamination on a 7 kW fuel cell sightseeing vehicle

<div class="section abstract"><div class="htmlview paragraph">Fuel cell technology can play a major role in reducing transportation-related emissions, especially in heavy-duty, long-haul applications. Consequent transfer of technology from air supply systems for combustion engines to cathode air paths serves as an enabler for necessary system cost reduction. To achieve the required system lifetime, the supply of clean air is essential. Gases like NO<sub>x</sub>, SO<sub>2</sub> and NH<sub>3</sub> poison the catalyst, leading to increased stack degradation rates. Effective removal with functionalized activated carbons enhances the catalyst´s lifetime. Research on real-life concentrations of these contaminants under different driving patterns and road profiles enables knowledge-based design of cathode air filter elements. To prevent flooding of components like air filter, humidifier, or stack, water separators are integrated at different position inside the system. Plastic air ducts with integrated sensors and flaps required to manage the air flow connect the different functional components. Broadband silencers are applied to reduce noises inside the system, e.g. generated by the compressor. Essential components like humidifier and air-cooler can easily be incorporated into the system. In the cathode air exhaust path, an additional water separator is applied to protect turbine blades and to prevent emission of splash water from the tailpipe. The consistent transfer of technology from air supply systems for combustion engines to cathode air paths enables cost-, noise and packaging-optimized, plausible system concepts with enhanced energy efficiency.</div></div>

Highly efficient cathode air filters are required to enable the required fuel cell system´s lifetime, especially under severe operating conditions. In addition, components like water separators, compressors, air ducts, coolers, humidifiers, sensors etc. are essential to supply cathode air at the right cleanliness, pressure, and temperature. The paper focuses on cathode air flow management on the stack inlet and outlet side. The approach to system design is holistic, meaning that not individual components are optimized independently, but on system level. Special emphasis is given to transferring state-of-the-art technology and products from internal combustion engine vehicle´s air intake systems to the cathode air path. Adaption of these components to the operating conditions of fuel cells and combining them with fuel cell-specific components yield intake and outlet systems with cost-, energy- and acoustically optimized functionality.

Fuel cell cathode air filters: Methodologies for design and optimization

Proton exchange membrane (PEM) fuel cells experience performance degradation, such as reduction in efficiency and life, as a result of poisoning of platinum catalysts by airborne contaminants. The best method for addressing fuel cell air contamination is by the inclusion of adsorptive filtration with a cathode air filter. In this paper, simulation for chemical adsorption behavior of air filter has been studied, which is based on Fluent. The adsorption of SO2 was simulated in the air filter, which structure was designed and optimized for a 5kW fuel cell stack system. Not only the distribution of SO2 capacity with time in filter could be shown, but also the durability of filter can be evaluated. Furthermore, the velocity of flow and pressure drop of filter also were simulated. The simulation study for chemical adsorption and hydrodynamics in fuel cell cathode air filter help to optimize air filter to be durable and effective.

Proton exchange membrane fuel cells (PEMFCs) are highly sensitive to the quality of gases supplied at both the anode and cathode. Greater attention has historically been given to anode-side contamination, as hydrogen produced via methods like steam methane reforming are known to carry well-established and consistent impurities such as carbon monoxide (CO), ammonia (NH3), and hydrogen sulfide (H2S), which can significantly impact fuel cell performance. Contamination at the cathode is also an important consideration, as atmospheric air is commonly used as the oxidant and can contain airborne impurities that negatively affect cell operation, especially in industrial and warehouse environments where relatively high concentrations of unique and sometimes unknown impurities can exist. Understanding how contaminants in the cathode air stream affect performance is essential for enhancing the reliability and durability of fuel cells in real-world conditions where air purity may vary.This poster will focus on ethylene, a hydrocarbon that can be found in several archetypal industrial and warehouse environments, and its effect on PEMFC performance when introduced into the cathode air feed. To investigate this, a combination of in-situ fuel cell testing and ex-situ electrochemical measurements were performed using Pt-based MEAs, with varying concentrations of ethylene supplied to the cathode. Upon ethylene exposure, the fuel cell exhibited an immediate voltage drop, with greater losses observed at higher contaminant concentrations. However, the voltage fully recovered once the ethylene was removed, indicating a reversible effect.To understand the mechanism behind the observed performance loss and recovery, constant voltage experiments and cyclic voltammetry (CV) were conducted. The results indicate that ethylene adsorbs onto the Pt catalyst surface, temporarily blocking active sites involved in the oxygen reduction reaction (ORR) without causing persistent poisoning. A range of mitigation strategies was evaluated, beginning with commercial particulate air filters, which had little to no effect on ethylene removal. To improve filtration, in-lab chemical filters were fabricated by dip-coating commercial filter substrates with active materials, including carbon black, Pt/C, and MnO2. Gas chromatography (GC) was used to confirm ethylene concentrations and track removal efficiency across different filter types. These findings provide valuable insights into PEMFC behavior under contaminated air conditions and suggest practical strategies to mitigate performance losses in real-world environments.

Study on the SO2 adsorption performance of dual-layer activated carbon cloth cathode air filter for high-power fuel cell

Air pollution is still a bitter truth in many locations in the world. In highly populated regions like metropolitan areas as well as in agricultural areas there are various airborne contaminants which can be harmful to organisms. Also fuel cells, especially PEMFC are sensitive to airborne contaminants.In most mobile and stationary PEM fuel cell systems, ambient air is used as oxidant gas at the cathode of the fuel cell. It is cost and weight saving because there is no need to install additional tank for pure oxygen and to refill it, but the performance of fuel cell can suffer beyond the oxygen gain from airborne contaminants, which also have the potential to accelerate degradation. To prevent that airborne contaminants reach the fuel cell cathode, air filter systems consisting of particle filter and additional activated carbon filter are installed at the cathode inlet.The focus here is on the investigation of the use of AVL THDAtm method to detect effects of airborne contaminants. THDA (total harmonic distortion analysis) is a patented online fuel cell monitoring method based on analyzing harmonic distortion effects of voltage drifts instead of single cell voltage measurement. So far it was successfully demonstrated for the detection of water issues like flooding and drying, and for low media supply issues on both cathode and anode side [1, 2].For the development and validation of the method, experiments with a PEMFC stack are going to be done on a fuel cell testbed equipped with an AVL X-Ion impedance analyzer. Specific air pollutant gases ammonia (NH3), sulfur dioxide (SO2) and nitrogen oxides (NOx) are going to be mixed into the cathode air in the ppb range. Their effects on PEMFC stack performance are going to be investigated with electrochemical impedance spectroscopy (EIS) and total harmonic distortion analysis. The cathode exhaust gas is also going to be analyzed by an FTIR gas analyzer.It is planned to test the PEMFC stack under different operating conditions, with various parameters and different cathode gas mix ratios while monitoring possible conversion of impurities via FTIR and the stack state of health using THDA and conventional technologies to understand the link between the effect of airborne contaminants on fuel cell stack performance, on its lifetime and to determine possible early indicators in the THDA signals.

The negative effects of airborne contaminants on polymer electrolyte membrane fuel cell (PEMFC) have already been shown in several publications. [1] Among these contaminants, ammonia (NH3) with its multistep reversible and irreversible effects is particularly significant. Recent studies on air quality in urban areas have revealed a notable increase in ammonia levels within a span of two years. [2] This rapid increase can be attributed to the growing prevalence of EURO-6 diesel vehicles equipped with selective catalytic reduction (SCR) cats, which results in ammonia slip during the nitrogen oxide reduction process in diesel engines. [2]Ambient air is the most common used oxidant gas in mobile and stationary PEM fuel cell systems. The performance of fuel cell can suffer beyond the oxygen gain from airborne contaminants, which also have the potential to accelerate degradation. To prevent that airborne contaminants reach the fuel cell cathode, air filter systems consisting of particle filter and specially for fuel cell requirements developed filter are installed at the cathode inlet. Despite the installation of an air filter system, airborne contaminants can still reach the fuel cell cathode.The focus of this investigation is on the effects of ammonia in PEM fuel cell stacks. In contrast to single cell operation, stack operation can introduce additional effects such as cell-to-cell inhomogeneities and varying degrees of ammonia-induced degradation among cells. For the investigation, experiments with a PEMFC stack are going to be done on a fuel cell testbed equipped with an impedance analyzer. Ammonia is going to be mixed into the cathode air in the ppb range. Its effects on PEMFC stack performance are going to be investigated with electrochemical impedance spectroscopy (EIS) and total harmonic distortion analysis (THDA). The cathode exhaust gas is also going to be analyzed by gas analyzers such as FTIR gas analyzer and mass spectrometry.It is planned to test the PEMFC stack under different operating conditions like temperature, relative humidity and pressure of inlet gases, with various parameters and different cathode gas mix ratios while monitoring possible conversion of impurities via FTIR and the stack state of health using THDA and conventional technologies to understand the link between the effect of ammonia on fuel cell stack performance, on its lifetime and to determine possible early indicators.

Proton exchange membrane fuel cells (PEMFCs) are a promising clean energy technology, but their performance and durability are highly sensitive to contaminants in both the fuel and oxidant streams. Among these, ethylene (C2H4) is of particular interest due to its presence in industrial and warehouse environments. This study investigates the impact of ethylene contamination on PEMFC performance when introduced into the cathode air feed. A combination of fuel cell performance testing, cyclic voltammetry, and gas chromatography is used to analyze the interaction of ethylene with the cathode catalyst. The presence of 20–300 ppm ethylene in air causes an immediate drop in the fuel cell operating voltage that is quickly recovered once the contaminant is removed, suggesting a reversible adsorption mechanism on the surface of the platinum cathode electrocatalyst, rather than the formation of strongly bound oxidation intermediates. Additionally, the study explores mitigation strategies by evaluating conventional and chemically modified air filters. While commercial air filters prove ineffective, a carbon supported platinum (Pt/Vulcan)‐coated filter demonstrates partial ethylene removal, reducing performance losses. These findings provide critical insights into ethylene contamination mechanisms and offer potential mitigation strategies to improve PEMFC reliability in real‐world applications.

Toluene adsorption performance study of cathode air filter for high-power hydrogen fuel cell vehicles

Filtration of cathode air is one of the challenges in operating proton-exchange membrane (PEM) fuel cells. The poisoning with air contaminants can lead to rapid performance degradation and initiate an aging process of the fuel cell. Various commercially available cathode filters are being tested in a laboratory gas test bench within the research project X-EMU (03B10502B and 03B10502B2). A literature review of harmful gas contaminants in the air used for the oxygen reduction reaction (ORR) on the cathode side was conducted. Experimental investigations took place at 40 °C with synthetic humid air containing low concentration contaminants such as ammonia, nitrogen dioxide, carbon monoxide, sulfur dioxide, hydrogen sulfide, and toluene. Test durations varied from 3 to 24 h depending on the filtration efficiency. Each gas contaminant showed different reactions with the investigated filters. The filters did not let sulfur-containing components pass. However, carbon monoxide could not be filtrated by any of the tested filters. The filtration of nitrogen oxides was not efficient for all tested filters, while additional filter materials were essential for a successful filtration of ammonia. Comparative results lead to a discussion of possible effects on a fuel cell with an outlook on optimization of the filtration behavior.

Cathode Air Cleaners to Protect Fuel Cells

Elimination of toxic products formation in vapor-feed passive DMFC operated by absolute methanol using air cathode filter

Evaluation of activated carbon adsorbent for fuel cell cathode air filtration