Cities full of toxic exhaust fumes – we all want them to be a thing of the past. There are a growing number of alternative drive technologies for better air quality – and in some cases they are already a viable option. The fuel cell is one of them, offering a flexible and sustainable alternative to regular combustion engines. However, hydrogen-powered vehicles are also affected by fine dust and noxious gases, and filters are needed to clean the air used for the chemical reaction in the fuel cell. Freudenberg Filtration Technologies is working to address these challenges and providing filtration solutions that combine chemical and particle filtration in order to ensure optimal performance.
Rising gas prices and ongoing climate change – it has never been so important to switch to environmentally friendly energy sources. Scientists and industry experts are focusing their efforts on finding climate-friendly transportation methods without sacrificing the convenience we are accustomed to. According to current studies, no single technology will replace the traditional combustion engine. Instead, it is expected that a variety of concepts will co-exist. All-electric vehicles still have a limited range, which makes them especially suited to shorter trips. However, people or companies that depend on reliable, long-distance solutions require vehicles with faster refueling. Larger cars, buses or trucks simply need more power than a single battery can provide. Fuel cells could take over where batteries fall short: It only takes a few minutes to refuel the hydrogen tank of a fuel-cell vehicle. The combination of battery and fuel cell also provides a greater range and more power. Experts estimate that there will be more than 100 million hydrogen-powered vehicles on the roads worldwide by 2050.
Hydrogen is a by-product of numerous chemical processes and can also be generated by renewable energy. A fuel cell consists of electrodes separated by a membrane. At the anode the hydrogen oxidizes and sets free electrons and protons. The positively charged protons pass through the membrane. To stimulate the electrochemical reaction, each electrode is covered with a catalyst – often platinum. The negatively charged electrons flow through an external circuit, generating electricity. At the cathode, oxygen is entering the cell and a reduction takes place resulting in water. A single fuel cell produces approximately one volt. In order to generate enough energy for a vehicle, the cells are arrayed and connected in series – so-called “stacks”. But the development of a new drive system doesn’t end with being able to generate enough power to move a car: The whole system needs to be adapted to the challenges that arise with the new engine, such as supplying the cell with clean air to prevent power loss.
In general, fuel cells use the oxygen in ambient air for their reactions. However, the surrounding air is not clean. The amount of harmful particles and gases in the air greatly depends on the surroundings – an industrialized metropolis might have a different mix of contaminants than a smaller city that is prone to traffic jams, whereas in coastal regions the salty air might be the biggest problem for the fuel cell. Depending on the level of air pollution, the charging system draws in large amounts of particles and noxious gases over time. What represents a health problem for humans also has a damaging impact on fuel cells.
While some particles and gases lead to short-term performance loss – resulting, for example, in a significant drop in vehicle speed or power – others can cause severe, irreparable damage to the fuel cell. Fine dust, for example, which tends to build up on the surfaces of sensors and turbochargers, influence the function and efficiency of the components and system periphery. Additionally, the particles block the flow channels of the fuel cell itself. This leads to a higher flow resistance and a permanent loss of energy. Salts and harmful gases cause a poisoning of both anode and cathode catalyst sides and a decrease in the catalyst activity – eventually making the fuel cells less effective. Sulfurous gases are especially harmful: Even small amounts of sulfur contaminants collecting on the components of the cell stack can eventually lead to a complete breakdown.
To protect the engine from these damaging effects, an intake air filter system is indispensable. Effective filtration can protect sensitive components, such as the catalyst material and the membranes used in the stack. Particle filter layers protect the system from fine dust, while chemical filter layers with specific adsorbent configurations, for example activated carbon, block harmful gases. To guarantee optimal filter efficiency, however, manufacturers have to make certain compromises. The more layers the filter consists of, the better the filtration. At the same time, too many layers lead to a rise in pressure drop, and the air compressor, which runs on part of the energy produced by the fuel cell, has to compensate for the flow loss. Accordingly, the overall efficiency of the system suffers from the air resistance and efficiency of the filter.
In terms of size, larger filters provide better pressure drop, efficiency and longevity. However, space is limited in the engine compartment and smaller filters fit in more easily, leaving room for other components. In the end, it is always a question of what degree of efficiency and lifetime manufacturers want to achieve. Thanks to its extensive experience in the mechanics of fuel cell systems, Freudenberg Filtration Technologies is able to use its internal synergies to provide customer-specific solutions that ensure high efficiency.
Freudenberg has been helping manufacturers use fuel cells from the outset. In 2001, the company began researching ways in which it could improve the functionality and efficiency of fuel cells. Today, several divisions of the Freudenberg Group, based in Weinheim, Germany, produce components to support fuel cells – for the automotive industry, for buses, trains and ships, and for stationary systems, such as combined heat and power units (CHPs). Freudenberg Sealing Technologies provides solutions to seal the different stack layers and prevent the reactants from leaking out and Freudenberg Performance Materials supplies gas diffusion layers, which optimize the gas flow within the cell. In the periphery of the fuel cell, humidifiers from Freudenberg Filtration Technologies protect the delicate membrane in the cell from drying out, while filter media specially developed for the unique requirements of fuel cells protect the catalyst material and the membranes in the stack, as well as system components, from contaminant gases and particles.