Classical solid oxide fuel cells (SOFCs) have 50 years technical history. They operate at high temperatures, use hydrogen as fuel and a solid oxide (ceramic) electrolyte to conduct oxide ions created at the cathode to the anode. The electrochemical oxidation of the oxide ions with the fuel occurs on the anode side. In our days more than 40 companies and thousands of research groups all over the world are working intensively towards a decrease of material costs and operating temperature, improvement of performance stability, fuel flexibility and efficiency.
In the last 20 years, due to the discovery of proton conductivity in perovskite-dopped cerates by Iwahara and co-workers more attention is drawn to proton conducting fuel cells (PCFCs) in which the electrolyte is a solid state proton conductor. Their main advantage is that water forms and leaves the system on the side exposed to air, as opposed to the traditional SOFCs. Since the more mobile proton is transported through the electrolyte, PCFCs have the potential to operate at lower temperatures (T = 500 - 800°C). However, the two designs have one principle disadvantage, which automatically decreases the electrical efficiency - the presence of water at the electrodes, which brings to:
The basic idea of the proposed new concept for a high temperature fuel cell consists in isolating the hydrogen and oxygen compartments from the exhaust water.
After this “promenade” in high temperature fuel cells the natural question that emerges is: ”Can’t we isolate both hydrogen and air/oxygen sides of the fuel cell from the exhaust water?”
The innovative concept steps on a three compartment fuel cell design realized by a junction between a PCFC anode part (anode/electrolyte) and a SOFC cathode part (electrolyte/cathode) through a mixed proton and oxide ion conducting porous ceramic membrane. Protons created at the anode progress toward the central membrane where they meet the oxide ions created at the cathode and produce water, which is evacuated through the interconnecting porous media. In this way hydrogen, oxygen and water are located in 3 independent compartments. The core of the design is the central membrane (CM), which should have both good mixed conductivity and porous microstructure to allow the evacuation of the water.
The most important advantages of the new design are that:
As in an internal combustion engine, the proposed concept allows for an easy and independent application of pressure on both the hydrogen and oxygen electrodes to tailor and enhace the efficiency of the system, which is impossible in standard SOFCs and PCFCs.
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