![]() Although the requirements called for 6,000 hours of operation, a single cell assembly operating at nominal recharge conditions operated in the laboratory for over 54,000 hours-making this sort of high-efficiency oxygen-generating system ideal for the International Space Station. The result of this unique design was a greatly simplified fluid system, with only the oxygen fluid circuit maintained at elevated pressure. A sintered powder metal porous plate provided structural support to the electrolysis cell membrane while operating at high differential pressure, simultaneously allowing fluid transport both to and from the bulk water stream and the electrode surface. An advanced cell design was built by Hamilton Sundstrand in the 1990s that permitted high-pressure gas generation without the need for a pressure vessel or complex pressure control system. ![]() Oxygen and hydrogen are generated in a stoichiometric ratio-two volume units of hydrogen for every one of oxygen-at a rate proportional to the applied cell current.īecause the membrane is non-porous, a PEM cell can safely separate product gases at superatmospheric pressures.Most of the design elements used to produce a water electrolysis cell stack were originally developed during the 1980s for submarine-based life support systems. Liquid water is also released at the cathode due to a process called electro-osmotic drag. The protons and electrons recombine at the cell cathode to produce hydrogen. The hydrogen ions migrate from the cell anode to the cell cathode, or hydrogen electrode, under the effect of the electric field imposed across the cell, while the electrons are transferred by a dc power source. In a PEM electrolyzer, water is oxidized at the oxygen electrode, or cell anode, to produce oxygen gas, releasing hydrogen ions (protons) and electrons. What makes the generator safe? The device uses a proton-exchange membrane (PEM) to separate the generated hydrogen and oxygen. The generator operates on a simple principle- electrolysis, the dissociation of oxygen and hydrogen from water through the application of electricity. It too has an on-board oxygen generator, though of a radically different design. The successor to Mir is the International Space Station. The generator relied upon an exothermic chemical reaction to create a breathable atmosphere for the crew of the space station. That fire was traced to an on-board oxygen generator. With their route to an escape capsule blocked by the flames, the crew could only watch as the fire licked at the aluminum hull before dying out after 14 minutes. It was a moment that bordered on catastrophe: A fire aboard the Mir space station in 1997 almost caused the loss of the orbiting platform and the deaths of its crew. ![]()
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