Innovators at NASA’s Glenn Research Center have developed a method for producing pure high-pressure oxygen via an electrochemical pumping process through a solid oxide electrolysis (SOE) cell stack. Glenn’s device can either concentrate the oxygen in the ambient atmosphere or extract the oxygen via the chemical reduction of carbon dioxide, water, or any combination of these substances. This solid-state device does not use any moving parts or any extra separation processes to purify the delivered oxygen. Instead, Glenn’s technology relies on a multi-stage stack design and an SOE process that includes an oxygen-ion-conducting ceramic membrane to generate high-pressure oxygen within a compact, noiseless device. This process has great potential for use in medical, industrial, and recreational applications.
The technology was originally conceived as a method to generate pressurized pure oxygen for extravehicular activity (EVA) suits worn on the International Space Station. The generator is an all-solid-state device that separates oxygen from air, water, or carbon dioxide and electrochemically pumps it to a high pressure in a multi-stage process. Glenn’s design features an SOE stack, based on bi-supported cell design, that is structurally supported by two electrode layers. Sandwiched between the cathode and anode sides is an oxygenion-conducting solid-state electrolyte membrane made of yttria-stabilized zirconia (YSZ). These membranes form the individual SOE cells within the stack, and each cell carries out a single stage of the multi-stage process, with each stage incrementally pressurizing the oxygen. A voltage (1.5 to 2 volts) is applied across the cell, and the air or other input is supplied to the cathode side, where the oxygen dissociates into oxygen ions. The YSZ membrane will conduct only the oxygen ions, producing pure, dry oxygen. The entire stack is wrapped in a glass ceramic seal, providing a pressure vessel for the device.
Glenn’s novel stack design allows for hermetic sealing, and does not require a compression-sealing mechanism or other spring-loaded hardware. Each cell is wired in parallel so the voltage can be controlled across each cell to avoid electrochemical reduction of the electrolyte. In addition, each cell is electrically insulated from other cells in the stack using a non-electronically conducting, ceramic-woven cloth YSZ layer. Because Glenn’s process resists fouling from water containing impurities or other debris, it does not require a high-purity water source as do other water electrolysis technologies. The oxygen product is also sterile for medical applications because of the high temperature (in excess of 600 °C) at which the process operates.
Potential applications include medical oxygen production for home use, medical oxygen systems for hospitals, refining systems (e.g., fluid catalytic cracking regenerators), syngas generation for gas to liquids (GTL) plants, industrial processes (e.g., smelting iron), and scuba diving and high-altitude sports.