UK scientists have revealed a decrease in oxygen production in low gravity
Scientists at the University of Glasgow in the UK have revealed that the electrolysis of water will produce less oxygen on the Moon and Mars, or will be more energy-intensive than on Earth, due to weaker gravity. The results, published in Nature Communication, allow us to understand in advance the problems that space colonies will face when consuming resources available on the celestial bodies of the Solar System.
The behavior of oxygen bubbles on the surface of an electrode immersed in water depends on gravity, which directly affects the efficiency of electrochemical oxygen production. Although researchers have conducted experiments with electrolyzers in zero gravity conditions during parabolic flight, there is no data on how they work under low gravity.
In microgravity, the predominant factor in the formation of oxygen bubbles is not buoyancy, which depends on gravity, but the force of interfacial tension, which holds the bubbles on the surface of the electrode while they grow. As a result, a thick layer of bubble foam forms around the electrode, which reduces the electrocatalytic area and increases ohmic resistance (that is, DC energy loss) and anode overvoltage, which corresponds to additional energy costs for electrolysis. In the conditions of hypergravity simulated in a centrifuge, the efficiency of electrolysis, on the contrary, increases.
To simulate an attraction smaller than Earth's, the researchers used centrifuges, where four electrolytic cells were placed, during a parabolic flight. Two modes of operation of the electrolyzer were studied — potentiostatic and galvanostatic. In the first case, the system maintains a constant value of the electrode potential, and in the second — the current strength. Although galvanostatic mode is used more often in industrial systems, voltage control below a certain level in potentiostatic modes may be important in order to reduce the decomposition of the electrolyte and avoid the appearance of undesirable impurities that complicate cleaning. In addition, it may contribute to incomplete reduction of oxides in the lunar regolith, as the most effective way to extract oxygen.
It turned out that in the conditions of lunar and Martian gravity (0.166g and 0.376g) under the potentiostatic regime, oxygen production can decrease by about 11 and 6 percent compared to terrestrial conditions (1g). In galvanostatic mode, an increase in energy consumption is possible due to a higher operating potential. In conditions of low gravity, such costs can be significant, which should be taken into account when designing space electrolyzers. In some cases, scientists believe, reducing oxygen production may even be preferable.
