Electrolysis less efficient in low gravity

Experiments on the vomit comet show that low gravity can make electrolysis of water less efficient. Could that hamper aims for a moonbase?

While it may sound like science fiction, space agencies are in the advanced stages of planning missions to put bases on the Moon and Mars. This means methods to generate oxygen for these lunar spacebases of the future are already in development, and researchers from ESA and the University of Glasgow have been paying serious attention to how we solve some of the other problems that accompany habitation in this lower gravity environment, including producing water and breathable air.

One source of the oxygen we need to stay alive is ice. Mined and melted, the resulting water can be converted into oxygen and hydrogen by using the process of electrolysis to split the molecules into their component molecules. 

But what role might gravity play, if any? According to Bethany Lomax and Mark Symes, who are studying the effects of lower gravitational fields on electrolysis, lowered gravity alters the buoyancy of oxygen bubbles and causes them to move more slowly. This decreases the rate at which more water can be decomposed and new oxygen bubbles can be formed, dropping the overall rate and efficiency of the process by up to 10%. Despite this cost, electrolysis still looks like a viable way to produce oxygen and hydrogen on the moon or Mars.

Surprisingly, to conduct their low gravity experiments, the duo didn't head into space. Instead they took their apparatus aboard the "vomit comet" - an Air Zero G Airbus A310 - that flies on a parabolic flight path up and down through the atmosphere, creating about 20 seconds of weightlessness on each dive for the occupants.

During these 20 second "weightlessness windows", they were able to using their device, comprising a small centrifuge with an electrolysis chamber inside, to accurately recreate the gravitational pull at the Moon's surface and measure the rates at which the electrolysis process would progress there.

The efficiency, they found, follows a clear trend across a range from eight times the gravity on Earth down to one-sixth the gravity on Earth.

The team are now studying how electrolysis of lunar rocks found on the moon’s surface can be used as alternative oxygen sources for human settlements.