Researchers have realized that direct photochemical reactions can provide the oxygen and hydrogen that humans need for long-term habitation on Mars or the Moon.
The International Space Station (ISS) relies on water electrolyzers powered by photovoltaics to obtain oxygen from water. But the two-step process—converting sunlight into electricity and then using the electricity to electrolyze water—is expensive.
A paper published this week said that about 1.5kW of the 4.6kW power budget of the ISS environmental control and life support system is consumed by the oxygen generator (OGA), which relies on electrolysis. The approach was a dead end for future space exploration and habitation, says the study, published in Nature Communications.
In addition to high power demands, the OGA and carbon dioxide reduction assembly “currently on board the ISS carry the challenge of being notoriously cumbersome and prone to failure due to outdated, inefficient or obsolete compartments,” it said.
As an alternative approach, lead researcher Katharina Brinkert, assistant professor of catalysis at the University of Warwick, assessed the viability of photoelectrochemical (PEC) devices to help the chances of long-term survival.
PEC devices use semiconductor materials to convert solar energy directly into chemical energy to produce hydrogen and oxygen without requiring intermediate electricity generation. The technology is the subject of intense research on Earth because it could help with the sustainable energy problem, but its potential in space has yet to be explored.
“This work aims to establish the theoretical foundations for the application of PEC devices in lunar and Mars habitats and makes the first attempt to investigate the feasibility of using them for oxygen production and carbon dioxide recycling,” Brinkert said in the paper.
The researchers concluded that it is possible, but with some caveats.
“Although the high long-term efficiency and power density of PEC devices are still an integral part of current ground-based research efforts, we have shown that the application of these devices can go beyond Earth and potentially contribute to the realization of human space exploration,” the report i said.
The research also looks at whether PEC devices can be built on an alien settlement using In-Situ Resource Utilization (ISRU), meaning what you can find where you land.
“The design of the device can draw on various semiconductor and electrocatalyst materials that are available on the Moon and Mars, and the necessary materials can eventually be produced through ISRU. Furthermore, we have previously demonstrated that PEC devices can operate efficiently in microgravity, and our theoretical analysis suggests that it can be suitably scaled up,” the study said. ®