Predicting the efficiency of oxygen-evolving electrolysis on the Moon and Mars

Establishing a permanent human presence on the Moon or Mars will require a secure supply of oxygen for life support and refueling. The electrolysis of water has attracted significant attention in this regard as water-ice may exist on both the Moon and Mars. However, to date there has been no study examining how the lower gravitational fields on the Moon and Mars might affect water electrolysis when compared to terrestrial conditions. This knowledge-gap hampers efforts to design electrolysis systems to support human habitation on these bodies. Herein we provide, for the first time, experimental data on the effects of gravitational fields on water electrolysis across the entire range from 0.166 g (lunar gravity) to 8 g (eight times the Earth’s gravity). Various gravitational levels were achieved through the use of a centrifuge system operating both in a terrestrial laboratory (1 g – 8 g) and also in freefall during parabolic flights on an Airbus A310 aircraft (<1 g). Through analysis of the effects of gravity on electrolytic currents and voltages, and also on the formation and evolution of oxygen bubbles on the surface of the anode (visualized in situ during electrolysis), we show that electrolytic oxygen production is reduced by around 11% under lunar gravity with our system compared to operation at 1 g. More importantly perhaps, our results indicate that electrolytic data collected using less resource-intensive ground-based experiments at elevated gravity (>1 g) may be extrapolated to gravitational levels below 1 g. The implication is that future investigations of electrolysis on the Moon or Mars can substitute parabolic flights with these much more accessible facilities.

在月球或火星建立永久人类驻留基地，需要可靠的氧气供应以保障生命维持与燃料补给。鉴于月球与火星上均可能存在水冰，水电解（water electrolysis）技术在此领域受到了广泛关注。然而迄今为止，尚无研究探讨相较于地球重力环境，月球与火星的弱重力场会如何影响水电解过程。这一认知空白掣肘了为保障这些天体上的人类驻留而开发电解系统的相关工作。本研究首次提供了覆盖0.166g（月球重力）至8g（地球重力的8倍）全范围重力场对水电解影响的实验数据。通过离心机系统可实现多种重力水平：在地球实验室中可实现1g至8g的重力环境，而在空客（Airbus）A310飞机的抛物线飞行过程中则可获得小于1g的自由落体重力环境。通过分析重力对电解电流、电压的影响，以及对阳极（anode）表面氧气气泡的形成与演化过程（电解过程中完成原位可视化观测），本研究发现，相较于1g重力环境下的运行结果，本系统在月球重力环境下的电解制氧量约降低11%。更为关键的是，本研究结果表明，利用资源消耗更低的地面高重力（>1g）实验所获得的电解数据，可外推至低于1g的重力环境。这意味着未来针对月球或火星电解过程的研究，可使用这些更易获取的实验设施替代抛物线飞行实验。