Hydrogen produced in a climate-friendly way is to replace oil as the universal fuel for industry. But in areas where the sun shines a lot, there is usually not much water. What can be done?
Hydrogen is seen as a beacon of hope for the energy transformation - it is to be used as a fuel for aircraft, ships and trucks, as a raw material for industry or as a fuel for heating systems. If it is produced with renewable energy from water, its manufacture is almost climate-neutral. However, in particularly sunny or windy regions, there is often not enough water for electrolysis. A research group led by chemical engineer Gang Kevin Li from the University of Melbourne has therefore developed a prototype that can take in moist air, extract the water from it and split it directly into the two gases oxygen and hydrogen. She presents the principle in the current issue of Nature Communications.
To reduce carbon dioxide emissions in industry, hydrogen (H2) is enormously important. When it is burned, only water is produced. In the particularly energy-intensive production of steel, hydrogen should one day replace coal. Certain processes in the chemical industry can only be made climate-friendly with green hydrogen. And gas-fired power plants are also to be operated with H2 in the future. Hydrogen is the most common chemical element in the universe. On Earth, however, it is found almost exclusively in the form of water.
Existing large-scale electrolysis plants often require complex material components, rare metals and access to pure fresh water. This can lead to competition for drinking water supplies, which are already limited in some parts of the world. These factors drive up the cost of hydrogen production and have so far limited widespread application.
Gang Kevin Li and his colleagues want to get around this problem by accessing water supplies that can be found in even the driest parts of the world, such as the Sahara Desert or the Australian outback. "At any given time, there are 12.9 trillion tons of water in the air," the scientists write, "universally available and inexhaustible." All it would take is efficient systems to access it. They have now shown that this is possible. Up to a minimum relative humidity of four percent, hydrogen can still be produced with this so-called "direct air electrolysis" (DAE).
At the heart of their electrolysis cell is a porous substance impregnated with sulfuric acid, which on the one hand serves as an electrolyte and on the other removes moisture from the ambient air. The researchers used platinum as the electrode material. They operated their module with solar energy and tested it for twelve days at a time for eight hours each. They collected the hydrogen and let the oxygen escape. In this way, they achieved an average production volume of 93 liters of pure hydrogen per hour and square meter of the cathode material.
While the authors write that their electrolyzes are scalable, they do not comment on the cost or potential environmental impact of their technology.