Hydrogels may be the answer to low cost hydrogen and clean energy
Researchers around the world have been looking for ways to enhance the efficiency and lower the cost of hydrogen production by improving the catalysts involved. Electrochemical hydrogen evolution reaction (HER) is a widely used method, but commercial the electrocatalysts are made from precious metals, which are expensive.
A research team from City University of Hong Kong developed a new, ultra-stable HER electrocatalyst, based on two-dimensional mineral gel nanosheets and does not contain any precious metals. The catalyst can be produced in large scale and can help achieve a lower hydrogen price in the future.
Single-atom catalysts have promising potential in catalytic HER applications because of their high activity, maximised atomic efficiency, and minimised catalyst usage. But the conventional fabrication process of single-atom catalysts is complicated. It generally involves introducing the targeted single-atom metal to the substrate precursor followed by thermal treatment, usually higher than 700℃, which requires a lot of energy and time.
In this regard, a research team co-led by CityU materials scientists have developed an innovative, cost-effective and energy-efficient way to produce a highly efficient HER single-atom electrocatalyst that uses precious-metal-free mineral hydrogel nanosheets as a precursor. Their findings were published in the scientific journal Nature Communications.
“Compared with other common single-atom substrate precursors, such as porous frameworks and carbon, we found that mineral hydrogels have great advantages for mass production of electrocatalysts due to the easy availability of the raw materials, simple and environmental-friendly synthetic procedure, and mild reaction conditions,” said lead researcher Professor Lu Jian, Chair Professor in the Department of Mechanical Engineering and the Department of Materials Science and Engineering at CityU.
Their electrocatalyst precursor is prepared using a simple method. First, solutions of polyoxometalate acid and ferric ions are mixed at room temperature, resulting in novel two-dimensional iron–phosphomolybdic-acid nanosheets. After excess water is removed by centrifugation, the nanosheets become mineral hydrogel free of any organic molecules. The process is much more convenient and economical than the previously reported processes that typically require high temperature and pressure, and longer time for the self-assembly of single-atom substrate precursors.
After a further phosphating treatment at 500 ℃, a single-iron-atom dispersed heterogeneous nanosheet catalyst is formed, avoiding the time-consuming fabrication process of loading single atoms on the substrate.
The experiments found that the new catalyst exhibits excellent electrocatalytic activity and long-term durability in the HER. “This is one of the best performances achieved by non-noble-metal HER electrocatalysts,” said Lu. “The unique idea of using mineral gel to synthesise monatomic dispersed heterogeneous catalysts provides an important theoretical basis and direction for the next step of scalable production of cheap and efficient catalysts, which can help contribute to lowering the cost of hydrogen production in the long run.”