Clean hydrogen energy is a viable alternative to fossil fuels and is critical to achieving carbon neutrality. Researchers around the world are looking for ways to increase the efficiency and reduce the cost of hydrogen production, particularly by improving the catalysts involved. Recently, a research team from the City University of Hong Kong (CityU) developed a new, ultra-stable electrocatalyst for the hydrogen evolution reaction (HER) based on two-dimensional mineral gel nanosheets and containing no noble metals. The catalyst can be produced on a large scale and can contribute to a lower hydrogen price in the future.
The electrochemical hydrogen evolution reaction (HER) is a widely used method for hydrogen generation. However, commercial HER electrocatalysts are made from noble metals, which are expensive. On the other hand, single-atom catalysts have promising potential for catalytic HER applications because of their high activity, maximized atomic efficiency, and minimized catalyst utilization. But the traditional manufacturing process of single atom catalysts is complicated. It generally involves introducing the desired single-atom metal into the substrate precursor, followed by a heat treatment, usually higher than 700 °C, which requires a lot of energy and time.
In this regard, a research team led jointly by CityU materials scientists has developed an innovative, low-cost, and energy-efficient method to fabricate a high-efficiency HER single-atom electrocatalyst using precious-metal-free mineral hydrogel nanosheets as a precursor.
“Compared to other common single-atom substrate precursors such as porous frameworks and carbon, we found that mineral hydrogels have great advantages due to the easy availability of the raw materials, the simple and environmentally friendly synthesis method, and the mass production of electrocatalysts under mild reaction conditions,” said Professor Lu Jian, Chair Professor at the Department of Mechanical Engineering (MNE) and the Department of Materials Science and Engineering (MSE) at CityU, who led the research.
Your electrocatalyst precursor is made using a simple procedure. First, solutions of polyoxometallic acid (PMo) and ferric ions (Fe3+) 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 hydrogels, free from any organic molecules. The method is much more convenient and economical than the previously described methods, which typically require high temperatures and pressures and a longer time for the self-assembly of single-atom substrate precursors.
After a further phosphating treatment (at 500℃) of this mineral gel precursor, a heterogeneous nanosheet catalyst with single iron atoms (“Fe/[email protected]”) is formed, avoiding the time-consuming manufacturing process of loading single atoms onto the substrate.
The experiments revealed that the new catalyst exhibits excellent electrocatalytic activity and long-term durability in the HER, exhibiting an overpotential of only 38.5 mV at 10 mA cm−2and ultra-stability with no degradation in performance over 600 hours at a current density of up to 200 mA cm−2.
‘This is one of the best performances achieved by base-metal HER electrocatalysts,’ said Professor Lu. “The unique idea of using mineral gels to synthesize monatomically dispersed heterogeneous catalysts provides important theoretical foundation and direction for the next step in scalable production of cheap and efficient catalysts that can help lower the cost of hydrogen production in the long-term.” “
Their results were published in the scientific journal nature communication entitled “Two-dimensional hydrogel-derived single-atom anchored heterostructures for ultrastable hydrogen evolution”.
The first author of the paper is Dr. Lyu Fucong from CityU. The corresponding authors are Professor Lu, Dr. Li Yangyang, associate professor of MSE, and Dr. Sun Ligang, assistant professor in the School of Science at the Harbin Institute of Technology.
The research was funded by Shenzhen-Hong Kong Science and Technology Innovation Cooperation Zone Shenzhen Park Project, National Key R&D Program of China, National Natural Science Foundation of China, Guangdong Basic and Applied Basic Research Foundation, Science, Technology and Innovation Commission of Shenzhen Municipality and the Hong Kong Innovation and Technology Commission through the Hong Kong Branch of National Precious Metals Material Engineering Research Center at CityU.
To address the problem of the high cost of commercial platinum-based electrocatalysts, the team led by Professor Lu recently made another breakthrough. They have provided a solution through the rational nanostructured alloy design to develop a high-performance, low-cost electrocatalyst.
Professor Lu’s team has conducted in-depth research on alloy nanostructures that have both crystalline and amorphous phases at the same time. They found that the local chemical inhomogeneity, short-range order, and strong lattice distortion in the nanocrystalline phase are desirable for catalysis application, while the amorphous phase can provide abundant active sites with lower energy barrier for the hydrogen evolution reaction. Hence, they devoted their research efforts to the design and construction of two-phase alloys as excellent electrocatalysts for hydrogen production.
They proposed a new strategy for the design of alloys and nanostructures based on thermodynamics. First, they predicted the compositional range of “crystal-amorphous” two-phase formation according to the Amorphous Formation Ability (GFA). They then successfully fabricated the aluminum-based alloy catalyst with a “crystalline-amorphous” biphasic nanostructure using the simple magnetron co-sputtering method.
Thanks to this nanostructure, the new catalyst showed better electrocatalytic performance in alkaline solution than the commercial platinum-based electrocatalyst with an overpotential of only 28.8 mV at 10 mA cm-2.
“In this novel aluminum-based alloy catalyst, we use ruthenium, which is cheaper than platinum, as the precious metal component. Therefore, it can be less expensive than the commercial platinum-based electrocatalysts,” Professor Lu said. “And apart from hydrogen evolution, the nano two-phase electrocatalytic mechanism can be applied to other catalytic systems. The ‘crystal glass’ nanostructure design offers a new approach to develop next-generation catalysts.”
The results were published in scientific advances, entitled “A Crystal Glass Nanostructured Al-Based Electrocatalyst for the Hydrogen Evolution Reaction”. dr Liu Sida, former postdoctoral fellow (currently Professor at Shandong University), and Mr. Li Hongkun, MSE PhD student, are the co-first authors. The corresponding authors are Professor Lu and Dr. Li from CityU and Professor Wu Ge from Xi’an Jiaotong University. Other CityU researchers include Dr. Zhou Binbin, a former postdoc at MNE (currently Research Associate Professor at Shenzhen National Institute of Advanced Electronic Materials Innovation), Mr. Zhong Jing and Ms. Li Lanxi, both MSE PhD students, and Mr. Yan Yang, MNE PhD student.