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Renewable energy (such as solar energy, wind energy, water level energy, etc.) is stored, transported, and transformed with hydrogen as a medium to achieve an economically friendly and sustainable economic configuration. At present, more than 95% of hydrogen comes from fossil fuels, and water is one of the important sources of hydrogen. The total energy of hydrogen extracted from it is 9,000 times that of fossil fuels. The electrolysis of water to hydrogen involves two important basic reactions, namely the reduction of the cathode water and the oxidation of the anode water. However, the limitation of the reaction kinetics requires providing an overvoltage that is higher than the theoretical decomposition voltage to accelerate the bipolar reaction, resulting in severe power loss. Some precious metals such as platinum, rhodium oxide, ruthenium oxide and the like can effectively reduce the activation energy barrier of the reaction and increase the reaction rate, but the expensive price limits its large-scale use in the electrolytic water industry.
Recently, Professor Yu Shuhong of the University of Science and Technology of China has developed a one-step synthesis technique and successfully achieved "chemical grafting" of cobalt selenide and molybdenum disulfide materials, and developed a water-reducing high-efficiency compound catalyst with hydrogen evolution properties close to that of precious metal platinum. The research results were published in the "Nature Communications" published on January 14.
The research group used a one-step method for the preparation of cobalt-selenide/molybdenum disulfide composite catalysts to exhibit excellent water-reducing catalytic activity, and the exchange current density reached 7.3×10-2 mA cm-2 in 0.5 M H2SO4 electrolyte (starting Potential - 11mV, Tafel slope 36 mV/decade).
It was found that the combination of these two materials forms a new cobalt-sulfur chemical bond at the interface. On the one hand, the coordination of cobalt and sulfur can regulate the electronic structure of molybdenum disulfide, reduce its Gibbs adsorption free energy to hydrogen, and thus enhance the adsorption of its active side sites to hydrogen intermediates and enhance its reaction kinetics; On the other hand, the interaction between sulfur and cobalt also brings about an electrocatalytic synergistic effect, so that the activity of cobalt selenide originally having a certain water reducing performance is further enhanced. The research group further cooperated with the research group led by Li Hua, a professor at Tsinghua University. Through DFT calculations, it was found that the hydrogen generation on this new type of composite catalyst only needs to overcome the energy of 1.13 eV (30.7 kcal mol-1) and it is easy to provide A small overpotential is reached. The experimental and calculation results show that the water reduction on the composite catalyst is a reaction process controlled by the adsorption and desorption of hydrogen adsorption. At the same time, the composite catalyst also exhibits excellent stability performance and is expected to replace platinum as a new generation of inexpensive hydrogen electrode materials.
In recent years, the research group has made a series of advances in the design and preparation of novel non-precious metal electrode materials for electrolytic water around the design of novel non-precious metal hydrogen electrode materials and oxygen electrode materials. Developed research on the development of new non-precious metal hydrogen electrode materials and oxygen electrode materials based on transition metal chalcogenide compounds. Through reasonable chemical “grafting†methods, inexpensive materials were selected and the synergistic reinforcing effect of the materials was used to design and prepare non-precious metal new compounds. The catalyst provides a new approach and is expected to provide the electrolyzed water industry with new, cheap, efficient, long-lasting water reduction and water oxidation electrocatalysts.
The group's earlier research also found that they discovered a layered cobalt-selenide-organic amine composite nanobelt (J.Am.Chem.Soc. 2009, 131, 7486-7487) with nickel oxide nanoparticles. Grafting can also achieve excellent "cooperative enhancement" effects. In this composite catalyst, nickel oxide can effectively open the OH bond of the surface-adsorbed water and generate hydrogen adsorption, while cobalt selenide can promptly combine with the generated adsorbed hydrogen to form hydrogen molecules. The experimental results show that the exchange current density of 1.4×10 −2 mA cm −2 is obtained by the complex energy (Angew. Chem. Int. Ed. 2013, 52, 8546-8550).
In addition, the research group has also made a series of progresses in the design of new non-precious metal water electrolysis anode materials. Because of the four-electron reaction involved, water oxidation is a more complicated process than water reduction (two-electron reaction). In a water electrolysis cell, the oxygen electrode has a greater overpotential demand with respect to the hydrogen electrode, resulting in a major power loss. Researchers in the international community took the lead in discovering that inexpensive cobalt selenide has its own intrinsic water oxidation activity. By introducing a new functional material, the electronic structure of the metal catalytically active center of the material can be adjusted, the adsorption energy of the oxygen intermediate is optimized, and the reaction rate of the oxygen electrode is greatly enhanced.
For example, trimanganese tetroxide/cobalt diselenide (J.Am.Chem.Soc. 2012, 134, 2930–2933) and cerium oxide/cobalt diselenide can be prepared by introducing trimanganese tetraoxide and germanium dioxide ( Small 2015, 11, 182-188) Composites, Tafel slopes for oxidation of water in 0.1 M KOH electrolyte are 64 mV/decade and 44 mV/decade, respectively, with the catalytic performance of cerium oxide/cobalt selenide even Exceeded commercial ceria electrocatalysts. The Tafel gradient of the composite catalyst with high specific surface area and high conductivity graphene and cobalt selenide is 40 mV/decade, and the TOF at 336 mV overpotential is 0.03565. 0.01724), which shows excellent kinetics of water oxidation reaction (ACS Nano 2014, 8, 3970-3978).
Based on a series of work in the field of energy-saving and efficiency-enhanced transition metal chalcogenide electrode materials, the research team was invited to write a review for the “Review of the Chemical Society†of the Royal Society of Chemistry, reviewing the progress made in this field and looking forward to the transition metal-based sulfur The prospects for designing high-efficiency energy conversion materials for family compounds (Chem. Soc. Rev. 2013, 42, 2986-3017).
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