University of Science and Technology of China proposes crystal phase mixing strategy to design extremely stable and high-performance electrocatalyst

[ Instrument Network Instrument R & D ] Hydrogen energy is a clean new energy technology with application prospects. Compared with the traditional methane steam reforming hydrogen production process and alkaline water electrolysis process, the proton exchange membrane water electrolysis device has significant advantages such as fast startup speed, high hydrogen purity, fast hydrogen production rate, large current density, and high energy efficiency, and is expected to become Next generation advanced clean hydrogen production method. However, non-platinum-based catalysts are generally unstable in acidic media, and active metal components are easily lost during electrolytic cell operation. At present, acidic electrolytic water membrane electrodes rely on platinum-based catalysts (Pt, Ir, Ru, etc.), which leads to excessive hydrogen production, which greatly limits the application and promotion of proton exchange membrane water electrolytic cells.

Recently, Yu Shuhong's team at the University of Science and Technology of China and his team of high-aware researchers proposed a "crystal phase mixing" strategy and successfully designed and developed a non-precious metal electrocatalyst that exhibits high stability in acid electrolytes. Researchers performed "severe" alkaline heat treatment (5 M KOH, 200oC) of cubic cobalt diselenide (CoSe2) to promote the transformation of cubic CoSe2 structure into orthogonal phase CoSe2, successfully preparing a novel mixed phase CoSe2 Structure, exhibits excellent water reduction electrochemical activity and stable performance in acidic media. Related research results, titled Polymorphic cobalt diselenide as extremely stable electrocatalyst in acidic media via a phase-mixing strategy, were published in Nature-Communications on November 25 (Nature Communications 2019, 10, 5338). The co-authors of the paper are Zhang Xiaolong, Hu Shaojin, and postdoctoral Zheng Yarong of the University of Science and Technology of China.

The researchers treated the cubic phase of CoSe2 by an alkaline thermal method, which caused part of the Co and Se atoms to escape from the cubic phase of CoSe2 crystals and generate atomic-level defects. The generation of these defects causes the Se-Se bond located in the cubic phase structure to rotate in its local area and transform into a quadrature phase structure. CoSe2 (3) is uniformly and uniformly distributed in the cubic phase and the orthogonal phase (Figure 1).

Electrochemical tests showed that the polarization curve of the mixed-phase CoSe2 catalyst did not change significantly after 50,000 cycles, and its overpotential at 10 mA cm-2 did not increase significantly after the catalyst worked for more than 400 hours. The catalyst prepared by "crystalline phase mixing" has far better stability in acid electrolyte than cubic phase and orthogonal phase CoSe2 catalysts (Figure 2).

Studies have found that this new cubic-orthogonal CoSe2 catalyst greatly enhances the covalent nature of Co and Se atoms, and gives the lattice a stronger bonding energy, making this cheap material acidic. The medium not only exhibits high water reduction activity, but also exhibits excellent stable performance (Figure 3).

This research provides a strategy for designing catalysts with high stability in acidic media through material crystal phase control in the future, and provides a low-cost, highly active, and stable catalyst material that can be practically operated in acidic media. Brand new ideas.

Relevant research was funded by the National Natural Science Foundation of China's innovation research group, the National Natural Science Foundation of China's key projects, the Chinese Academy of Sciences 'cutting-edge science key research project, the Chinese Academy of Sciences' Nanoscience Innovation Center, and the Suzhou Nanotechnology Collaborative Innovation Center.