China University of science and technology put forward the strategy of crystal phase mixing to design highly stable high performance electrocatalyst in acid environment

Hydrogen energy is the most promising and efficient new energy technology Compared with the traditional methane steam reforming hydrogen production process and alkaline electrolytic water process, the proton exchange membrane water electrolysis device has the advantages of fast start-up speed, high hydrogen purity, fast hydrogen production rate, high current density and high energy efficiency, which is expected to become the next generation of advanced clean hydrogen production method However, the non platinum based catalysts are generally unstable in acid medium, and the active metal components are easily lost in the operation of electrolytic cell At present, the membrane electrode of acid electrolyzed water relies on platinum based catalysts (PT, IR, Ru, etc.), which leads to the high composition of hydrogen production, which greatly limits the application and promotion of proton exchange membrane water electrolysis cell Recently, academician Yu Shuhong of University of science and technology of China and Professor Gao Jian's research group put forward a strategy of "crystal phase mixing", and successfully designed and developed a non noble metal electrocatalyst which can show high stability in acid electrolyte The cubic phase of cobalt selenide (cose 2) was treated with a "severe" alkaline heat treatment (5 mkoh, 200 OC) to change the partial structure of the cubic phase of cose 2 into the orthorhombic phase of cose 2, and a novel mixed phase of cose 2 was successfully prepared, showing excellent electrochemical activity and stability for water reduction in acid medium Relevant research results were published in nature communications (DOI: 10.1038 / s41467-019-12992-y) under the title of "polymer cobalt diselenide as extremely stable electronics in acidic media via a phase mixing strategy" The first co authors of this paper are Zhang Xiaolong, Hu Shaojin and Zheng Yalong, doctoral students of the University of science and technology of China The researchers treated the cube phase cose 2 by alkali heat method, and some of the CO and Se atoms escaped from the perfect cube phase cose 2 crystal, resulting in atom level defects However, the formation of these defects makes the se se bond in the cubic phase structure rotate in its local area and transform it into the orthogonal phase structure, and finally obtain the cose 2 with uniform distribution of the mixture of the cubic phase and the orthogonal phase (Fig 1) Figure 1 Preparation and structure diagram of mixed phase cose 2 catalyst (source: nature Communications) electrochemical test shows that the polarization curve of mixed phase cose 2 catalyst does not change significantly after 50000 cycles, and the over potential of catalyst at 10 Ma cm-2 does not increase significantly after more than 400 hours of operation The excellent stability of the catalyst prepared by "crystal phase mixing" in acid electrolyte is much better than that of cose 2 catalyst prepared by cubic phase and orthogonal phase Figure 2 Comparison of catalytic activity and stability of mixed phase, cubic phase and orthorhombic phase catalysts in acid medium by water reduction The covalency between CO and Se atoms endows the lattice with stronger bonding energy, which makes this cheap material show not only high water reducing activity in acid medium, but also excellent stability (Fig 3) Figure 3 Understanding of mechanism of excellent electrochemical stability of mixed phase cose 2 catalyst (source: nature Communications) This study provides a catalyst strategy with high stability in acid medium through material crystal phase control design, and a new idea for developing catalyst materials with low cost, high activity and high stability that can actually operate in acid medium The related research is supported by the innovation research group of NSFC, key projects of NSFC, key research projects of cutting edge science of Chinese Academy of Sciences, excellent innovation center of nanoscience of Chinese Academy of Sciences, collaborative innovation center of Suzhou nanotechnology, etc.