Graphdiyne (GDY), as a new type of carbon material with a two-dimensional planar network structure composed of sp - and sp2 hybrid carbon atoms, has a high degree of conjugated system, regular and orderly pores, adjustable electronic structure, excellent conductivity and unique physical and chemical properties, which has quickly attracted extensive attention of researchers and become the forefront of current carbon material research. However, Graphyne based composites, due to their interface interaction, can effectively adjust the local electronic structure of the interface, showing higher catalytic activity or selectivity, have great potential applications in energy storage, electrochemistry, photocatalysis, electronics and other fields. At present, most catalysts are designed to significantly increase the number of Active site or the contact area of Active site, while the strategy of increasing the type of intrinsic Active site is rarely reported. The introduction of Chemical bond at the molecular interface has been proved to be an effective means to promote the interfacial charge transfer, optimize the Gibbs free energy, and then accelerate the reaction kinetics process. Therefore, it may be a very effective method to create new intrinsic active site by reasonably constructing interfacial Chemical bond, and then regulate the catalytic activity of active materials.
With the support of the National Natural Science Foundation of China, the Ministry of Science and Technology and Central China Normal University, the Guo Yanbing research group of the Institute of Environmental and Applied Chemistry of Central China Normal University has designed and synthesized a series of catalysts through the regulation of interface structure in recent years, which have shown excellent performance (Appl. Catalog., B, 2020, 265, 118469, ACS Appl. Mater. Interfaces, 2020, 12, 7091-7101, Catalog.: Sci. Technol., 2020, 10, 1661-1674). In addition, Guo Yanbing research group conducted systematic research on the involvement of sp carbon atoms in activating molecular oxygen. They synthesized a Cu TCNQ (tetracyano para benzoquinone dimethyl) nanowire array catalyst with carbon nitrogen triple bonds and carbon carbon triple bonds, and found that the C Å N bond regulated by metal copper can effectively activate molecular oxygen (ACS Appl. Material. Interfaces, 2018, 10, 17167-17174). Recently, they have been working in the renowned journal Environment in the field of the environment Sci.: Nano published a Critical Review article, which systematically introduced the unique structure, physical and chemical properties of Graphyne and its composite nanomaterials and their potential application prospects in the field of environmental remediation (Environment. Sci.: Nano, 2021, DOI: 10.1039 /D1EN00231G.).
Recently, the research group prepared three-dimensional self-supported graphdiyne/molybdenum oxide (GDY/MoO3) composite materials with interface "sp hybrid C-O-Mo bond" through precise interface regulation, and realized the application in the field of high current density hydrogen evolution. This work first predicted through DFT theoretical calculations that only GDY and molybdenum oxide MoO3 could form a chemical bond in the form of "sp hybrid C-O-Mo bond" (graphene cannot form a chemical bond with MoO3), and the formation of this chemical bond would help graphdiyne /molybdenum oxide (GDY/MoO3) to adsorb more water molecules (Figure 1). Then, GDY/MoO3 electrocatalyst with sp hybrid C-O-Mo bond was successfully prepared on 3D self-supported substrate copper foam by in-situ growth method. The structure and morphology of GDY/MoO3 were characterized by Raman, X-ray photoelectron spectroscopy (XPS) and X-ray near-side absorption spectroscopy (XANES) (FIG. 2). The results show that MoO3 is loaded on the surface of GDY with nanoparticles with an average particle size of 3.45 nm, and the SP-hybrid form of C atom in GDY forms a chemical bond with MoO3 (C-O-Mo bond), which is consistent with the DFT calculation results.
Figure 1. (a) GDY/MoO3 and Graphene/MoO3 optimized atomic structures; (b) Water molecular adsorption energy of GDY, GDY/MoO3, MoO3
Figure 2. Synthesis and interface structure characterization of GDY/MoO3
Based on the structural characterization and interface structure study of GDY/MoO3, it is applied to high current hydrogen evolution reaction and seawater hydrogen evolution. Further studies showed that the successful construction of the "interfacial sp hybrid C-O-Mo bond" enabled MoO3 to have a new intrinsic catalytic active site (non-oxygen vacancy active site), greatly increased the number of hydrogen evolution active sites (8 times that of pure MoO3), and promoted charge transfer (25 times that of pure MoO3) and the dissociation process of H2O molecules. The construction of this interface structure (sp hybrid C-O-Mo bond) enables GDY/MoO3 to achieve high current density hydrogen evolution (³ 1.2A cm-2), and exhibits good hydrogen evolution stability in alkaline electrolytes and natural seawater (Figure 3). This study provides a reference and a solid step forward for the industrial large-scale application of hydrogen evolution electrocatalysts.
Figure 3. (a) Schematic diagram of the adsorption positions of H2O molecules on GDY/ MOO3-VO and pure MoO3; (b) Polarization curve of the sample in 0.1M KOH solution; (c) Time-current curve of GDY/MoO3 at 0.1 M KOH and natural seawater
the results were published in the Journal of the American Chemical Society (J. Am. Chem. Soc., 2021, 143, 8720−8730). It is entitled "Interfacial sp C-O-Mo Hybridization Originated High-current Density Hydrogen Evolution." Master student Yao Yuan and doctoral student Zhu Yuhua are the co-first authors of this paper, and Professor Guo Yanbing and Associate Professor Luo Zhu are the corresponding authors.
