Robust Hydrophobic Materials by Surface Modification in Transition-Metal Diborides

Mechanical properties and multifunctionality of AlB2-type transition metal diborides. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022;35:074002. [PMID: 36541538 DOI: 10.1088/1361-648x/aca85f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Transition metal diborides (TMdBs,P6/mmm, AlB₂-type) have attracted much attention for decades, due to TMdBs can be conductors, superconductors, magnetism materials, and catalysts. The layered structure caused by the borophene subunit is the source of functions and also makes TMdBs a potential bank of Mbene. However, TMdBs also exhibit high hardness which is not supposed to have in the layered structure. The high hardness of TMdBs arises from covalent bonds of boron-boron (B-B) and strongp-dorbit hybridization of B and TM. While strong B-TM bonds will eliminate the layered structure which may damage the functional properties. Understanding the basic mechanism of hardness and function is significant to achieve optimal TMdBs. This work summarizes the basic properties of TMdBs including hardness, superconductor, and catalytic properties. It can be found that Young's modulus (E) and Shear modulus (G) are beneficial for the hardness of TMdBs and the Poisson's ratio is the opposite. Increasing the atomic radius of TM brings an improvement in the hardness of TMdBs before it reaches the highest value of 1.47 Å, beyond which hardness decreases. Besides, TMdBs also have excellent activity comparable with some noble metals for hydrogen evolution reaction, which is closely related to the d-band center. More importantly, higher valence electron concentrations were found to be adverse to the hardness and superconductivity of TMdBs and greatly affect their catalytic properties. This review is of guiding significance for further exploring the relationship between structures and properties of TMdBs.

Surface Modification towards Integral Bulk Catalysts of Transition Metal Borides for Hydrogen Evolution Reaction

Transition metal borides (TMBs) are promising catalysts for hydrogen evolution reaction (HER). While the commercially available TMBs indicate poor HER performance due to powder electrode and low activity sites density, optimizing commercial TMBs for better HER performance is urgent. To break through the challenge, a new strategy is proposed to compose integral bulk electrodes with needle surfaces in TMBs. The integral bulk electrodes in TiB2, ZrB2, and HfB2 are formed under high pressure and high temperature (HPHT), and the nanoneedle morphology is constructed by chemical etching. In the three materials, the smallest overpotential is 346 mV at 10 mA cm−2 in the HCl etched bulk TiB2 electrode, which is about 61.9% higher than commercial TiB2 powder. Better performance arises from better conductivity of the integral bulk electrode, and the nano morphology exposes the edge sides of the structure which have high activity site density. This work is significant for developing new kinds of bulk TMBs catalysts.