Large-Scale Synthesis of Electrochemically Active Titanium Diboride-Based Nanosheets by High-Energy Ball Milling

Abstract

AlB2-type layered metal diborides have sought renewed research attention in recent years on account of their ability to yield XBenestheir quasi-two-dimensional (2D) counterparts. These quasi-2D nanostructures present exciting avenues to utilize the rich science offered by metal diborides. While a range of approaches have been developed to exfoliate layered metal diborides, the ability to obtain XBenes in a scalable manner is in its incipient stagesthis is a critical bottleneck in translating their rich nanoscience into tangible technology. In this work, we present a scalable approach that employs high-energy ball milling to exfoliate titanium diboride (TiB2) into its quasi-2D counterparts at the gram scale. We first show that milling TiB2 crystals for an optimal duration (6 h) and at a specific balls-to-powder ratio (20:1) yields multi-layer-thick nanosheets (∼5–10 nm thick). Second, by using Rietveld refinement and Raman spectroscopy, we show that the chemical integrity of TiB2 is retained to a large extent upon exfoliationthere is an associated formation of defects within the crystal structure of TiB2 that evolve with milling. Finally, we show that upon milling, the native electrochemical activity of TiB2 is enhanced by several folds. This ability to obtain nanosheets of TiB2 in a scalable manner using a high-energy ball mill bridges a critical missing link in the fast-growing science on nanoscaling AlB2-type metal borides.

Review and Perspectives of Electrochemical Energy Conversion and Storage in Metal Diborides and XBenes

“…Specifically, MgB 2 is the most explored metal diboride where these methods are utilized for exfoliation. Further, mechanical ball milling has emerged as a prominent method for exfoliating layered materials. ,, This technique takes advantage of high rotational speeds during the milling processes, leading to rapid collisions within the bulk material. These collisions generate shear and vertical impact forces, aiding in the exfoliation process.…”

“…One of the earliest MgB 2 nanosheet experimental realizations was made in 2015 by Das and colleagues . Researchers worldwide have synthesized 2D nanostructures from AlB 2 -type metal borides primarily by top-down approaches such as chemical exfoliation, , ultrasonication, , cation exchange, dissolution and recrystallization process, , cosolvent exfoliation, , and mechanical ball milling. , …”

“…AlB 2 -type metal borides are primarily layered materials where boron planes are stitched together by metal atoms, constituting a mixture of covalent and ionic bonding. − Owing to their strong covalent bonding in M–B and B–B bonds, metal diborides offer higher chemical and thermal durability for electrochemical activities than conventional metal nitrides and carbides. − The space geometry of these diborides is P 6/ mmm , which imparts to them unique physicochemical properties that are different from other borides . These properties include high melting point (∼3020 °C for TiB 2 ), high hardness (∼23 GPa for ZrB 2 ), good electrical conductivity (∼1500 S/cm for TiB 2 ), high thermal conductivity (∼125 W/mK for ZrB 2 ), , and chemical inertness.…”

“…(a) Impression of the research contributions related to metal diborides when searched with keyword “metal diborides” [Web of Science] and (b) timeline depicting exfoliation of different layered metal diborides spanning a period from 2015 to 2022. ,,− ,,,, New approaches such as dissolution and recrystallization were developed in addition to conventional methods like metal borohydride reduction, the molten salt method, etc.…”

Insights into the Unanticipated Chemical Reactivity of Functionalized Nanosheets Derived from TiB2

“…We have shown that nanosheets from TiB 2 can be derived by dissolution and recrystallization, 16 cosolvent-assisted exfoliation, 23 surfactant-assisted exfoliation, 36 and, very recently, mechanical exfoliation. 37 Among these methods, dissolution and recrystallization was our first attempt at exfoliating TiB 2 . The uniqueness of this method lay in the fact that rather than a top-down exfoliation process, TiB 2 crystals underwent a complete dissolution in aqueous hydrogen peroxide and later recrystallized by way of laterally oriented attachment into quasi 2D sheets.…”