Vacancy Rich TiB2 Nanosheets Promote Electrochemical Ammonia Synthesis.

The ability to exfoliate transition metal diborides has led to a renewed interest in their prospect to be applied as catalysts for electrochemical reactions. This is due to an enhanced access to the unprecedented interfaces these nanomaterials offer. In this work, we show that nanosheets exfoliated from TiB2 exhibit vacancies that facilitate an excellent interface for catalyzing nitrogen reduction reaction (NRR). We found that these nanosheets demonstrate a high selectivity toward NH3 because of their abiity to preferentially chemisorb and activate N2. These nanosheets exhibit a superlative NH3 yield of 318 µg h-1 cm-2 at -0.2 V versus RHE with a faradaic efficiency of 57%. We also found how the relative ratios of Ti and B atoms in these nanosheets can affect the NH3 yield and faradaic efficiency. We supplement these results with DFT studies that indicate that it is the creation of frustrated Lewis pairs along with the Ti-B synergy that induces a push-and-pull effect; this in turn favors N2 activation and lowers the energy barrier for NRR. Furthermore, we explored B-exposed and Ti-exposed surfaces to understand how different surfaces affect the reaction yield and efficiency and found that Ti-exposed surfaces with boron divacancy have the highest propensity for NRR. The maiden insights presented in this study on the role of transition metal-boron synergy and interfaces present significant additions to the fast-expanding knowledge on nanoscaled metal borides.

Nitrogen adsorption via charge transfer on vacancies created during surfactant assisted exfoliation of TiB2.

Titanium diboride (TiB2), a layered ceramic material, comprised of titanium atoms sandwiched in between honeycomb planes of boron atoms, exhibits a promising structure to utilize the rich chemistry offered by the synergy of titanium and boron. TiB2 has been primarily investigated and applied in its bulk form. This perspective is, however, fast evolving with a number of efforts aimed at exfoliating TiB2. Here, we show that it is possible to delaminate TiB2 into ultrathin, minimally functionalized nanosheets with the aid of surfactants. These nanosheets exhibit crystalline nature and their chemical analysis reveals vacant sites within the nanosheets. These vacancies facilitate the chemisorption of N2 onto the TiB2 nanosheets under ambient conditions without the aid of any energy, this finding was unexpected. This remarkable activity of TiB2 nanosheets is attributed to vacancies and the Ti-B synergy, which enhance the adsorption and activation of N2. We obtained supplemental insights into the N2 adsorption by Density Functional Theory (DFT) studies, which reveal how charge transfer among Ti, B, and N2 results in N2 adsorption. The DFT studies also show that nanosheets having more vacancies result in increased adsorption when compared with nanosheets having less vacancies and bulk TiB2.