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Hydrogen boride (HB) or hydrogenated borophene sheets are recently realized two-dimensional materials that are composed of only two light elements, boron and hydrogen. However, their catalytic activity has not been experimentally analyzed. Herein, we report the catalytic activity of HB sheets in ethanol reforming. HB sheets catalyze the conversion of ethanol to ethylene and water above 493 K with high selectivity, independent of the contact time, and with an apparent activation energy of 102.8 ± 5.5 kJ/mol. Hence, we identify that HB sheets act as solid-acid catalysts.

Two-dimensional hydrogen boride (HB) sheets were recently demonstrated to act as a solid acid catalyst in their hydrogen-deficient state. However, both the active sites and the mechanism of the catalytic process require further elucidation. In this study, we analyzed the conversion of ethanol adsorbed on HB sheets under vacuum during heating using in situ Fourier transform infrared (FT-IR) absorption spectroscopy with isotope labelling. Up to 450 K, the FT-IR peak associated with the OH group of the adsorbed ethanol molecule disappeared from the spectrum, which was attributed to a dehydration reaction with a hydrogen atom from the HB sheet, resulting in the formation of an ethyl species. At temperatures above 440 K, the number of BD bonds markedly increased in CD3CH2OH, compared to CH3CD2OH; the temperature dependence of the formation rate of BD bonds was similar to that of the dehydration reaction rate of ethanol on HB sheets under steady-state conditions. The rate-determining step of the dehydration of ethanol on HB was thus ascribed to the dehydrogenation of the methyl group of the ethyl species on the HB sheets, followed by the immediate desorption of ethylene. These results show that the catalytic ethanol dehydration process on HB involves the hydrogen atoms of the HB sheets. The obtained mechanistic insights are expected to promote the practical application of HB sheets as catalysts.

Two-dimensional (2D) materials are promising for applications in a wide range of fields because of their unique properties. Hydrogen boride sheets, a new 2D material recently predicted from theory, exhibit intriguing electronic and mechanical properties as well as hydrogen storage capacity. Here, we report the experimental realization of 2D hydrogen boride sheets with an empirical formula of H1B1, produced by exfoliation and complete ion-exchange between protons and magnesium cations in magnesium diboride (MgB2) with an average yield of 42.3% at room temperature. The sheets feature an sp2-bonded boron planar structure without any long-range order. A hexagonal boron network with bridge hydrogens is suggested as the possible local structure, where the absence of long-range order was ascribed to the presence of three different anisotropic domains originating from the 2-fold symmetry of the hydrogen positions against the 6-fold symmetry of the boron networks, based on X-ray diffraction, X-ray atomic pair dist...

A recent experiment demonstrated that ultrasonication of MgB2 in water yields Mg-deficient hydroxyl-functionalized boron nanosheets at room temperature. Herein, we examined the mechanism of nanosheet formation. Analysis of the reaction products and temporal variation in pH and H2 production shows that the reaction between MgB2 and water comprises two steps: (i) an ion-exchange process between protons and a part of Mg cations of MgB2 with its exfoliation and (ii) the hydrolysis reaction between Mg-deficient boron hydride and water to produce H2 and Mg-deficient hydroxyl-functionalized boron sheets. The sheets with a stacking periodicity of 0.70 nm were obtained as the supernatant of the reaction product of water with MgB2. The stacking sheets can be further exfoliated if the reaction is conducted under ultrasonication. The derived nanosheets are composed of sp2-bonded boron framework and possess a disordered structure containing hydroxyl species and oxidized magnesium.

Electronic states of a free-standing hydrogenated monolayer boron (HB) sheet were studied via soft X-ray spectroscopies at the B K-shell absorption edge and first-principles calculations. The HB sheet is semimetallic with electron and hole pockets at the Y and Γ points, respectively. The electron band results from the B-H-B bonds formed during synthesis from a MgB2 crystal, while the hole band is kept through the process and originates from a honeycomb lattice boron layer or borophene in MgB2. Our results suggest that the HB sheet is a promising two-dimensional material for realizing new boron-based or superconducting nanodevices.

The discovery of novel lightweight materials with metallic properties is important for future smart applications, and two-dimensional materials with metallic conductivity are quite rare in this regard. Herein, we report an electrically conductive two-dimensional hydrogen boride material (borophane) that was synthesized in powder form by an ion-exchange reaction. The produced freestanding borophane was amorphous by X-ray diffractometry and found to consist of curved layers of elongated hexagonal networks of boron and hydrogen atoms that bridge pairs of boron atoms with H/B ratio of 1.0. This hexagonal borophane exhibits metallic conduction with a conductivity of 0.13 S cm−1 at around room temperature, and a unique metal-to-insulator transition at around 30 °C.

Two-dimensional (2D) materials are promising for applications in a wide range of fields because of their unique properties. Hydrogen boride sheets, a new 2D material recently predicted from theory, exhibit intriguing electronic and mechanical properties as well as hydrogen storage capacity. Here, we report the experimental realization of 2D hydrogen boride sheets with an empirical formula of H