A Simple Molten Salt Route to Crystalline β-MoB2 Nanosheets with High Activity for the Hydrogen Evolution Reaction

Molybdenum borides have been of interest due to their potential applications as electrocatalysts for the hydrogen evolution reaction (HER). As one of the common molybdenum borides, beta-MoB2 is deemed to exhibit low electrocatalytic activity due to the presence of puckered B layers, and improvement of its behavior is hindered by the lack of convenient synthetic methods. Herein, we report the synthesis of crystalline beta-MoB2 for the first time via the simple reaction of MoCl3 and B at 850 degrees C in LiCl-KCl. The as-prepared beta-MoB2 sample was shown to exhibit a nanosheet structure with a large Brunauer-Emmett-Teller surface area of 48 m(2)/g. Such beta-MoB2 nanosheets exhibit promising HER activity in acidic medium with an overpotential of 187 mV at a current density of 10 mA/cm(2) and a Tafel slope of 49.3 mV/decade, which is much better than that of the known bulk beta-MoB2 and even close to the results of beta-MoB2 that is commonly recognized as the best molybdenum boride electrocatalyst for HER. The high HER activity of beta-MoB2 nanosheets results from the large surface area that allows more active sites to be exposed, which compensates for the disadvantage arising from the intrinsic structure of beta-MoB2.

Automated summary

This study reports the first synthesis of crystalline beta-MoB2 nanosheets with a large surface area, showing excellent HER activity in acidic medium. The high activity of beta-MoB2 nanosheets is attributed to the large surface area allowing more active sites to be exposed.