Search

Transition‐metal borides (TMBs) have recently attracted attention as excellent hydrogen evolution (HER) electrocatalysts in bulk crystalline materials. Herein, we show for the first time that VB and V3B4 have high electrocatalytic HER activity. Furthermore, we show that the HER activity (in 0.5 m H2SO4) increases with increasing boron chain condensation in vanadium borides: Using a −23 mV overpotential decrement derived from −0.296 mV (for VB at −10 mA cm−2 current density) and −0.273 mV (for V3B4) we accurately predict the overpotential of VB2 (−0.204 mV) as well as that of unstudied V2B3 (−0.250 mV) and hypothetical "V5B8" (−0.227 mV). We then derived an exponential equation that predicts the overpotentials of known and hypothetical VxBy phases containing at least a boron chain. These results provide a direct correlation between crystal structure and HER activity, thus paving the way for the design of even better electrocatalytic materials through structure–activity relationships. [ABSTRACT FROM AUTHOR]

Molybdenum-based materials have been considered as alternative catalysts to noble metals, such as platinum, for the hydrogen evolution reaction (HER). We have synthesized four binary bulk molybdenum borides Mo2B, α-MoB, β-MoB, and MoB2 by arc-melting. All four phases were tested for their electrocatalytic activity (linear sweep voltammetry) and stability (cyclic voltammetry) with respect to the HER in acidic conditions. Three of these phases were studied for their HER activity and by X-ray photoelectron spectroscopy (XPS) for the first time; MoB2 and β-MoB show excellent activity in the same range as the recently reported α-MoB and β-Mo2C phases, while the molybdenum richest phase Mo2B show significantly lower HER activity, indicating a strong boron-dependency of these borides for the HER. In addition, MoB2 and β-MoB show long-term cycle stability in acidic solution. [ABSTRACT FROM AUTHOR]