Unexpected Correlation Between Boron Chain Condensation and Hydrogen Evolution Reaction (HER) Activity in Highly Active Vanadium Borides: Enabling Predictions

Abstract

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 V₃ B₄ have high electrocatalytic HER activity. Furthermore, we show that the HER activity (in 0.5 m H₂ SO₄ ) 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 V₃ B₄ ) we accurately predict the overpotential of VB₂ (-0.204 mV) as well as that of unstudied V₂ B₃ (-0.250 mV) and hypothetical "V₅ B₈ " (-0.227 mV). We then derived an exponential equation that predicts the overpotentials of known and hypothetical V_x B_y 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.