High Elastic Strain Directly Tunes the Hydrogen Evolution Reaction on Tungsten Carbide

Elastic strain provides a direct means to tune a material's electronic structure from both computational and experimental vantage points and can thus provide insights into surface reactivity via changes induced by electronic structure shifts. Here we investigate the role of elastic strain on the catalytic activity of tungsten carbide (WC) in the hydrogen evolution reaction. WC makes an interesting material for such investigations as it is an inherently promising catalyst that can sustain larger elastic strains (e.g., -1.4 to 1.4%) than common transition-metal catalysts, such as Pt or Ni (e.g., -0.4 to 0.4%). On the basis of density functional theory calculations, a compressive uniaxial strain is expected to cause weakening of the surface hydrogen interaction of 10-15 meV per percent strain, while a tensile strain is calculated to strengthen the surface-hydrogen interaction by a similar magnitude. Sabatier analysis suggests that weakening of the surface-hydrogen interaction would enhance catalysis. We prepared 20 nm thin films of WC supported on thick polymer substrates and mechanically subjected them to uniaxial tensile and compressive loading, while the films catalyze hydrogen evolution in an electrochemical cell. We report a systematic shift in the hydrogen evolution sweeps of cyclic voltammetry measurements: Compressive strain increases the activity, and tensile strain has the opposite effect. The magnitude of the shift was measured to be 10-20 mV per 1% strain, which agrees well with the computations and corresponds to 5-10% of the difference in the overpotentials of WC and Pt. These results were further substantiated through chronoamperometry measurements and highlight how strain can be used to systematically improve catalytic activity.