Dynamic Tuning of a Thin Film Electrocatalyst by Tensile Strain

We report the ability to tune the catalytic activities for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by applying mechanical stress on a highly n-type doped rutile TiO 2 films. We demonstrate through operando electrochemical experiments that the low HER activity of TiO 2 can reversibly approach those of the state-of-the-art non-precious metal catalysts when the TiO 2 is under tensile strain. At 3% tensile strain, the HER overpotential required to generate a current density of 1 mA/cm 2 shifts anodically by 260 mV to give an onset potential of 125 mV, representing a drastic reduction in the kinetic overpotential. A similar albeit smaller cathodic shift in the OER overpotential is observed when tensile strain is applied to TiO 2 . Results suggest that significant improvements in HER and OER activities with tensile strain are due to an increase in concentration of surface active sites and a decrease in kinetic and thermodynamics barriers along the reaction pathway(s). Our results highlight that strain applied to TiO 2 by precisely controlled and incrementally increasing (i.e. dynamic ) tensile stress is an effective tool for dynamically tuning the electrocatalytic properties of HER and OER electrocatalysts relative to their activities under static conditions.