Synergistic Contribution of the Strain and Magnetic Field in Ferromagnetic NiMnIn Heusler Alloy Films for the Hydrogen Evolution Reaction.

The external field-assisted hydrogen evolution reaction (HER), beyond modifying electrocatalysts themselves, has garnered significant research attention. However, achieving synergy between multiple fields to enhance the HER performance remains challenging and is not well-explored. Here, NiMnIn Heusler alloy thin films are fabricated using pulsed laser deposition on flexional Cu substrates. Due to the different adsorption free energy under tensile strain (TS) and compressive strain (CS), the most significant enhancement of the electrocatalytic HER activities for the NiMnIn film is observed in the 1.9% TS state, while the CS state of the NiMnIn film shows negative effects. Furthermore, when an external magnetic field is coupled to the 1.9% tensile-strained NiMnIn film, the total overpotential is reduced by 28.6% at a current density of -50 mA cm. This improvement is attributed to a synergistic effect that enhances the H adsorption stability and accelerates the H desorption process. This work demonstrates the effectiveness of combining multiple external fields and presents a promising strategy for advancing electrocatalysis.