Synergistic Contribution\nof the Strain and Magnetic\nField in Ferromagnetic NiMnIn Heusler Alloy Films for the Hydrogen\nEvolution Reaction

The external field-assisted hydrogen evolution reaction\n(HER),\nbeyond modifying electrocatalysts themselves, has garnered significant\nresearch attention. However, achieving synergy between multiple fields\nto enhance the HER performance remains challenging and is not well-explored.\nHere, NiMnIn Heusler alloy thin films are fabricated using pulsed\nlaser deposition on flexional Cu substrates. Due to the different\nadsorption free energy under tensile strain (TS) and compressive strain\n(CS), the most significant enhancement of the electrocatalytic HER\nactivities for the NiMnIn film is observed in the 1.9% TS state, while\nthe CS state of the NiMnIn film shows negative effects. Furthermore,\nwhen an external magnetic field is coupled to the 1.9% tensile-strained\nNiMnIn film, the total overpotential is reduced by 28.6% at a current\ndensity of −50 mA cm<sup>–2</sup>. This improvement\nis attributed to a synergistic effect that enhances the H adsorption\nstability and accelerates the H<sub>2</sub> desorption process. This\nwork demonstrates the effectiveness of combining multiple external\nfields and presents a promising strategy for advancing electrocatalysis.