Spin Polarization and Phase Transformation-Aided Efficient Overall Water Splitting Using Ni₅₀Mn₁₈Ga₂₅Cu₇ Ferromagnetic Shape Memory Heusler Alloy

We demonstrate experimentally that the combination of half-metallic property and shape memory features of the Ni₅₀Mn₁₈Ga₂₅Cu₇ (NMGC) alloy can synergistically catalyze both the oxygen and hydrogen evolution reactions, leading to excellent water splitting. NMGC, a copper-doped nickel-based ferromagnetic shape memory alloy, undergoes first-order martensite to austenite phase transition with temperature variations. The martensite phase of NMGC demonstrates remarkable efficiency for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). With a large current density of 414 ± 3.8 mA/cm² at 2.9 V, an OER overpotential of only 220 ± 1.7 mV at 20 mA/cm², and a HER overpotential of 282 ± 2.2 mV at -10 mA/cm², NMGC (martensite) exhibits superior electrocatalytic performance compared to the austenite phase. Additionally, under a 5000 Oe external magnetic field, NMGC (martensite) shows a significant reduction of 52 mV in OER overpotential and 6 mV for HER, highlighting the promising role of spin and phase in enhancing the water-splitting kinetics.