Hydrogen evolution characteristics of Ni–Mn microencapsulated MlNi3.03Si0.85Co0.60Mn0.31Al0.08 alloys in 6 M KOH

Nickel–manganese alloys were coated from sulphate baths by electrodeposition with ‘Packed Bed’ technique on the surface of proprietary lanthanum rich non-stoichiometric MlNi3.03Si0.85Co0.60Mn0.31Al0.08 (Ml = lanthanum rich misch metal) hydrogen storage alloy particles. The structure and nature of the microencapsulated alloys were characterized using X-ray diffraction (XRD) and electron paramagnetic resonance (EPR). The hydrogen evolution reaction (HER) was investigated in 6 M KOH at 30 °C by galvnostatic cathodic polarisation technique. The effects of Ni/Mn ratio in the bath and deposition current density were studied. Among the investigated depositions, Ni150Mn100 (30) and Ni150Mn10 (60) (concentration of Ni and Mn salts in electrodeposition bath given in grams per liter; electrodeposition current density (CD) given within brackets in milliamphere per square centimeter) coated samples exhibited the highest activity towards the HER. It can be concluded that disordered paramagnetic coatings with Ni concentrations above 80 at.% exhibit higher catalytic activity towards HER. The Tafel mechanism is the easiest pathway for HER on most of the studied coatings. However, some of the Ni-rich coatings prefer the Volmer–Tafel path and one sample [Ni150Mn150 (80)] prefers the Heyrovsky–Volmer path.