Service life test of the NiSn coatings as cathodes for hydrogen evolution in industrial chlor-alkali electrolysis

In this work the “service life test” (SLT) of the NiSn alloy coatings as cathodes for the hydrogen evolution reaction (HER), deposited onto Ni 40 mesh at different current densities from the bath containing 0.1 mol dm−3 SnCl2 + 0.3 mol dm−3 NiCl2 + 0.6 mol dm−3 K4P2O7 + 0.3 mol dm−3 NH2CH2COOH at 50 °C, was investigated and compared with that recorded for the commercial Ni–RuO2 De Noraʹs (DN) cathode. The morphology and chemical compositions of all NiSn samples were investigated by SEM and EDS techniques before and after the SLT. HER during the SLT has also been monitored by EIS technique. The chemical compositions of surfaces of all NiSn alloy samples, as well as EIS results, were found to depend on the number of cycles performed during the SLT. The decrease of their catalytic activity for the HER in 32 wt.% NaOH at 90 °C with increasing the number of cycles (about 20–25 mV after 25 cycles) was practically identical to that for DN cathode, while NiSn samples deposited at −30 mA cm−2, −60 mA cm−2 and −100 mA cm−2 possessed lower overpotential for the HER before and after SLT in comparison with that for the DN cathode. It is confirmed by the SEM–EDS and EIS analysis of the NiSn samples that the minor loss of the catalytic activity for the HER is the consequence of the change of chemical composition of NiSn coatings and decrease of the active surface area. This decrease is ascribed to partially eroded NiSn coatings due to oxygen evolution during the SLT.