Effect of ammonium on low-temperature electrodeposition of Ni–P alloys

A previous way of electrodepositing Ni-P alloy containing about 6-8 at.% phosphorus, which has a high catalytic activity for hydrogen evolution reaction (HER), is not capable of growing a thick coating having good physical stability. In this study, ammonium chloride was added increasingly between 0.5 and 4 M to the electrolyte containing 0.2 M NiCl2 and 0.1 M NaH2PO2 to examine its effect on the Ni-P electrodeposition. It was found that phosphorus content in the alloy increased almost linearly with only the addition of ammonium chloride. This result showed that the catalyst Ni-P alloy could be prepared using a low concentration of the phosphorus-offering reagent and a high concentration of ammonium, instead of using a conventional bath containing a relatively high phosphorus-offering reagent. Such a way made it feasible to grow the thick Ni-P coating containing the proper phosphorus for HER. (C) 2003 Elsevier Science B.V. All rights reserved.