B20 "Electroless" Nickel Plating

Description
Reduction of nickel ion by hypophosphite ion is catalyzed by a copper surface. A nickel plating forms on the penny which acts as the catalyst for this reaction. Although the solution of nickel and hypophosphite is stable for several days without a catalyst, the reaction takes place in a few minutes with a suitable catalyst. This technique may also be used on the surface of a nonconductor which has been treated with a suitable catalyst for the nickel reduction.

Equation
Ni²⁺ + H₂PO₂^- + H₂O --> Ni + H₂PO₃^- + 2 H⁺

Reference
MetalsFinishing 50th Guidebook Directory, Metals and Plastics Publications, Inc.,Hackensack, N.J., (1982) p520.