Electrodeposition and properties of Со-Re alloys

Abstract

The present paper considers the electrodeposition of CoRe alloys from a citrate and a citrate-pyrophosphate electrolyte. It has been shown that coatings containing up to 67 at.% Re are deposited from a citrate electrolyte with a current efficiency of 20–40%, and that the use of a citrate-pyrophosphate electrolyte allows the current efficiency for the alloy to be increased, but the coating contains a smaller amount of rhenium – 13.5 аt.%. The corrosion tests carried out in solutions of 3.5% NaCl and 1 M KOH show that the optimal deposition current density in a citrate electrolyte is 30–40 mА·сm−2, at which the most fine-crystalline coatings is formed, which has a corrosion resistance of 3.0 and 1.6 kΩ·сm2 for corrosive solutions. The coating deposited from a citrate-pyrophosphate electrolyte is an interstitial solid solution of rhenium in cobalt, which allows a high corrosive resistance to be achieved, with the high cobalt content giving soft magnetic properties to alloys. The CoRe alloys show electrocatalytic activity in the hydrogen evolution reaction and allow one to reduce by an order of magnitude the exchange current density and by 220 mV the hydrogen overpotential relative to cobalt.