Electrodeposition, composition and properties of cobalt–rhenium alloys coatings

Abstract

This paper compares the chemical composition, current efficiency, crystal structure, as well as the magnetic, electrocatalytic, and corrosion properties of CoRe electrolytic alloys deposited from alkaline electrolytes of two complex compositions: monoligand citrate and polyligand citrate pyrophosphate ones. It is shown that with the deposition of alloys from citrate electrolytes it is possible to obtain X-ray amorphous coatings with high rhenium content (up to 78 at% of Re). In a citrate–pyrophosphate electrolyte, the electroreduction of cobalt proceeds with a low overvoltage, so the proportion of rhenium in the coating decreases sharply (to 12 at% of Re); and the coatings are formed with a crystalline structure. Changing the ratio of alloy components in a wide range makes it possible to obtain both non-magnetic coatings and ferromagnetic ones. The relationship between the electrocatalytic properties of alloys in the hydrogen evolution reaction and the corrosion resistance of coatings in an alkaline medium is found in a wide range of rhenium concentrations, in which it cannot be traced for electrolytic alloys of other refractory metals (Mo and W) due to the impossibility of obtaining alloys containing more than 35 at% of molybdenum or tungsten.