Silver-Tungsten induced codeposition: Influence of pH and carboxylic acid form in a DMH-based electrolyte

• Silver-tungsten coatings were successfully electrodeposited from DMH electrolyte • Tungsten contents close to optimal for functional properties without thiourea. • The induced codeposition mechanism is coherent with an intermediate bimetallic complex • Silver ion reduction is under mass transport control and tungsten under kinetic • No silver-tungsten reduction was possible with less than two protonated carboxyl groups Silver-tungsten coatings were successfully electrodeposited on platinum and copper substrates from a non-toxic 5.5-dimethylhydantoin electrolyte at low pH and two different carboxylic acid forms: citrate or tartrate. Tungsten contents remain at low levels compared to former works, but close to the values considered as optimal for functional properties without having to recourse to controversial substances such as thiourea. Electrochemical studies by linear sweep voltammetry allow to distinguish two typical behaviors and give interesting insight into the induced codeposition mechanism. Silver-tungsten codeposition only occurred at pH 2.0 and 3.5 using citrates and at pH 2.0 using tartrates, corresponding to the forms H 3 Cit, H 2 Cit -2 , and H 2 Tar, respectively. No silver-tungsten reduction was possible with less than two protonated carboxyl groups on either tartrate or citrate ions. Separate silver and tungsten lattice are both present in the resulting alloy. Grain and crystallite sizes were observed by SEM. XPS investigations show that for our low W content alloys, silver is found to be metallic whereas tungsten is present in oxide form. The carbon peaks and also gaps between peaks when N is absent indicate that citrates are present in the coating, unlike DMH.