The effect of quaternary ammonium compounds on the electrodeposition of ZnCo alloys from an alkaline chloride-gluconate electrolyte was studied. A thermodynamic analysis was performed which indicated that Zn(OH)(4)(2-) should be the predominant zinc species, whereas for cobalt the mixed hydroxy-gluconate complexes CoL3(OH)(2) and CoL(OH)(2) are expected to be prevalent. The electrodeposition of the alloy from this alkaline medium was found to be anomalous, but increasing the cobalt content in the bath caused the cobalt content in the deposit to increase. The effects of three quaternary ammonium compounds, N-benzyl-3-carboxylpyridinium chloride (3NCP), N-benzyl-triethylammonium chloride, and tetraethylammonium hydroxide, on the electrochemical behavior of ZnCo deposition were studied. The incorporation of these additives in the electrolytes modified the composition, morphology, and crystallographic structure of the ZnCo-alloy deposits. Cyclic voltammetry indicated the formation of several alloy phases as cobalt was added to these zinc baths. 3NCP had the greatest impact on the process, limiting the Co content and changing the structure of the deposit. (C) 2007 The Electrochemical Society.