Tin-cobalt electrodeposition from sulfate-gluconate baths

The electrodeposition of tin + cobalt alloys from a slightly acidic sulfate -gluconate bath on both vitreous carbon and copper substrates has been stud ied for different [Sn(II)]/[Co(II)] ratios in the bath, varying between 1/1 0 and 1/2. A relationship between the electrochemical stripping analysis an d the morphology of the deposits has been found. Two different types of dep osit were obtained. At low [Sn(II)]/[Co(II)] ratios and relatively high dep osition rates a nodular, cobalt-rich, nanocrystalline coating was obtained, while at high [Sn(II)]/[Co(II)] ratios and low deposition rates a new, wel l-defined tetragonal SnCo phase was obtained, with cell parameters of a = 3 .087 Angstrom and c = 5.849 Angstrom. This structure favours hydrogen evolu tion.