Factorial design in the electrodeposition of Co-Mo coatings and their evaluations for hydrogen evolution reaction

The present study aimed at investigating the influence of the electrodeposition current density and pH of the plating solution on chemical composition, electrodeposition current efficiency and on the roughness factor of the electrodeposited Co-Mo coatings. The coatings with higher roughness factor were evaluated as cathodes for hydrogen evolution reaction in alkaline medium. The electrodeposition current densities were 30 mA cm−2, 45 mA cm−2 and 60 mA cm−2 and the values of pH of the plating solutions were 6, 7 and 8. The two-level and centre-point factorial design was applied. Coatings showed cracks and amorphous structures. The pH had a positive effect on the Mo percentage and on the roughness factor of the coatings. The current density had the highest effect on the current efficiency and electroactive area of the coatings. Increasing the value of this parameter, the current efficiency decreased from 31.63% to 17.65% and roughness factor presented relative increase of 27.53-78.74. The Volmer reaction was the determining step and the apparent activation energy was 18.40 kJ mol−1 in the hydrogen evolution reaction.