Electrodeposited Co-Mo-TiO2 Electrocatalysts for the Hydrogen Evolution Reaction

Co-Mo-TiO2 composite and Co-Mo alloy thin films were galvanostatically electrodeposited and their HER electrocatalytic properties assessed, in order to better understand the role of added micro-scale TiO2 particles. During electrodeposition, the metal ion partial current densities were enhanced with the inclusion of the particle, resulting in a higher current efficiency but with no change in the HER side reaction. However, a significant change in the HER occurred in a 1 M NaOH electrolyte with the composites compared to their alloy counterparts. The deposit surface area was examined in a ferricyanide electrolyte to assess the HER exchange current density and overpotential in the alkaline electrolyte. The HER exchange current density with composites containing TiO2 exhibited values nearly 1 mA/cm2, approximately 3 times higher than the Co-Mo alloys. The overpotential at a cathodic current density of 10 mA/cm2, ƞ10, of the Co-Mo-TiO2 composites was low, with the best value reaching 68 mV, which is 40 mV smaller than their alloy counterparts. The Tafel slope of all deposits with TiO2 were similar in the range of 70-75 mV/decade, indicating that not one step in a Volmer-Heyrovsky mechanism is rate determining.