(544bl) Electrodeposited Co-Mo-TiO2 Composites for the Hydrogen Evolution Reaction

Co-Mo alloys and the oxides that form at their surfaces in basic electrolytes are well known as excellent electrocatalysts for hydrogen generation.^1-3 Motivated by reports of the enhancement of the hydrogen evolution reaction (HER) by the addition of titania in Ni-P,^4-5 composites of Co-Mo-TiO₂ were fabricated and characterized. Co-Mo-TiO₂ composites were electrodeposited onto copper rotating cylinder electrode substrates from citrate electrolytes, and deposited galvanostatically at room temperature. The composite composition, morphology, HER exchange current density and Tafel slopes were characterized. The addition of titania particles to the Co-Mo matrix did not significantly change the composition ratio. The HER kinetics were dependent on both the Mo and titania composition. The exchange current density exhibited a parabolic, or volcano-type, behavior with the Mo composition in the deposit. At the maximum value of the exchange current density, the addition of titania further increases its value approximately 3 times. The Tafel slope decreases as the Mo content increases, and with the addition of titania it does not significantly change. The value of the Tafel slope indicates that the mechanism of HER on Co-Mo and Co-Mo-TiO₂ does not follow the same rate determining Volmer step as Pt.

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