Electrocatalysis on model titania supported platinum

Abstract

High throughput electrochemical screening and rotating ring disc electrode measurements have been used to investigate carbon, titania and niobium doped titania as supports for platinum electrocatalysts.  The effect of support and catalyst loading on the surface redox behaviour, CO stripping, methanol oxidation and oxygen reduction activity of the platinum has been investigated.  TEM has been used to characterise the morphology of the platinum on these supports at several different loadings.

With platinum supported on carbon, general trends with decreasing loading of platinum were found.  These included a negative shift of the platinum oxide reduction peak potential, a positive shift of the CO stripping peak potential and peak broadening, and a negative potential shift of the oxygen reduction curve.  The negative shift of the platinum oxide reduction peak was found to coincide with a decrease in platinum particle size.  The CO stripping peak shifted significantly positive at loadings where layers of platinum began to break up into particles, and became broader as the particle size decreased.  The overpotential need for oxygen reduction appeared to increase with decreasing particle size and correlated well with the shift of the platinum oxide reduction peak.  This suggests that the origin of the overpotential for platinum oxide reduction is the origin for the overpotential for oxygen reduction.

With platinum supported on titania and niobium doped titania, with decreasing loading of platinum, the platinum oxide formation and reduction reaction appeared to become less reversible (i.e. slower electron transfer).  The irreversibility of the reaction increased as the particle size of platinum decreased.  This irreversibility may account for the increasing overpotential seen for the CO stripping peak and eventual disappearance of the feature with decreasing platinum loading and the loss in methanol oxidation activity.  It may also account for the significant increase in overpotential for the oxygen reduction reaction seen as particles (rather than a continuous layer) of platinum begins to form on the support material.

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