Catalyst hydrogen underpotential deposition

Similar measurements for the cases of supported nanosized catalysts require preparation of the electrode in a specific way. Usually, catalyst is dispersed in suitably chosen media and desired amount is transfer to solid electrode serving as electrical contact [11]. This issue will be elaborated in more details later on. When stable thin catalyst layer is prepared cyclic voltammetry may be used to investigate surface electrochemical processes (Figure 4). In contrast to single-crystal and polycrystalline surface additional factor arises - namely, these processes depend also on the particle size. For example, in the case of supported Pt nanocatalysts it was observed that both hydrogen underpotential deposition and adsorption of oxygen species are clearly dependent on the particle size [12]. In specific, it was observed that smaller particles are more oxophilic and that surface oxidation is more irreversible for smaller particles. 

Figure 4. Cyclic voltammograms of Pt-poly disk electrode and Pt/C catalysts (40 wt.% Pt, Alfa Aesar), recorded at 50 mV s in de-aeiated 0.1 mol dm HCIO4 solution. Cyclic voltammograms are normalized by real surface area of Pt assessed by investigating hydrogen underpotential deposition.

In this paper we report the application of bimetallic catalysts which were prepared by consecutive reduction of a submonolayer of bismuth promoter onto the surface of platinum. The technique of modifying metal surfaces at controlled electrode potential with a monolayer or sub-monolayer of foreign metal ("underpotential" deposition) is widely used in electrocatalysis (77,72). Here we apply the theory of underpotential metal deposition without the use of a potentiostat. The catalyst potential during promotion was controlled by proper selection of the reducing agent (hydrogen), pH and metal ion concentration. 

Electrochemical Active Surface Area (ESCA) of Pt-based catalysts through the hydrogen adsorption/desorption peak area, CO stripping, and underpotential deposition of copper (Cu-UPD) methods. 

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