(Ion Power Poster Award Winner) The Catalytic Behaviour of Pt Clusters on Au and Pd/Au As a Function of Their Surface Coverage and Density

Pt bimetallic structures such as Pt core-shell layers, alloys and clusters on different substrates have been a focus of intense research because they generally exhibit properties different from bulk Pt. The often improved catalytic activity of these structures makes them highly attractive for fuel cells applications[1].

Our understanding and decoupling of the effects responsible for the enhanced catalytic behaviour, such as bi-functional, electronic and ensemble effects, is incomplete. Numerous studies have been conducted so far with the aim of correlating surface activity with the structure and distribution of Pt on or in the catalyst surface [2-5]. It has been shown  that the catalytic activity of Pt nanoparticles decorated with ruthenium clusters (Ru/Pt catalyst) is twice that of the commercial 50 : 50 Ru/Pt alloy catalyst [2]. An enhancement of CO tolerance has been also found on supported Pt/Ru catalyst obtained by spontaneous deposition for a considerably lower Pt loading than in commercial catalyst[3]. The modified Au surface with Pt nanosize clusters [6] coverage as low as 15-25% of the substrate area, exhibit very high activity and incredible selectivity toward dehydrogenation of formic acid (HCOOH).

Our interest in this work are 2-dimensional model systems of Pt clusters electrodeposited on Au and Pd/Au. We used different electrochemical protocols to control Pt clusters’ size,  i.e. in terms of diameter, height and distribution: i) spontaneous adsorption of [PtCl₄]^2- complex and its potential controlled reduction e.g. the method often called ‘spontaneous deposition’ (SD) [2, 7] and ii) modified surface limited redox replacement (SLRR) method based on the galvanic replacement or partial underpotentially deposited metal layers. For each method successive application of optimized electrodeposition protocols yielded increased Pt surface coverage ranging from 0.25 to 1 area fraction. The surface coverage of Pt/Au and Pt/Pd/Au as well as the active area were determined electrochemically using H-UPD and CO-adsorption. The Pt clusters structure such the diameter, height and distribution were examined by scanning tunnelling microscopy (STM). The catalytic behaviour of Pt- nanostructures is analysed during HCOOH electro-oxidation and it is illustrated in the figure bellow.

References

1.            M. Debe, Nature, 2012. 486: 43.

2.            W. Chrzanowski; H. Kim and A. Wieckowski, Catal. lett., 1998. 50:  69.

3.            S. Brankovic; J. McBreen and R. Adzic, J. Electroanal. Chem., 2001. 503:  99.

4.            S. Bae; D. Gokcen; P. Liu; P. Mohammadi and S. Brankovic, Electrocatal., 2012. 3:  203.

5.            B. Du and Y. Tong, Phys. chem. lett., 2005. 109(38):  17775.

6.            M. Obradović; A. Tripković and S. Gojković, Electrochim. Acta, 2009. 55:  204.

7.            Chrzanowski and Wieckowski, Langmuir, 1997. 13:  5974.