(Invited) A Coverage Dependent Behavior of Pt on Au Deposited Using Surface Limited Redox Replacement

Different Pt bimetallic nanostructures, such as ultrathin Pt overlayers, alloys and nano-clusters, have been a focus of intense research because of their enhanced catalytic activity compared to the bulk Pt. Over the last few decades our fundamental understanding of the effects responsible for their electro catalytic behavior, such as bifunctional, electronic and ensemble effects, has advanced by the development of theoretical models and studies on model 2D systems enabled by development of new electrodeposition methods and routines to control their structure [1-4].

Studies of Pt-nanoclusters have shown strong correlation of surface activity with the structure and distribution of Pt on the surface [4, 5]. An enhancement of CO tolerance on supported Pt/Ru catalysts obtained by spontaneous deposition has been shown at a considerably lower Pt loading than on the commercial catalysts [6]. The modified Au surface with Pt nanosize clusters coverage as low as 15-25% of the substrate area, exhibit very high activity and improved selectivity toward dehydrogenation of formic acid (HCOOH) [7]. Most recently formation of Pt monolayer catalysts and nanoclusters using Surface Limited Redox Replacement (SLRR) method has been used to show the effect of strain and morphology on the catalytic behaviour [4].  

Here in this work we present the study of Pt-nanoclusters on Au substrate as a function of their size, and areal coverage. We compared the design of Pt nanoclusters using two electrochemical approaches: i) spontaneous deposition (SD) i.e. reduction of the spontaneously adsorbed Pt-complex and ii) the surface limited redox replacement (SLRR) method based on the redox  replacement of  Pb underpotentially deposited layers.  For each method successive application of optimized electrodeposition protocols yielded increased Pt surface coverage ranging from 0.25 to 1 area fraction. Using two different methods enabled design of nanocluster with varied cluster sizes and the areal coverage of Au. The structure and distribution of Pt nanoclusters was determined by electrochemical techniques (H-UPD and CO adsorption) and scanning tunneling microscopy (STM). Their catalytic behavior was analyzed and compared during formic acid electro-oxidation.

References:

1. W. Chrzanowski; H. Kim and A. Wieckowski, Catal. lett., 50 (1998),  69.

2. S. R. Brankovic, J. X. Wang, R. R. Adzic. Surf. Sci. 474, (2001), L173.

3. L. Bromberg, M. Fayette, B. Martens, Z. Luo, Y. Wang, D. Xu, J. Zhang, J. Fang, and N. Dimitrov, Electrocatalysis, 2013, 4 (2013), 24.

4. R. Loukrakpam, Q. Yuan, V. Petkov, L. Gan, S. Rudi, R. Yang, Y. Huang, S.R. Brankovic and P. Strasser, Phys.Chem.Chem.Phys.,16 (2014), 18866.

5. B. Du and Y. Tong, J. Phys. Chem. B, 109 (2005), 17775.

6. S. Brankovic; J. McBreen and R. Adzic, J. Electroanal. Chem., 503 (2001),  99.

7. M. Obradović; A. Tripković and S. Gojković, Electrochim. Acta, 55 (2009),  204.