First insights of the Pdpt/C and Pdptru/C Electrocatalysts Towards Glycerol Electro-Oxidation in Alkaline Medium

Abstract

Platinum is a powerful and widely catalyst used for oxidation of various molecules like glycerol [i] . Compared to others catalysts (example Au), Pt has a lower oxidation potential in alkaline medium, however shows low kinetics for the reaction [ii] ,[iii] . Furthermore several studies have shown that the glycerol electrooxidation on Pt electrodes leads to the formation of various by-products causing decrease in the efficiency of the systemiv. Another disadvantage of Pt as catalysts is that platinum is an expensive noble metal and has low natural abundance.In this study we used PdPt and PdPtRu based electrocatalysts for glycerol electro-oxidation in alkaline medium. The carbon-supported materials were prepared by formic acid medium[iv]. After thorough physic-chemical characterizations, they were evaluated with regards to the glycerol electro-oxidation reaction. The experiments were conducted in 1.0 M NaOH solutions at 25°C, in absence/presence of 0.1 M of glycerol.In absence of glycerol, the cyclic voltammograms (CV) for all electrocatalysts show typical behavior of Pd, Pt and Ru materials. In presence of glycerol, Pd25Pt25Ru50/C electrocatalyst presented better performance; the onset potential for this material was close to 0.4 V vs. RHE, similar to Pt/C and the maximum peak current obtained was 107 mA cm-2, against 76 mA cm-2obtained for Pt/C electrocatalyst.FTIR measurements for all electrocatalysts were assessed to investigate the possible by-products from the glycerol electro-oxidation reaction (Fig. 1). For all materials, Pt/C, Pd/C, Pd50Pt50/C and Pd25Pt25Ru50/C, was possible identify four main absorption bands from glycerol electro-oxidation, which clearly evidence that the main products from glycerol electro-oxidation reaction are the same for any of these catalysts. The absorption band at 1308 cm-1 is typical of oxalate ions and it is presented in all electrocatalysts. The double band at 1349 and 1382 cm-1 are typical of formate ions standard spectra. The double band was only seen for Pd/C and Pd25Pt25Ru50/C electrocatalysts.As glycerol electro-oxidation leads to the formation of various by-products, formic acid can be one, however platinum electrocatalysts is able to oxidize formate ion to CO2. These results are consistent, since for Pt/C (Fig. 1B) electrocatalysts was not identified the double band feature of formic acid, however a single band was identified at 1387 cm-1, feature of carbonate from CO2. Pd50Pt50/C (Fig. 1C) electrocatalysts exhibited similar behavior for Pt/C.Then, according to results obtained from FTIR spectroscopy, the electro-oxidation of glycerol on Pt/C and Pd50Pt50/C electrocatalysts leads to the formation of by-products such as oxalate, carbonate and other carboxylates (1572 cm-1), whereas Pd/C and Pd25Pt25Ru50/C (Fig. 1A and B, respectively) leads to the formation of oxalate, formate and carboxylates ions. Probably, carbonate also may be produced but the presence of double band in the range of 1349 – 1382 cm-1 may be overlapped the carbonate band. This seems to mean that the higher amount of Pt in the catalysts contribute to the oxidize glycerol directly to CO2.The authors thank Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (particularly, process n. 2012/10856-7) [[i]]Garcia, R. Besson, M. Gallezot, P. Chemoselective catalytic oxidation of glycerol with air on platinum metals. Appl Catal A: Gen . v. 127, p. 165-176, 1995. [[ii]]Gomes, J. F. Tremiliosi-Filho, G. Spectroscopic studies of the glycerol electro-oxidation on polycrystalline Au and Pt surfaces in acidic and alkaline media. Electrocatalysis. v. 2, p. 96- 105. 2011.[[iii]]Kwon, Y. Schouten, P. J. Koper, M. T. M. Mechanism of the catalytic oxidation of glycerol on polycrystalline gold and platinum electrodes. ChemCatChem. v. 3, p. 1176-1185. 2011.[[iv]]Pinheiro, A.L.N. Oliveira-Neto, A. de Souza, E.C. Perez, J. Paganin, V.A. Ticianelli, E.A. Gonzalez, E.R. Electrocatalysis on noble metal and noble metal alloys dispersed on high surface area carbon. J. New Mater. Electrochem. Syst. 6 (2003)