Journal of Power Sources 205 (2012) 207–214 Contents lists available at SciVerse ScienceDirect Journal of Power Sources jo ur nal homep age: www.elsevier.com/locate/jpowsour Investigation of methanol electrooxidation on Pt and Pt–Ru in H 3 PO 4 using MEA with PBI–H 3 PO 4 membrane A.D. Modestov a,∗ , M.R. Tarasevich a , Hongting Pu b a A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Prosp. 31, Moscow 119071, Russia b Institute of Functional Polymers, School of Materials Science & Engineering, Tongji University, Shanghai 201804, China a r t i c l e i n f o Article history: Received 25 November 2011 Received in revised form 11 January 2012 Accepted 12 January 2012 Available online 21 January 2012 Keywords: PBI DMFC Methanol Electrooxidation Pt Pt–Ru a b s t r a c t Electrochemical oxidation of methanol on Pt/C and Pt–Ru/C electrocatalysts was studied by slow scan rate voltammetry at 130–190 ◦ C. The effects of partial pressures of water, methanol, and CO on the methanol electrooxidation rate were determined. It was found that methanol oxidation on Pt–Ru/C proceeds pri- marily via the “indirect” route through the formation of strongly adsorbed intermediate CO ads , while on Pt methanol electrooxidation occurs primarily via “direct” route through the formation of weakly adsorbed intermediates. At 140 ◦ C activity of Pt–Ru/C in methanol electrooxidation was found 2 orders of magnitude higher than that of Pt/C. Methanol oxidation reaction orders per water and methanol vapor pressures were determined. The main features of methanol electrooxidation both on Pt and Pt–Ru were accounted for assuming Langmuir–Hinshelwood mechanism of respective RDS. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Current lack of infrastructure for hydrogen supply and stor- age makes methanol a promising fuel for fuel cells. Methanol can be produced from coal, natural gas or biomass via production of synthesis gas and its hydrogenation. Catalytic hydrogenative con- version of carbon dioxide to methanol is a way of carbon dioxide chemical recycling [1,2]. Complete oxidation of methanol in acidic electrolytes is a 6-electron reaction forming CO 2 : CH 3 OH + H 2 O = CO 2 + 6H + + 6e - (1) Standard potential value for the methanol/oxygen fuel cell at room temperature is 1.2 V [3,4]. The spread of direct methanol fuel cells (DMFC) is hindered by sluggish methanol oxidation kinetics. Methanol oxidation mechanism is rather complex [3–13]. A simpli- fied diagram of it is shown in Scheme 1. It consists of two different pathways [10]. A route [14–16], which leads to CO 2 through the for- mation of strongly adsorbed carbon monoxide, reactions (a)–(f), (i), is often called “indirect” path. This route involves four consecutive reactions of dehydrogenation, resulting in formation of adsorbed ∗ Corresponding author. Tel.: +7 495 9522387; fax: +7 495 9525308. E-mail address: modestov@elchem.ac.ru (A.D. Modestov). CO ads , and its oxidation in Langmuir–Hinshelwood reaction (f) with adsorbed active oxygen containing species OH ads : CO ads + OH ads → COOH ads (2) Reaction (f) is followed by fast electrochemical reaction (i). OH ads species are formed in fast reversible water oxidation reac- tion [14,17]: H 2 O ↔ OH ads + H + + e - (3) Formation of adsorbed carbon monoxide on Pt in methanol electrooxidation was detected by various types of IR spectroscopy [12,17–27]. Characteristics of adsorbed CO layer formed on Pt elec- trode by oxidation of methanol were determined by radioactive labeling [28], also. Reaction (f) is considered a rate determining stage (RDS) of the methanol electrooxidation on both Pt and Pt–Ru, which proceeds by the “indirect” route. This reaction is also an RDS in electrochemical oxidation of CO on these electrodes [5,29,30]. The second “direct” reaction route leads to formation of formic acid, formaldehyde, methyl formate, methanaldimethylac- etal in addition to carbon dioxide. It includes reactions (a)–(d), Lagmuir–Hinshelwood reaction (g) of intermediate species CHO ads with adsorbed OH ads , and fast reactions (h) and (i). All soluble compounds, which are formed in the “direct” route are omitted in Scheme 1 for simplicity. Actuality of this methanol electrooxida- tion route was proved by detection of formic acid, formaldehyde, methyl formate, and methanaldimethylacetal along with carbon dioxide by DEMS [31–35] and on-line mass spectrometry [9,36,37]. 0378-7753/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2012.01.089