Low-Temperature Synthesis of a PtRu∕Nb[sub 0.1]Ti[sub 0.9]O[sub 2] Electrocatalyst for Methanol Oxidation

Abstract

Niobium was doped into anatase TiO2 support at 10 mol % Nb0.1Ti0.9O2 using sol-gel chemistry. A PtRu/Nb0.1Ti0.9O2 catalyst was synthesized by LiBH4 reduction in tetrahydrofuran. The methanol electro-oxidation activity of the catalyst shows that this oxide support was electrically conductive. The current A/gPt was 6% higher on the PtRu/Nb0.1Ti0.9O2 catalyst compared to a commercial PtRu/C catalyst at 25°C. The electrochemically active surface area of the PtRu/C was 94% higher than PtRu/Nb0.1Ti0.9O2, thus the current per active site was 100% higher on PtRu/Nb0.1Ti0.9O2. A membrane electrode assembly with PtRu/Nb0.1Ti0.9O2 had 46% higher current A/gPt than an equivalent E-TEK membrane electrode assembly at 70°C. conducting material. 3,5 with an electrical conductivity in the range of 0.2-1.5 S/cm and a surface area of 1m 2 /g. 3 This high- temperature synthesis method shows promising results, but it leads to a low surface area material that requires long synthesis times. Because TiO2 undergoes a phase transition from anatase to the less catalytically active rutile near 700°C, 6 the high-temperature synthe- sis may also reduce some catalytic promotion of methanol oxidation by the support. In this paper, a low-temperature synthesis route for Nb0.1Ti0.9O2 via a surfactant templating method is presented. The support was characterized using Brunauer-Emmett-Teller BET, X-ray diffrac- tion XRD, and transmission electron microscopy TEM tech- niques. A colloidal method was then used to deposit platinum and ruthenium nanoparticles onto the Nb-doped titania supports. Their catalytic activity toward the electrochemical oxidation of methanol was compared to commercial PtRu on carbon via cyclic voltamme- try CV on the catalysts deposited onto a disk electrode and direct methanol fuel cell DMFC test on the catalysts fabricated in mem- brane electrode assembles MEAs. Experimental Synthesis of an Nb0.1Ti0.9O2 support.— The synthesis of the Nb0.1Ti0.9O2 support was done through a modification of the proce- dure of Yan et al. 7 First, 0.030 mol of the template, octadecyl- amine, were mixed in a 250 mL beaker with 75 mL of dehydrated ethanol for 30 min with magnetic agitation. Second, 0.010 mol of niobiumV ethoxide was added to the solution and allowed to mix for 15 min. Then, 0.090 mol of titaniumIV butoxide was added to the solution and mixed for 15 min. Next, 54 mL of deionized water was added to the beaker, stirring was stopped, and the gel was aged for 48 h. The gel was filtered and then the template was removed using solvent extraction. For the solvent extraction, 92 mL dehy- drated ethanol and 8 mL of concentrated HCl were added to a round bottom flask containing the filtered sample. The mixture was then boiled under reflux for 12 h. The product of the solvent extraction was then mixed with 200 mL of dehydrated ethanol. This mixture was adjusted to a pH of 10 with NaOH. The resulting Nb0.1Ti0.9O2 was then dried at 100°C in a vacuum oven for 12 h.