Preparation, characterization, and electrochemical studies of catalaysts for ethanol electrooxidation and their application in direct ethanol fuel cell (DEFC)

Author(s)

Thiago dos Santos Almeida

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (PCARP/BC)
• Defense date: 2014-06-25

Examining board members

Adalgisa Rodrigues de Andrade; Paulo Olivi; Giuseppe Abíola Câmara da Silva; Edson Antonio Ticianelli; Germano Tremiliosi Filho

• Advisor: Adalgisa Rodrigues de Andrade

Abstract

This work investigated catalysts for ethanol electrooxidation in acidic and alkaline media, focusing on how the methodology used to synthesize the catalyst and catalyst composition affected the electrochemical activity toward ethanol oxidation. First, this study evaluated how thermal decomposition of polymeric precursors (DPP) and reduction by microwave irradiation (MW) influenced the structure, morphology, particle size, and catalytic activity of Pt(75)Sn(25)/C. The MW method was more efficient: it furnished catalysts with smaller particle size, better distribution on the carbon support and higher catalytic activity in acidic medium as compared with the same catalyst composition prepared by the DPP method. Next, this work examined how addition of a third metal, Ni, Pd, Rh, or Ru, to the PtSn/C composition impacted ethanol oxidation in acidic medium. Obtaining PtSn-M ternary catalysts by MW was not an easy task, the composition of the resulting PtSn-M were significantly deviated from the desired nominal composition, especially in the case of Ni, for which the reduction method was inefficient. The obtained nanoparticles measured about 3.0 nm and were well distributed on the carbon support. Addition of the third metal by the MW method did not improve the catalytic activity of PtSn/C; indeed, the activities and power densities achieved for the PtSnM catalysts lay below the activity and power density of the PtSn/C catalyst. However, infrared spectroscopy showed that the presence of the third metal made ethanol electrooxidation more selective toward certain reaction products. ln contrast to the traditional step-by-step experiments, application of combinatorial electrochemistry as a tool to discover the most active compositions for ethanol electrooxidation helped to map 91 compositions (Pt, PtM and PtSnM, M = Ni , Fe, Ru, or Pd) simultaneously, by fluorescence assays. This mapping revealed that Pt(80)Sn(10)Fe(10), Pt(80)Sn(10)Ni(10), Pt(70)Sn(20)Pd(10) and Pt(70)Sn(10)Ru(20) were the most active for ethanol electrooxidation. Synthesis of these compositions on a large scale and ethanol electrooxidation tests evidenced excellent catalytic activity and power density, mainly for the composition containing Fe. Finally, ethanol oxidation studies in alkaline media using the catalysts PdFe and PdNi evaluated how the amount of these metals affected the catalytic activity of Pd. Synthesis of these catalysts by reduction via MW afforded PdFe and PdNi with small particle size and well distributed on the carbon support. The catalytic activities proved that the compositions containing 50% Fe or Ni were the best for ethanol oxidation, especially the composition containing Ni, which presented high catalytic activity and excellent stability. (AU)

• FAPESP's process: 09/15034-2 - Preparation, characterization and application of trimetalics catalysts PtSnX (x= Ni, PD, RH e W) for direct ethanol oxidation fuel cell
• Grantee: Thiago dos Santos Almeida
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)