Operando analysis of direct methanol fuel cell catalyst and electrolyte transport properties

Direct methanol fuel cells (DMFCs) are an excellent option for portable power because of the high energy density and ease of handling of condensed methanol. DMFCs can potentially provide a clean source of energy by converting the methanol fuel into electricity. Advancements required for commercialization include improvements in (i) electrocatalyst activity and stability, (ii) membrane resistance to methanol crossover, (iii) water and heat management, and (iv) the durability of the polymer electrolyte membrane. Chapter 1 provides the reader with a brief introduction on some of these issues.;In Chapter 2 the potential dependent CO2 exhaust from the cathode was monitored by on-line electrochemical-mass spectrometry with air and with H2 at the cathode. The precise determination of the crossover rates methanol and CO2, enabled by the subtractive normalization of the methanol/air to the methanol/H2 ECMS data, shows that methanol decreases the membrane viscosity and thus increases the diffusion coefficients of sorbed membrane components.;DMFC commercialization demands stable operation for at least thousands of hours (e.g. 5000 h), while fuel cell vehicles and residential power generators require 40,000 hours, which is difficult to achieve. Chapter 3 describes a study on a 5 cm2 direct methanol fuel cell using unsupported PtRu and Pt catalysts, and ambient air at the cathode was operated at 100 mA/cm2 and 60°C for 110 hours. X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) and electrochemical methods characterized the anode and cathode catalysts before and after lifetime testing. A comparison of the DMFC of this study with literature reports show that although the performance of DMFCs catalyzed with unsupported catalysts have substantially superior performance, the initial degradation rates of DMFCs with unsupported catalysts is greater.;Chapter 4 describes an in situ XRD analysis of a Johnson Matthey Pt black catalyst, deposited on a carbon paper gas-diffusion-layer (GDLs), which was studied at 100, 200 and 300°C over periods of months in vacuum and in air. The Pt was deposited onto the GDLs from catalyst inks using standard fuel cell membrane-electrode-assembly procedures.;In Chapter 5 a sonochemically prepared PtRu (3:1) and Johnson Matthey PtRu (1:1) were analyzed by X-ray absorption spectroscopy (XAS) in operating liquid feed direct methanol fuel cells. The total metal loadings were 4 mg/cm 2 unsupported catalysts at the anode and cathode of the membrane electrode assembly. Ex-situ XRD lattice parameter analysis indicates partial segregation of the Ru from the PtRu fcc alloy in both catalysts.