Electrocatalysis and electrocatalysts for low temperature fuel cells: fundamentals, state of the art, research and development

This article deals with electrocatalysis and electrocatalysts for low temperature fuel cells and also with established means and methods in electrocatalyst research, development and characterization. The intention is to inform about the fundamentals, state of the art, research and development of noble metal electrocatalysts for fuel cells operating at low temperatures

The high activity of PtBi/C electrocatalysts for ethanol electro-oxidation in alkaline medium

Pt/C, Bi/C and PtBi/C (Pt:Bi atomic ratios of 90:10, 70:30 and 50:50) electrocatalysts were prepared by borohydride reduction using H2PtCl6·6H2O and Bi(NO3)3·5H2O as metal sources and Vulcan XC72 as carbon support. The obtained electrocatalysts were characterized by energy-dispersive X-ray analysis, X-ray diffraction, transmission electron microscopy and cyclic voltammetry. The activity of the electrocatalysts for ethanol electro-oxidation was studied by chronoamperometry. PtBi/C electrocatalysts showed a significant increase of performance compared to Pt/C, while Bi/C showed no activity. Also, the performances of the PtBi/C electrocatalysts for ethanol electro-oxidation in alkaline medium were very superior to the ones obtained in acid medium. Keywords: PtBi/C electrocatalysts, Ethanol electro-oxidation, Alkaline medium, Fuel cel

PtRu/C Electrocatalysts Prepared Using Gamma and Electron Beam Irradiation for Methanol Electrooxidation

PtRu/C electrocatalysts (carbon-supported PtRu nanoparticles) were prepared in a single step submitting water/2-propanol mixtures containing Pt(IV) and Ru(III) ions and the carbon support to gamma and electron beam irradiation. The electrocatalysts were characterized by energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM), and cyclic voltammetry and tested for methanol electrooxidation. PtRu/C electrocatalyst can be prepared in few minutes using high dose rate electron beam irradiation while using low dose rate gamma irradiation some hours were necessary to prepare it. The obtained materials showed the face-centered cubic (fcc) structure of Pt and Pt alloys with average nanoparticle sizes of around 3 nm. The material prepared using electron beam irradiation was more active for methanol electrooxidation than the material prepared using gamma irradiation

Electrochemical and impedance spectroscopy studies in H2/O2 and methanol/O2 proton exchange membrane fuel cells

This works report results of the structural and the electrochemical characterization of membrane electrode assemblies (MEA) for proton exchange membrane fuel cells (PEMFC) under various cell conditions using different MEA production processes. Electrochemical impedance spectroscopy (EIS) was applied “on-line” (in situ) as a tool for diagnosis concerning the cell performance. MEA with a 25-cm2 surface area were prepared using Pt/C and Pt–Ru/C commercial electrocatalysts from E-TEK and Pt–Ru/C electrocatalysts produced by the alcohol reduction process. The catalytic ink was applied directly onto the carbon cloth or, alternatively, onto the Nafion® membrane. Two carbon cloth thicknesses were tested as diffusion layers in the MEA: 0.346 mm (common) and 0.424 mm (ELAT). An increase of the electrocatalytic activity can be obtained by pH control in the alcohol reduction process, possibly due to the better particle dispersion and the smaller particle sizes observed. In addition, a slower current decay in the ohmic region was observed using the thinner carbon cloth. This can be related to a lower resistance of the gas flow through the cloth to the catalytic active layer. Different types of methanol feed were employed in the experiments: by humidification and by evaporation. The results showed that the choice of suitable methods for catalyst preparation as well as for MEA production enhance PEMFC performance

Glycerol Electrooxidation in Alkaline Medium Using Pd/C, Au/C and PdAu/C Electrocatalysts Prepared by Electron Beam Irradiation

Pd/C, Au/C and PdAu/C electrocatalysts with different atomic ratios prepared using electron beam irradiation were tested for glycerol electrooxidation in single alkaline direct glycerol fuel cell (ADGFC). X-ray diffractograms (XRD) of PdAu/C electrocatalysts showed the presence of Pd (fcc) and Au (fcc) phases. Cyclic voltammetry (CV) and chronoamperometry showed that PdAu/C electrocatalyst with Pd:Au atomic ratio of 50:50 demonstrated superior activity for glycerol electrooxidation, at room temperature. In situ Fourier transform infrared spectroscopy by attenuated total reflectance (ATR-FTIR) experiments were performed for the electrocatalysts, identifying oxalate, glycerate ion, 1,3-dihydroxy-2-propanone, glyceraldehyde and glycolate as products of glycerol electrooxidation. Experiments with single ADGFC were carried out from 50 to 90 ºC, using Pd/C electrocatalyst; the best performance was obtained at 80 ºC