Electrooxidation of methanol in sulfuric acid solution was studied using Pt, Pt/Ni(1:1 and 3:1), Pt/Ru/Ni(5: 4:1 and 6:3.5:0.5), and Pt/Ru(1:1) alloy nanoparticle catalysts, in relation to methanol oxidation processes in the direct oxidation methanol fuel cell. The Pt/Ni and Pt/Ru/Ni alloys showed excellent catalytic activities compared to those of pure Pt and Pt/Ru. The role of Ni as a catalytically enhancing agent in the oxidation process was interrogated using cyclic voltammetry, chronoamperometry, X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray diffraction. X-ray diffraction data showed alloy formation for all Pt/Ni, Pt/Ru/Ni, and Pt/Ru nanoparticles, whereas X-ray photoelectron spectroscopy confirmed that chemical states of Pt were exclusively metallic. The presence of metallic Ni, NiO, Ni(OH) 2 , NiOOH, metallic Ru, RuO 2 , and RuO 3 was also confirmed. We found that the Pt4f binding energies for the Pt/Ni and Pt/Ru/Ni alloy nanoparticles were lower than those for clean Pt nanoparticles. The oxides that serve as the oxygen donors for the oxidation process, and the change in the electronic structure of the Pt component in the alloys versus those in Pt and Pt/Ru collectively account, we believe, for enhancement in rates of methanol oxidation. The difference in the peak shift in Pt4f between Pt/Ni and Pt/Ru alloy nanoparticles is discussed by using electronegativities of the three components: Pt, Ru, and Ni. A comparison between the alloy nanoparticle composition and that of disk alloy electrodes under similar conditions was made in terms of the surface-tovolume ratio and surface segregation of the alloying components.

Ordered uniform porous carbon frameworks with pore sizes in the range of 10 to ∼1000 nm were synthesized against removable colloidal silica crystalline templates by carbonization of phenol and formaldehyde as a carbon precursor. The porous carbons were used as supports for a Pt(50)−Ru(50) alloy catalyst to study their supporting effect on the anodic performance of the catalyst in a direct methanol fuel cell (DMFC). The use of the ordered uniform porous carbons resulted in much improved catalytic activity for methanol oxidation in the fuel cell probably due to their high surface areas, large pore volumes, and three-dimensionally interconnected uniform pore structures, which allow a higher degree of dispersion of the catalysts and efficient diffusion of reagents. In general, the smaller the pore sizes in the porous carbons were, the better the catalytic activity for methanol oxidation was. In addition, as pore sizes are getting smaller, the structural integrity with good pore interconnection seems to be getting more important for the catalytic oxidation of methanol. Among the porous carbons studied in this work, the one with about 25 nm in pore diameter (PtRu−C-25) showed the highest performance with power densities of ∼58 and ∼167 mW/cm2 at 30 and 70 °C, respectively. These values roughly correspond to ∼70 and ∼40% increase as compared to those of a commercially available Pt−Ru alloy catalyst (E-TEK), respectively.

Conversion of low-grade waste heat into electricity is an important energy harvesting strategy. However, abundant heat from these low-grade thermal streams cannot be harvested readily because of the absence of efficient, inexpensive devices that can convert the waste heat into electricity. Here we fabricate carbon nanotube aerogel-based thermo-electrochemical cells, which are potentially low-cost and relatively high-efficiency materials for this application. When normalized to the cell cross-sectional area, a maximum power output of 6.6 W m−2 is obtained for a 51 °C inter-electrode temperature difference, with a Carnot-relative efficiency of 3.95%. The importance of electrode purity, engineered porosity and catalytic surfaces in enhancing the thermocell performance is demonstrated.

Pt/Ru (1:1), Pt/Ni (1:1), and Pt/Ru/Ni (5:4:1) electrocatalysts for use in direct methanol fuel cells (DMFCs) were synthesized by reduction with NaBH4 combined with freeze-drying and their activity as a methanol oxidation catalyst was examined at different temperatures. The onset potential of Pt/Ru/Ni (5:4:1) was lower than that of Pt/Ru (1:1) and current density of Pt/Ru/Ni (5:4:1) was larger than that of Pt/Ru (1:1). In addition, Pt/Ru/Ni (5:4:1) had a larger turnover number and a smaller activation energy for methanol oxidation than Pt/Ru (1:1). Polarization and power density data in a liquid-feed DMFC unit cell test were in good agreement with the voltammetry and chronoamperometry data, for which Pt/Ru/Ni (5:4:1) showed a higher catalytic activity than Pt/Ru (1:1). The role of Ni from the standpoint of the oxidation states of Ni and the modification of the electronic structure of Pt by X-ray photoelectron spectroscopy is discussed. © 2003 The Electrochemical Society. All rights reserved.