Carbon supported electrocatalysts for the reduction of oxygen can be screened quickly by using a rotating disk electrode (RDE) when an appropriate material is used as a binder to hold the catalyst on the disk electrode. The results obtained with RDE in an oxygen-saturated H₂SO₄ solution mimic those measured for a full-cell H₂/O₂ solid polymer electrolyte setup. This result is demonstrated with a cobalt phthalocyanine-on-carbon black catalyst pyrolyzed at various temperatures ranging from 400 to 1100^oC. When the catalyst is held on the disk electrode with electropolymerized pyrrole, a broad maximum of activity for the reduction of oxygen is observed for pyrolysis temperatures ranging between 600 and 900^oC. When the catalyst is dispersed in a Nafion film on the disk electrode, a sharp maximum in its activity is observed at the pyrolysis temperature of 600^oC, in agreement with its behavior in a full-cell setup.
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The life tests, at 100 and 200 mA/cm² in a solid-polymer fuel cell, indicate that the Pt-Cr-Cu/C catalyst is relatively more active than the Pt/C catalyst even after operating the cell for 300 h. The elemental analysis of the anode and cathode catalysts, before and after the stability test, indicate an excessive loss of copper from the cathode. The enhanced activity of this catalyst is explained in terms of its improved wetting of the catalyst particles and of the Raney-type Pt-Cr-Cu alloy formation. Click to read more

 

The effect of base metal oxide (nonnoble metal oxide) in a Pt-Cr-Cu alloy catalyst is investigated for the oxygen reduction reaction in a solid-polymer-electrolyte fuel cell. The cathode mass activities at 0.9V for Pt-Cr-Cu alloy, and a mixture of Pt-Cr-Cu alloy with base metal oxide are compared. The enhancement factor is largest (about 2 times) for the mixture of Pt-Cr-Cu alloy with base metal oxide, compared to Pt-Cr and Pt-Cr-Cu alloys (about 2 times). The higher electrocatalytic activity of this material may be due to the combined effects of the Pt-Cr-Cu alloy and the base metal oxide. The physical and electrochemical characterizations are carried out using various techniques like x-ray diffraction, transmission electron microscopy, cyclic voltammetry, polarization, and ac impedance.

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Pt/C catalysts with two different Pt crystallite sizes [as-received (20 weight percent (w/o) Pt/C powder from E-TEK) and heat-treated (900°C in inert atmosphere)] were analyzed for the reduction of oxygen in half-cells using rotating disk electrodes. Measurements in HF (1.17 M) show that the specific activity of the catalysts increases with the Pt crystallite size. In contrast, measurements in H₂S0₄ (1.17 M) indicate that the specific activity is nearly independent of the Pt crystallite size. One of the reasons for the difference in behavior observed between these acids is the difference in specific adsorption of anions on the Pt sites from H₂50₄ (adsorbing) and HF (nonadsorbing) solutions. This study indicates that both the oxygen reduction reaction and anion adsorption on the Pt sites are crystallite-size sensitive in H₂50₄ solution. In solid polymer fuel cells (SPFCs), the anions are anchored on the backbone of the polymer matrix, and hence only a minimal anion adsorption is expected on the Pt sites of gas diffusion electrodes. From results of the present study, it is believed that the Pt/membrane interface in SPFCs could be better mimicked by the Pt/HF interface rather than the Pt/H2S04 interface. Click to read more

 

Four platinum-based catalysts with different catalytic activity for the oxygen reduction reaction have been prepared and tested in polymer fuel cells (PFCs) and in half-cells with
H₂SO₄ and HF electrolytes. The activity results of PFCs at 0.9 V versus RHE (reversible hydrogen electrode) can be mimicked in parallel by the results obtained in HF electrolyte but not by the results obtained in H₂SO₄ electrolyte. This paper concludes that the pre-screening of a huge number of Pt-based catalysts for the selection of potential catalysts for the PFCs can be carried out by a rapid half-cell technique with a non-adsorbing electrolyte such as HF. Click to read more

 

Traditionally, the energy production of a grid connected Photovoltaic (PV) system is predicted as a product of STC (standard test conditions; 1000 W/m², 25^oC and Air mass 1.5 Global) power rating of the modules and TMY (typical meteorological years) sunhours of the site. This simple energy prediction does not account for the negative influence of module operating temperatures, module light efficiency, loss of photons at high incident angles and influence of spectral changes. As a result end users and experienced much lower energy production than predicted. Click to read more