Catalytic Desulfurization of Carbon Black on a Platinum Oxide Electrode

Abstract

Organically bound sulfur is a common impurity in carbon blacks, such as vulcanized carbon and coal. Whereas this organosulfur is usually removed by heating to high temperatures, we describe a low-temperature method to desulfurize solid carbon via oxidation (ultimately to SO4 2-) on a Pt catalyst in oxygenated aqueous media. The reaction is monitored on Vulcan carbon, which is the favored support for the Pt catalysts used in fuel-cell electrodes but which has a high concentration (nominally 5000 ppm) of organosulfur. Vulcan carbon is electrodesulfurized by dispersing it in a heated, dilute HNO3 electrolyte where it can physically contact a Pt mesh anode that is maintained as Pt oxide. After 40−180 min of electrolysis in oxygenated solution at +1.0 V versus Pd/H, sulfate is present in the electrolyte (as measured by precipitation of BaSO4). X-ray photoelectron spectroscopy of the dried, electrodesulfurized carbon shows that ∼30% of the near-surface organosulfur is removed. The remaining sulfur presumably does not react because it does not physically contact the hydrous platinum oxide (PtO x H y ) at the electrode surface. Minimal desulfurization occurs at 0.2 V versus Pd/H, when the Pt mesh surface is composed of Pt0. These electrochemical results show that oxidized Pt is the catalyst necessary for oxidative desulfurization. In deoxygenated solution, electrodesulfurization still occurs for electrolyses at +1.0 V versus Pd/H, but SO4 2- is not generated, indicating that SO2 is the partial oxidation product. The surface area and total oxygen content of the carbon are unaffected by the electrodesulfurization process. This simple, low-temperature method for desulfurization should be applicable to other forms of solid carbon containing organosulfur moieties.

Deactivation of Pt/VC proton exchange membrane fuel cell cathodes by SO2, H2S and COS

“…Deactivation models for anode poisoning predict that saturation is caused by competitive site adsorption between hydrogen and sulfur [47]. The resistance of platinum oxide to sulfur poisoning has been shown in earlier work [17,18]. The influence of adsorption of SO 2 onto oxygen covered Pt surfaces has been studied by DFT [27].…”

“…Sulfur also can be oxidized to sulfate by a redox process with platinum oxide (or platinum hydroxide) and water [17,18].…”

Proton exchange membrane fuel cell contamination model: Competitive adsorption followed by a surface segregated electrochemical reaction leading to an irreversibly adsorbed product

“…For instance, the contaminant concentration is affected by the scavenging effect of liquid water, adsorption/reaction on carbon within the cell [19,20] and the presence of sulfur on the catalyst carbon support [21]. Therefore, even if a fraction of these effects are reduced by treating the catalyst carbon support or carbon gas diffusion layer to remove the sulfur [22][23][24], the contaminant concentration at the catalyst surface represents an effective value which is smaller than the contaminant concentration in the inlet stream.…”

Amperometric Determination of Ascorbic Acid on an Au Electrode Modified by a Composite Film of Poly(3,4-ethylenedioxythiophene) and Superconductive Carbon Black

“…45 In this work, superconductive carbon black (SCB), owing to its superior conductivity, large specific surface area, high stability and better integration, was selected as a functional incorporation component to prepare a PEDOT-SCB composite film modified gold electrode. [46][47][48] To the best of our knowledge, there has been no report on the fabrication and application of a PEDOT-SCB modified Au electrode for the electrocatalytic oxidation and determination of AA. Herein, the electrochemical behavior of AA on a PEDOT-SCB modified Au electrode was thoroughly investigated, and a sensitive electrochemical sensor for the determination of AA was also developed.…”