Electrochemical Hydrogen Adsorption Research Articles

Effect of chemisorbed sulfur on the electrochemical hydrogen adsorption and recombination reactions on Pt (111)

The effect of preadsorbed sulfur on the cathodic hydrogen adsorption and recombination reactions was quantitatively studied on a platinum (111) surface in acid aqueous medium. The sulfur coverage was measured by a radiotracer technique. In the presence of sulfur the rate of the overall hydrogen evolution reaction (HER) is strongly lowered. This effect is attributed to a poisoning by sulfur of the sites of adsorption of hydrogen. The weakly bonded hydrogen species involved in the HER is not adsorbed in the same sites as the strongly bonded hydrogen species adsorbed at underpotential. Different poisoning effects by sulfur are observed on the two kinds of sites. The measurements are well fitted by a model in which one isolated sulfur atom blocks three adsorption sites of weakly bonded hydrogen.

Combined electrochemical/surface science investigations of Pt/Cr alloy electrodes

Chromium addition improves the performance of carbon-supported Pt electrodes for oxygen reduction in phosphoric acid fuel cells. To clarify the role of chromium and its chemical nature at the electrode surface, we have performed a combined electrochemical/surface science investigation of a series of bulk PtxCr1−x alloys (0≤x≤1). In this paper we report the surface characterization of the starting electrodes by XPS, electrochemical results from cyclic voltammetry in 85% phosphoric acid, and postelectrochemical surface characterization. For Cr contents less than 40%, the electrodes were quite stable up to +1.6 V versus dynamic hydrogen electrode (DHE). The surface Cr was largely oxidized to Cr+3 for surfaces at open circuit and those exposed at potentials <+1.4 V. For intermediate Cr levels, Cr was leached from the surface region by +1.5 V, leaving a porous Pt electrode with increased electrochemical hydrogen adsorption capacity. For Pt0.2 Cr0.8, treatments at +1.4 V and above led to the appearance of Pt+4 and Cr+6 species, apparently stabilized in a porous phosphate overlayer up to 50 Å thick. The Pt electrochemical hydrogen adsorption capacity was simultaneously increased by a factor of 15.

Chemical characterization by Auger electron spectroscopy and voltammetry of platinum electrode surfaces prepared in the gas phase

The aim of this work was to find conditions of preparation of a clean platinum surface for electrochemical experiments. Auger electron spectroscopy shows that the main contaminants of the platinum surfaces treated in Ar glow discharge are nitrogen and oxygen while the carbon content is reduced to a low level. Voltammetry shows that after glow discharge a surface compound is irreversibly oxidized. This compound is stable in air and is chemically oxidized by oxygen in presence of water. This compound is probably NO formed and adsorbed from residual atmosphere during glow discharge. When present it inhibits electrochemical adsorption of hydrogen by blocking pairs of hydrogen adsorption sites. The cleanliness of the surface prepared in the present conditions is such that after desorption of NO the electrode immediately adsorbs 95% of the maximum quantity of hydrogen adsorbed by the same electrode electrochemically activated.