Study on the influence of the thickness of nanostructured rhodium films toward electrooxidation of adsorbed carbon monoxide

Abstract

Carbon-supported rhodium thin films with various thicknesses are grown by varying the number of laser pulses, Nlp (from 5000 to 50,000) under 2 Torr of He background atmosphere using the pulsed laser deposition method. The thin films are characterized for their morphological features and structural properties. It is observed that smooth dense 2D nanosheets of Rh are obtained with 5000 Nlp, whereas higher Nlp yields to highly porous Rh films. X-ray photoelectron spectroscopy reveals that both metallic Rh and Rh3+ are present at the surface of the Rh films. Nevertheless, the amount of metallic Rh increased as the Nlp increased. The influence of the thickness of the Rh films on the tolerance to CO, a poison that strongly adsorbs on the surface of catalysts in fuel cells reactions, was investigated through anodic stripping voltammetry. It is found that Rh film deposited with 50,000 Nlp exhibits the highest electroactive surface area (27.90 cm2 vs. 1.20 cm2 of Pt), the lowest onset potential of CO electrooxidation (0.47 V vs. 0.60 V Pt), and a net charge corresponding to electrooxidation of the CO adlayer of 424 μC cm−2 (vs. 358 μC cm−2 of Pt). Such high tolerance to CO poisoning is explained on the basis of the elevated porosity and roughness of the Rh surface. Indeed, a roughness factor of 90.5 for Rh against about 3.8 for Pt grows under analogous deposition conditions of pressure and number of laser pulses.