UHV, Electrochemical NMR, and Electrochemical Studies of Platinum/Ruthenium Fuel Cell Catalysts

Abstract

It is well-known that platinum/ruthenium fuel cell catalysts show enhanced CO tolerance compared to pure platinum electrodes, but the reasons are still being debated. We have combined cyclic voltammetry (CV), temperature programmed desorption (TPD), electrochemical nuclear magnetic resonance, and radio active labeling to probe the origin of the ruthenium enhancement in Pt electrodes modified through Ru deposition. The results prove that the addition of ruthenium not only modifies the electronic structure of all the platinum atoms but also leads to the creation of a new form of adsorbed CO. This new form of CO may be ascribed to CO chemisorbed onto the "Ru" region of the electrode surface. TPD and CV results show that the binding of hydrogen is substantially modified due to the presence of Ru. Surprisingly though, TPD indicates that the binding energy of CO on platinum is only weakly affected. Therefore, the changes in the bond energy of CO due to the ligand effect only play a small role in enhancing CO tolerance. Instead, we find that the main effect of ruthenium is to activate water to form OH. Quantitative estimates based on the TPD data indicate that the bifunctional mechanism is about four times larger than the ligand effect.

Electrooxidation of Carbon Monoxide at Ruthenium–Modified Platinum Nano‐particles: Evidence for CO Surface Mobility

“…This phenomenon has already been observed by cyclic voltammetry at Ru-modified electrodes for both Pt (hkl) electrodes [19±23] and non-supported Pt nanoparticles [12,25,26]. In addition, using spectroscopic methods such as IR reflectance spectroscopy [19,20,27] or solid state NMR spectroscopy [12,28], two types of CO species have been identified on the electrode surface. It is therefore very likely that CO surface mobility is related to the kinetics of CO and methanol oxidation at PtRu electrodes.…”

Ethanol electrooxidation on Pt-Sn and Pt-Sn-W bulk alloys

“…A catalytic effect can also be explained by the ligand effect where the metal M atoms close to Pt are expected to influence the density of electronic states of Pt, leading to the weakening of the Pt-CO bond. [36][37][38][39] The present work focuses on ethanol oxidation on Pt alloy catalysts (Pt-Sn and Pt-Sn-W) prepared by an arc-melting furnace process. Chronoamperometric measurements were performed with each catalyst in order to compare their electroactivities to that of Pt alone.…”

Particle growth behavior of carbon-supported Pt, Ru, PtRu catalysts prepared by an impregnation reductive-pyrolysis method for direct methanol fuel cell anodes

“…High-surface area PtRu alloy supported on carbon black is one of the most promising materials as an anode catalyst for DMFC , because of its high tolerance against carbon monoxide poisoning. The promotion effect of Ru has been mainly discussed based on the so-called "bifunctional mechanism" [4][5][6] or "ligand effect" [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] or a mixture of both.…”