Vivek S. Murthi

Correlation of Water Activation, Surface Properties, and Oxygen Reduction Reactivity of Supported Pt–M/C Bimetallic Electrocatalysts Using XAS

An analysis of X-ray absorption spectroscopy XAS data X-ray absorption near-edge structure XANES and extended X-ray absorption fine structure EXAFS at the Pt L3 edge for Pt‐M bimetallic materials M = Co, Cr, Ni, Fe and at the Co K edge for Pt‐Co is reported for Pt‐M/C electrodes in HClO4 at different potentials. The XANES data are analyzed using the method, which utilizes the spectrum at some potential V minus that at 0.54 V reversible hydrogen electrode RHE representing a reference spectrum. These data provide direct spectroscopic evidence for the inhibition of OH chemisorption on the cluster surface in the Pt‐M. This OH chemisorption, decreasing in the direction Pt Pt‐Ni Pt‐Co Pt‐Fe Pt‐Cr, is directly correlated with the previously reported fuel cell performance electrocatalytic activities of these bimetallics, confirming the role of OH poisoning of Pt sites in fuel cells. EXAFS analysis shows that the prepared clusters studied have different morphologies, the Pt‐Ni and Pt‐Co clusters were more homogeneous with M atoms at the surface, while the Pt‐Fe and Pt‐Cr clusters had a “Pt skin.” The cluster morphology determines which previously proposed OH inhibition mechanism dominates, the electronic mechanism in the pres

Potential Shift for OH(ads) Formation on the Pt Skin on Pt3Co ( 111 ) Electrodes in Acid Theory and Experiment

A study combining theoretical predictions and experimental measurements was made to gain an understanding of the beneficial effect of alloying cobalt into platinum for electroreduction of oxygen. Carbon-supported Pt 3 Co catalyst particles were characterized by X-ray diffraction spectroscopy and X-ray absorption near-edge structure, which gave evidence for a surface layer composed of Pt, called the Pt skin. Electrochemical measurements were made in 1 M trifluoromethane sulfonic acid with a rotating ring disk setup. Cyclic voltammetry showed significantly less oxide formation in the >0.8 V range over the skin on the alloy compared to nonalloyed Pt. Tafel plots showed a 50-70 mV reduction in overpotential for O 2 reduction over the Pt skin. The Vienna Ab Initio Simulation Program was used for calculating H 2 O and OH adsorption bond strengths on the Pt skin on Pt 3 Co(111) for comparison with prior work with the Pt(111) surface. The bond strength variations were used to estimate the shift in reversible potential for OH a d s formation from H 2 O a d s oxidation. A shift of 80 mV was found, which indicates that an increase in the reversible potential for OH a d s formation correlates with the decrease in overpotential for O 2 reduction over the Pt skin on Pt 3 Co nanoparticles.

Highly Dispersed Alloy Catalyst for Durability

Achieving Department of Energys (DOEs) stated 5000-hour durability goal for light-duty vehicles by 2015 will require membrane electrode assemblies (MEAs) with characteristics that are beyond the current state of the art. Significant effort was placed on developing advanced durable cathode catalysts to arrive at the best possible electrode for high performance and durability, as well as developing manufacturing processes that yield significant cost benefit. Accordingly, the overall goal of this project was to develop and construct advanced MEAs that will improve performance and durability while reducing the cost of proton exchange membrane fuel cell (PEMFC) stacks. The project, led by UTC Power, focused on developing new catalysts/supports and integrating them with existing materials (membranes and gas diffusion layers (GDLs)) using state-of-the-art fabrication methods capable of meeting the durability requirements essential for automotive applications. Specifically, the project work aimed to lower platinum group metals (PGM) loading while increasing performance and durability. Appropriate catalysts and MEA configuration were down-selected that protects the membrane, and the layers were tailored to optimize the movements of reactants and product water through the cell to maximize performance while maintaining durability.