Underpotential deposition (upd) of copper has been used to characterize platinum, ruthenium, and platinumruthenium high-surface-area unsupported (powder black) electrocatalysts. The surface areas thus obtained compare favorably with those determined by the more conventional electrochemical methods of monolayer CO and hydrogen oxidation. The differing adsorption energies for Cu on either Pt or Ru allow the peaks for upd copper deposited on alloy Pt-Ru to be resolved into their constituent components. Thus, in addition to the surface area, the surface composition of the Pt-Ru electrocatalyst can be determined. This approach distinguishes between bare ruthenium (i.e., metallic) and oxidized ruthenium sites as the upd copper does not deposit on the latter. The ruthenium surface area is found to remain high up to 0.45 V (vs RHE) and then to fall linearly with potential. Polarization at high potentials [1.45 V (vs RHE)] leaves a material in which metallic ruthenium cannot be recovered by electrochemical reduction. This is caused by oxidation of the ruthenium to a state that either dissolves in the aqueous phase and is lost or produces a form of oxidized ruthenium that is in a state that cannot be electrochemically reduced.
The economic viability of low temperature fuel cells as clean energy devices is enhanced by the development of inexpensive oxygen reduction reaction catalysts. Heat treated iron and nitrogen containing carbon based materials (Fe–N/C) have shown potential to replace expensive precious metals. Although significant improvements have recently been made, their activity and durability is still unsatisfactory. The further development and a rational design of these materials has stalled due to the lack of an in situ methodology to easily probe and quantify the active site. Here we demonstrate a protocol that allows the quantification of active centres, which operate under acidic conditions, by means of nitrite adsorption followed by reductive stripping, and show direct correlation to the catalytic activity. The method is demonstrated for two differently prepared materials. This approach may allow researchers to easily assess the active site density and turnover frequency of Fe–N/C catalysts.
The mechanism and kinetics of the hydrogen oxidation reaction (hor) has been investigated using carbon-supported single particles of Pt electrocatalyst with radii as small as 40 nm. The high mass transport rates on
such small particles enable us to investigate the rapid kinetics of the hor in the absence of diffusion limitations.
Surface kinetic controlled polarization curves during the electrochemical oxidation of hydrogen molecules in
acid solution have been obtained in the entire H UPD region, showing features obviously different from
those obtained on normal micrometer electrodes or in RDE experiments. For instance, two current plateaus
rather than one are seen during the steady-state polarization of the hor on electrodes made of small particles.
Upon decreasing the size of the Pt particles, the two current plateaus show greater separation and become
better defined. A theoretical model for the steady-state polarization of the hor has been developed in which
UPD H atoms of various states are considered as the reactive intermediates and the Frumkin adsorption
mode is assumed for the atomic H on Pt electrodes. It is shown that the first current plateau represents the
limiting reaction rate under adsorption or combined adsorption−diffusion control while the second plateau
current corresponds to the limiting diffusion-controlled reaction rate. It is pointed out that Tafel plots that
have been frequently used for kinetics analysis in the hor are meaningless, especially in the potential region
below 0.05V vs RHE. The polarization curves are fitted with a general polarization equation derived according
to our model. The fitting shows that the hor on Pt proceeds most likely via the Tafel−Volmer reaction
mechanism rather than the Heyrovsky−Volmer mechanism. These results have significant implications on
the understanding and modeling of the reactions in solid polymer electrolyte fuel cells.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.