Abstract
Platinum is a main catalyst for the electroreduction of oxygen, a reaction of primary importance to the technology of low-temperature fuel cells. Due to the high cost of platinum, there is a need to significantly lower its loadings at interfaces. However, then O2-reduction often proceeds at a less positive potential, and produces higher amounts of undesirable H2O2-intermediate. Hybrid supports, which utilize metal oxides (e.g., CeO2, WO3, Ta2O5, Nb2O5, and ZrO2), stabilize Pt and carbon nanostructures and diminish their corrosion while exhibiting high activity toward the four-electron (most efficient) reduction in oxygen. Porosity of carbon supports facilitates dispersion and stability of Pt nanoparticles. Alternatively, the Pt-based bi- and multi-metallic catalysts, including PtM alloys or M-core/Pt-shell nanostructures, where M stands for certain transition metals (e.g., Au, Co, Cu, Ni, and Fe), can be considered. The catalytic efficiency depends on geometric (decrease in Pt–Pt bond distances) and electronic (increase in d-electron vacancy in Pt) factors, in addition to possible metal–support interactions and interfacial structural changes affecting adsorption and activation of O2-molecules. Despite the stabilization of carbons, doping with heteroatoms, such as sulfur, nitrogen, phosphorus, and boron results in the formation of catalytically active centers. Thus, the useful catalysts are likely to be multi-component and multi-functional.
Highlights
The rapid growth of energy consumption and the necessity to reduce greenhouse gas emissions associated with energy production have been promoting a search for alternative energy sources
The present study addresses different approaches and concepts toward the more efficient utilization of the platinum catalytic nanostructures during oxygen reduction reaction (ORR)
Reactivity of low-Pt-content catalytic materials for oxygen reduction largely depends on the choice of carbon support, its modification or functionalization, as well as addition of cocatalytic active sites or components
Summary
The rapid growth of energy consumption and the necessity to reduce greenhouse gas emissions associated with energy production have been promoting a search for alternative energy sources. Considerable attention has been dedicated to materials based on titanium oxides as durable catalytic supports for PEMFC applications due to their inherent stability under various electrochemical conditions, high corrosion resistance, and enhancement of electrocatalytic activity through the bilateral interactions effect originating from the combination of catalytic metal nanoparticles and TiOx [41,42,43,44]. To overcome this problem and facilitate distribution of electrons at ZrO2 -containing interfaces, an important strategy involves application of nitrogen-doped carbons together with ZrO2 nanostructures [59] It is apparent from the diagnostic electrochemical experiments that Pt nanoparticles, which are well-dispersed on such supports, exhibit higher activity during ORR, when compared to the performance of those without zirconium oxide. Oxides, WO3−y (0 < y < 1), were characterized by fast electron transfers, good proton mobility, and high porosity, as well as by high reactivity toward reductions in such inert reactants as oxohalogenates and hydrogen peroxide
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