Elucidation of role of graphene in catalytic designs for electroreduction of oxygen

Graphene is, in principle, a promising material for consideration as component (support, active site) of electrocatalytic materials, particularly with respect to reduction of oxygen, an electrode reaction of importance to low-temperature fuel cell technology. Different concepts of utilization, including nanostructuring, doping, admixing, preconditioning, modification or functionalization of various graphene-based systems for catalytic electroreduction of oxygen are elucidated, as well as important strategies to enhance the systems' overall activity and stability are discussed

Evaluation of Reduced-Graphene-Oxide Aligned with WO3-Nanorods as Support for Pt Nanoparticles during Oxygen Electroreduction in Acid Medium

Hybrid supports composed of chemically-reduced graphene-oxide-aligned with tungsten oxide nanowires are considered here as active carriers for dispersed platinum with an ultimate goal of producing improved catalysts for electroreduction of oxygen in acid medium. Here WO3 nanostructures are expected to be attached mainly to the edges of graphene thus making the hybrid structure not only highly porous but also capable of preventing graphene stacking and creating numerous sites for the deposition of Pt nanoparticles. Comparison has been made to the analogous systems utilizing neither reduced graphene oxide nor tungsten oxide component. By over-coating the reduced-graphene-oxide support with WO3 nanorods, the electrocatalytic activity of the system toward the reduction of oxygen in acid medium has been enhanced even at the low Pt loading of 30 microg cm-2. The RRDE data are consistent with decreased formation of hydrogen peroxide in the presence of WO3. Among important issues are such features of the oxide as porosity, large population of hydroxyl groups, high Broensted acidity, as well as fast electron transfers coupled to unimpeded proton displacements. The conclusions are supported with mechanistic and kinetic studies involving double-potential-step chronocoulometry as an alternative diagnostic tool to rotating ring-disk voltammetry.Comment: arXiv admin note: text overlap with arXiv:1805.0315

Electrocatalytic properties of platinum nanocenters electrogenerated at ultra-trace levels within zeolitic phosphododecatungstate cesium salt matrices

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Towards 'Pt-free' Anion-Exchange Membrane Fuel Cells: Fe-Sn Carbon Nitride-Graphene 'Core-Shell' Electrocatalysts for the Oxygen Reduction Reaction

We report on the development of two new Pt-free electrocatalysts (ECs) for the oxygen reduction reaction (ORR) based on graphene nanoplatelets (GNPs). We designed the ECs with a core-shell morphology, where a GNP core support is covered by a carbon nitride (CN) shell. The proposed ECs present ORR active sites that are not associated to nanoparticles of metal/alloy/oxide, but are instead based on Fe and Sn sub-nanometric clusters bound in coordination nests formed by carbon and nitrogen ligands of the CN shell. The performance and reaction mechanism of the ECs in the ORR are evaluated in an alkaline medium by cyclic voltammetry with the thin-film rotating ring-disk approach and confirmed by measurements on gas-diffusion electrodes. The proposed GNP-supported ECs present an ORR overpotential of only ca. 70 mV higher with respect to a conventional Pt/C reference EC including a XC-72R carbon black support. These results make the reported ECs very promising for application in anion-exchange membrane fuel cells. Moreover, our methodology provides an example of a general synthesis protocol for the development of new Pt-free ECs for the ORR having ample room for further performance improvement beyond the state of the art

Heat-Treated Transition Metal Hexacyanometallates with Trace Amount of Pt As Electrocatalysts for the Oxygen Reduction Reaction Based on Nitrogen Doped Graphene: Catalysts Development and Electrode Structure Design

In the recent research years is observed huge interest in design of new functional nanomaterials for developing new electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. The research has been focused on developing carbon nanostructures especially graphene/graphene oxide materials with the different transition metals (e.g. Co, Ni, Ag, Au, Cu, Mn) analogue of polynuclear Prussian Blue, namely with ultra-thin Co, and Ni hexacyanoferrate layers and trace amount of platinum for fuel cell applications. Electrocatalysts based on graphene and graphene-oxide (GO) are more homogeneous and possess properties such as excellent conductivity, good chemical stability and can be functionalized in a controlled manner. Following the heat-treatment step at higher temperatures, some thermal decomposition of the cyanometallate network occurs and, consequently, metallic sites are generated. Their formation and distribution are facilitated by the voltammetric potential cycling in acid and alkaline electrolytes. The most promising electrocatalytic results with respect to the reduction of oxygen (the highest currents and the most positive electroreduction potentials) have been obtained when graphene nanostructures are combined with analogue of polynuclear Prussian Blue and trace amount of Pt nanoparticles. What is even more important that, due to the presence of the polynuclear cyanoferrate modifier or linker, the amounts of the undesirable hydrogen peroxide intermediate are significantly decreased. An electrocatalytic system, that utilizes metal hexacyanometallates nanoparticles with trace amount of Pt modified graphene and graphene related materials, is developed and characterized here using transmission electron microscopy and such electrochemical diagnostic techniques as cyclic volammetry and rotating ring-disk voltammetry in a 0.5 M H2SO4 electrolyte and in a 0.1 M KOH electrolyte and upon introduction (as cathode) to the low-temperature hydrogen-oxygen fuel cell. Comparative measurements have been performed against the model noble metal (Vulcan-supported platinum nanoparticles) catalyst

Reduced-Graphene-Oxide with Traces of Iridium or Gold as Active Support for Pt Catalyst at Low Loading during Oxygen Electroreduction

Chemically-reduced graphene-oxide-supported gold or iridium nanoparticles are considered here as active carriers for dispersed platinum with an ultimate goal of producing improved catalysts for electroreduction of oxygen in acid medium. Comparison is made to the analogous systems not utilizing reduced graphene oxide. High electrocatalytic activity of platinum (loading up to 30 µg cm-2) dispersed over the reduced-graphene oxide-supported Au (up to 30 µg cm-2) or Ir (up to 1.5 µg cm-2) nanoparticles toward reduction of oxygen has been demonstrated using cyclic and rotating ring-disk electrode (RRDE) voltammetric experiments. Among important issues are possible activating interactions between gold and the support, as well as presence of structural defects existing on poorly organized graphitic structure of reduced graphene oxide. The RRDE data are consistent with decreased formation of hydrogen peroxide