Abstract:A series of monodisperse, sterically stabilized colloids of electrocatalytically active ruthenium dioxide hydrate (RUOZ-XHZO) with diameters between 40 and 160 nm are used to examine the relationship between particle size, catalyst concentration, and the heterogeneously catalyzed rate of water oxidation by cerium(1V) ions in dilute nitric acid. Reaction rate is linearly dependent upon catalyst concentration for all particle sizes. Rate constants vary with particle radius raised to the power -1.7 and exhibit ab… Show more
“…In parallel to these bottom-up approaches during the 1970s and 1980s, top-down methods to fabricate and utilize nanometer-sized monometallic electrodes were developed toward the end of that decade . Finally, a language transition in the electrochemical materials literature from “colloidal” − to “nano” − commenced in the early 1990s and was completed in the mid-2000s. By then, nanoelectrochemistry also addressed nanoelectrodeposition and nanopatterning of surfaces using scanning probe microscopy .…”
Nanomaterial science and electrocatalytic science have entered a successful "nanoelectrochemical" symbiosis, in which novel nanomaterials offer new frontiers for studies on electrocatalytic charge transfer, while electrocatalytic processes give meaning and often practical importance to novel nanomaterial concepts. Examples of this fruitful symbiosis are dealloyed core-shell nanoparticle electrocatalysts, which often exhibit enhanced kinetic charge transfer rates at greatly improved atom-efficiency. As such, they represent ideal electrocatalyst architectures for the acidic oxygen reduction reaction to water (ORR) and the acidic oxygen evolution reaction from water (OER) that require scarce Pt- and Ir-based catalysts. Together, these two reactions constitute the "O-cycle", a key elemental process loop in the field of electrochemical energy interconversion between electricity (free electrons) and molecular bonds (HO/O), realized in the combination of water electrolyzers and hydrogen/oxygen fuel cells. In this Account, we describe our recent efforts to design, synthesize, understand, and test noble metal-poor dealloyed Pt and Ir core-shell nanoparticles for deployment in acidic polymer electrolyte membrane (PEM) electrolyzers and PEM fuel cells. Spherical dealloyed Pt core-shell particles, derived from PtNi precursor alloys, showed favorable ORR activity. More detailed size-activity correlation studies further revealed that the 6-8 nm diameter range is a most desirable initial particle size range in order to maximize the particle Ni content after ORR testing and to preserve performance stability. Similarly, dealloyed and oxidized IrO core-shell particles derived from Ni-rich Ir-Ni precursor particles proved highly efficient oxygen evolution reaction (OER) catalysts in acidic conditions. In addition to the noble metal savings in the particle cores, the Pt core-shell particles are believed to benefit in terms of their mass-based electrochemical kinetics from surface lattice strain effects that tune the adsorption energies and barriers of elementary steps. The molecular mechanism of the kinetic benefit of the dealloyed IrO particle needs more attention, but there is mounting evidence for ligand hole effects in defect-rich IrO shells that generate preactive oxygen centers.
“…In parallel to these bottom-up approaches during the 1970s and 1980s, top-down methods to fabricate and utilize nanometer-sized monometallic electrodes were developed toward the end of that decade . Finally, a language transition in the electrochemical materials literature from “colloidal” − to “nano” − commenced in the early 1990s and was completed in the mid-2000s. By then, nanoelectrochemistry also addressed nanoelectrodeposition and nanopatterning of surfaces using scanning probe microscopy .…”
Nanomaterial science and electrocatalytic science have entered a successful "nanoelectrochemical" symbiosis, in which novel nanomaterials offer new frontiers for studies on electrocatalytic charge transfer, while electrocatalytic processes give meaning and often practical importance to novel nanomaterial concepts. Examples of this fruitful symbiosis are dealloyed core-shell nanoparticle electrocatalysts, which often exhibit enhanced kinetic charge transfer rates at greatly improved atom-efficiency. As such, they represent ideal electrocatalyst architectures for the acidic oxygen reduction reaction to water (ORR) and the acidic oxygen evolution reaction from water (OER) that require scarce Pt- and Ir-based catalysts. Together, these two reactions constitute the "O-cycle", a key elemental process loop in the field of electrochemical energy interconversion between electricity (free electrons) and molecular bonds (HO/O), realized in the combination of water electrolyzers and hydrogen/oxygen fuel cells. In this Account, we describe our recent efforts to design, synthesize, understand, and test noble metal-poor dealloyed Pt and Ir core-shell nanoparticles for deployment in acidic polymer electrolyte membrane (PEM) electrolyzers and PEM fuel cells. Spherical dealloyed Pt core-shell particles, derived from PtNi precursor alloys, showed favorable ORR activity. More detailed size-activity correlation studies further revealed that the 6-8 nm diameter range is a most desirable initial particle size range in order to maximize the particle Ni content after ORR testing and to preserve performance stability. Similarly, dealloyed and oxidized IrO core-shell particles derived from Ni-rich Ir-Ni precursor particles proved highly efficient oxygen evolution reaction (OER) catalysts in acidic conditions. In addition to the noble metal savings in the particle cores, the Pt core-shell particles are believed to benefit in terms of their mass-based electrochemical kinetics from surface lattice strain effects that tune the adsorption energies and barriers of elementary steps. The molecular mechanism of the kinetic benefit of the dealloyed IrO particle needs more attention, but there is mounting evidence for ligand hole effects in defect-rich IrO shells that generate preactive oxygen centers.
“…Note that the linear dependency of the reaction rate on the nano-catalysts concentration has been reported in previous experimental studies [101][102][103][104]. Moreover, it is assumed that the heat of the reaction is small enough not to affect the dynamics through k R which will be considered constant.…”
The interface of two approaching fluids in porous media becomes unstable at strong enough flow rates when the viscosity of the displacing fluid is less than that of the displaced one. This phenomenon is studied to address the effect of nanoparticles (NPs) dispersed in the displacing fluid assumed fully miscible with the displaced one. The problem is first studied under isothermal conditions. The effects of the NP-induced additional properties such as the viscosity of the nanofluid, the Brownian diffusivity and the NP deposition are addressed on both the flow instability and the flow configuration. It was found that NPs attenuate the instability of an initially unstable flow, but this effect is mitigated in the presence of NP deposition. Moreover, the Brownian diffusivity was found to have a destabilizing effect, but
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