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•Electrolyte additives drive the propagation of etch fronts in high melting alloys during dealloying.•Free standing np-Ir electrodes exhibit a significant enhancement in OER activity ...and stability.•HCD performance is a consequence of reduced electrode resistivity for np-Ir.
The dearth of appropriate electrocatalysts for stable anodic water splitting, oxygen evolution reaction (OER), in acid has given rise to concerted efforts toward making iridium-based high aspect ratio nanomaterials, as iridium and its higher valent oxides have been shown time and again to exhibit the most optimal balance between activity and durability. Here, we show a dealloying strategy to synthesize free-standing 3D, oxide skinned nanoporous Ir electrocatalysts (np-Ir) with demonstrated enhanced activity and durability in comparison to more traditional IrOx nanoparticulate catalysts. The metallic core and absence of any binder/support result in low electrode and charge transfer resistance, ultimately giving rise to lower OER overpotentials and improved activity.
Polymer electrolyte membrane fuel cell (PEMFC) electrodes with a 0.07 mgPt cm–2 Pt/Vulcan electrocatalyst loading, containing only a sulfonated poly(ionic liquid) block copolymer (SPILBCP) ionomer, ...were fabricated and achieved a ca. 2× enhancement of kinetic performance through the suppression of Pt surface oxidation. However, SPILBCP electrodes lost over 70% of their electrochemical active area at 30% RH because of poor ionomer network connectivity. To combat these effects, electrodes made with a mix of Nafion/SPILBCP ionomers were developed. Mixed Nafion/SPILBCP electrodes resulted in a substantial improvement in MEA performance across the kinetic and mass transport-limited regions. Notably, this is the first time that specific activity values determined from an MEA were observed to be on par with prior half-cell results for Nafion-free Pt/Vulcan systems. These findings present a prospective strategy to improve the overall performance of MEAs fabricated with surface accessible electrocatalysts, providing a pathway to tailor the local electrocatalyst/ionomer interface.
•Formation of carbon quantum dots by simply immersing a polymer in an organic solvent is reported•Mean size of these quantum dots is around 3 nanometers and thickness around 2–3 nanometers•These ...quantum dots are also nitrogen functionalized•High degree of crystallinity also exhibited by these quantum dots
Carbon quantum dots (CQDs) are 0-dimensional carbon nanoparticles that display quantum confinement effects. Since their first discovery, an impressive library of CQD synthesis schemes has been developed. In this study we present a set of findings, that we came across serendipitously, that lead to an unintended formation of CQDs. We found, that a mere contact between a common polymeric material and an organic solvent resulted in a fluorescent dispersion. Detailed investigations revealed that the dispersion is made up of CQDs. Our analysis shows that these quantum dots exhibit primarily a blue fluorescence and are in the size range of 2–5 nm; these quantum dots are also nitrogen functionalized, and also show a good degree of crystallinity. Such a counterintuitive insight, to the best of our knowledge hasn't been reported earlier. Through this study we aim to bring this strange phenomenon to light and hope that these results would act as helpful inputs in the design of experiments.
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Ionic liquid interlayers improve the oxygen reduction reaction (ORR) kinetics on bulk and nanostructured catalysts for both Pt and alloyed-Pt materials. Despite the demonstrated performance ...enhancement at the half-cell and membrane electrode assembly level, the mechanism of the improvement is not fully understood. In this work, we combine single-crystal experiments with microkinetic modeling to uncover the origin of the ORR kinetic improvement on Pt(111) in the presence of ionic liquids and hydrophobic cations. With the incorporation of a modified Frumkin isotherm, our model accurately simulates the disorder–order transition observed in hydroxyl and bisulfate adsorption on Pt(111) under acidic conditions. Voltametric analysis shows that ionic liquids impact solvation to break so-called scaling relations between the adsorption strength of OHad and Oad, but these effects have little impact on ORR activity. Instead, destabilized OHad reduces the overall hydroxyl (spectator) coverage, resulting in higher availability of active sites.
Ionic liquid interlayers improve the oxygen reduction reaction (ORR) kinetics on bulk and nanostructured catalysts for both Pt and alloyed-Pt materials. Despite the demonstrated performance ...enhancement at the half-cell and membrane electrode assembly level, the mechanism of the improvement is not fully understood. In this work, we combine single-crystal experiments with microkinetic modeling to uncover the origin of the ORR kinetic improvement on Pt(111) in the presence of ionic liquids and hydrophobic cations. With the incorporation of a modified Frumkin isotherm, our model accurately simulates the disorder–order transition observed in hydroxyl and bisulfate adsorption on Pt(111) under acidic conditions. Voltametric analysis shows that ionic liquids impact solvation to break so-called scaling relations between the adsorption strength of OHad and Oad, but these effects have little impact on ORR activity. Instead, destabilized OHad reduces the overall hydroxyl (spectator) coverage, resulting in higher availability of active sites.
Ultrasonication within organic solvents is widely used to exfoliate layered materials and produce two-dimensional (2D) nanostructures. Several 2D materials synthesized by such liquid-phase ...exfoliation (LPE) approaches are reported to exhibit photoluminescence. In these approaches, it is presumed that while the 2D nanostructures are derived from the layered parent material undergoing delamination, the organic solvent serves as a dispersing medium. However, in this study, we show that the organic solvent also contributes toward formation of 2D nanostructures that are optically active. We show that the bare organic solvent, when exposed to ultrasonication, transforms into 2D photoluminescent carbon quantum dots (CQDs) that display blue, cyan, green, and yellow emissions depending upon the excitation wavelength. Although this finding is intuitive, it has remained unacknowledged in the design of experiments, which require ultrasonication of layered materials in organic solvents. Our results suggest that optical properties of dispersions obtained by LPE embody a contribution not only from the 2D nanostructures derived from the layered material but also from the 2D CQDs that are formed as a natural result of the liquid medium being exposed to ultrasonication. We anticipate that this new physical insight would form an important addition to the guidelines for exfoliation and help in rightly inferring the optical properties of the 2D material dispersions produced by these methods.
The role that interfacial water plays in both promoting and inhibiting the electrochemical oxygen reduction reaction (ORR) remains somewhat unclear and controversial. Here, we use electroanalytical ...chemistry, spectroscopy, and microkinetic modeling to probe the impact of hydrophobic ionic liquid (IL) thin films on interfacial water structure and its role in promoting or inhibiting the ORR. Through the use of in situ ATR-SEIRAS, we find that the IL thin films limit the content of water at the interface and prevent the formation of hydrogen bond stabilized water organization. The impact of this exclusion of water on the promotion of the ORR is through the reduced coverage of OHad spectator species. The decreased solvation of “active” OHad species weakens its interaction with the catalyst surface, lowering the barrier to the last step in the ORR mechanism. This “destabilized” OHad impact on ORR kinetics is confirmed through a microkinetic model. The results presented here highlight the mechanistic pathway through which hydrophobic ILs enhance ORR kinetics and point to pathways to both further improve this performance enhancement and the potential for integration of hydrophobic ILs into other technologically relevant elementary electrochemical reactions.
In this work, we present an approach to nanoscale titanium diboride (TiB2), a layered ceramic from the metal diboride family, by investigating its interaction with a co-solvent containing water and ...isopropanol (IPA). It is gradually being established that layered metal diborides can be exfoliated in liquid phase to yield 2D counterparts. However, these reports have not yet systematically investigated the suitability of a solvent to exfoliate these ionic layered materials. Such a prospect is primarily limited by the fact that the theories available to rationally select exfoliating solvents are applicable only for van der Waals (vdW) layered materials. We show that it is possible to identify an optimal exfoliating medium for TiB2 by using co-solvents. We tested the exfoliation of TiB2 in isopropanol (IPA)-water co-solvent mixtures at different IPA concentrations, and established that a 10% isopropanol-water co-solvent results in optimal exfoliation. The resultant nanosheets are extremely thin (~3–5 nm) and exhibit a mild degree of oxy-functionalization. We observed that the original structural integrity of nanosheets (TiB2 lattice) is maintained to a large extent after exfoliation. We also validated the findings by using Surface Tension Component Matching (STCM) and studied the exfoliation of TiB2 in acetonitrile (ACN). This resulted in a lower degree of exfoliation as expected, but led us to obtain nearly pristine TiB2 nanosheets. The new physical insights presented in this work can serve as a guide to predict the exfoliation of TiB2 in other prospective solvents.
The role that interfacial water plays in both promoting and inhibiting the electrochemical oxygen reduction reaction (ORR) remains somewhat unclear and controversial. Here, we use electroanalytical ...chemistry, spectroscopy, and microkinetic modeling to probe the impact of hydrophobic ionic liquid (IL) thin films on interfacial water structure and its role in promoting or inhibiting the ORR. Through the use of in situ ATR-SEIRAS, we find that the IL thin films limit the content of water at the interface and prevent the formation of hydrogen bond stabilized water organization. The impact of this exclusion of water on the promotion of the ORR is through the reduced coverage of OHad spectator species. The decreased solvation of “active” OHad species weakens its interaction with the catalyst surface, lowering the barrier to the last step in the ORR mechanism. This “destabilized” OHad impact on ORR kinetics is confirmed through a microkinetic model. Furthermore, the results presented here highlight the mechanistic pathway through which hydrophobic ILs enhance ORR kinetics and point to pathways to both further improve this performance enhancement and the potential for integration of hydrophobic ILs into other technologically relevant elementary electrochemical reactions.
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