Microwave-Assisted Synthesis of Cu@IrO₂ Core-Shell Nanowires for Low-Temperature Methane Conversion

A facile microwave-assisted synthesis was developed for the tunable fabrication of a Cu@IrO2 core@shell nanowire motif. Experimental parameters, such as (i) the reaction time, (ii) the method of addition of the Ir precursor, (iii) the capping agent, (iv) the reducing agent, and (v) the capping agent-to-reducing agent ratio, were subsequently optimized. The viability of other methods based on the previously reported literature, such as refluxing, stirring, and physical sonication, was studied and compared with our optimized microwave-assisted protocol in creating our as-prepared materials. It should be noted that the magnitude of the IrO2 shell could be tailored based on varying the Cu:Ir ratio coupled with judicious variations in the amounts of the capping agent and the reducing agent. Structural characterization techniques, such as XRD, XPS, and HRTEM (including HRTEM-EDS), were used to analyze our Cu@IrO2 motifs. Specifically, the shell could be reliably tailored from sizes of 10, 8, 6, and 3.5 nm with corresponding Cu:Ir ratios of 10:1, 15:1, 20:1, and 25:1, respectively. Moreover, the structural integrity of the motifs was probed and found to have been maintained after not only heat treatment but also the post-methane conversion process, indicative of an intrinsically high stability. Both components within the CuO-IrO2 interface were able to activate methane at temperatures between 400 and 500 K with a reduction of the associated metal cations (Cu2+ → Cu1+; Ir4+ → Ir3+) and the deposition of CHx fragments on the surface, as clearly observed in the ambient-pressure XPS results. Thus, on the basis of their stability and chemical activity, these core-shell materials could be very useful for the catalytic conversion of methane into “higher-value” chemicals

Platinum-Modified Cobalt Oxide/Cobalt Nanotubes as Multifunctional Electrocatalysts in Alkaline and Acidic Conditions

Nanostructure platinum is an effective catalyst that is active toward a broad range of electrochemical processes over a wide range of pH values. However, its high cost and low abundance prevent its widespread use in practical devices. A promising strategy to overcome the limitations of platinum is to combine platinum with less expensive and more abundant transition metals. In this report, we employ an ambient, template-based approach to prepare monodisperse Co nanotubes (NTs) and modify them with platinum via an electroless deposition process. The composition of the resulting Pt modified Co NTs (Pt-Co NTs) can be varied by controlling the Pt ion concentration in the electroless deposition step. The resulting Pt-Co NTs have a hierarchical structure consisting of Pt-Co NTs coated with an amorphous Co-oxide film. The amorphous Co-oxide coating activates the Pt-Co NTs to the oxygen evolution reaction (OER) leading to a 9-fold enhancement in the OER activity in an 80% (by mass) Pt-Co NT relative to pure Pt nanowires. The surface oxide coating can be selectively removed by cycling the Pt-Co NTs in an acidic solution. Removing the oxide film activates the Pt-Co NTs toward methanol oxidation (MOR) and oxygen reduction (ORR) reactions. In both cases, the trends in MOR and ORR activity follow a volcano-type dependence as a function of composition. The catalyst with the optimum composition of 60% Pt has a 4-fold increase in the specific activity for MOR and maintains a +20 mV shift in the half-wave potential for ORR relative to that of pure Pt nanowires

Probing the Physicochemical Behavior of Variously Doped Li₄Ti₅O₁₂ Nanoflowers

This study thoroughly investigated the synthesis of not only 4 triply-doped metal oxides but also 5 singly-doped analogues of Li4Ti5O12 for electrochemical applications. In terms of synthetic novelty, the triply-doped materials were fabricated using a relatively facile hydrothermal method for the first-time, involving the simultaneous substitution of Ca for the Li site, Ln (i.e., Dy, Y, or Gd) for the Ti site, and Cl for the O site. Based on XRD, SEM, and HRTEM-EDS measurements, the resulting materials, incorporating a relatively homogeneous and uniform dispersion of both the single and triple dopants, exhibited a micron-scale flower-like morphology that remained apparently undamaged by the doping process. Crucially, the surface chemistry of all of the samples was probed using XPS in order to analyze any nuanced changes associated with either the various different lanthanide dopants or the identity of the metal precursor types involved. In the latter case, it was observed that the use of a nitrate salt precursor versus that of a chloride salt enabled not only a higher lanthanide incorporation but also the potential for favorable N-doping, all of which promoted a concomitant increase in conductivity due to a perceptible increase in Ti3+ content. In terms of the choice of lanthanide system, it was observed via CV analysis that dopant incorporation generally (albeit with some notable exceptions, especially with Y-based materials) led to the formation of higher amounts of Ti3+ species within both the singly and triply-doped materials, which consequentially led to the potential for increased diffusivity and higher mobility of Li+ species with the possibility for enabling greater capacity within these classes of metal oxides