Postsynthetic treatment of nickel–iron layered double hydroxides for the optimum catalysis of the oxygen evolution reaction

D.T., S.J., J.C., and V.N. wish to thank the support of the ERC CoG, 3D2DPring (GA 681544) and PoC Powering_eTextiles (GA 861673) and SFI AMBER (12/RC/2278_P2). The authors would like to thank the Advanced Microscopy Lab and CRANN Trinity College Dublin for providing STEM-EDX measurements. This publication has emanated from research supported in part by a grant from Science Foundation Ireland under Grant number 12/RC/2278_P2. For the purpose of Open Access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission. Publisher Copyright: © 2021, The Author(s).Nickel–iron-layered double hydroxide (NiFe LDH) platelets with high morphological regularity and submicrometre lateral dimensions were synthesized using a homogeneous precipitation technique for highly efficient catalysis of the oxygen evolution reaction (OER). Considering edge sites are the point of activity, efforts were made to control platelet size within the synthesized dispersions. The goal is to controllably isolate and characterize size-reduced NiFe LDH particles. Synthetic approaches for size control of NiFe LDH platelets have not been transferable based on published work with other LDH materials and for that reason, we instead use postsynthetic treatment techniques to improve edge-site density. In the end, size-reduced NiFe LDH/single-wall carbon nanotube (SWCNT) composites allowed to further reduce the OER overpotential to 237 ± 7 mV ( = 0.16 ± 0.01 μm, 20 wt% SWCNT), which is one of the best values reported to date. This approach as well improved the long-term activity of the catalyst in operating conditions.publishersversionpublishe

Phase & Morphology Engineered Surface Reducibility of MnO2 Nano-heterostructures: Implications on Catalytic Activity Towards CO Oxidation

This work addresses two vital aspects of catalytic nanohybrids viz., a chemistry-based control of crystallographic phase/ morphology that serves as a handle for engineering the surface reducibility and correlating the catalytic activity to the reducibility. We would like to emphasize that the material addressed in this paper is an earth-abundant oxide MnO2, much favorable for practical applications in terms of cost and availability

Phase & morphology engineered surface reducibility of MnO2 nano-heterostructures: Implications on catalytic activity towards CO oxidation

An understanding of the surface reducibility of a catalytically active oxide support is a pre-requisite to understanding its catalytic behavior. In this work, we report that through a stringent control over the phase and morphology of catalytically active MnO2 supports, a control over the surface reducibility can be achieved. Through temperature-programmed reduction (TPR), we prove a higher availability of lattice oxygen for the alpha-MnO2 phase, compared to that of beta-MnO2. Furthermore, by modifying the synthesis method, we could engineer the morphology of the alpha-phase into nanoflowers which in turn leads to a higher surface area, further enhancing the activity. On the engineered support, decoration of Pt nanoparticles can lower the full conversion temperature for CO oxidation at a considerably low temperature

Ba-Addition Induced Enhanced Surface Reducibility of SrTiO3: Implication on Catalytic Aspects

This work compares the capacity of generating the surface oxygen vacancies over SrTiO3, BaTiO3 and the mixed Sr0.5Ba0.5TiO3. This aspect is elucidated by significantly different chemical states of the elements on the surface of the three materials. Along with the fundamental materials aspect, CO oxidation studies complement the highest surface reducibility of the Sr0.5Ba0.5TiO3 catalyst. With detailed adsorption-desorption studies, we report that the A-site cation substitution renders a better surface-reducibility induced catalytic activity for CO oxidation

Reduced SrTiO3-Supported Pt-Cu Alloy Nanoparticles for Preferential Oxidation of CO in Excess Hydrogen

In this work, we employ Pt-Cu alloy nanoparticles supported on reduced-SrTiO3 (RSTO) to obtain a poisoning-resistant catalyst in the desired operative temperature range. The changing Cu concentration in the Pt-Cu bimetallic alloy elucidates the trend of changing efficiency, selectivity and stability of CO conversion over the bimetallic catalyst. Among the various compositions, we find that Pt40Cu60­ is the most effective catalyst to target CO oxidation by competing with the the undesirable H2 oxidation. Here, we report interesting results on the trade-off between the selectivity of CO conversion as well as the maximum CO conversion (%) over the catalyst. The difference in CO adsorption over monometallic Pt and bimetallic Pt-Cu catalysts is well-reflected by the controlled adsorption-desorption studies. </p

Single crystalline ultrathin gold nanowires: Promising nanoscale interconnects

Using first principles based density functional calculation we study the mechanical, electronic and transport properties of single crystalline gold nanowires. While nanowires with the diameter less than 2 nm retain hexagonal cross-section, the larger diameter wires show a structural smoothening leading to circular cross-section. These structural changes significantly affect the mechanical properties of the wires, however, strength remains comparable to the bulk. The transport calculations reveal that the conductivity of these wires are in good agreement with experiments. The combination of good mechanical, electronic and transport properties make these wires promising as interconnects for nano devices. Copyright 2013 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. http://dx.doi.org/10.1063/1.4796188

Semiconductor-like Sensitivity in Metallic Ultrathin Gold Nanowire-Based Sensors

Due to the ease of modification of electronic structure upon analyte adsorption, semiconductors have been the preferred materials as chemical sensors. At reduced dimension, however, the sensitivity of semiconductor-based sensors deteriorates significantly due to passivation, and often by increased band gap caused by quantum confinement. Using first-principles density functional theory combined with Boltzmann transport calculations, we demonstrate semiconductor-like sensitivity toward chemical species in ultrathin gold nanowires (AuNWs). The sensing mechanism is governed by the modification of the electronic structure of the AuNW as well as scattering of the charge carriers by analyte adsorption. Most importantly, the sensitivity exhibits a linear relationship with the electron affinities of the respective analytes. Based on this relationship, we propose an empirical parameter, which can predict an analyte-specific sensitivity of a AuNW, rendering them as effective sensors for a wide range of chemical an alytes

Scalable faceted voids with luminescent enhanced edges in WS2 monolayers

A scalable approach is needed in the formation of atomically flat edges with specific terminations to enhance local properties for optoelectronic, nanophotonic and energy applications. We demonstrate point defect clustering-driven faceted void formations with luminescent enhanced edges in WS2 monolayers during large-scale CVD growth and controlled annealing. With the aid of aberration-corrected scanning transmission electron microscopy (AC-STEM) high angle annular dark field (HAADF) imaging, we probed atomic terminations of S and W to explain observed luminescence enhancement in alternate edges. Faceted void formation in monolayer WS2 was found to be sensitive to annealing temperature, time, gas environment and precursor supply. Our observations of areal coverage evolution over time revealed competition between monolayer WS2 growth and void formation at 850 degrees C. While the initial stage was dominated by monolayer growth, defect generation and void growth dominated at later stages and provided an optimum processing window for monolayer WS2 as well as faceted void growth. Growth of faceted voids not only followed the geometry of monolayer facets but also showed similar atomic terminations at the edges and thus enabled local manipulation of photoluminescence enhancement with an order of magnitude increase in intensity. The developed CVD processing enabled multi-fold increase in the luminescent active edge length through the formation of faceted voids within the WS2 monolayer