Tailored magnetic and magnetoelectric responses of polymer-based composites

The manipulation of electric ordering with applied magnetic fields has been realized on magnetoelectric (ME) materials, however, their ME switching is often accompanied by significant hysteresis and coercivity that represents, for some applications, a severe weakness. To overcome this obstacle, this work focus on the development of a new type of ME polymer nanocomposites that exhibits tailored ME response at room temperature. The multiferroic nanocomposites are based on three different ferrite nanoparticles, Zn0.2Mn0.8Fe2O4 (ZMFO), CoFe2O4 (CFO) and Fe3O4 (FO), dispersed in a piezoelectric co-polymer poly(vinylindene fluoride-trifluoroethylene), P(VDF-TrFE), matrix. No substantial differences were detected on the time-stable piezoelectric response of the composites (≈ -28 pC.N−1) with distinct ferrite fillers and for the same ferrite content of 10wt.%. Magnetic hysteresis loops from pure ferrite nanopowders showed different magnetic responses. ME results of the nanocomposite films with 10wt.% ferrite content revealed that the ME induced voltage increases with increasing DC magnetic field until a maximum of 6.5 mV∙cm−1∙Oe−1, at an optimum magnetic field of 0.26 T, and 0.8 mV∙cm−1∙Oe−1, at an optimum magnetic field of 0.15T, for the CFO/P(VDF-TrFE) and FO/P(VDF-TrFE) composites, respectively. On the contrary, the ME response of the ZMFO/P(VDF-TrFE) exposed no hysteresis and high dependence on the ZMFO filler content. Possible innovative applications such as memories and information storage, signal processing, ME sensors and oscillators have been addressed for such ferrite/PVDF nanocomposites.We thank Dr. E. Carbó-Argibay for his assistance with TEM analysis. This work is funded by FEDER funds through the “Programa Operacional Factores de Competitividade – COMPETE” and by national funds from FCT – Portuguese Foundation for Science and Technology in the framework of the strategic project Strategic Project PEST-C/FIS/UI607/2014. The authors also thank funding from Matepro –Optimizing Materials and Processes”, ref. NORTE-07-0124 FEDER-000037”, co-funded by the “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte), under the “Quadro de Referência Estratégico Nacional” (QREN), through the “Fundo Europeu de Desenvolvimento Regional” (FEDER). P. Martins acknowledges also support from FCT GRANT SFRH/BPD/96227/201

Merging solution processing and printing for sustainable fabrication of Cu(In,Ga)Se2 photovoltaics

The targeted global decarbonization demands the urgent replacement of conventional fossil fuel with low carbon technologies. For instance, solar energy is abundant, inexhaustible, non-polluting, and low-priced; however, to produce energy on a large scale with reliable, cost-efficient, and environmentally friendly methods remains a challenge. The outstanding optical properties of Cu(In,Ga)Se2 thin film photovoltaics and their intrinsic compatibility with industrial-scale production are paving the way towards this technology. However, most of the activity in the field relies on the use of non-environmentally friendly methodologies to achieve solution-processed flexible and lightweight photovoltaics with significant efficiencies. Importantly, there is a search for more sustainable alternatives that are compatible with roll-to-roll industry to improve the cost-effectiveness and sustainability of photovoltaics without compromising the photovoltaic performance. Herein, we review cost-efficient and sustainable fabrication methodologies that complement the current high- energy-demanding vacuum-based fabrication of Cu(In,Ga)Se2 photovoltaics. The existent non-vacuum deposition methods of Cu(In,Ga)Se2 photoabsorbers are presented and precursors and solvents used in ink formulations are discussed in terms of sustainability. The approaches resulting in most efficient photovoltaic cells are highlighted. Finally, all-solution-processed Cu(In,Ga)Se2 photovoltaics are reviewed, along with the non-vacuum deposition methods of the individual layers, contributing to an even higher throughput and low-cost production. This review highlights the relevance and potential of sustainable non-vacuum methodologies, as well as the need of further investigation in this field to ultimately give access to high-end CIGS PVs with low-cost fabrication.We thank the members of the Nanochemistry Research Group (http://nanochemgroup.org) at INL for insightful discussions and support. This study was conducted with financial support from the Portuguese funding institution FCT – Fundaç ̃ao para Ciˆencia e Tecnologia (PTDC/CTM-ENE/5387/2014, PTDC/NAN-MAT/28745/2017, UID/FIS/04650/2020, UID/QUI/0686/2020, PTDC/FIS-MAC/28157/2017 and SFRH/BD/121780/2016) and Basque Government Industry Department (ELKARTEK and HAZITEK)

Superstructural Ordering in Hexagonal CuInSe 2 Nanoparticles

International audienceChalcogenide semiconducting nanoparticles are promising building blocks for solution-processed fabrication of optoelectronic devices. In this work, we report a new large-scale colloidal synthesis of metastable CuInSe 2 nanoparticles with hexagonal plate-like morphology. Powder X-ray diffraction analysis of the nanoparticles showed that the structure of the nanoparticles is not simple hexagonal wurtzite-type CuInSe 2 (space group P6 3 mc), indicating the formation of an ordered superstructure. Detailed insight into this structural aspect was explored by high-resolution electron microscopy, and the results evidence an unreported chemical ordering within the synthesized CuInSe 2 nanoparticles. Specifically, while the Se sublattice is arranged in perfect wurtzite subcell, Cu and In are segregated over distinct framework positions, forming domains with lower symmetry. The arrangement of these domains within the hexagonal Se substructure proceeds through the formation of a number of planar defects, mainly twins and antiphase boundaries. As a semiconductor, the synthesized material exhibits a direct optical transition at 0.95 eV, which correlates well with its electronic structure assessed by density functional theory calculations. Overall, these findings may inspire the design and synthesis of other nanoparticles featuring unique chemical ordering; thus, providing an additional possibility of tuning intrinsic transport properties. © 2018 American Chemical Society

Electrocatalytic water oxidation over AlFe 2 B 2

We report excellent electrocatalytic performance by AlFe 2 B 2 in the oxygen-evolution reaction (OER). The inexpensive catalytic material, prepared simply by arc-melting followed by ball-milling, exhibits high stability and sustained catalytic performance under alkaline conditions. The overpotential value of 0.24 V observed at the current density of 10 mA cm -2 remained constant for at least 10 days. Electron microscopy and electron energy loss spectroscopy performed on the initial ball-milled material and on the material activated under electrocatalytic conditions suggest that the catalytic mechanism involves partial leaching of Al from the layered structure of AlFe 2 B 2 and the formation of Fe 3 O 4 nanoclusters on the exposed [Fe 2 B 2 ] layers. Thus, the AlFe 2 B 2 structure serves as a robust supporting material and, more importantly, as a pre-catalyst to the in situ formed active electrocatalytic sites. Comparative electrochemical measurements demonstrate that the electrocatalytic performance of the AlFe 2 B 2 -supported Fe 3 O 4 nanoclusters substantially exceeds the results obtained with unsupported nanoparticles of Fe 3 O 4 , FeB, or such benchmark OER catalysts as IrO 2 or RuO 2 . The excellent catalytic performance and long-term stability of this system suggests that AlFe 2 B 2 can serve as a promising and inexpensive OER electrocatalyst. © The Royal Society of Chemistry

Electrocatalytic water oxidation over AlFe 2 B 2

International audienceWe report excellent electrocatalytic performance by AlFe 2 B 2 in the oxygen-evolution reaction (OER). The inexpensive catalytic material, prepared simply by arc-melting followed by ball-milling, exhibits high stability and sustained catalytic performance under alkaline conditions. The overpotential value of 0.24 V observed at the current density of 10 mA cm -2 remained constant for at least 10 days. Electron microscopy and electron energy loss spectroscopy performed on the initial ball-milled material and on the material activated under electrocatalytic conditions suggest that the catalytic mechanism involves partial leaching of Al from the layered structure of AlFe 2 B 2 and the formation of Fe 3 O 4 nanoclusters on the exposed [Fe 2 B 2 ] layers. Thus, the AlFe 2 B 2 structure serves as a robust supporting material and, more importantly, as a pre-catalyst to the in situ formed active electrocatalytic sites. Comparative electrochemical measurements demonstrate that the electrocatalytic performance of the AlFe 2 B 2 -supported Fe 3 O 4 nanoclusters substantially exceeds the results obtained with unsupported nanoparticles of Fe 3 O 4 , FeB, or such benchmark OER catalysts as IrO 2 or RuO 2 . The excellent catalytic performance and long-term stability of this system suggests that AlFe 2 B 2 can serve as a promising and inexpensive OER electrocatalyst. © The Royal Society of Chemistry

Al-Induced In Situ Formation of Highly Active Nanostructured Water-Oxidation Electrocatalyst Based on Ni-Phosphide

We report a simple low-cost concept for the preparation of water-oxidation electrocatalyst via modification of self-supported Ni5P4-Ni2P foam catalyst precursor with Al. As an anode for alkaline oxygen evolution reaction, this material exhibits an impressive Tafel slope of 27 mV dec(-1) and offers anodic current densities of 10, 100, and 300 mA cm(-2) at overpotentials of merely 180, 247, and 312 mV, respectively. Moreover, the anode demonstrates high operational stability, as reflected by a steady-state performance for more than 8 days. Combining state-of-the-art electron microscopy and photoelectron spectroscopy, we investigated the role of the Al dopant in the formation of active Ni(OH)(2)/NiO/Ni5P4-Ni2P nanocatalyst, which exhibits oxygen-evolving activity among the highest reported to date

Al-Induced In Situ Formation of Highly Active Nanostructured Water-Oxidation Electrocatalyst Based on Ni-Phosphide

International audienceWe report a simple low-cost concept for the preparation of water-oxidation electrocatalyst via modification of self-supported Ni5P4-Ni2P foam catalyst precursor with Al. As an anode for alkaline oxygen evolution reaction, this material exhibits an impressive Tafel slope of 27 mV dec(-1) and offers anodic current densities of 10, 100, and 300 mA cm(-2) at overpotentials of merely 180, 247, and 312 mV, respectively. Moreover, the anode demonstrates high operational stability, as reflected by a steady-state performance for more than 8 days. Combining state-of-the-art electron microscopy and photoelectron spectroscopy, we investigated the role of the Al dopant in the formation of active Ni(OH)(2)/NiO/Ni5P4-Ni2P nanocatalyst, which exhibits oxygen-evolving activity among the highest reported to date

Template-directed self-organization of colloidal PbTe nanocrystals into pillars, conformal coatings, and self-supported membranes

We demonstrate the formation of three morphologies relevant for integration with miniaturized devices—microscale pillars, conformal coatings, and self-supported membranes—via template-directed self-organization of lead telluride (PbTe) colloidal nanocrystals (NCs). Optimizing the self-organization process towards producing one of these morphologies typically involves adjusting the surface chemistry of the particles, as a means of controlling the particle-particle and particle-template interactions. In contrast, we have produced each of the three morphologies of close-packed NCs by adjusting only the solvent and concentration of NCs, to ensure that the high quality of the ca. 10-nm PbTe NCs produced by hot-injection colloidal synthesis, which we used as model “building blocks,” remains consistent across all three configurations. For the first two morphologies, the NCs were deposited as colloidal suspensions onto micropatterned silicon substrates. The microscale cuboid pillars (1 μm × 1 μm × 0.6 μm) were formed by depositing NC dispersions in toluene onto templates patterned with resist grid motifs, followed by the resist removal after the slow evaporation of toluene and formation of the micropillars. Conformal coatings were produced by switching the solvent from toluene to a faster drying hexane and pouring NC dispersions onto silicon templates with topographically patterned microstructures. In a similar process, self-supported NC membranes were formed from NC dispersions in hexane on the surface of diethylene glycol and transferred onto the micropatterned templates. The demonstrated combination of bottom-up self-organization with top-down micropatterned templates provides a scalable route for design and fabrication of NC ensembles in morphologies and form-factors that are compatible with their integration into miniaturized devices.M.P. acknowledges a post-doctoral fellowship from INL. This work was supported by the UTBORN-PT project (UTAP-EXPL/CTE/0050/2017) funded by FCT, the PrintPV project (PTDC/CTM-ENE/5387/2014) co-funded by FCT and ERDF COMPETE 2020 funds, and the CritMag project (PTDC/NAN-MAT/28745/2017) co-funded by FCT and POCI funds.Peer reviewe