Search

Nanoporous Ca3Co4O9 exhibits high thermoelectric properties and low thermal conductivity and can be made mechanically flexible by nanostructural design. To improve the mechanical flexibility with retained thermoelectric properties near room temperature, however, it is desirable to incorporate an organic filler in this nanoporous inorganic matrix material. Here, double-layer nanoporous Ca3Co4O9/PEDOT:PSS thin films were synthesized by spin-coating PEDOT:PSS into the nanopores. The obtained hybrid films exhibit high Seebeck coefficient (~+130 mu V/K) and thermoelectric power factor (0.75 mu W cm(-1) K-2) at room temperature with no deterioration in electrical properties after cyclic bending tests (98% preservation of electrical conductivity after 1000 cycles bending to a bending radius of 3 mm). Compared with the nanoporous Ca3Co4O9 thin film, the mechanical flexibility of the hybrid film can be effectively improved after hybrid with PEDOT:PSS with only a slight decrease of the thermoelectric properties. Funding Agencies|Knut and Alice Wallenberg Foundation [KAW 2020.0196]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Link?ping University [2009 00971]; Swedish Research Council [2021-03826]; Swedish Energy Agency [46519-1]; China Scholarship Council

Controllable engineering of the nanoporosity in layered Ca

Thin-film Ni-Ca3Co4O9 and Ni-Mo thermocouples were prepared by stepwise magnetron-sputtering/annealing synthesis using masks. Compared with Ni-Mo thin film thermocouples, Ni-Ca3Co4O9 thin film thermocouples have higher output voltage due to large positive Seebeck voltage (153 mu V/K for single thermocouple and 912 mu V/ K for 6-series thermocouple). The maximum output voltage from the thermocouple is 70 mV was obtained for a hot-end temperature of 105 degrees C for Ni-Ca3Co4O9 for a 6-series thermocouple. The stability of Ca3Co4O9 films and the ability to make free-standing films, together with the high Seebeck coefficient, show that these thin-film oxides can be used as p-type leg in thermocouples, with implications for use in free-standing and flexible thermoelectric devices. Funding Agencies|Knut and Alice Wallen-berg Foundation [KAW 2020.0196]; Swedish Research Council [2021-03826]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linko?ping University [2009 00971]; Swedish Energy Agency [46519-1]; China Scholarship Council

Controlling nanoporosity to favorably alter multiple properties in layered crystalline inorganic thin films is a challenge. Here, we demonstrate that the thermoelectric and mechanical properties of Ca

Hybrids between biopolymeric materials and low-cost conductive carbon-based materials are interesting materials for applications in electronics, potentially reducing the need for materials that generate environmentally harmful electronic waste. Herein we investigate a scalable ball-milling method to form graphene nanoplatelets (GNPs) by milling graphite flakes with aqueous dispersions of proteins or protein nanofibrils (PNFs). Aqueous GNP dispersions with high concentrations (up to 3.2 mg mL–1) are obtained under appropriate conditions. The PNFs/proteins help to exfoliate graphite and stabilize the resulting GNP dispersions by electrostatic repulsion. PNFs are prepared from hen egg white lysozyme (HEWL) and β-lactoglobulin (BLG). The GNP dispersions can be processed into free-standing films having an electrical conductivity of up to 110 S m–1. Alternatively, the GNP dispersions can be drop-cast on PET substrates, resulting in mechanically flexible films having an electrical conductivity of up to 65 S m–1. The drop-cast films are investigated regarding their thermoelectric properties, having Seebeck coefficients of about 50 μV K–1. By annealing drop-cast films and thus carbonizing residual PNFs, an increase of electrical conductivity, coupled with a modest decrease in Seebeck coefficient, is obtained resulting in materials displaying power factors of up to 4.6 μW m–1 K–2., A green method for preparation of graphene nanoplatelets is presented and the thermoelectric properties of the GNP materials are investigated.

The layered cobaltates A(x)CoO(2) (A = Li, Na, Ca, Ba, Sr) are of interest for energy applications such as thermoelectrics and batteries. However, it is challenging to obtain these phases in pure from as thin films. Here, phase-pure CaxCoO2 (x similar to 0.5) thin films were obtained by annealing of Ca(OH)(2)/Co3O4 multilayers made by moisture treatment of sputter-deposited CaO/Co3O4 multilayer films. The pure CaxCoO2 thin films exhibit an average optical transmittance of approximately 36% in the visible region and greater than 70% in the near-infrared (NIR) region. In addition, the electrical conductivity can be increased by incorporating a secondary Ca3Co4O9 phase into the CaxCoO2 thin film without large changes in optical properties and Seebeck coefficient. (C) 2021 The Authors. Published by Elsevier Ltd. Funding Agencies|Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows program [KAW 2020.0196]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [200900971]; Swedish Energy AgencySwedish Energy Agency [46519-1]; China Scholarship CouncilChina Scholarship Council

This work reports on sputter depositions carried out from a compound (Ti,Zr)(2)AlC target on Al2O3(0 0 0 1) substrates at temperatures ranging between 500 and 900 degrees C. Short deposition times yielded 30-40 nm-thick Al-containing (Ti,Zr)C films, whereas longer depositions yielded thicker films up to 90 nm which contained (Ti,Zr)C and intermetallics. At 900 degrees C, the longer depositions led to films that also consisted of solid solution MAX phases. Detailed transmission electron microscopy showed that both (Ti,Zr)(2)AlC and (Ti,Zr)(3)AlC2 solid solution MAX phases were formed. Moreover, this work discusses the growth mechanism of the thicker films, which started with the formation of the mixed (Ti,Zr)C carbide, followed by the nucleation and growth of aluminides, eventually leading to solid state diffusion of Al within the carbide, at the highest temperature (900 degrees C) to form the MAX phases. Funding Agencies|Swedish research council VR-RFISwedish Research Council [2017-00646_9]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research [RIF14-0053]; Euratom research and training programme 2014-2018 [740415]; Stiftelsen Olle Engkvist ByggmastareSwedish Research Council [184-561]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [KAW 2015.0043]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-MatLiU) [2009 00971]; Research Foundation FlandersFWO [AKUL/1319]

Introducing porosity is attractive for tailoring electronic, thermal, and mechanical properties of inorganic materials. Nanoporosity is typically either inherent in crystallographic channels in the structure or obtained by external templating during synthesis and sintering. However, controllably engineering porosity in materials with laminated crystal structures without channels remains a challenge. Here, we demonstrate the realization of faceted and oriented nanopores in textured Ca3Co4O9-a laminated ceramic with a misfit-layered structure of importance for thermoelectric applications-from chemical reactions in CaO/Co3O4 multilayers. We show that CaO conversion to Ca(OH)(2) and the cobalt oxide stoichiometry are key determinants of nanoporosity. Adjusting the unreacted CaO fraction alters the nanopore size and fraction and the thermoelectric properties of Ca3Co4O9. The preferred orientation of Ca3Co4O9 is underpinned by the texture of the reactant multilayers and reactant-product crystallographic relationships and density difference. Oriented pore formation is attributed to basal plane removal driven by local densification of textured Ca3Co4O9 nuclei through growth and impingement. These findings point to possibilities for controllably engineering nanoporosity and properties in a variety of inorganic materials with laminated crystal structures. Funding Agencies|Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows program [KAW 2020.0196]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Swedish Energy AgencySwedish Energy AgencyMaterials & Energy Research Center (MERC) [46519-1]; China Scholarship CouncilChina Scholarship Council

Multicomponent or high-entropy ceramics show unique combinations of mechanical, electrical, and chemical properties of importance in coating applications. However, generalizing controllable thin-film processes for these complex materials remains a challenge. Here, understoichiometric (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr, 0.12 ≤ x ≤ 0.30) films were deposited on Si(100) substrates at 400 °C by reactive magnetron sputtering using single elemental targets. The influence of ion energy during film growth was investigated by varying the negative substrate bias voltage from ∼10 V (floating potential) to 130 V. The nitrogen content for the samples determined by elastic recoil detection analysis varied from 34.9 to 43.8 at. % (0.12 ≤ x ≤ 0.30), and the metal components were near-equimolar and not affected by the bias voltage. On increasing the substrate bias, the phase structures of (TiZrTaMe)N1–x (Me = Hf, Nb, or Mo) films evolved from a polycrystalline fcc phase to a (002) preferred orientation along with a change in surface morphology from faceted triangular features to a dense and smooth structure with nodular mounds. All the four series of (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr) films exhibited increasing intrinsic stress with increasing negative bias. The maximum compressive stress reached ∼3.1 GPa in Hf- and Cr-containing films deposited at −130 V. The hardness reached a maximum value of 28.0 ± 1.0 GPa at a negative bias ≥100 V for all the four series of films. The effect of bias on the mechanical properties of (TiNbZrMe)N1–x films can thus guide the design of protective high-entropy nitride films. Funding Agencies|VINNOVA Competence Centre FunMat-II [2016-05156]; VINNOVA research infrastructure grantVinnova [2020-00825]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; M-ERA.net [2013-02355]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [2020.0196]; Electron Microscopy Laboratory at Linkoping University; Swedish Research CouncilSwedish Research CouncilEuropean Commission [VR 2018-04139]; VR-RFI [2017-00646_9]; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [RIF14-0053]

Independently controlling electronic and thermal transport in solids is a challenge, because these properties are coupled. Here, we show that disordered nanoporosity in Ca3Co4O9 thin films can decrease the thermal conductivity without significantly hampering electronic transport. Scanning thermal microscopy was used to determine the out-of-plane thermal conductivity and estimate the in-plane values. Nanoporous Ca3Co4O9 films exhibit a thermal conductivity of 0.82 W m(-1) K-1, which is nearly twofold lower than that obtained from nonporous Ca3Co4O9 films. Nanoporous Ca3Co4O9 exhibit a room-temperature electrical resistivity of 4 m omega cm, which is comparable to polycrystalline Ca3Co4O9 and twice that reported for single-crystal Ca3Co4O9. Our results suggest that controlling nanoporosity and their degree of disorder can offer a means of decoupling electrical and thermal properties in materials. Funding Agencies|Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Knut and Alice Wallenberg foundation through the Wallenberg Academy Fellows program [KAW-2020.0196]; Swedish Research Council (VR) [2016-03365]; Swedish Energy Agency [46519-1]

There is a growing need for the electrode with high mass loading of active materials, where both high energy and high power densities are required, in current and near-future applications of supercapacitor. Here, an ultrathin Co3S4 nanosheet decorated electrode (denoted as Co3S4/NF) with mass loading of 6 mg cm−2 is successfully fabricated by using highly dispersive Co3O4 nanowires on Ni foam (NF) as template. The nanosheets contained lots of about 3∼5 nm micropores benefiting for the electrochemical reaction and assembled into a three-dimensional, honeycomb-like network with 0.5∼1 μm mesopore structure for promoting specific surface area of electrode. The improved electrochemical performance was achieved, including an excellent cycliability of 10,000 cycles at 10 A g−1 and large specific capacitances of 2415 and 1152 F g−1 at 1 and 20 A g−1, respectively. Impressively, the asymmetric supercapacitor assembled with the activated carbon (AC) and Co3S4/NF electrode exhibits a high energy density of 79 Wh kg−1 at a power density of 151 W kg−1, a high power density of 3000 W kg−1 at energy density of 30 Wh kg−1 and 73 % retention of the initial capacitance after 10,000 charge-discharge cycles at 2 A g−1. More importantly, the formation process of the ultrathin Co3S4 nanosheets upon reaction time is investigated, which is benefited from the gradual infiltration of sulfide ions and the template function of ultrafine Co3O4 nanowires in the anion-exchange reaction.