Low-temperature electrodeposition approach leading to robust mesoscopic anatase TiO2 films

Anatase TiO2, a wide bandgap semiconductor, likely the most worldwide studied inorganic material for many practical applications, offers unequal characteristics for applications in photocatalysis and sun energy conversion. However, the lack of controllable, cost-effective methods for scalable fabrication of homogeneous thin films of anatase TiO2 at low temperatures (ie. < 100 °C) renders up-to-date deposition processes unsuited to flexible plastic supports or to smart textile fibres, thus limiting these wearable and easy-to-integrate emerging technologies. Here, we present a very versatile template-free method for producing robust mesoporous films of nanocrystalline anatase TiO2 at temperatures of/or below 80 °C. The individual assembly of the mesoscopic particles forming ever-demonstrated high optical quality beads of TiO2 affords, with this simple methodology, efficient light capture and confinement into the photo-anode, which in flexible dye-sensitized solar cell technology translates into a remarkable power conversion efficiency of 7.2% under A.M.1.5G conditions

Boron-Based Functional Additives Enable Solid Electrolyte Interphase Engineering in Calcium Metal Battery

Calcium-metal batteries have received growing attention recently after several studies reporting successful metal plating and stripping with organic electrolytes. Given the low redox potential of metallic calcium, its surface is commonly covered by a passivation layer grown by the accumulation of electrolyte decomposition products. The presence of borate species in this layer has been shown to be a key parameter allowing for Ca2+ migration and favoring Ca electrodeposition. Here, boron-based additives are evaluated in order to tune the SEI composition, morphology, and properties. The decomposition of a BF3-based additive is studied at different potentiostatic steps and the resulting SEI layer was thoroughly characterized. SEI growth mechanism is proposed based on both experimental data and DFT calculations pointing at the formation of boron-crosslinked polymeric matrices. Several boron-based adducts are explored as SEI-forming additives for calcium-metal batteries paving the way to very rich chemistry leading to Ca2+ conducting SEI.Funding from the European Union's Horizon 2020 research and innovation program H2020 are acknowledged: European Research Council (ERC-2016-STG, CAMBAT, grant agreement no. 715087 and ERC-2020-STG, HiPeR−F, grant agreement no. 950625) and H2020-MSCA-COFUND-2016 (DOC-FAM, grant agreement no. 754397). A.P. is grateful to the Spanish Ministry for Economy, Industry and Competitiveness Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S). D.F., C.C. and R.D. thank the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01) for financial support. K.R. and M.L. gratefully acknowledge the research funding by the Slovenian Research Agency (P1-0045, N1-0189). Alistore-European Research Institute is gratefully acknowledged for financial support through the postdoc grant to C.B. The SR-FTIR experiments were performed at MIRAS beamline at ALBA Synchrotron with the collaboration of ALBA staff. All DFT calculations were carried out at the Wroclaw Centre for Networking and Supercomputing within grant no. 346.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Évolution des silicates dans les milieux interstellaires, circumstellaires et cométaires (le rôle de l'irradiation et de la température)

Suite au développement des techniques d'observation et d'analyse, notre connaissance de la poussière silicatée dans les environnements astrophysiques a beaucoup évolué. Le cycle de vie de la poussière débute aœc sa formation autour des étoiles en fin de vie. Par la pression des vents stellaires, elle est ensuite injectée dans le milieu interstellaire (MIS) dans lequel elle transite. Enfin, elle peut être incorporée dans les disques d'accrétion autour des étoiles jeunes. Lors de ces différentes étapes, elle est soumise à diverses sollicitations qui induisent des modifications structurales ou chimiques. L'un des objectifs de cette thèse est d'abord de déterminer les modifications chimiques et morphologiques de la poussière silicatée quand elle est soumise à une irradiation ionique dans les ondes de choc de supernovae. Pour cela, nous avons effectué des expériences d'irradiation ionique (H+ et He+) à basse énergie in situ dans un spectroscope de photoélectrons (XPS). Les suivis chimiques et morphologiques ont été réalisés par XPS et par microscopie à force atomique. Le second objectif de cette thèse est d'indiquer comment la poussière amorphe évolue lors de son incorporation dans les régions internes du dIsque d'accrétion autour des étoiles jeunes. Nous avons ainsi mis en place des traitements thermiques de silicates amorphes in situ dans un microscope électronique en transmission (MET) et en four sous atmosphère contrôlée. Les évolutions microstructurales et chimiques ont été observées à l'aide d'un MET associé à un spectroscope à dispersion d'énergie. Nous avons montré qu'une irradiation ionique induit des modifications chimiques et morphologiques. Dans le milieu mterstellaire, les ondes de choc de supernovae sont donc des évènements très propices à modifier les matériaux initialement issus des étoiles en fin de vie. Les produits de recristallisation obtenus suite aux recuits sont très dépendants de la pression partielle d'oxygène imposée. Les microstructures obtenues sont souvent comparables avec celles observées dans les objets les plus primitifs de notre système solaire (poussière interplanétaire ou cométaire) La recristallisation du précurseur interstellaIre dans la partie interne du disque d'accrétion est donc un moyen pour former des phases qui sont ensuite incorporées dans les astéroïdes ou les comètes.LILLE1-BU (590092102) / SudocSudocFranceF

Impact of Sulfide-based Solid Electrolyte Particle Size Distribution on the Electrochemistry of ASSB via Impedance Study

14th International Workshop on Impedance Spectroscopy (IWIS), Chemnitz, GERMANY, SEP 29-OCT 01, 2021International audienceSulfide based solid electrolytes (SE) offer high ionic conductivity and can be processed at a low temperature (cold pressing) and hence have been used extensively by the battery community in their quest for the development of all-solid-state batteries (ASSB). In this study, we try to investigate the impact of Argyrodite (Li6PS5Cl) particle size and its distribution, on the solid electrolyte (SE), cathode composite and in turn on the overall performance of the battery. Electrochemical Impedance Spectroscopy (EIS) provides key insights in the understanding of the behaviour of different SE. EIS in this particular study has been used to extract (i) the ionic conductivity of solid electrolytes (sigma(SE)) with small (< 20 mu m) and large particle size (50-150 mu m) distribution, (ii) the effective ionic conductivity (sigma(cathode.copm)) in their respective cathode composites, (iii) the tortuosity based on ionic conductivity (tau(cond)). The following are the highlights of this study: 1) On Solid Electrolyte itself: Given the same amount and same pressure, the ionic conductivity of large particle size distribution is higher. Consequently, the saturation pressure (Pressure to reach the highest ionic conductivity) is lower for large particle size. 2) On Cathode composite and its cycling: the composites with large particle size show the highest compacity values among all and also is the best performing cell. 3) Ionic conductivity-based tortuosity calculated which varied in the range 1.9-2.5. 1.9 being the lowest for large particles

Structural and optical characterization of electrodeposited CdSe in mesoporous anatase TiO2 for regenerative quantum-dot-sensitized solar cells

We investigated CdSe-sensitized TiO2 solar cells by means of electrodeposition under galvanostatic control. The electrodeposition of CdSe within the mesoporous film of TiO2 gives rise to a uniform, thickness controlled, conformal layer of nanostructured CdSe particles intimately wrapping the anatase TiO2 nanoparticles. This technique has the advantage of providing not only a fast method for sensitization (<5 min) but also being easily scalable to the sensitization of large-area panels. XRD together with SAED analysis highlight that the deposit of CdSe is exclusively constituted of the hexagonal polymorph. In addition, hierarchical growth has also been shown, starting from the formation of a TiO2-CdSe core-shell structure followed by the growth of an assembly of CdSe nanoparticles resembling cauliflowers. This assembly exhibits at its core a mosaic texture with crystallites of about 3 nm in size, in contrast to a shell composed of well-crystallized single crystals between 5 and 10 nm in size. Preliminary results on the photovoltaic performance of such a nanostructured composite of TiO2 and CdSe show 0.8% power conversion efficiency under A.M. 1.5 G conditions-100 mW cm(-2) in association with a new regenerative redox couple based on cobalt(+III/+II) polypyridil complex (V-oc = 485 mV, J(sc) = 4.26 mA cm(-2), ff = 0.37)

Reversible Anion Insertion in Molecular Phenothiazine‐Based Redox‐Active Positive Material for Organic Ion Batteries

International audienceThe increasing demand for rechargeable batteries induces the development of greener and better devices. Significant advances have been made in the last decade together with a renewed interest in organic electrode materials. Thus, stable electron-donating organic materials are candidates for ``greener'' molecular batteries (metal-free). Herein, we report the design of a monomeric p-type N-substituted phenothiazine salt as an efficient anionic host structure working reversibly in a dual-ion cell configuration using lithium as the negative electrode. Investigation of different electrolyte salts, LiClO4, LiPF6, and LiTFSI in PC (propylene carbonate), reveals that lithium 4-(10H-phenothiazin-10-yl) benzoate (LiPHB) exhibits a high operating potential (approximate to 3.7 vs. Li+/Li) corresponding to a one-electron process with a reversible specific capacity of 86 mAh g(-1) in a LiClO4-based electrolyte, exhibiting an extraordinary cycling stability over 500 cycles at 0.2 C. Such impressive results are rendering LiPHB a promising scaffold for developing next-generation molecular organic batteries

MnO Conversion Reaction: TEM and EELS Investigation of the Instability under Electron Irradiation

International audienceActive materials in batteries suffer from deleterious chemical and structural evolutions during cycling. To follow these modifications, transmission electron microscopy and associated techniques (EELS, EDX) are of great use. However, these materials can undergo drastic changes under the electron beam. In this study the various microstructural and chemical evolutions induced by electron irradiation were thoroughly investigated at different charging states on a MnO material reacting through the conversion process leading to nanoparticles. During the electron irradiation, compounds pulverization, nanograins growth as well as the formation of manganese carbide were observed. Consequently, knowing the modifications the sample can undergo under electron irradiation and managing to the best the TEM parameters (spot size, aperture size…) to limit its effect can be of help to avoid misinterpretation and to fully understand the mechanisms, which occur during cycling

Reversible Anion Insertion in Molecular Phenothiazine-Based Redox-Active Positive Material for Organic Ion Batteries

International audienceThe increasing demand for rechargeable batteries induces the development of greener and better devices. Significant advances have been made in the last decade together with a renewed interest in organic electrode materials. Thus, stable electron-donating organic materials are candidates for ``greener'' molecular batteries (metal-free). Herein, we report the design of a monomeric p-type N-substituted phenothiazine salt as an efficient anionic host structure working reversibly in a dual-ion cell configuration using lithium as the negative electrode. Investigation of different electrolyte salts, LiClO4, LiPF6, and LiTFSI in PC (propylene carbonate), reveals that lithium 4-(10H-phenothiazin-10-yl) benzoate (LiPHB) exhibits a high operating potential (approximate to 3.7 vs. Li+/Li) corresponding to a one-electron process with a reversible specific capacity of 86 mAh g(-1) in a LiClO4-based electrolyte, exhibiting an extraordinary cycling stability over 500 cycles at 0.2 C. Such impressive results are rendering LiPHB a promising scaffold for developing next-generation molecular organic batteries

Enhancement of the hydrogen release of Mg(BH4)2 by concomitant effects of nano-confinement and catalysis

International audienc

Enhancement of the hydrogen release of Mg(BH4)2 by concomitant effects of nano-confinement and catalysis

International audienceMagnesium borohydride, Mg(BH4)2, is an interesting material for hydrogen storage due to its high hydrogen content (14.9 wt.% of H2). Unfortunately, a temperature of at least 350 °C is needed for releasing its hydrogen and the rehydrogenation process is only feasible under harsh conditions (950 bar H2 and 300 °C). In order to improve the performances of this compound, we analyze in this study the concomitant effects of nano-confinement into mesoporous carbons and addition of Nisingle bondPt catalysts. This study uses different characterization tools to determine the effects of both nano-confinement and catalysts onto the pathway of decomposition. Usually, bulk Mg(BH4)2 decomposes in several steps passing through intermediate species for which activation energies are high. In this study, we show that the confinement and catalyst addition on Mg(BH4)2 result in a single step of hydrogen release and an activation energy below that of the bulk material with a value of 178 ± 14 kJ mol−1 as determined by the Kissinger's method. Interestingly, the hydrogen release is fully completed, i.e. 8H atoms per Mg(BH4)2 formula unit are released, in less than 2 h at 350 °C