With the objective to achieve high-performance photoactive 2D films, a variety of large-surface-area, nanostructured films composed of 2D transition metal dichalcogenides (TMDCs) building blocks was successfully self-assembled using a customized, surface-functionalized, metallic sulfide template. Since 2D/2D contacts in these nanostructured films were anticipated to play a crucial role in charge carrier transport properties, control of 2D/2D contact properties was explored by varying 2D building block sizes and film-forming processes. High-resolution trans-mission electron microscopy (HRTEM) deep characterization of morpho-logical properties of 2D/2D contacts using focused ion beam (FIB) cross-sections reveals a variety of contact configurations mainly depending on the 2D building block thickness. Particularly, the effects of nanostructuration on 2D/2D contact characteristics such as the contact density, plane/plane vs edge/plane contact ratio, and contact boundary angles are clearly demonstrated on a large range of MoS2, WS2 and WSe2 building blocks varying from monolayers to nanoflakes, displaying various thicknesses. Correlations with electrical and photoelectrochemical properties demonstrate that the 2D/2D contact surface area, 2D/2D contact density, and contact boundary angles are key parameters controlling the recombination of photogenerated carriers. These findings are validated both on p-WSe2 and p-WS2 nanostructured films with photocurrents up to 4.5 mA cm-2 for the photoelectrochemical decomposition of H2O.

Large scale development of the 2D transition metal di-chalcogenides (TMDC) relies on landmark improvement in performance, which could emerge from nanostructuration. Using p-WS2 nanoflakes with different degrees of exfoliation and fracturing, perspectives were provided to develop high-surface-area 2D p-WS2 films for the photocatalytic hydrogen generation. The critical role of inter-nanoflakes contacts within high-surface-area 2D films was demonstrated, highlighting the benefit of plane/plane versus edge/plane contacts. Evidence of the high density of surface states displayed by these 2D films was provided through electrochemical measurements. In addition to operating as recombination centers, the surface states were shown to give rise to deleterious Fermi-level pinning (FLP), which dramatically decreased the efficiency of charge carrier separation. Lastly, promising strategies yielding FLP suppression via surface states modification were proposed. In particular, use of a multifunctional ultrathin film displaying healing, catalytic, and n-type semiconduction properties was shown to greatly enhance charge carrier separation and transport to the photo-electrode/electrolyte interface. When the 2D photoelectrodes were fabricated with the above prerequisites (i. e., a high proportion of plane/plane contacts and a successful surface states chemical modification), a photocurrent up to 4.5 mA cm-2 was achieved for the first time on 2D p-WS2 photocathodes for hydrogen generation.

2D photoactive materials may offer interesting opportunities in photocatalytic devices since they combine strong light absorption and shortening of charge carriers' diffusion path. Because of their high surface defect concentration and the formation of a majority of edge/plane vs plane/plane contacts between the anisotropic building blocks, surface defect passivation and improvement of charge carrier transport are critical for the large development of high surface area, 2D photo-catalysts. Here, we propose a hetero-structure nanoporous network with a patch-like coating as high performance 2D photo-catalysts. The hetero-structured building blocks are composed of a photo-active WSe2 nanoflake in direct contact with both a conducting rGO nanosheet and an ultrathin layer of healing catalyst. The resulting nanoporous film achieves a H-2 evolution photocurrent density up to 5 mA cm(-2) demonstrating that the patch-like hetero-structures represent an effective strategy to simultaneously improve hole collection, defect passivation and charge transfer. These hetero-structures made of an ultrathin healing catalyst layer represent promising building blocks for the bottom-up fabrication of high surface area photocathodes particularly for 2D photo-catalysts displaying high defect concentration.

2D semiconducting nanosheets of Transition Metal Dichalcogenides are attractive materials for solar energy conversion because of their unique absorption properties. Here, we show that Mo thio- and oxo-thio-complexes anchored on 2D p-WSe2 nanosheets considerably boost water splitting under visible light irradiation with photocurrent density up to 2.0 mA cm(-2) at -0.2 V/NHE. Besides developing high electro-catalytic activity, the Mo-complexes film is also shown to be capable of healing surface defects. We propose that the observed healing of surface defects arises from the strong adsorption on point defects of the 2D WSe2 substrate of Mo complexes such as (MoS4)(2-), (MoOS3)(2-), (Mo2S6O2)(2-) as supported by DFT calculations. In addition, the thio-, oxo-thio Mo complexes films are shown to enhance charge carrier separation and migration favouring the hydrogen evolution reaction, putting forward the use of thio-, oxo-thio-Mo complexes as a multicomponent passivation layer exhibiting multiple properties.

Layered oxides have been intensively studied for decades for their characteristics as electrode materials or their physical properties resulting from their structure. In this work, we present a modification of layered oxide NaVO2 via liquid exfoliation technique in water. This oxide has VOx layers with Na ions trapped in between. The goal of this process is to initiate sodium removal from the lattice, which will result in the structural transformations. During this sodium deintercalation, we observed drastic changes in the structure and electrochemical behavior of the oxide. Following water treatment, NaVO2 exhibited nearly linear slopping discharge voltage profile and none of the multi-step reaction potential plateaus were observed, contrary to the profile of the pristine powder. Interestingly, this material structure was able to cycled reversibly within a much larger voltage window, with decent capacity value (ca 160 mA h/g), compare to pristine NaVO2. Thanks to this change of behavior, the active material mean operating voltage was increased.

2D semiconducting nanosheets of Transition Metal Dichalcogenides are attractive materials for solar energy conversion because of their unique absorption properties. Recently, Hydrogen evolution reaction (HER) was achieved with thin 2D WSe2 nanosheets activated by well-known precious metal catalysts. Here, we propose noble-metal-free, Mo thio- and oxo-thio-complexes anchored on 2D p-WSe2 nanosheets for efficient water splitting under visible light irradiation with photocurrent density up to 2.0 mA cm-2 at -0.2 V/NHE. These Mo thio and oxo-thio- molecular complexes films represent an ideal class of catalysts, well-suited to functionalize 2D materials since they are stable in aqueous environments, cheap, environmentally benign to synthesize and process. Besides developing high electro-catalytic activity, the Mo complexe films were shown to display ability to heal surface defects. We propose that the observed healing of surface defects arises from the strong adsorption on point defects of the 2D WSe2 substrate of Mo-complexes such as (MoS4)2-, (MoOS3)2-, (Mo2S6O2)2- as shown from DFT calculations. In addition to display catalytic and healing effects, the thio-, oxo-thio Mo complexes films which spontaneously formed at well-defined pH were shown to enhance charge carrier separation and migration for the Hydrogen Evolution Reaction, thus representing an example of multicomponent passivation layer exhibiting multiple properties.

As one possible alternative metal to lithium in ion batteries, potassium has recently attracted considerable attention as a result of its geochemical abundance and low cost. In this work, a detailed study of the electrochemical properties of potassium ion storage was performed using reduced graphene oxide (rGO) aerogel as a negative electrode material. The influence of the nature of the electrolyte and the drying methods used were investigated in order to optimize the electrochemical performance of freeze-dried rGO in potassium-ion batteries (PIBs). Electrochemical impedance spectroscopy (EIS) were used to assess the performance of our rGO material in PIBs. Used as the negative electrode, freeze-dried rGO can deliver a high capacity of 267 mA h/g at C/3 rate together with 78% capacity retention during 100 cycles, combined with high rate capability (92 mA h/g at 6.7C). This set of results makes rGO aerogel a promising electrode material for PIBs.

Cu2ZnSnS4 (CZTS) shows great potential for photovoltaic application because of its non-toxic earth-abundant components and good optoelectronic properties. Combining low-cost and environmentally friendly routes would be the most favorable approach for the development of CZTS solar cells. In this context, development of Cu2ZnSnS4 (CZTS) films from all-aqueous CZTS nanocrystals inks represents an interesting challenge. Here, we have highlighted a condensation regulation by the alkali ion size observed in the alkali series Li+ < Na+ < K+ < Rb+ < Cs+, and demonstrated the chemical stability of Cu2ZnSnS4 surfaces in basic aqueous dispersions. Data such as optimal nanocrystal size, critical cracking thickness and average thickness to fabricate micron crack-free films from all-aqueous chalcogenide nanocrystals dispersions were determined. From these results, a proof of concept for the formation of a crack-free film of 2.2 μm formed from an all-aqueous CZTS nanocrystals ink is given. When employing low-cost materials, removal of carbon impurities represents another important challenge. With the objective to fabricate residue-free films, a specific annealing strategy is proposed involving a high temperature purification step under Se partial pressure. Carbon removal is thus achieved via the CSe2 gas formation, simultaneously to the amorphous domains crystallization as demonstrated by Raman spectroscopy. These source data favoring the formation of residue-free, crack-free, annealed films should assist the large scale development of CZTS solar cells from low-cost and environmentally friendly, all -aqueous inks.

Highly water-soluble, discrete, heterometallic, chalcogenide oligomers displaying various valences in a single metal chalcogenide oligomer are proposed for functional films.

In this paper, we propose to study the impact of very low filler content (0.005 wt.%) of graphite nanoflakes (80 nm), multi-layer (5-20 nm) and few-layer (1-2 nm) graphene on the electrical conductivity of an epoxy nanocomposite. The results highlight that an improvement of the quality of the exfoliation process of graphene, particularly in few-layer graphene/epoxy, allows decreasing the DC electrical conductivity (by a factor 100 compared to neat epoxy) in a large range of electric field from 1 to 10 kV/mm. This novel property could allow decreasing space charge trapping within the insulator bulk at the origin of long-term electrical ageing.

A high-temperature gas-templating strategy is proposed to synthesize Cu2ZnSnS4 (CZTS) nanocrystals for all-aqueous solar inks. Our gas templating process route involves the in-situ generation and stabilization of nanosized gas bubbles into a molten KSCN-based reaction mixture at 400 °C. Chemical insights of the templating gas process are provided such as the simultaneous formation of gas bubbles and CZTS nuclei highlighting the crucial role of the nucleation stage on the sponge and resulting nanocrystals properties. The high porosity displayed by the resulting CZTS nanocrystals facilitates their further post-fragmentation, yielding individualized nanocrystals. The advantages of our high temperature gas templating route are illustrated by the following: (i) the low defect concentration displayed by the highly crystalline nanocrystals, (ii) the synthesis of CZTS nanocrystals displaying S2− polar surfaces after ligand exchange. The good photoluminescence properties recorded on the pure CZTS nanocrystals reveal potential for exploration of new complex chalcogenide nanocrystals useful for various applications including photovoltaics and water splitting. Here we demonstrate that using these building blocks, a CZTS solar cell can be successfully fabricated from an environment-friendly all-aqueous ink.

CuInS2 was synthesized, with a yield of 70% by reaction in molten KSCN at 400 °C of CuCl2 and InCl3 with a ratio KSCN/Cu=15. The homogeneous powder obtained is constituted of nano-sized grains (70–100 nm), with a specific surface area of 6 m2/g and a band gap Eg of 1.5 eV.

Using discrete, ultrafine alumina, highly dense transparent (71% real in‐line transmission, RIT, λ = 640 nm) ceramics were achieved with grain size as small as 260 nm using standard SPS sintering. We show that use of La3+ as a dopant greatly reduces sensitivity to the sintering temperatures. Transparent alumina were achieved in a large range of sintering temperatures, 1140°C < T < 1200°C, thus providing better reliability and flexibility into the fabrication of large sintered transparent ceramic bodies.

A sol–gel method was proposed to prepare copper II molybdate α-CuMoO4 powders. A gel was first obtained via the polymerizable complex method, using citric acid as complexing and polymerizing agent, dried at 120°C and decomposed at 300°C. A calcination in the temperature range 400–500°C for 2h led to the pure phase α-CuMoO4. The different powders obtained were characterized by X ray diffraction analysis and by transmission (TEM) and scanning (SEM) electron microscopies.Ceramics were prepared using conventional sintering and spark plasma sintering (SPS) techniques. A maximal relative density of 94.8% was reached after conventional sintering at 520°C for 2h. In the case of SPS, the densification was optimized by varying the temperature, the time and the applied pressure. Higher densities, up to 98.7%, were obtained at very low temperature, i.e., 300°C, for 5min only under a pressure of 225MPa.

SPS-produced α-alumina samples are prepared from powders doped with different amounts of Zr4+ and La3+ cations. Zr4+ cations segregate at grain boundaries. m-ZrO2 particles are formed at 570 but not at 280catppm. A β-alumina LaAl11O18 structure is found at 310catppm when the lanthanum grain boundary solubility limit is exceeded (∼200catppm). 100catppm La is sufficient to block the diffusion path across grain boundaries and inhibit grain growth. Both doping cations disturb the grain boundary diffusion whatever their amount. They delay the densification at higher temperatures while limiting grain growth. The real in-line transmittance (RIT) of α-alumina is improved due to the reduced grain size. Nevertheless, increasing the cation amount leads to an increase in porosity or even the formation of secondary phase particles, both detrimental for optical properties. Finally, optimised amounts of cation of 200 and 150catppm are found for La- and Zr-doped alumina, respectively.

A process route for the fabrication of solvent-redispersible, surfactant-free Cu₂ZnSnS₄ (CZTS) nanoparticles has been designed with the objective to have the benefit of a simple sulfide source which advantageously acts as (i) a complexing agent inhibiting crystallite growth, (ii) a surface additive providing redispersion in low ionic strength polar solvents and (iii) a transient ligand easily replaced by an carbon-free surface additive. This multifunctional use of the sulfide source has been achieved through a fine tuning of ((Cu²⁺)(a)(Zn²⁺)(b)(Sn⁴⁺)(c)(Tu)(d)(OH⁻)(e))(t⁺), Tu = thiourea) oligomers, leading after temperature polycondensation and S²⁻ exchange to highly concentrated (c > 100 g l⁻¹), stable, ethanolic CZTS dispersions. The good electronic properties and low-defect concentration of the sintered, crack-free CZTSe films resulting from these building blocks was shown by photoluminescence investigation, making these building blocks interesting for low-cost, high-performance CZTSe solar cells.

A general route to the synthesis of surfactant-free CuInS2 (CIS), Cu2CoSnS4 (CCTS) and Cu2ZnSnS4 (CZTS) nanocrystals dispersible in low boiling point solvents is proposed. These nanocrystal inks should be of great interest to the fabrication of thin film absorbers of chalcogenide solar cells.

A slurry of α-Al2O3 was doped with Mg, Zr and La nitrates or chlorides, in various amounts in the range 150–500wtppm and then freeze-dried to produce nanosized doped powder (∼150nm). The powder was sintered by SPS to yield transparent polycrystalline alpha alumina. The influence of the nature of the doping element and the starting salt, the thermal treatment before sintering and the sintering temperature on the transparency of the ceramics were investigated. The transparency of the ceramics of nanosized Al2O3 was shown to depend mainly on the way the powder was prepared, the nature of the doping salt also had an effect. Finally, a high real inline transmittance, reaching 48.1% was achieved after optimization.