Rachid Essehli

Crystal structure of the alluaudite Ag2Mn3(VO4)3

Abstract The new compound Ag2Mn3(VO4)3 was synthesized by hydrothermal and solid state reaction routes, and its crystal structure was determined from single-crystal X-ray diffraction data. Ag2Mn3(VO4)3 crystallizes with a monoclinic symmetry, space group C2/c, with a=11.8968(11) Å, b=13.2057(13) Å, c=6.8132(7) Å, β=111.3166(15) (°) and V=997.16(17) Å3 (Z=4). Its crystal refinement yielded the residual factors R(F)=0.0249 and wR(F2)=0.0704 for 95 parameters and 1029 independent reflections at a 3σ(I) level. Ag2Mn3(VO4)3 can be considered as a new member of the AA′MM′2(XO4)3 alluaudite family. The specific arrangement of M and M′ octahedral sites and of X tetrahedral sites gives rise to two different channels aligned along the crystallographic c-axis and containing the A and A′ sites. The A, A′, M, and X sites are fully occupied by Ag+, Mn2+, and V5+, respectively; whereas a Mn2+/Mn3+ mixture is observed in the M′ site.

Graphene nanoplatelets doping of P3HT:PCBM photoactive layer of bulk heterojunction organic solar cells for enhancing performance

Hybrid organic photovoltaic (OPV) cells based on conjugated polymers photoactive materials are promising candidates for flexible, high-performance and low-cost energy sources owing to their inexpensive materials, cost-effective processing, and ease of fabrication by simple solution processes. However, the modest PV performance obtained to date -in particular the low power conversion efficiency (PCE)- has impeded the large scale deployment of OPV cells. The low PCE in OPV solar cells has been mainly attributed to low carrier mobility, which is closely correlated to the transport diffusion length of the charge carriers within the photoactive layers. The 2D graphene material can be an excellent candidate for assisting the charge transport improvement in the active layer of OPV cells due to its huge carrier mobility, thermal and chemical stability, and its compatibility with the solution process. In this work, we report on the improvement of optoelectronic properties and photovoltaic performance of graphene nanoplatelets (GNP) doped P3HT:PCBM photoactive blended layers, integrated into a bulk heterojunction (BHJ) organic photovoltaic based device, using PEDOT:PSS on ITO/glass substrate. First, the light absorption capacity was observed to increase with respect to the GNP contents while the photoluminescence showed a clear quenching, indicating electrons transfer between the graphene sheets and the polymeric matrix. Then, the incorporation of GNP into the BHJ active layer has resulted in enhanced PV performance with respect to a reference cell, and the best PV performances were obtained with 3 wt. % of GNP loading, with an open-circuit voltage of 1.24 V, a short-circuit current density value of 6.18 mA/cm2, a fill factor of 47.12 %, and a power conversion efficiency of about 3.61 %. We believe that the obtained results contribute to the development of organic photovoltaic devices and to the understanding of the impact of sp2-bonded carbon therein.Hybrid organic photovoltaic (OPV) cells based on conjugated polymer photoactive materials are promising candidates for flexible, high-performance and low-cost energy sources owing to their inexpensive materials, cost-effective processing and ease of fabrication by simple solution processes. However, the modest PV performance obtained to date-in particular the low power conversion efficiency (PCE)-has impeded the large scale deployment of OPV cells. The low PCE in OPV solar cells is mainly attributed to the low carrier mobility, which is closely correlated to the transport diffusion length of the charge carriers within the photoactive layers. The 2D graphene material could be an excellent candidate for assisting charge transport improvement in the active layer of OPV cells, due to its huge carrier mobility, thermal and chemical stability, and its compatibility with the solution process. In this work, we report on the improvement of the optoelectronic properties and photovoltaic performance of graphene nanoplatelet (GNP)-doped P3HT:PCBM photoactive blended layers, integrated into a bulk heterojunction (BHJ) organic-photovoltaic-based device, using PEDOT:PSS on an ITO/glass substrate. First, the light absorption capacity was observed to increase with respect to the GNP content, while the photoluminescence showed clear quenching, indicating electron transfer between the graphene sheets and the polymeric matrix. Then, the incorporation of GNP into the BHJ active layer resulted in enhanced PV performance with respect to the reference cell, and the best PV performance was obtained with 3 wt.% of GNP loading, with an open-circuit voltage of 1.24 V, a short-circuit current density value of 6.18 mA cm-2, a fill factor of 47.12%, and a power conversion efficiency of about 3.61%. We believe that the obtained results contribute to the development of organic photovoltaic devices and to the understanding of the impact of sp2-bonded carbon therein.

Fabrication and evaluation of Rb2Co(H2P2O7)2·2H2O/waterborne polyurethane nanocomposite coating for corrosion protection aspects

Here we investigate the influence of new acidic pyrophosphate (Rb2Co(H2P2O7)2·2H2O) (DP) incorporation in waterborne polyurethane (WBPU) coatings on the corrosion protection efficiency of WBPU coatings for carbon steel in 3.5% NaCl solution. We used potentiodynamic polarization, electrochemical frequency modulation (EFM) and pull-off adhesion and O2 gas permeability measurements to measure the corrosion protection efficiency of the WBPU coating. The dispersion of the DP nano-particles into the WBPU matrix was characterized via TEM observations. We find that the corrosion resistance and mechanical properties of the WBPU coating increase with incorporation of DP nano-particles into the WBPU coating.

Synthesis and performance evaluation of nanostructured NaFexCr1−X(SO4)2 cathode materials in sodium ion batteries (SIBs)

This research work focuses on the synthesis and performance evaluation of NaFexCr1−X(SO4)2 (X = 0, 0.8 and 1.0) cathode materials in sodium ion batteries (SIBs). The novel materials having a primary particle size of around 100–200 nm were synthesized through a sol–gel process by reacting stoichiometric amounts of the precursor materials. The structural analysis confirms the formation of crystalline, phase pure materials that adopt a monoclinic crystal structure. Thermal analysis indicates the superior thermal stability of NaFe0.8Cr0.2(SO4)2 when compared to NaFe(SO4)2 and NaCr(SO4)2. Galvanostatic charge/discharge analysis indicates that the intercalation/de-intercalation of a sodium ion (Na+) into/from NaFe(SO4)2 ensues at about 3.2 V due to the Fe2+/Fe3+ active redox couple. Moreover, ex situ XRD analysis confirms that the insertion/de-insertion of sodium into/from the host structure during charging/discharging is accompanied by a reversible single-phase reaction rather than a biphasic reaction. A similar sodium intercalation/de-intercalation mechanism has been noticed in NaFe0.8Cr0.2(SO4)2which has not been reported earlier. The galvanostatic measurements and X-ray photoelectron spectroscopy (XPS) analysis confirm that the Cr2+/Cr3+ redox couple is inactive in NaFexCr1−X(SO4)2 (X = 0, 0.8) and thus does not contribute to capacity augmentation. However, suitable carbon coating may lead to activation of the Cr2+/Cr3+ redox couple in these inactive materials.