The recovery and utilization of carbon dioxide (CO 2 ) is the key to achieve the targets of peak carbon dioxide emissions and carbon neutrality. The Na-CO 2 battery made with cheap alkali metal sodium and greenhouse gas CO 2 is an effective strategy to consume CO 2 and store clean renewable energy. However, the liquid electrolyte volatilization in the open battery system and inevitable dendrite growth restrict the application of Na-CO 2 batteries. In this work, magnesium-doped Na 3 Zr 2 Si 2 PO 12 (NZSP) was studied as a solid electrolyte for solid-state Na-CO 2 batteries. The ionic conductivity of Na 3.2 Zr 1.9 Mg 0.1 Si 2 PO 12 reaches 1.16 mS cm −1 at room temperature by replacing Zr ions in Na 3 Zr 2 Si 2 PO 12 with Mg ions, and the structural changes are analyzed by neutron powder diffraction. The composite electrolyte consisting of highly conductive Na 3.2 Zr 1.9 Mg 0.1 Si 2 PO 12 and high processability poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is utilized for the first time to assemble a solid-state Na-CO 2 battery. The cell shows a full discharge capacity of 7720 mAh g −1 at 200 mA g −1 . The middle gap voltage is lower than 2 V after 120 cycles at 200 mA g −1 and at a cut-off capacity of 500 mAh g −1 . This work demonstrates a promising strategy to design highperformance solid-state Na-CO 2 batteries.

The pyrochlores (H 3 O) x Sb x Te (2-x) O 6 (x = 1, 1.1 and 1.25) obtained by ion exchange from K x Sb x Te (2-x) O 6 oxides were used as catalysts for the conversion of fructose to 5-hydroxymethylfurfural (HMF) in H 2 O/Methyl isobutyl ketone (MIBK). The structure of the resulting compounds as well as the location of the H 3 O + units inside the three-dimensional network, were determined by XRD from powder samples. The effect of factors such as reaction time and temperature on the formation of HMF was studied. A fructose conversion of 99% and a yield of 59% were achieved after 120 min of reaction time and at 150°C temperature. The percentage of substitution of the cations Sb and Te in the position B of the pyrochlore was determinant to achieve the maximum incorporation of H 3 O + ions in the pyrochlore structure, which allowed to correlate the density of acidic sites present in the materials and their catalytic activity.

Three defect pyrochlores KNbWO6·xH2O, KNbTeO6 and KSbWO6 were synthesized by solid state reaction at 750 °C, from stoichiometric mixtures of K2C2O4, Sb2O3, Nb2O5, WO3 and 20% excess TeO2. A neutron powder diffraction (NPD) data analysis allowed unveiling some structural features. They are all defined in the cubic F d 3 ¯ m space group symmetry, with α = 10.5068(1) Å, 10.2466(1) Å and 10.2377(1) Å, respectively. Difference Fourier synthesis for KNbWO6·xH2O clearly showed the presence of crystallization water, with extra O’ oxygen and H+ atoms that were located from NPD data. These O’ oxygen atoms are placed at 32e Wyckoff sites, conforming a K2O’ sublattice interpenetrated with the covalent framework constituted by (Nb,W)O6 octahedra. The H+ ions coordinate the O’ atoms at partially occupied 96g Wyckoff sites while K+ ions shift also along 32e sites, but closer to the 16c special site (0,0,0). By contrast, extra H2O molecules are absent in the other two pyrochlores: in KNbTeO6 and KSbWO6 K+ ions are shifted along 32e (x,x,x) sites further away from the origin than for the previous material, and the higher covalency of the octahedral network determines more compact structures, with shorter B–O distances and narrower B–O–B angles in the proposed AB2O6 defect pyrochlore structure.