Synergy of diffraction and spectroscopic techniques to unveil the crystal structure of antimonic acid

The elusive crystal structure of the so-called ‘antimonic acid’ has been investigated by means of robust and state-of-the-art techniques. The synergic results of solid-state magic-angle spinning nuclear magnetic resonance spectroscopy and a combined Rietveld refinement from synchrotron X-ray and neutron powder diffraction data reveal that this compound contains two types of protons, in a pyrochlore-type structure of stoichiometric formula (H3O)1.20(7)H0.77(9)Sb2O6. Some protons belong to heavily delocalized H3O+ subunits, while some H+ are directly bonded to the oxygen atoms of the covalent framework of the pyrochlore structure, with O–H distances close to 1 Å. A proton diffusion mechanism is proposed relying on percolation pathways determined by bond-valence energy landscape analysis. X-ray absorption spectroscopy results corroborate the structural data around Sb5+ ions at short-range order. Thermogravimetric analysis and differential scanning calorimetry endorsed the conclusions on the water content within antimonic acid. Additional 0.7 water molecules per formula were assessed as moisture water by thermal analysis.

Theoretical Investigation of Proton Diffusion in Dion–Jacobson Layered Perovskite RbBiNb2O7

Perovskite materials are considered to be promising electrolyte membrane candidates for electrochemical applications owing to their excellent proton- or oxide-ion-conducting properties. RbBiNb2O7 is a double-layered Dion–Jacobson perovskite oxide, with Pmc21 symmetry. In this study, the electronic structure and proton-diffusion properties of bulk RbBiNb2O7 were systematically investigated using first-principles calculations. The unique layered crystal structure of RbBiNb2O7 plays a crucial role in proton storage and proton conductivity. Different proton-diffusion steps in RbBiNb2O7 were considered, and the activation energies of the relevant diffusion steps were evaluated using the climbing image-nudged elastic band (CI-NEB) technique. The proton diffusion in RbBiNb2O7 presents a two-dimensional layered characteristic in the a-b plane, owing to its layered crystalline nature. According to the transition state calculations, our results show that the bulk RbBiNb2O7 exhibits good proton-transport behavior in the a-b plane, which is better than many perovskite oxides, such as CaTiO3, CaZrO3, and SrZrO3. The proton diffusion in the Rb–O and Nb–O layers is isolated by a higher energy barrier of 0.86 eV. The strong octahedral tilting in RbBiNb2O7 would promote proton transport. Our study reveals the microscopic mechanisms of proton conductivity in Dion–Jacobson structured RbBiNb2O7, and provides theoretical evidence for its potential application as an electrolyte in solid oxide fuel cells (SOFCs).

A high capacity small molecule quinone cathode for rechargeable aqueous zinc-organic batteries

Rechargeable aqueous zinc-organic batteries are promising energy storage systems with low-cost aqueous electrolyte and zinc metal anode. The electrochemical properties can be systematically adjusted with molecular design on organic cathode materials. Herein, we use a symmetric small molecule quinone cathode, tetraamino-p-benzoquinone (TABQ), with desirable functional groups to protonate and accomplish dominated proton insertion from weakly acidic zinc electrolyte. The hydrogen bonding network formed with carbonyl and amino groups on the TABQ molecules allows facile proton conduction through the Grotthuss-type mechanism. It guarantees activation energies below 300 meV for charge transfer and proton diffusion. The TABQ cathode delivers a high capacity of 303 mAh g−1 at 0.1 A g−1 in a zinc-organic battery. With the increase of current density to 5 A g−1, 213 mAh g−1 capacity is still preserved with stable cycling for 1000 times. Our work proposes an effective approach towards high performance organic electrode materials.

Unveiling the crystal structure of ‘antimonic acid’: short- and long-range perspectives

The elusive crystal structure of the socalled “antimonic acid” has been investigated by means of robust and state-of-the-art techniques. The synergic results of solidstate magicangle spinning nuclear magnetic resonance spectroscopy and a combined Rietveld refinement from synchrotron X-ray and neutron powder diffraction data reveal that this compound contains two types of protons, in a pyrochloretype structure of stoichiometric formula (H3O)1.20(7)H0.77(9)Sb2O6. Some protons belong to heavily delocalized H3O+ subunits, while some H+ are directly bonded to the oxygen atoms of the covalent framework of the pyrochlore structure, with O − H distances close to 1 Å. A proton diffusion mechanism is proposed relying on percolation pathways determined by bondvalence energy landscape analysis. Xray absorption spectroscopy results corroborate the structural data around Sb5+ ions at shortrange order. Thermogravimetric analysis and differential scanning calorimetry endorsed the conclusions on the water content within antimonic acid. Additional 0.7 water molecules per formula were assessed as moisture water by thermal analysis.

Application of clayware ceramic separator modified with silica in microbial fuel cell for bioelectricity generation during rice mill wastewater treatment

Ceramic separators have recently been investigated as low-cost, robust, and sustainable separators for application in microbial fuel cells (MFC). In the present study, an attempt has been made to develop a low-cost MFC employing a clayware ceramic separator modified with silica. The properties of separators with varying silica content (10%–40% w/w) were evaluated in terms of oxygen and proton diffusion. The membrane containing 30% silica exhibited improved performance compared to the unmodified membrane. Two identical MFCs, fabricated using ceramic separators with 30% silica content (MFCS-30) and without silica (MFCC), were operated at hydraulic retention time (HRT) of 12 h with real rice mill wastewater having chemical oxygen demand (COD) of 3,200 ± 50 mg/L. The maximum volumetric power density of 791.72 mW/m3 and coulombic efficiency of 35.77% was obtained in MFCS-30, which was 60.4% and 48.5%, respectively, higher than that of MFCC. The maximum COD and phenol removal efficiency of 76.2% and 58.2%, respectively, were obtained in MFCS-30. MFC fabricated with modified ceramic separator demonstrated higher power generation and pollutant removal. The presence of hygroscopic silica in the ceramic separator has improved its performance in terms of hydration properties and proton transport.