Photovoltaic Rudorffites: Lead-Free Silver Bismuth Halides Alternative to Hybrid Lead Halide Perovskites.

Hybrid CPbX3 (C: Cs, CH3 NH3 ; X: Br, I) perovskites possess excellent photovoltaic properties but are highly toxic, which hinders their practical application. Unfortunately, all Pb-free alternatives based on Sn and Ge are extremely unstable. Although stable and non-toxic C2 ABX6 double perovskites based on alternating corner-shared AX6 and BX6 octahedra (A=Ag, Cu; B=Bi, Sb) are possible, they have indirect and wide band gaps of over 2 eV. However, is it necessary to keep the corner-shared perovskite structure to retain good photovoltaic properties? Here, we demonstrate another family of photovoltaic halides based on edge-shared AX6 and BX6 octahedra with the general formula Aa Bb Xx (x=a+3 b) such as Ag3 BiI6 , Ag2 BiI5 , AgBiI4 , AgBi2 I7 . As perovskites were named after their prototype oxide CaTiO3 discovered by Lev Perovski, we propose to name these new ABX halides as rudorffites after Walter Rüdorff, who discovered their prototype oxide NaVO2 . We studied structural and optoelectronic properties of several highly stable and promising Ag-Bi-I photovoltaic rudorffites that feature direct band gaps in the range of 1.79-1.83 eV and demonstrated a proof-of-concept FTO/c-m-TiO2 /Ag3 BiI6 /PTAA/Au (FTO: fluorine-doped tin oxide, PTAA: poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], c: compact, m: mesoporous) solar cell with photoconversion efficiency of 4.3 %.

An aqueous electrolyte of the widest potential window and its superior capability for capacitors.

A saturated aqueous solution of sodium perchlorate (SSPAS) was found to be electrochemically superior, because the potential window is remarkably wide to be approximately 3.2 V in terms of a cyclic voltammetry. Such a wide potential window has never been reported in any aqueous solutions, and this finding would be of historical significance for aqueous electrolyte to overcome its weak point that the potential window is narrow. In proof of this fact, the capability of SSPAS was examined for the electrolyte of capacitors. Galvanostatic charge-discharge measurements showed that a graphite-based capacitor containing SSPAS as an electrolyte was stable within 5% deviation for the 10,000 times repetition at the operating voltage of 3.2 V without generating any gas. The SSPAS worked also as a functional electrolyte in the presence of an activated carbon and metal oxides in order to increase an energy density. Indeed, in an asymmetric capacitor containing MnO2 and Fe3O4 mixtures in the positive and negative electrodes, respectively, the energy density enlarged to be 36.3 Whkg-1, which belongs to the largest value in capacitors. Similar electrochemical behaviour was also confirmed in saturated aqueous solutions of other alkali and alkaline earth metal perchlorate salts.

NMR studies on effects of temperature, pressure, and fluorination on structures and dynamics of alcohols in liquid and supercritical states.

We measured 1H NMR chemical shifts (delta H) and 1H and 2H NMR spin-lattice relaxation times (1H- and 2H-T1) of methanol, ethanol, 2-propanol, 2,2,2-trifluoroethanol, and 1,1,1,3,3,3-hexafluoro-2-propanol in the temperature range from 298 to 673 K at reduced pressures ( Pr = P/ Pc) of 1.22 and 3.14. The delta H values showed that the degree (X HB) of hydrogen bonding decreased in the order of methanol > ethanol >2-propanol > H2O, and that the hydrogen bonding was much affected by fluorination, because of the intramolecular H-F interactions in supercritical (sc) states. Moreover, 1H- T 1 measurements revealed that the relaxation processes of OH groups in nonfluoroalcohols are controlled by dipole-dipole (DD) and spin-rotation (SR) mechanisms below and above the critical temperature (Tc), while the cross-correlation effects connected with intramolecular DD interactions between a carbon atom and an adjacent proton played an important role for hydrocarbon groups (CHn, n = 1-3) under sc conditions. This interpretation was also supported by two other results. The first is that the intramolecular H-F interactions strongly inhibit the internal rotation of CH and CH2 groups of sc fluoroalcohols, and the second is that the molecular reorientational correlation times (tauc(D)) obtained from 2H- T 1 values of deuterated hydrocarbon groups (CDn ) at temperatures above T c have significantly less temperature dependence than those of OD groups. Actually, the apparent activation energy (DeltaEa) for molecular reorientational motions in sc alcohols was smaller compared with liquid alcohols, being about 1 order of magnitude.

Gasification reaction of organic compounds catalyzed by RuO2 in supercritical water.

Nearly complete gasification of organic compounds has been achieved by stoichiometrically insufficient amounts of RuO2 in supercritical water (SCW) to provide CH4, CO2 and H2, all the hydrogen atoms of which originate from water, and the catalytic effect of RuO2 results from a redox couple of Ru(IV)/Ru(II) induced by SCW.