A pure zinc borate, Zn[B 12 O 14 (OH) 10 ], has been synthesized and characterized by XRD, FT-IR, simultaneous TG-DTA techniques, and chemical analysis. The molar enthalpy of solution of Zn[B 12 O 14 (OH) 10 ] (s) in 1 mol·dm −3 HCl(aq) was measured by microcalorimeter at T = 298.15 K. The molar enthalpy of solution of ZnO(s) in the mixture solvent of 2.00 cm 3 of 1 mol·dm −3 HCl(aq) and calculated amount of H 3 BO 3 was also measured. With the incorporation of the previously determined enthalpy of solution of H 3 BO 3 (s) in 1 mol·dm −3 HCl(aq), together with the use of the standard molar enthalpies of formation for ZnO(s), H 3 BO 3 (s), and H 2 O(l), the standard molar enthalpy of formation of −(9646.6 ± 9.6) kJ·mol −1 at T = 298.15 K was obtained on the basis of an appropriate thermochemical cycle. In addition, the molar enthalpy of formation of −9492.7 kJ·mol −1 for [B 12 O 14 (OH) 10 ] 2− has also been estimated by a group contribution method, which has been used to predict the Δ f H m θ of a series of transition metal borates of M[B 12 O 14 (OH) 10 ] (M II = Mn, Zn, Fe, Co, Ni). These estimated data have been used to further compare the stability of this series of transition metal borates.
Sisi Wu,Jing Yang,Ning Qin,Yingzhi Li,Haiou Wang,Yong-Wei Zhang,Qing Wang,Zhouguang Lu
LiO2 is a critical intermediate of oxygen reduction reaction in nonaqueous Li–O2 batteries that largely determines the discharge capacity and cycling stability. Currently, functional redox mediators that can promote the solution reaction route by enhancing the solvation of LiO2 have attracted tremendous interest to increase the attainable capacity. Conversely, redox mediators that quench LiO2 and facilitate the surface reaction route receive little attention. Here, we provide an in-depth exploration of the catalytic pathway and effect of a superoxide quencher that modulates the surface growth of Li2O2. Surprisingly, the predomination of the surface reaction route by ethyl viologen helps deliver a capacity as much as that promoted by the solution reaction route. The findings of this work provide a new direction of screening and evaluating functioning redox mediators for Li–O2 batteries.
危险品化学品经营许可证（带存储）