The local structural changes of ZrW2O8 after ammoniation treatment.

Orthorhombic Dy2W3O12 shows NTE (−2.6 × 10−5 °C−1) in the temperature range of 150–500 °C. So far, this value is the largest coefficient of negative thermal expansion in the A2W3O12 family (A = rare earth element).

The electrochemical reduction mechanism of Mn in LiMn2O4 in molten salt was studied. The results show that in the NaCl-CaCl2 molten salt, the process of reducing from Mn (IV) to manganese is: Mn (IV)→Mn (III)→Mn (II)→Mn. LiMn2O4 reacts with molten salt to form CaMn2O4 after being placed in molten salt for 1 h. The reaction of reducing CaMn2O4 to Mn is divided into two steps: Mn (III)→Mn (II)→Mn. The results of constant voltage deoxidation experiments under different conditions show that the intermediate products of LiMn2O4 reduction to Mn are CaMn2O4, MnO, and (MnO)x(CaO)(1−x). As the reaction progresses, x gradually decreases, and finally the Mn element is completely reduced under the conditions of 3 V for 9 h. The CaO in the product can be removed by washing the sample with deionized water at 0 °C.

In order to study the process of Fe3O4 reduction by melt electro-deoxidation. Electrochemical method was used to analyze the reduction mechanism of Fe3O4 in NaCl-CaCl2 melts. The effects of cell voltage and time on the product were discussed through constant cell voltage electrolysis. The results showed: (1) The reduction of solid Fe3O4 to metallic Fe is a two-step process for obtaining electrons. (2) The transformation process (600 min, 0–1.0 V) of the electrolysis products with the increase of the cell voltage is as follows: Fe3O4 → FeO → FeO + Fe → Fe. (3) The intermediate product Ca2Fe2O5 was formed (2.0 V, 10–300 min), which inhibited the deoxygenation process in the early stage of the reaction. When the electrolysis time exceeds 60 min, the main reaction is the reduction of Ca2Fe2O5 to Fe.

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Massive deployment of lithium-ion battery inevitably causes a large amount of solid waste. To be sustainably implemented, technologies capable of reducing environmental impacts and recovering resources from spent lithium-ion battery have been an urgent task. The electrochemical reduction of LiNiO2 to metallic nickel has been reported, which is a typical cathode material of lithium-ion battery. In this paper, the electrochemical reduction behavior of LiNiO2 is studied at 750 °C in the eutectic NaCl-CaCl2 molten salt, and the constant cell voltage electrolysis of LiNiO2 is carried out. The results show that Ni(III) is reduced to metallic nickel by a two-step process, Ni(III) → Ni(II) → Ni, which is quasi-reversible controlled by diffusion and electron transfer. After electrolysis for 6 h at 1.4 V, the surface of LiNiO2 cathode is reduced to metallic nickel, with NiO and a small amount of Li0.4Ni1.6O2 detected inside the partially reduced cathode. After prolonging the electrolysis time to 12 h, LiNiO2 is fully electroreduced to metallic nickel, achieving a high current efficiency of 98.60%. The present work highlights that molten salt electrolysis could be an effective protocol for reclamation of spent lithium-ion battery.

Polycrystalline Ho2W3O12 is prepared by calcination of stoichiometric amounts of Ho2O3 and WO3 in air (1100 °C, 10 h) with different cooling treatments (850 °C plus furnace cooling or 1100 °C plus quenching in H2O) to probe the relationship between phase formation and preparative conditions.

The electrochemical reduction process of ZnFe2O4 in NaCl-CaCl2 melts was studied. Thermodynamic analysis shows that the reduction process of ZnFe2O4 is carried out in multiple steps, and it is difficult to reduce Fe3+ to Fe in one step. Electrochemical tests revealed that the reduction process of ZnFe2O4 includes three steps: First, Fe3+ is reduced to Fe in two steps, then Zn2+ is reduced to Zn in one step. The reduction of Fe3+ on the Mo electrode is a reversible process controlled by diffusion, while the reduction of Zn2+ is an irreversible process controlled by diffusion. The influence of electrolysis voltage and temperature on the process of electric deoxidation has also been studied. It is indicated that properly increasing the temperature is conducive to the diffusion of oxygen ions, thereby increasing the deoxidation rate. With the gradual increase of voltage, the reduction process of ZnFe2O4 is ZnFe2O4 → FeO + ZnO → Fe + ZnO → Fe + Zn.