Yelong Zhang

Amorphous Li2 O2 : Chemical Synthesis and Electrochemical Properties.

When aprotic Li-O2 batteries discharge, the product phase formed in the cathode often contains two different morphologies, that is, crystalline and amorphous Li2 O2 . The morphology of Li2 O2 impacts strongly on the electrochemical performance of Li-O2 cells in terms of energy efficiency and rate capability. Crystalline Li2 O2 is readily available and its properties have been studied in depth for Li-O2 batteries. However, little is known about the amorphous Li2 O2 because of its rarity in high purity. Herein, amorphous Li2 O2 has been synthesized by a rapid reaction of tetramethylammonium superoxide and LiClO4 in solution, and its amorphous nature has been confirmed by a range of techniques. Compared with its crystalline siblings, amorphous Li2 O2 demonstrates enhanced charge-transport properties and increased electro-oxidation kinetics, manifesting itself a desirable discharge phase for high-performance Li-O2 batteries.

Understanding oxygen reactions in aprotic Li-O2 batteries*

Although significant progress has been made in many aspects of the emerging aprotic Li-O2 battery system, an in-depth understanding of the oxygen reactions is still underway. The oxygen reactions occurring in the positive electrode distinguish Li-O2 batteries from the conventional Li-ion cells and play a crucial role in the Li-O2 cells performance (capacity, rate capability, and cycle life). Recent advances in fundamental studies of oxygen reactions in aprotic Li-O2 batteries are reviewed, including the reaction route, kinetics, morphological evolution of Li2O2, and charge transport within Li2O2. Prospects are also provided for future fundamental investigations of Li-O2 chemistry.

Dealloyed silver nanoparticles as efficient catalyst towards oxygen reduction in alkaline solution

Silver nanoparticles(Ag NPs) were prepared by dealloying Mg-Ag alloy precursor. The obtained Ag NPs have an average ligament size of (50±10) nm. Electrocatalytic activity of Ag NPs towards oxygen reduction reaction( ORR) in 0.1 mol/L NaOH solution was assessed via cyclic voltammetry(CV), rotating ring disk electrode(RRDE) techniques, and electrochemical impedance spectroscopy(EIS). The electrochemical active area for the ORR was evaluated by means of the charge of the underpotential deposition(UPD) of lead(Pb) on Ag NPs. The CV results indicate that Ag NPs have a higher current density and more positive onset potential than the bulk Ag electrode. RRDE was employed to determine kinetic parameters for O2 reduction. Ag NPs exhibit a higher kinetic current density of 25.84 mA/cm2 and a rate constant of 5.45×10–2 cm/s at–0.35 V vs. Hg/HgO. The number of electrons(n) involved in ORR is close to 4. Further, EIS data show significantly low charge transfer resistances on the Ag NPs electrode. The results indicate that the prepared Ag NPs have a high activity and are promising catalyst for ORR in alkaline solution.