Systematic Approach to Synthesize Different MnO₂ Crystalloid Structures and their Application in Fuel Cell/Battery Systems

Abstract

In this work we synthesized various types (α-, -, -, and δ-) of MnO 2 via redox method and investigated the effect of potassium ion content and synthesis temperature on the crystalloid structure formation. It was found that increasing the synthesis temperature and decreasing the potassium ion content leads to MnO 2 with small tunnel structures. It is thus assumed that the large potassium ions work as a template for bigger void spaces and that low temperatures can further increase the void space due to weaker Brownian movement of the molecules during synthesis. The samples were then analyzed with X-ray diffraction and scanning electron microscope and cycled in an alkaline electrolyte. From the results, it was found that MnO 2 with small tunnel structures ( and ) showed better stability than the large tunnel structures (α and δ) and thus an improved cycle life as secondary battery electrode.

Electrochemical Performance of Tunnelled and Layered MnO2 Electrodes in Aluminium-Ion Batteries: A Matter of Dimensionality

“…30 It can be observed that T-KMn (δ-MnO 2 lamellar phase) shows higher content of K + and H 2 O than SG-KMn (α-MnO2 tunnelled phase), in agreement with previously reported results. 31 Electrochemical characterization.-In order to study the electrochemical behaviour of the samples, charge and discharge experiments were initially carried out at 100 mA g −1 with a voltage window ranging from 0.5 to 2.4 V. The potential window is limited by the degradation of the electrolyte above 2.4 V, and by the possible irreversible Mn reduction below 0.5 V. 17,32 Figure 3a shows the specific charge and discharge capacity obtained as a function of cycle number for the SG-KMn sample. The observed initial discharge capacity was ∼150 mA h g −1 , which stabilized at 120 mA h g −1 after 15 cycles, with over 95% of coulombic efficiency.…”

λ-MnO2Positive Electrode for Fuel Cell/Battery Systems

“…We conducted preliminary tests with λ-MnO 2 and found that λ-MnO 2 has a slightly higher chemical charge rate than γ-MnO 2 , despite a lower surface area. 17,18 As summarized in Table I, its capabilities in terms of cyclability and capacity are similar to γ-MnO 2 and more promising than other structures. Thus, in this paper, we analyzed the possibility of using λ-MnO 2 in a FCB system by comparing its performance in terms of ORR rate (fuel cell mode), redox cycling (battery mode), and chemical charging (FCB mode) with that of γ-MnO 2 .…”