EQCM study of the electrodeposition of manganese in the presence of ammonium thiocyanate in chloride-based acidic solutions

Rechargeable Aqueous Mn-Metal Battery Enabled by Inorganic-Organic Interfaces

Aqueous batteries that use metal anodes exhibit maximum anodic capacity, whereas the energy density is still unsatisfactory partially due to the high redox potential of the metal anode. Current metal anodes are plagued by the dilemma that the redox potential of Zn is not low enough, whereas Al, Mg, and others with excessively low redox potential cannot work properly in aqueous electrolytes. Mn metal with a suitably low redox potential is a promising candidate, which was rarely explored before. Here, we report a rechargeable aqueous Mn-metal battery enabled by a well-designed electrolyte and robust inorganic-organic interfaces. The inorganic Sn-based interface with a bottom-up microstructure was constructed to preliminarily suppress water decomposition. With this bubble-free interface, the organic interface can be formed via an esterification reaction of sucrose triggered by acyl chloride in the electrolyte, generating a dense physical shield that isolates water while permitting Mn²⁺ diffusion. Hence, a Mn symmetric cell achieves a superior plating/stripping stability for 200 hours, and a Mn||V₂ O₅ battery maintains approximately 100 % capacity after 200 cycles. Moreover, the Mn||V₂ O₅ battery realizes a much higher output voltage than that of the Zn||V₂ O₅ battery, evidencing the possibility of increasing the energy density through using a Mn anode. This work develops a systematic strategy to stabilize a Mn-metal anode for Mn-metal batteries, opening a new door towards enhanced voltage of aqueous batteries.

The effect of two anionic membranes (AMI 7001s and Neosepta AMX) on the electrodeposition of manganese from sulphate solutions

The effect of two different anionic membranes on manganese deposition was studied in a two-compartment electrochemical reactor with a titanium cathode and a dimensionally stable RuO₂|Ti anode. Chronopotentiometry, ICP-OES, SEM, XRD and elemental mapping were used to understand the changes in concentration and characteristics of the metallic deposition at different current densities with the anionic membranes AMI 7001s and Neosepta AMX. The results demonstrate that AMI reduces more manganese than AMX below −100 A m⁻², generating more metallic deposition but also more low-solubility manganous by-products, whereas both membranes exhibited similar behaviours above −100 A m⁻² reaching the maximum current efficiency (63%) at −200 A m⁻². It was also observed that the membranes have a significant effect on sulphate consumption since they are anions.

A more stable deposit was obtained with both membranes at current densities greater than 100 A m⁻² and maximum efficiency of 63% at −200 Am⁻² (with a purity of 92%), but the consumption of sulphate ions is different in each.

A rechargeable aqueous manganese-ion battery based on intercalation chemistry

Aqueous rechargeable metal batteries are intrinsically safe due to the utilization of low-cost and non-flammable water-based electrolyte solutions. However, the discharge voltages of these electrochemical energy storage systems are often limited, thus, resulting in unsatisfactory energy density. Therefore, it is of paramount importance to investigate alternative aqueous metal battery systems to improve the discharge voltage. Herein, we report reversible manganese-ion intercalation chemistry in an aqueous electrolyte solution, where inorganic and organic compounds act as positive electrode active materials for Mn2+ storage when coupled with a Mn/carbon composite negative electrode. In one case, the layered Mn0.18V2O5·nH2O inorganic cathode demonstrates fast and reversible Mn2+ insertion/extraction due to the large lattice spacing, thus, enabling adequate power performances and stable cycling behavior. In the other case, the tetrachloro-1,4-benzoquinone organic cathode molecules undergo enolization during charge/discharge processes, thus, contributing to achieving a stable cell discharge plateau at about 1.37 V. Interestingly, the low redox potential of the Mn/Mn2+ redox couple vs. standard hydrogen electrode (i.e., -1.19 V) enables the production of aqueous manganese metal cells with operational voltages higher than their zinc metal counterparts.

Selenium and sulphur reactions involved in manganese reduction from sulphate solutions

Electrochemical reduction of ionic species during manganese deposition from sulphated aqueous solutions has been studied in an electrochemical reactor with two anionic exchange membranes. Thermodynamic analysis, voltammetries, and chronopotentiometries were used to determine the reaction mechanism of the reductions developed, with the results demonstrating that the effect of the elemental selenium on the hydrogen evolution leads to the formation of elemental sulphur by reducing the sulphate ions with both membranes. It was also evident that in the range of −25 to −50 A m⁻² the electrodeposition of metallic manganese begins, with minimal interference from parasitic reactions.

Electrochemical reduction of ionic species during manganese deposition from sulphated aqueous solutions has been studied in an electrochemical reactor with two anionic exchange membranes.

Prediction of Morphological Properties of Smart-Coatings for Cr Replacement, Based on Mathematical Modelling

In this paper we present an extension of a mathematical model for the morphological evolution of metal electrodeposits – recently developed by some of the authors – accounting for mass-transport of electroactive species from the bulk of the bath to the cathode surface. The implementation of mass-transport effects is specially necessary for the quantitative rationalisation of electrodeposition processes from ionic liquids, since these electrolytes exhibit a viscosity that is notably higher than that of cognate aqueous solutions and consequently mass-transport control is active at all practically relevant plating rates. In this work we show that, if mass-transport is coupled to cathodic adsorption of ionic liquid species and surface diffusion of adatoms, it can lead to electrodeposit smoothing. This seemingly paradoxical theoretical result has been validated by a series of Mn electrodeposition experiments from aqueous baths and eutectic ionic liquids. The latter solutions have been shown to be able to form remarkably smoother coatings than the former ones. Mn electroplates have been proposed for Cd replacement and their corrosion protection performance seems comparable, but so far the required surface finish quality has not been achieved with aqueous electrolytes. Ionic liquids thus seem to provide a viable approach to aeronautic-grade Mn electroplating.