Investigation of cavity microelectrode technique for electrochemical study with manganese dioxides

Enhanced Desalination Performance Using Phosphate Buffer-Mediated Redox Reactions of Manganese Oxide Electrodes in a Multichannel System

Water desalination mediated by electrochemical reactions to directly capture and release salt at electrode materials offers a low-voltage method for producing freshwater. Developing new system designs has allowed electrode materials to maximize their capacity for salt separation, especially when a multichannel system is used to introduce a separate electrode rinse solution. Here, we show that the use of an additive can provide a new strategy for improving electrode capacity and, hence desalination performance, which so far has been limited to increasing the electrolyte concentration. A custom-built, 2/2-channel flow cell divided by two cation exchange membranes and an anion exchange membrane was fed with 50 mM NaCl as the feed (two inner channels) and 0.5 M NaCl containing up to 0.1 M phosphate as the electrode rinse (two outer channels). Using manganese oxide electrodes with phosphate buffer-mediated redox reactions exhibited an improved desalination capacity of 68.0 ± 5.2 mg g-1 (0.55 mA cm-2) and a rate of 5.6 ± 1.3 mg g-1 min-1 (0.96 mA cm-2). The improvement was attributed to the buffer that served as a proton donor for promoting the H+ insertion reaction of amorphous or poorly crystalline MnO2. Additionally, the buffering capacity against acidification and the creation of insoluble manganese phosphate on the electrode surface prevented the dissolution of Mn2+, which could otherwise occur at the anode due to a decrease in the local pH upon H+ deinsertion. Thus, the use of manganese oxide electrodes coupled with phosphate provides a new strategy of increasing electrode capacity for water desalination.

Electrode Design for MnO2-Based Aqueous Electrochemical Capacitors: Influence of Porosity and Mass Loading

The purpose of this study is to highlight the influence of some fabrication parameters, such as mass loading and porosity, which are not really elucidated and standardized during the realization of electrodes for supercapacitors, especially when using metal oxides as electrode materials. Electrode calendering, as one stage during the fabrication of electrodes, was carried out step-by-step on manganese dioxide electrodes to study the decreasing porosity effect on the electrochemical performance of a MnO₂ symmetric device. One other crucial parameter, the mass loading, which has to be understood and well used for realistic supercapacitors, was investigated concurrently. Gravimetric, areal and volumetric capacitances are highlighted, varying the porosity for low-, medium- and large-mass loading. Low-loading leads to the best specific capacitances but is not credible for realistic supercapacitors, except for microdevices. Down 50% porosities after calendering, capacitances are increased and become stable faster, suggesting a faster wettability of the dense electrodes by the electrolyte, especially for high-mass loading. EIS experiments performed on electrodes without and with calendering lead to a significant decrease of the device’s time response, especially at high loading. A high-mass loading device seems to work as a power battery, whereas electrode calendaring, which allows decreasing the time response, leads to an electrical behavior closer to that expected for a supercapacitor.

Microwave absorption enhancement by adjusting reactant ratios and filler contents based on 1D K–MnO2@PDA and poly(vinylidene fluoride) matrix

One-dimensional K–MnO₂ nanorods were prepared by a wet chemical process. Dopamine hydrochloride (PDA) layers with various thicknesses were coated and finally, the composites were filled in a poly(vinylidene fluoride) (PVDF) matrix using the hot-molding procedure. The complex permittivity and permeability of the K–MnO₂@PDA/PVDF composites could be adjusted by reactant amount ratios and filler contents. The minimum reflection loss could reach −49.4 dB and an effective absorption bandwidth (<−10 dB) covering 11.12 GHz was achieved with 20% filler content when the reactant amount ratio between K–MnO₂ and PDA was 4 : 0.375, which was derived from effective internal polarization processes. It is expected that these novel composites can be used as high-performance microwave absorbers.

The microwave absorption properties of K–MnO₂@PDA/PVDF composites are greatly enhanced due to appropriate reactant amount ratios and filler contents, which result in an effective internal polarization process.

Real-time monitoring of phenazines excretion in Pseudomonas aeruginosa microbial fuel cell anode using cavity microelectrodes

Phenazines are a kind of metabolites that can mediate extracellular Pseudomonas aeruginosa (P. aeruginosa) cells in microbial fuel cells (MFCs). However, it is still not clear that whether and how the excretion profile of phenazines is affected by the operating MFC. Here, we report a real time analysis approach based on a cavity microelectrode electrochemical sensor to investigate the phenazines excretion behavior of P. aeruginosa during MFC operation. The phenazine concentration increases at first 72 h, reaches a plateau and decreases after 120 h and also shows local dependent variation. It is dependent on the MFC current generation profile but also affect by the biofilm formation. Accordingly, a mechanism about phenazines excretion in MFC anode and the phenazines mediated extracellular electron transfer of the P. aeruginosa anode is proposed. This work provides a novel strategy for self-mediated extracellular electron transfer analysis in the operating MFCs.

A facile, morphology-controlled synthesis of potassium-containing manganese oxide nanostructures for electrochemical supercapacitor application

A chemical reduction-based, morphology-controlled synthesis of K-containing manganese oxide nanostructures for electrochemical supercapacitor application.