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In this work, a membraneless microbial fuel cell (MFC) with an empty volume of 1.5 mL, fed continuously with hydrolysed urine, was tested in supercapacitive mode (SC-MFC). In order to enhance the power output, a double strategy was used: i) a double cathode was added leading to a decrease in the equivalent series resistance (ESR); ii) the apparent capacitance was boosted up by adding capacitive features on the anode electrode. Galvanostatic (GLV) discharges were performed at different discharge currents. The results showed that both strategies were successful obtaining a maximum power output of 1.59 ± 0.01 mW (1.06 ± 0.01 mW mL−1) at pulse time of 0.01 s and 0.57 ± 0.01 mW (0.38 ± 0.01 mW mL−1) at pulse time of 2 s. The highest energy delivered at ipulse equal to 2 mA was 3.3 ± 0.1 mJ. The best performing SC-MFCs were then connected in series and parallel and tested through GLV discharges. As the power output was similar, the connection in parallel allowed to roughly doubling the current produced. Durability tests over ≈5.6 days showed certain stability despite a light overall decrease., Graphical abstract Image 1, Highlights • Air-breathing microbial fuel cell was tested in supercapacitive mode. • A double cathode addition lead to a decrease in ohmic resistance. • Apparent capacitance was boosted up by adding capacitive features. • Maximum power output of 1.59 mW (1.06 mW mL−1) was reached at tpulse 0.01s. • Series and parallel connections improved the galvanostatic discharges.

Supercapacitive microbial fuel cells (SC-MFCs) are an emerging and promising field that has captured the attention of scientists in the past few years. This hybridization consists in the integration of supercapacitive features in the MFC electrodes to boost the performance output. The MFC anaerobic and aerobic enviroments induce self-polarization of the electrodes. The electrodes can be discharged galvanostatically and then self-recharged by the biotic/abiotic environments. During the discharge, two main phenomena named electrostatic and faradaic take place but the separation and quantification of the two contributes seems to be challenging. Galvanostatic discharges of SC-MFC produce at least one order of magnitude higher current/power compared with continuous operations, making it promising for pulsed type applications.

© 2020 Elsevier Ltd Metal recovery from wastes is essential for a circular economy and minimising present-day society environmental footprint. In this study, we combined electrodialysis with bioleaching of fly ashes for enhanced metal recovery from municipal solid waste incineration residues. Results showed that the use of low-level direct current with acidophilic bacteria enhanced metal recovery in the catholyte when compared to the abiotic experiment supplied with direct current and the bioleaching experiment without direct current. The use of electrodialysis with bioleaching showed increased performance on the removal and recovery of metals in the catholyte such as Al, Cd, Co, Li, Pb, and Zn. While Co and Ni were selectively mobilised by bioleaching, Cu, Cr, Cd and Li showed highly elevated concentrations by combining both techniques. These results are proof of concept of combined methods will allow optimising the process, especially varying the liquid to solid ratio, mixing, duration of the experiments, and pH control in the anolyte.

A self-stratified microbial fuel cell fed with human urine with a total internal volume of 0.55 ml was investigated as an internal supercapacitor, for the first time. The internal self-stratification allowed the development of two zones within the cell volume. The oxidation reaction occurred on the bottom electrode (anode) and the reduction reaction on the top electrode (cathode). The electrodes were discharged galvanostatically at different currents and the two electrodes were able to recover their initial voltage value due to their red-ox reactions. Anode and cathode apparent capacitance was increased after introducing high surface area activated carbon embedded within the electrodes. Peak power produced was 1.20 ± 0.04 mW (2.19 ± 0.06 mW ml−1) for a pulse time of 0.01 s that decreased to 0.65 ± 0.02 mW (1.18 ± 0.04 mW ml−1) for longer pulse periods (5 s). Durability tests were conducted over 44 h with ≈2600 discharge/recharge cycles. In this relatively long-term test, the equivalent series resistance increased only by 10% and the apparent capacitance decreased by 18%., Graphical abstract Image 1, Highlights • Supercapacitive microbial fuel cells fed with human urine were investigated. • Galvanostatic discharges were studied and key parameters presented. • ESR and capacitance were improved by adding supercapacitive features. • Highest power obtained was 1.20 ± 0.04 mW (2.19 ± 0.06 mW ml−1) for a tpulse of 0.01 s. • Stability over 2600 cycles of discharge/self-recharge (44 h) was shown.

Graphical abstract Supercapacitive Microbial Desalination Cell is here presented with unprecedented performances. Anode and cathode act as negative and positive electrode of an internal supercapacitor that is discharged and self-recharged. Maximum power of 3 W m−2 is recorded., Highlights • The concept of supercapacitive microbial desalination cell is here presented. • The device is able to degrade organics, desalinate and generate power simultaneously. • An additional electrode overcomes cathode ohmic losses and boost up power output. • Maximum power achieved was 3.0 W m−2 (2.1 mW). • 7600 discharge/self-recharge cycles were demonstrated over 44 h., In this work, the electrodes of a microbial desalination cell (MDC) are investigated as the positive and negative electrodes of an internal supercapacitor. The resulting system has been named a supercapacitive microbial desalination cell (SC-MDC). The electrodes are self-polarized by the red-ox reactions and therefore the anode acts as a negative electrode and the cathode as a positive electrode of the internal supercapacitor. In order to overcome cathodic losses, an additional capacitive electrode (AdE) was added and short-circuited with the SC-MDC cathode (SC-MDC-AdE). A total of 7600 discharge/self-recharge cycles (equivalent to 44 h of operation) of SC-MDC-AdE with a desalination chamber filled with an aqueous solution of 30 g L−1 NaCl are reported. The same reactor system was operated with real seawater collected from Pacific Ocean for 88 h (15,100 cycles). Maximum power generated was 1.63 ± 0.04 W m−2 for SC-MDC and 3.01 ± 0.01 W m−2 for SC-MDC-AdE. Solution conductivity in the desalination reactor decreased by ∼50% after 23 h and by more than 60% after 44 h. There was no observable change in the pH during cell operation. Power/current pulses were generated without an external power supply.

The use of ionic liquids based on 1-buthyl-3-methyl-imidazolium as electrolytes in an activated carbon//poly(3-methylthiophene) hybrid supercapacitor was investigated. Preliminary results of the electrochemical characterization of electrodes sized for practical use in the supercapacitor and of a laboratory scale cell are reported and compared to those with propylene carbonate-tetraethylammonium tetrafluoroborate as electrolyte. Keywords: Ionic liquid, Supercapacitor, Poly(3-methylthiophene), Activated carbon, Electrolyte