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.
Keywords: AC, activated carbon; AEM, anion exchange membrane; AdE, additional electrode; Additional Electrode (AdE); BES, bioelectrochemical system; CB, carbon black; CDI, capacitive deionization; CEM, cation exchange membrane; Canode, anode capacitance; Ccathode, cathode capacitance; Ccell, cell capacitance; Cell ESR, equivalent series resistance of the cell; DC, desalination chamber; DI, deionized water; EDLC, electrochemical double layer capacitor; Epulse, energy obtained by the pulse; Fe-AAPyr, iron aminoantypirine; GLV, galvanostatic discharges; High power generation; KCl, potassium chloride; KPB, potassium phosphate buffer; MDC, membrane capacitive deionization; MDC, microbial desalination cell; MFC, microbial fuel cell; NaCl, sodium chloride; NaOAc, sodium acetate; OCV, open circuit voltage; ORR, oxygen reduction reaction; PGM-free, platinum group metals-free; PTFE, polytetrafluoroethylene; Pmax, maximum power; Power/current pulses; Ppulse, power obtained by the pulse; RA, anodic anode ohmic resistance; RC, cathodeic ohmic resistance; RO, reverse osmosis; SC, solution conductivity; SC-MDC, supercapacitive microbial desalination cell; SC-MDC-AdE, supercapacitive microbial desalination cell with additional electrode; SC-MFC, supercapacitive microbial fuel cell; SHE, standard hydrogen electrode; Supercapacitive Microbial Desalination Cell (SC-MDC); Transport phenomena; V+, oc, cathode potential in open circuit; Vmax, OC, original maximum voltage in open circuit condition; Vmax, practical voltage; V−, oc, anode potentials in open circuit; ipulse, , current pulses; tpulse, time of the pulse; trest, rest time; ΔVcapacitive, difference between Vmax and Vfinal (at the end of tpulse), voltage capacitive decrease drop; ΔVohmic, cathode, cathode ohmic drop; ΔVohmic, difference between Vmax,OC and Vmax, ohmic drop.