Active Control of Irreversible Faradic Reactions to Enhance the Performance of Reverse Electrodialysis for Energy Production from Salinity Gradients

Abstract

Irreversible faradic reactions in reverse electrodialysis (RED) are an emerging concern for scale-up, reducing the overall performance of RED and producing environmentally harmful chemical species. Capacitive RED (CRED) has the potential to generate electricity without the necessity of irreversible faradic reactions. However, there is a critical knowledge gap in the fundamental understanding of the effects of operational stack voltages of CRED on irreversible faradic reactions and the performance of CRED. This study aims to develop an active control strategy to avoid irreversible faradic reactions and pH change in CRED, focusing on the effects of a stack voltage (0.9− 5.0 V) on irreversible faradic reactions and power generation. Results show that increasing the initial output voltage of CRED by increasing a stack voltage has an insignificant impact on irreversible faradic reactions, regardless of the stack voltage applied, but a cutoff output voltage of CRED is mainly responsible for controlling irreversible faradic reactions. The CRED system with eliminating irreversible faradic reactions achieved a maximum power density (1.6 W m −2 ) from synthetic seawater (0.513 M NaCl) and freshwater (0.004 M NaCl). This work suggests that the control of irreversible faradic reactions in CRED can provide stable power generation using salinity gradients in large-scale operations.

Fouling and Mitigation Behavior of Foulants on Ion Exchange Membranes with Surface Property in Reverse Electrodialysis

“…A bench-scale RED stack is composed of twenty cell pairs (twenty-one CEMs and twenty AEMs), polytetrafluoroethylene (PTFE) spacers (0.1 mm thickness) between the membranes, and a pair of platinum-coated titanium mesh electrodes (50 mm diameter, Sung Wing Technology Co., Hong Kong, China) at both ends of a bench-scale RED stack as described in the previous study [ 20 , 27 ]. It was operated at room temperature (22 ± 2 °C).…”

Feasibility of Producing Electricity, Hydrogen, and Chlorine via Reverse Electrodialysis

“…Recent developments in RED such as the use of profiled membranes 2 and electrode segmentation 3 have improved the overall performance of the system. The research focusing on the impact of RED feeds, 4 membrane permselectivity, 5 concentration of multivalent ions in RED feed solutions, 6 use of capacitive electrodes, 7 and co-ion and osmotic transport 8,9 has provided a deeper understanding and facilitated the construction of prototypes and pilot plants from the lab scale. 10,11 While RED has been conventionally used for electricity generation, a part of the obtained energy is utilized at the electrodes to perform the redox reactions.…”

Fouling Mitigation of Ion Exchange Membranes in Energy Conversion Devices

“…Energy conversion devices being developed recently require polymeric electrolytes for ion conduction [1][2][3][4][5][6][7][8][9][10][11][12][13], which are generally called ion-exchange membranes (IEMs). IEMs have a special property to exclude coions which have the same charge to covalently fixed functional groups such as sulfonic acid groups for cation exchange membranes (CEMs) or quaternary ammonium groups for anion exchange membranes (AEMs).…”

“…RED uses the cell configuration to separate two main streams by alternately assembled CEMs and AEMs to provide permselective ion transports of cations and anions through CEMs and AEMs, respectively [6,8], along with the reversible redox couple such as ferri-/ferrocyanide (Fe(CN) 6 3− /Fe(CN) 6 4− ) in an electrode stream. As mentioned, membrane fouling is unavoidable problems to result in a decrease in harvesting electrical energy due to an increase in electrical resistance of IEMs which is generally caused by the interaction with non-charged and charged inorganic/organic matters [15][16][17][18][21][22][23].…”