Effect of inorganic filler size on electrochemical performance of nanocomposite cation exchange membranes for salinity gradient power generation

MOF-Derived Nanoporous Carbon Incorporated in the Cation Exchange Membrane for Gradient Power Generation

Ion exchange membranes (IEMs), as a part of the reverse electrodialysis (RED) system, play an important role in salinity gradient power (SGP) generation. Structure optimization of IEMs is critical to increase the power production by RED. In this work, metal organic framework (MOF)-derived nanoporous carbons (hollow zeolitic imidazolate framework (ZIF)-derived nanoporous carbons, HZCs) were incorporated in a sulfonated poly (2, 6-dimethyl-1,4-phenylene oxide) (sPPO) membrane to prepare an organic−inorganic nanocomposite cation exchange membrane (CEM). Physicochemical properties, electrochemical properties, and power generation of the synthesized nanocomposite membranes with different HZCs loading were characterized. The results show that the incorporated HZCs could tailor the microstructure of the membrane matrix, providing a superior performance of the nanocomposite membrane. With a HZCs loading of 1.0 wt.%, the nanocomposite membrane possessed the highest permselectivity of 77.61% and the lowest area resistance of 0.42 Ω·cm², along with a super gross power density of 0.45 W/m², which was 87.5% (about 1.87 times) higher than that of the blank sPPO membrane. Therefore, incorporating of an appropriate amount of HZCs in the ion-exchange membrane can improve the performance of the membrane, providing a promising method to increase the power generation of the RED system.

Heat to Hydrogen by RED-Reviewing Membranes and Salts for the RED Heat Engine Concept

The Reverse electrodialysis heat engine (REDHE) combines a reverse electrodialysis stack for power generation with a thermal regeneration unit to restore the concentration difference of the salt solutions. Current approaches for converting low-temperature waste heat to electricity with REDHE have not yielded conversion efficiencies and profits that would allow for the industrialization of the technology. This review explores the concept of Heat-to-Hydrogen with REDHEs and maps crucial developments toward industrialization. We discuss current advances in membrane development that are vital for the breakthrough of the RED Heat Engine. In addition, the choice of salt is a crucial factor that has not received enough attention in the field. Based on ion properties relevant for both the transport through IEMs and the feasibility for regeneration, we pinpoint the most promising salts for use in REDHE, which we find to be KNO3, LiNO3, LiBr and LiCl. To further validate these results and compare the system performance with different salts, there is a demand for a comprehensive thermodynamic model of the REDHE that considers all its units. Guided by such a model, experimental studies can be designed to utilize the most favorable process conditions (e.g., salt solutions).

Principles of reverse electrodialysis and development of integrated-based system for power generation and water treatment: a review

Reverse electrodialysis (RED) is among the evolving membrane-based processes available for energy harvesting by mixing water with different salinities. The chemical potential difference causes the movement of cations and anions in opposite directions that can then be transformed into the electrical current at the electrodes by redox reactions. Although several works have shown the possibilities of achieving high power densities through the RED system, the transformation to the industrial-scale stacks remains a challenge particularly in understanding the correlation between ion-exchange membranes (IEMs) and the operating conditions. This work provides an overview of the RED system including its development and modifications of IEM utilized in the RED system. The effects of modified membranes particularly on the psychochemical properties of the membranes and the effects of numerous operating variables are discussed. The prospects of combining the RED system with other technologies such as reverse osmosis, electrodialysis, membrane distillation, heat engine, microbial fuel cell), and flow battery have been summarized based on open-loop and closed-loop configurations. This review attempts to explain the development and prospect of RED technology for salinity gradient power production and further elucidate the integrated RED system as a promising way to harvest energy while reducing the impact of liquid waste disposal on the environment.

Heterogeneous PVC cation-exchange membrane synthesis by electrospinning for reverse electrodialysis

Blue energy (or salinity gradient energy) is a renewable, carbon-neutral, and continuous electrical energy source that can be obtained via the reverse electrodialysis (RED) technique. The viability of this technology strictly depends on the performance and cost of the ion-exchange membranes (IEMs) that compose the RED units; designing the optimal membrane represents a critical challenge due to the complex relation between the performance, properties, and structure of the membrane. In this work, we present our findings on an electrospun cation-exchange membrane based on polyvinyl chloride (PVC), a strongly acidic cation exchange resin, with sodium dodecyl sulfate (SDS) as an additive. We contrast it with a similar membrane produced with the more conventional casting solution technique. The electrospinning technique provides thinner and more homogeneous membranes than those synthesized via casting. The membranes were characterized using morphological, spectroscopic, and analytical methods. Scanning electron microscopy images depicted an intertwined nanofiber mesh within the membrane. We also synthesized the same electrospun cation exchange membrane without SDS; this membrane presented 63% less swelling, and a significant increase in the fixed charge density (CDfix) (119.6 meq/g) when compared to its casting solution counterpart (34 meq/g). This suggests an enhanced permselectivity, and thus better performance for blue energy generation in RED units.

High Performance Hybrid Energy Storage with Potassium Ferricyanide Redox Electrolyte

We demonstrate stable hybrid electrochemical energy storage performance of a redox-active electrolyte, namely potassium ferricyanide in aqueous media in a supercapacitor-like setup. Challenging issues associated with such a system are a large leakage current and high self-discharge, both stemming from ion redox shuttling through the separator. The latter is effectively eliminated when using an ion exchange membrane instead of a porous separator. Other critical factors toward the optimization of a redox-active electrolyte system, especially electrolyte concentration and volume of electrolyte, have been studied by electrochemical methods. Finally, excellent long-term stability is demonstrated up to 10 000 charge/discharge cycles at 1.2 and 1.8 V, with a broad maximum stability window of up to 1.8 V cell voltage as determined via cyclic voltammetry. An energy capacity of 28.3 Wh/kg or 11.4 Wh/L has been obtained from such cells, taking the nonlinearity of the charge-discharge profile into account. The power performance of our cell has been determined to be 7.1 kW/kg (ca. 2.9 kW/L or 1.2 kW/m(2)). These ratings are higher compared to the same cell operated in aqueous sodium sulfate. This hybrid electrochemical energy storage system is believed to find a strong foothold in future advanced energy storage applications.