In the quest to harness the untapped potential of salinity gradient energy, researchers have made significant strides in understanding the performance of ion-exchange membranes (IEMs), a critical component in reverse-electrodialysis (RED) technology. A recent study, published in the journal *Separations* (formerly known as *Separations*), led by Junyi Lv from the Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education at Dalian University of Technology, sheds light on the factors influencing the permselectivity of IEMs, a key determinant in the efficiency of RED systems.
Reverse-electrodialysis technology holds promise for generating power and producing hydrogen by converting the salinity gradient energy between concentrated and diluted solutions into electromotive force (EMF). However, the efficiency of RED stacks heavily relies on the permselectivity of the ion-exchange membranes used. Permselectivity refers to the membrane’s ability to selectively allow certain ions to pass through while blocking others, a crucial factor in maximizing energy conversion.
Lv and his team conducted a comprehensive experimental evaluation to investigate the influences of solution concentration, ion species, and solution temperature on the permselectivity of IEMs. Their findings reveal that the permselectivity of IEMs decreases with increasing concentrations of potassium acetate (KAc), lithium chloride (LiCl), and lithium bromide (LiBr) solutions, for both concentrated and dilute solutions.
The study also compared the permselectivity of different ionic species. “We found that potassium ions (K+) demonstrate a higher permselectivity than lithium ions (Li+), and both are smaller than ammonium ions (NH4+) under the same conditions,” Lv explained. Additionally, when testing different anions with potassium salts, the permselectivity order was acetate (Ac−) > bromide (Br−) > chloride (Cl−).
Temperature also played a significant role in the permselectivity of IEMs. A slight increase in solution temperature enhanced permselectivity due to increased ionic mobility. However, excessive temperatures were found to be detrimental to membrane stability, ultimately reducing permselectivity.
The research highlights that ions with low hydration energy, a small hydration radius, and high mobility exhibit higher permselectivity. This understanding could pave the way for the development of more efficient IEMs tailored for specific ionic species and conditions, ultimately enhancing the performance of RED technology.
The commercial implications of this research are substantial. As the world seeks sustainable and renewable energy sources, salinity gradient energy presents a largely untapped resource. Improving the efficiency of RED technology through advanced IEMs could make a significant impact on the energy sector, contributing to a more diverse and sustainable energy mix.
Lv’s work not only advances our scientific understanding but also brings us closer to practical applications. “Our findings provide a foundation for optimizing IEMs and improving the overall efficiency of RED systems,” Lv stated. This research is a stepping stone towards more efficient and cost-effective energy solutions, potentially revolutionizing the way we harness energy from salinity gradients.
As the energy sector continues to evolve, the insights gained from this study will be instrumental in shaping future developments in RED technology and other membrane-based processes. The journey towards sustainable energy is complex, but with each breakthrough, we edge closer to a cleaner, more efficient energy future.