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

Abstract

Reverse electrodialysis (RED) is a technology to generate electricity from two streams with different salinities. While RED systems have been conventionally used for electricity generation, recent works explored combining RED for production of valuable gases. This work investigates the feasibility of producing hydrogen and chlorine in addition to electricity in an RED stack and identifies potential levers for improvement. A simplified one-dimensional model is adopted to assess the technical and economic feasibility of the process. We notice a strong disparity in typical current densities of RED fed with seawater and river water and that in typical water (or chloralkali) electrolysis. This can be partly mitigated by using brine and seawater as RED feeds. Considering such an RED system, we estimate a hydrogen production of 1.37 mol/(m 2 h) and an electrical power density of 1.19 W/m 2 . Although this exceeds previously reported hydrogen production rates in combination with RED, the levelized costs of products are 1−2 orders of magnitude higher than the current market prices at the current state. The levelized costs of products are very sensitive to the membrane price and performance. Hence, going forward, manufacturing thinner and highly selective membranes is required to make the system competitive against the consolidated technologies.

Counter-ion Conductivity and Selectivity Trade-Off for Commercial Ion-Exchange Membranes at High Salinities

“…6−9 Recently, there has been growing interest in using IEMs in additional applications that involve highly saline solutions. These include treatment of desalination brines and wastewater from oil and gas extraction via electrodialysis, 10−12 energy generation from brines using reverse electrodialysis, 13,14 mineral extraction from naturally occurring brines, 15−17 and hydrogen production via direct seawater electrolysis. 18,19 However, exposing IEMs to concentrated salt solutions can significantly worsen their performance, as the ability of IEMs to selectively transport ions stems from their higher charge concentrations compared to the surrounding solution.…”

“…Notable exceptions, wherein significantly greater concentrations are utilized, include chlorine/caustic soda production via the chlor-alkali process and salt production via a combination of electrodialysis and crystallization, as demonstrated in Japan, Korea, Taiwan, and Kuwait. − Recently, there has been growing interest in using IEMs in additional applications that involve highly saline solutions. These include treatment of desalination brines and wastewater from oil and gas extraction via electrodialysis, − energy generation from brines using reverse electrodialysis, , mineral extraction from naturally occurring brines, − and hydrogen production via direct seawater electrolysis. , However, exposing IEMs to concentrated salt solutions can significantly worsen their performance, as the ability of IEMs to selectively transport ions stems from their higher charge concentrations compared to the surrounding solution. To advance the previously mentioned technologies, it is crucial to develop better performing IEMs under high-salinity conditions.…”

Predicting the Conductivity–Selectivity Trade-Off and Upper Bound in Ion-Exchange Membranes

“…In the context of CO 2 electrolysis for carbon capture, , the transport of co-ions across AEMs influences the hydration and stability of the membrane, the activity and selectivity of the catalyst, − and salt precipitation on the gas-diffusion electrodes. ,, Effectively managing co-ion selectivity while preserving counter-ion conductivity is crucial for optimizing product output and prolonging the life of the membrane–electrode assembly. Recent studies have also explored the impact of cations transporting alongside OH – across AEMs in water electrolysis for hydrogen fuel production. − Here, electrolytes like KOH, neutral salts, seawater, and impure water sources serve as alternatives to ultrapure DI water, which is expensive to produce. − Co-ion transport across AEMs can enhance catalyst activity, − but if left unregulated, it may lead to the large buildup of pH gradients (with the use of near-neutral pH feeds) and catalyst fouling. , Lastly, in emerging salinity gradient power technologies, such as reverse electrodialysis, the counter-ion/co-ion selectivity of IEMs plays a central role in determining the efficiency of the device. − …”