Energy Harvesting from Brines by Reverse Electrodialysis Using Nafion Membranes

Abstract

Ion exchange membranes (IEMs) have consolidated applications in energy conversion and storage systems, like fuel cells and battery separators. Moreover, in the perspective to address the global need for non-carbon-based and renewable energies, salinity-gradient power (SGP) harvesting by reverse electrodialysis (RED) is attracting significant interest in recent years. In particular, brine solutions produced in desalination plants can be used as concentrated streams in a SGP-RED stack, providing a smart solution to the problem of brine disposal. Although Nafion is probably the most prominent commercial cation exchange membrane for electrochemical applications, no study has investigated yet its potential in RED. In this work, Nafion 117 and Nafion 115 membranes were tested for NaCl and NaCl + MgCl2 solutions, in order to measure the gross power density extracted under high salinity gradient and to evaluate the effect of Mg2+ (the most abundant divalent cation in natural feeds) on the efficiency in energy conversion. Moreover, performance of commercial CMX (Neosepta) and Fuji-CEM 80050 (Fujifilm) cation exchange membranes, already widely applied for RED applications, were used as a benchmark for Nafion membranes. In addition, complementary characterization (i.e., electrochemical impedance and membrane potential test) was carried out on the membranes with the aim to evaluate the predominance of electrochemical properties in different aqueous solutions. In all tests, Nafion 117 exhibited superior performance when 0.5/4.0 M NaCl fed through 500 µm-thick compartments at a linear velocity 1.5 cm·s−1. However, the gross power density of 1.38 W·m−2 detected in the case of pure NaCl solutions decreased to 1.08 W·m−2 in the presence of magnesium chloride. In particular, the presence of magnesium resulted in a drastic effect on the electrochemical properties of Fuji-CEM-80050, while the impact on other membranes investigated was less severe.

Tuning the Electrochemical Properties of Novel Asymmetric Integral Sulfonated Polysulfone Cation Exchange Membranes

“…However, heterogeneous IEMs have several prominent advantages from a mechanical strength and cost-effectiveness point of view [ 12 ]. An order of magnitude reduction in the suitable homogeneous IEM price is required for an economically feasible RED operation [ 13 , 14 ].…”

“…However, heterogeneous IEMs have several prominent advantages from a mechanical strength and cost-effectiveness point of view [12]. An order of magnitude reduction in the suitable homogeneous IEM price is required for an economically feasible RED operation [13,14]. Different preparation methods were described in the literature for homogenous IEMs: (i) the polycondensation of a charged monomer, (ii) the functionalization of a prepared polymer film, and (iii) the preparation of membrane from a dissolved polyelectrolyte [15].…”

Effects of Hydration and Temperature on the Microstructure and Transport Properties of Nafion Polyelectrolyte Membrane: A Molecular Dynamics Simulation

“…The chemical structure of Nafion [ 36 ] is shown in Figure 1 , for Nafion 117, x = 7 and y = z = 1. In this work, each Nafion chain consisted of 10 monomers, so the n in Figure 1 is 10.…”

The Application of Cation Exchange Membranes in Electrochemical Systems for Ammonia Recovery from Wastewater

“…However, the sulfonic acid groups attached to the polymer chains in the CEMs increase the hydrophilicity of the membranes, which facilitates the water uptake of a CEM. The water uptake of a typical CEM, Nafion N117, is 11.7%, owing to the hydrophilic portions of the membrane as well as the existence of hydrated ionic groups inside the membrane [ 69 ].…”