Abstract
Salinity-gradient power (SGP), generated through reverse electrodialysis (RED), offers a promising low-carbon solution for energy recovery from seawater–river gradients and desalination brines. However, large-scale deployment is hindered by mineral scaling on ion-exchange membranes (IEMs), which increases electrical resistance and accelerates the performance degradation. This study investigated the individual and synergistic effects of gypsum and silica scaling on RED performance, using model solutions that replicate typical desalination brines. Under pure NaCl conditions, the open-circuit voltage (OCV) reached 0.82 V, and the power density (Pd) was approximately 1.1 W/m2 at an optimal reverse current of 0.12 A. The introduction of gypsum reduced the OCV and Pd to 0.67 V and 0.78 W/m2, while silica fouling caused declines to 0.78 V and 0.70 W/m2, respectively. Notably, when gypsum and silica coexisted, a pronounced synergistic fouling effect was observed, resulting in an OCV decrease to 0.59 V and nearly 50% loss in Pd. Electrochemical analysis and SEM/EDS membrane autopsies revealed that crystalline gypsum and amorphous silica formed compact composite layers, markedly increasing stack resistance and accelerating performance deterioration beyond the sum of individual effects. The study revealed that multivalent ions dominate gypsum scaling, which thickens boundary layers, elevates stack resistance, and suppresses power output. Comparative analysis demonstrated that cation-exchange membranes (CEMs) were more resistant to scaling than anion-exchange membranes (AEMs). Overall, the study clarifies fouling mechanisms in RED stacks and provides practical guidance for integrating RED with membrane distillation (MD) to achieve energy-efficient desalination.