Salinity gradient energy can be directly converted to electrical power using reverse electrodialysis (RED) and other technologies, but reported power densities have been too low for practical applications. Here, the RED stack performance was improved by using 2,6-dihydroxyanthraquinone and ferrocyanide as redox couples. These electrolytes were then used in a flow battery, to produce an integrated RED stack and flow battery (RED-FB) system capable of capturing, storing, and discharging salinity gradient energy. Energy captured from the RED stack was discharged in the flow battery at a maximum power density of 3.0 kW/m2-anode, which was similar to the flow batteries charged by electrical power and could be used for practical application. Salinity gradient energy captured from the RED stack was recovered from the electrolytes as electricity with a 30% efficiency, and the maximum energy density of the system was 2.4 kWh/m3-anolyte. The combined RED-FB system overcomes many limitations of previous approaches to capture, store, and use salinity gradient energy from natural or engineered sources.