The Feasibility of Energy Extraction from Acidic Wastewater by Capacitive Mixing with a Molecular-Sieving Carbon Cathode

Capacitive mixing is a newly emerging technique for the production of renewable energy from differences in salinity. The method is based on the controlled mixing of two streams with different salt concentrations which are alternatingly brought into contact with pre-charged porous electrodes, taking advantage of the fact that modification of the electrical double layer of the electrodes results in changes in the solution salinity. In most research, the renewable energy resources are seawater and river water. Here, we demonstrate that energy extraction by capacitive mixing can take place with acidic wastewater and seawater as energy resources. This concept is proved by means of the fabrication of a proton-selective carbon cathode (the negatively polarized electrode), achieved by carbonation of cellulose filter paper, followed by mild activation in concentrated nitric acid. Considerable energy extraction was demonstrated even when the concentration of the saline solution was tenfold that of the acidic solution.