Reverse electrodialysis (RED) is an electrically driven process for the extraction of usable energy from the Gibbs free energy of mixing. Past research efforts have focused on the improvement of power density through higher voltages, large cell numbers, and overall reduction of stack resistance, yet the process remains far from optimized. One of the principal problems is the shadow spacer effect where limited conductivity near the spacer decreases the amount of electrical transport. We have improved this technology by incorporating ion exchange wafers in each cell, shortening the diffusion pathways, limiting the shadow spacer effect, and obtaining net power densities of approximately 0.32 W/m(2) for reverse electrodeionization (REDI) compared to 0.01 W/m(2) for the RED case. Further, we have found that applying voltage to the system gives an increase in the overall power extraction efficiency due to wafer optimization and the non-ohmic behavior at low voltages. This is the first study incorporating electrodeionization techniques in RED systems. We also investigated the use of REDI in hydraulic fracturing and obtained a net power density of approximately 0.79 W/m(2) using produced water. This technology could be utilized for processing of produced water from hydraulic fracturing operations to provide some of the power used at the well site (when mixing with fresh water for re-fracking) with no greenhouse gas emissions. Using REDI at fracking sites, an industrial process that has been mired by environmental concerns can take positive steps toward developing and adopting sustainable practices. (c) 2016 Published by Elsevier B.V.