Energy Conversion From Salinity Gradient Using Microchip With Nafion Membrane

Abstract

When a concentrated salt solution and a diluted salt solution are separated by an ion-selective membrane, cations and anions would diffuse at different rates depending on the ion selectivity of the membrane. The difference of positive and negative charges at both ends of the membrane would produce a potential, called the diffusion potential. Thus, electrical energy can be converted from the diffusion potential through reverse electrodialysis. This study demonstrated the fabrication of an energy conversion microchip using the standard micro-electromechanical technique, and utilizing Nafion junction as connecting membrane, which was fabricated by a surface patterned process. Through different salinity gradient of potassium chloride solutions, we experimentally investigated the diffusion potential and power generation from the microchip, and the highest value measured was 135 mV and 339 pW, respectively. Furthermore, when the electrolyte was in pH value of 3.8, 5.6, 10.3, the system exhibited best performance at pH value of 10.3; whereas, pH value of 3.8 yielded the worst.

High Osmotic Power Generation via Nanopore Arrays in Hybrid Hexagonal Boron Nitride/Silicon Nitride Membranes

“…When considering reverse electrodialysis, membranes with excellent cationic/anionic selectivity, low resistivity, good mechanical stability, and antifouling properties are required for their practical usability and potential scalability. Most of the research in osmotic energy has focused on the development of nanoporous membranes from various advanced materials, including polymers − and ceramics, ,− because of their mechanical stability and rich chemistry that enables unique ionic selectivity tuning. However, the thickness of these materials (≥500 nm) lowers the osmotic conductance, and lack of precision over the pore size distribution limits the obtainable power density.…”

Power Generation by Reverse Electrodialysis in a Microfluidic Device with a Nafion Ion-Selective Membrane

“…The redox potential produced at different concentration ratios ( C H : C L ) can be expressed by the following Nernst relation [ 24 , 25 ]: where R , T , z , F and γ are the gas constant, absolute temperature, charge number, Faraday constant and mean activity coefficient, respectively. The diffusion potential can be expressed as [ 21 ]: where is the transference number for the cations and can be expressed as t + = j + /( j + + j − ), where j + and j − are the cation and anion fluxes, respectively. The transference number provides an index of the ion selectivity of the membrane.…”

“…For an RED system, the energy conversion efficiency is defined as the ratio of the output electrical energy to the input Gibbs free energy of mixing. Moreover, the efficiency obtained under the maximum power condition, η max, power , can be expressed as [ 21 , 27 ]: …”

“…In particular, it was shown that for the considered nanopores, the highest diffusion coefficient and power generation (45 pW) were obtained using the KCl solution. Chang et al [ 21 ] investigated the diffusion potential and power generation performance of a microchip containing a Nafion ion-selective membrane given the use of three different electrolyte solutions with pH values of 3.8, 5.6 and 10.3, respectively. The performance of the device was found to improve with an increasing pH value, with a diffusion potential of 135 mV and a power generation of 339 pW observed for the electrolyte with a pH value of 10.3.…”