Controlled movement of ionic species in confined space is a critical physicochemical process for electrochemical energy stored in synthetic and biological nanosystems, and in conversion of electrical signals. Naturally, many organisms possess intrinsic skills to convert intracellular energy into action potentials with nanoscale ionic conductors in form of ionic pumps and channels, termed as bioelectrogenesis.
A case in point is the electric eel (Electrophorus electricus). Its electric organs are stacked with electrocyte cells linked in parallel and series and generating approximately 600-volt electrical shocks. Motivated by this functionality, ion-channel-mimetic nanofluidic systems have been developed into layered 2-dimensional nanomaterials necessary for energy conversion as well as storage. These have exhibited potential applications for supercapacitors, water treatment, and tailored diagnostics.
Researchers led by professor Wei Guo from Chinese Academy of Sciences developed a 2D-nanofluidic reverse electrodialysis system consisting positively or negatively charged nanochannels cascaded in graphene oxide membranes. They focused on demonstrating the system’s application for effective osmotic energy conversion. Via pre-assembly modification, surface charge polarity of the 2D nanochannels was covalently tuned from negative to positive. Their work is published in peer-reviewed journal, Advanced Functional Materials.
1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide was added to a graphene oxide dispersion in N,Ndimethylformamide and the mixture stirred followed by 1-aminopropyl-3- methylimidazolium bromide addition. The authors isolated the resulting positively charged graphene oxide by centrifuging. Hydrochloric acid was added in a bid to exchange the counter bromide ions with chloride.
Graphene oxide dispersion was filtered via a cellulose ester membrane and dried to eliminate residual water. The authors adopted a mild thermal annealing process in order to enhance water stability of the hydrophilic graphene oxide membranes. The researchers set the interlayer gap between the graphene oxide membranes to about 1 nm. By coupling a pair of oppositely charged membranes into a 3-compartment electrochemical cell, initiated by a two-way transmembrane chemical gradient, cations were moved preferentially by negative membrane to one side, while anions were apt to move to the other side via the positive graphene oxide membrane. This led to perfect charge separation and created superposed potential difference as well as an ionic flux between the two electrodes.
The researchers found that the output power density was about 0.77Wm-2 when sea water was mixed with river water with 0.5 and 0.01 molar sodium chloride concentrations, respectively. The power density was approximately 54% higher than when using commercial ion exchange membranes. Tandem alternating graphene oxide membrane pairs generated up to 2.7V that could be used to power electronic gadgets. Apart from the simple salt solutions, renewable electrolyte solutions including acid rain, industrial waste water, fruit juice, physiological electrolyte from human metabolism, and thermolytic solutions can be applied as energy sources.
This is the first time that osmotic power harvested from synthetic nanofluidic devices can power real electronic apparatus. These results provide an elementary approach for developing cascading nanofluidic circuits for various applications in water treatment and biomedicine.
Jinzhao Ji1, Qian Kang2,3,4, Yi Zhou2,5, Yaping Feng2, Xi Chen1, Jinying Yuan1, Wei Guo2, Yen Wei1, and Lei Jiang2Osmotic Power Generation with Positively and Negatively Charged 2D Nanoﬂuidic Membrane Pairs. Advanced Functional Materials 2017, 27, 1603623.Show Affiliations
- Department of Chemistry and Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing, P. R. China
- CAS Key Laboratory of Bio-inspired Materials and Interfacial Science, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, P. R. China
- Department of Chemistry, Northeast Normal University, Changchun, Jilin, P. R. China</li
- Department of Chemistry, Capital Normal University, Beijing, P. R. China
- School of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing, P. R. China
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