M. García-Gabaldón

Layer-by-Layer Modification of Cation Exchange Membranes Controls Ion Selectivity and Water Splitting

The present study investigates the possibility of inducing monovalent ion permselectivity on standard cation exchange membranes, by the layer-by-layer (LbL) assembly of poly(ethyleneimine) (PEI)/poly(styrenesulfonate) (PSS) polyelectrolyte multilayers. Coating of the (PEI/PSS)N LbL multilayers on the CMX membrane caused only moderate variation of the ohmic resistance of the membrane systems. Nonetheless, the polyelectrolyte multilayers had a substantial influence on the monovalent ion permselectivity of the membranes. Permselectivity comparable to that of a commercial monovalent-ion-permselective membrane was obtained with only six bilayers of polyelectrolytes, yet with significantly lower energy consumption per mole of Na(+) ions transported through the membranes. The monovalent ion permselectivity stems from an increased Donnan exclusion for divalent ions and hydrophobization of the surface of the membranes concomitant to their modification. Double-layer capacitance obtained from impedance measurements shows a qualitative indication of the divalent ion repulsion of the membranes. At overlimiting current densities, water dissociation occurred at membranes with PEI-terminated layers and increased with the number of layers, while it was nearly absent for the PSS-terminated layers. Hence, LbL layers allow switching on and turning off water splitting at the surface of ion exchange membranes.

Ceramic anion-exchange membranes based on microporous supports infiltrated with hydrated zirconium dioxide

Anion-exchange membranes made from inexpensive ceramic materials were synthesized by using a simple procedure based on incorporating particles of an ion exchanger into a host microporous structure. Microporous ceramics produced from alumina and kaolin were used as supports, and their internal voids were functionalized by direct precipitation of hydrated ZrO2. The addition of starch as pore former to the sintering mixture induces the formation of pores within the micrometer range, where the subsequent deposition of hydrated ZrO2 occurred preferentially. An increase in the loading of hydrated ZrO2 particles improved the ion exchange capacity (IEC) and induced anion-selective properties on the membranes. However, when more than six infiltration cycles were performed, the membrane porosity was substantially reduced. Electrochemical measurements conducted in acidic and neutral media corroborated the implication of the hydrated ZrO2 particles on the development of concentration polarization and confirmed the strong relationship existing between the membrane porosity and electrical conductivity. Conversely, chronopotentiometric curves showed that the membranes practically lack of ion-exchange properties when tested under alkaline conditions. The methodology proposed to synthesize ceramic ion-conducting membranes could significantly broaden the utilization of electromembrane processes in industrial applications where the use of polymeric membranes is restricted due to their expensive cost or poor chemical stability.

Ceramic Membranes for Continuous Regeneration of Spent Chromium Plating Baths

Ceramic membranes have been synthesised for use as separators in electrochemical reactors employed for recycling spent chromium plating baths. Different membrane synthesis process variables (raw materials, forming method, etc.) have been studied to enable producing prototypes with suitable characteristics for use as low-cost separators.

Chronopotentiometric study of ceramic cation-exchange membranes based on zirconium phosphate in contact with nickel sulfate solutions

Abstract In this article, the innovative cation-exchange membranes obtained from ceramic materials are presented. Different microporous ceramic supports were obtained from an initial mixture of alumina and kaolin, to which a varying content of starch was added in order to obtain supports with different pore size distributions. The deposition of zirconium phosphate into the porous supports generates membranes with cation-exchange properties. The fabrication of ion-exchange membranes which could resist aggressive electrolytes such as strong oxidizing spent chromium plating baths or radioactive solutions would allow the application of electrodialysis for the decontamination and regeneration of these industrial effluents. The performance of the manufactured membranes was studied in nickel sulfate solutions by means of chronopotentiometry. An increase of the membrane voltage drop during chronopotentiometric measurements was observed in some membranes, which seems to be a consequence of concentration polarizati...

Improving the Signal Propagation at 2.4 GHz Using Conductive Membranes

When IEEE 802.11 at 2.4-GHz signal crosses different surfaces, it is generally reduced, but we have seen that it does not happen for all materials. Conductive membranes are able to transport electric charges when they are submerged into water with electrolytes, so we take profit of their features in order to know in which cases the received signal strength indicator (RSSI) can be improved. In order to achieve our goal, the RSSI is measured at different distances using different environments for the membranes, air, and water environment with different conductivities (distillated water, tap water, and salty water). Results show that different membranes environment produce different signal strengths. Moreover, they can be positive or negative depending on the environment of the membranes and the distance from the access point. In some cases, we registered an increase of more than 14 dBm of the signal when we were using those membranes.