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Tianjin University’s Research Achievements Published in Nature

 

Inspired by stomata in cactus plants, which allow water in at night but close up in hotter and drier conditions, Tianjin University Professor Michael D. Guiver and his co-workers have successfully prepared a self-humidifying membrane with high ionic conductivity in high temperature and low humidity conditions. Michael is a professor in the State Key Laboratory of Engine Combustion of Tianjin University and was involved in the National 1000-plan for Foreign Experts. The study was published online in the April 28th issue of Nature.

The paper titled “Nanocrack-regulated self-humidifying membranes” was completed by Professor Michael and Professor Young Moo Lee from Hanyang University (Korea) together, with Michael a co-corresponding author of the paper. In high temperature and low humidity conditions, the dehydration of ion-exchange membranes results in ionic conductivity greatly decreasing. Concentrating on this problem, Michael and colleagues have successfully prepared self-humidifying membranes maintaining high ionic conductivity in high temperature and low humidity conditions.

 

The basic concept of self-humidifying nanovalved membrane

a. A hydrophobic coating layer provides a self-controlled mechanism for water conservation using nanometre-sized cracks (nanocracks) tuned by membrane swelling behavior in response to external humidity conditions, which act as nanovalves.

b. Atomic Force Microscope images reveal the self-controlled mechanism of plasma-coated membranes.

c. Voronoi diagram analysis and tessellation entropy verified controllable nanocrack surface pattern images of plasma-coated membrane in hydration and dehydration.

Ion-exchange membranes are widely used in ion conduction, water filtration, power generation by reverse electro dialysis, energy storage and flow batteries. Since water content directly affects the ion transportation in the membranes, membrane hydration is of great importance to many applications, especially proton-exchange membrane fuel cells and reverse electro dialysis. Usually, external hydration systems were used to keep the membranes hydrated, but the system was complex and the cost was very high. Membrane hydration has become one of the technical bottle-necks limiting the large scale application of proton-exchange membrane fuel cells. In recent decades, scientists have made great progress in regulating chemical structures, micro-morphology even segment composition of polymeric matrixes, to combine the hydrophobic and hydrophilic properties, but they failed to solve the fundamental problem of the water-conserving effect decreasing rapidly under high temperatures.

Michael and his colleagues developed a smart self-regulating surface-modified membrane without external humidification, and the surface-modification technique can be used on a variety of membranes. They deposited a thin layer (8 – 260 nanometers thick) of a highly water-repellent material on the surface of the membrane, helping the membrane to retain moisture by swelling after absorbing water and contracting after losing water. The nanocracks on the membrane’s surface expand in high-humidity environments as the membrane swells, allowing the membrane to absorb more water and rapidly transport ions. But nanocracks close in low-humidity conditions, substantially decreasing water evaporation from the membrane, and retaining relatively high ionic conductivity. Herein, the nanocracks work as nanoscale valves. The experiments show that this technique improves ion transportation significantly in high temperature and low humidity condition.

The clever surface-modification technique has drawn considerable attention from international scholars. This paper was reviewed on the synchronous Research News & Views of Nature by Jovan Kamcev and Benny D. Freeman, both of who are researchers from the Center for Energy and Environmental Resources of the University of Texas at Austin. “A cracked coating that prevents them from drying out in low-humidity conditions is a boon for devices, such as fuel cells, which need hydrated membranes to function.” They stressed that “Controlling ion-exchange membrane dehydration under low-humidity has been a formidable technical and scientific barrier limiting membrane performance. This powerful technique will contribute to various applications of high-performance membranes.”

 

Professor Michael

Professor Michael is committed to research on functional materials, acquiring many great achievements in this field. He was involved in the “Recruitment Program for Foreign Experts” in 2014, and has worked full-time in the State Key Laboratory of Engine Combustion of Tianjin University since October 2014. Additionally, Professor Michael is also now an important member of the Collaborative Innovation Center of Chemical Science and Engineering (Tianjin).

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