Hongli Yang is a doctoral student at the Digital Cellulose Center, and with her latest research, she has created a highly conductive, low-cost nanocellulose-based ionic membrane. The new membrane is promising for electrochemical energy technology, such as redox flow batteries. The abundant natural resource of cellulose, combined with a simple production process makes the new membrane low-cost compared to the current commercial non-biodegradable membrane.

The research within the Digital Cellulose Center is conducted by academic and industry partners, as well as Ph.D. students. The Ph.D. students affiliated with the center are involved in many of the research projects to further generate new knowledge within the field of digital cellulose. Hongli Yang is one of the Ph.D. students within the center and a guest blogger for this post.

Crosslinked nanocellulose-based membranes with excellent ion conductivity

Ionic membranes with excellent ion conductivity and selectivity have been broadly utilized in various applications, such as energy conversion and harvesting, ultrafiltration, water treatment, and biotechnologies. However, the current commercial membrane on the market is high-cost and non-biodegradable.

My research project mainly focuses on ion transport and the related applications of cross-linked nanocellulose-based membranes. The purpose is to fabricate the ionic membranes by using low-cost and green material sources, that can be used as an alternative to the commercial membrane.

Cellulose nanofibrils (CNFs) are sustainable and biodegradable materials since they can be extracted from abundant natural resources. I used 1,2,3,4-butanetetracarboxylic acid (BTCA) as a crosslinker to successfully fabricate freestanding crosslinked CNF membranes. This crosslinked membrane has exhibited remarkable ion conductivity and selectivity in my research, up to more than 8mS/cm at 0.1 M KCl under pH 8.


The first fabricated ionic nanocellulose-based membrane using BTCA

With this research, we have for the first time fabricated an ionic nanocellulose-based membrane using BTCA as a crosslinker. In addition, detailed research work encompassing the microstructural and surface charge changes of such membranes with different crosslinker content and their effects on the ion transport performance has not previously been demonstrated. I have studied their relationships through fundamental science to better understand the ion transport properties and the feasibility of the membranes in various applications.

Biodegradable ionic membranes for various applications

The research team and I have confirmed that BTCA crosslinked CNF membranes can be used for applications including redox flow batteries and osmotic power generators. I am now investigating the performance of crosslinked cellulose nanofibril membranes for the application of redox flow batteries. The results demonstrate great promise for crosslinked CNF in the upscaled preparation of membranes and applications, particularly electrochemical energy technologies. The next step of the research is to find more possibilities of applications based on the current crosslinked CNF membranes and combine these membranes with cationic CNF films to fabricate bipolar membranes.

In the redox flow battery, the crosslinked membrane is the separator to transport the ions and prevent the active molecule from penetrating to the other side. Redox flow batteries can also be used to harvest and convert energy. Based on the Reverse electrodialysis (RED) technique, ions passing through a stack of ion-selective membranes can generate energies under a salt concentration gradient. In the above technologies, crosslinked CNF membrane has a great potential to replace the expensive commercial membranes.

Replacing traditional polymer with renewable materials

I have researched a lot about traditional polymer materials and their advanced applications before starting with my Ph.D. studies. However, traditional polymer materials would bring a great burden to the global environment. I was curious if we can replace traditional polymer with green and renewable materials to realize various functionalities. Digital Cellulose Center provided a great chance for me to further study materials science and possible applications of green forest materials and finish my doctorate dissertation.

What makes me excited is that the process from green materials to renewable energy can be achieved. For example, we obtained membranes from sustainable cellulose materials, meanwhile, due to their remarkable properties, in turn, they can generate renewable energies in some applications, such as osmotic power generators. I plan to continue on this green material area and explore more possibilities on my academic path.

Hongli Yang, 29, residing in Norrköping, Sweden. Ph.D. student at Laboratory of Organic Electronics (LOE), Linköping University. Supervisors: Associate Professor Isak Engquist, Professor Magnus Berggren and Dr. Viktor Gueskine.

Read Hongli Yang’s new research, published in Carbohydrate Polymers: “The effect of crosslinking on ion transport in nanocellulose-based membranes”.