Date of Award


Document Type


Degree Name

Master of Science (MS)


Chemical Engineering

Committee Chair/Advisor

Eric M. Davis

Committee Member

Mark E. Roberts

Committee Member

Kyle S. Brinkman


As the development of energy storage technologies for renewable energy sources continues to garner attention, vanadium redox flow batteries (VRFBs) have emerged as promising source for grid-scale energy storage. A major component of the VRFB is the ion exchange membrane (IEM), as it serves to physically separate the two liquid electrolytes and also directly impacts the battery’s capacity, efficiency, and cost. The current industry standard IEM, Nafion™, not only accounts for a large portion of the cost of the VRFB but also suffers from poor proton selectivity. Herein, we have synthesized sulfonated poly(ether ether ketone) (SPEEK) composite membranes containing amine functionalized softwood Kraft lignin. The lignin amination was performed via epoxidation of the hydroxyl groups of the lignin, followed by amination. The addition of amine groups was verified using 31P, 1H, 13C Nuclear Magnetic Resonance (NMR), as well as Fourier-transform infrared spectroscopy (FTIR), as well as elemental analysis. After amination, the lignin was combined with SPEEK, and membranes containing 5 and 15 mass % aminated lignin were fabricated via solution casting. Notably, the aminated lignin composite membrane showed reduced vanadyl ion permeability compared to the neat SPEEK membrane. Transmission electron microscopy (TEM) showed a reduction in lignin aggregation and more uniform dispersion of the aminated lignin compared to its nonaminated counterpart. The ion exchange capacity (IEC) and equilibrium water uptake (EWU) for these ionomers were evaluated and compared to the neat SPEEK membrane, as well as SPEEK membranes containing unmodified lignin. Results from this analysis showed that ionomers containing aminated lignin exhibited lower IEC values compared to the neat SPEEK membrane but significantly higher EWU compared to unmodified lignin composite membrane. Combining the increase in the EWU, decrease in IEC, and the dispersion state of the lignin, the aminated lignin was postulated to interact with the sulfonic groups of the SPEEK altering membrane properties compared to the unmodified lignin sample. Overall, results from this work demonstrated how chemical functionalization of lignin can be used to tune the SPEEK–lignin composite membrane properties, providing a pathway forward for the development of more cost-effective ionomer composites containing polymer from renewable feedstocks.

Available for download on Tuesday, December 31, 2024