Title: Phosphonated SBA-15/Phosphonated PSEBS composite membranes for high temperature proton exchange membrane fuel cells

Biography:

D. Sangeetha is an Assistant Professor in the Department of Mechanical Engineering, Anna University. Her Google scholar citation is 1739 with an h-index of 23 and i-10 index of 52.  She has 2 granted Indian patents in the field of Fuel Cells.  Twelve students have completed their Ph.D. under her guidance.  She has successfully carried out a number of sponsored research projects funded by various agencies like DST, DBT, BRNS, CSIR, UGC and ICMR and 5 students are presently pursuing their Ph.D. in various fields like fuel cells, desalination, biopolymers for drug delivery and tissue engineering applications under her guidance.

She was awarded the Active Researcher Award 2012 by Anna University.  She was awarded the H. Nandy Memorial Award at the Indian Engineering Congress 2014. She is also the recipient of Womens Achiever Award 2017 as recognized by Anna University.  As a students mentor, she was awarded twice for the Student Innovative Project Award 2017 and 2018 in the Dept. of Mechanical Engineering by CTDT, Anna University. She received the Wenlock Endowment Scholarship for the year 2016-2017 for high impact research publication in 2018 by Anna University. Dr Sangeetha Dharmalingam has been certified as Professional Engineer in Metallurgy and Materials Engineering Discipline by The Institution of Engineers (India) in 2019.

Abstract

Proton exchange membrane fuel cells (PEMFC) are increasingly becoming an attractive energy source for the future due to their portability, silent operation and high power density. Efforts have been made to improve their efficiency as well as in making the technology affordable. Several parameters come into play in the context of fuel cell efficiency, of which the operating temperature is of prime importance. Specifically, high temperature PEM fuel cell (HTPEMFC) has greater merits such as higher efficiency, improved tolerance of the electrodes against carbon monoxide poisoning, faster reaction kinetics, and effective heat transfer. Since the proton conductivities of commonly used perfluorinated membranes, such as Nafion, is highly dependent on external humidification, their operating temperature is limited to 100 °C. Hence one of the biggest challenges in PEMFC is fabricating a thermally stable membrane which can operate at temperatures above 100 °C under anhydrous conditions.

In the present work phoshonated SBA-15/phosphonated Poly(styrene-ethylene-butylene-styrene) (PSEBS) composite membranes are developed for high temperature fuel cell electrolyte. Mesoporous Santa Barbara Amorphous (SBA-15) was synthesized and it was grafted with phosphonate functionality using a simple two-step process involving chloromethylation and subsequent phosphonation. The phosphonated SBA-15 (PSBA-15) was characterized using Fourier transform infra-red (FTIR) spectroscopy, solid state ¹³C Nuclear magnetic resonance (NMR), ²⁹Si NMR, ³¹P NMR for confirming successful modification. Morphology features were verified by small angle X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Transmission electron microscopy TEM analyses. Poly(styrene-ethylene-butylene-styrene) (PSEBS) was chosen as the base polymer and phosphonic acid functional groups were grafted onto the polymer using the aforementioned approach, where chloromethyl (-CH₂Cl) groups were attached to the main chain using Friedel Craft’s alkylation, followed by the phosphonation of the chloromethylated polymer by the Michaels-Arbuzov reaction resulting in phosphonated PSEBS (PPSEBS). The functionalisation was confirmed using NMR and FTIR spectroscopy studies. Composite PPSEBS/PSBA-15 membranes were fabricated with different filler concentrations (2, 4, 6, and 8%) of PSBA-15. Various studies such as water uptake, ion exchange capacity and the proton conductivity of the composite membranes were undertaken with respect to fuel cell applications. From the studies, it was found that the PPSEBS/PSBA-15 membrane with 6% wt of filler exhibited maximum proton conductivity of 8.62 mS/cm at 140 °C. Finally, membrane electrode assembly (MEA) was fabricated using PPSEBS/6% PSBA composite membrane, Platinium (Pt) anode, Pt cathode and was tested in an in-house built fuel cell setup. A maximum power density of 226 mW/cm² and an open circuit voltage of 0.89 V was achieved at 140 °C under un-humidified condition.