Simultaneous improvement of power density and durability of sulfonated poly(ether ether ketone) membrane by embedding <scp> CeO <sub>2</sub> ‐ATiO <sub>2</sub> </scp> : A comprehensive study in low humidity proton exchange membrane fuel cells
Hariprasad Ranganathan, Mohanraj Vinothkannan, Ae Rhan Kim, Vijayapradeep Subramanian, Min‐Suk Oh, Dong Jin Yoo
Abstract
Herein, we describe the incorporation of cerium oxide-coated amine-functionalized titania nanorods (CeO2-ATiO2) as a bifunctional nanofiller in sulfonated poly(ether ether ketone) (SPEEK) as a cost-effective and high-performance proton exchange membrane (PEM) for PEM fuel cells (PEMFCs). Facile and effective functionalization of TiO2 was performed using amine-containing organic moieties, followed by coating the ATiO2 nanorods with CeO2. A simple solution casting method was employed to incorporate CeO2-ATiO2 into the SPEEK matrix with various weight ratio of 0.5%, 1%, 2%, 4%, or 6%. The successful incorporation of prepared nanofiller in the SPEEK membrane matrix was confirmed by structural and morphological studies such as Fourier transform infrared, X-ray diffractometer, scanning electron microscopy, and atomic force microscope of the SPEEK/CeO2-ATiO2 composite membranes. The presence of ATiO2 improved proton conductivity while CeO2 alleviated the chemical degradation of the membrane by scavenging free radicals. The proton conductivity of an SPEEK/CeO2-ATiO2 (2 wt%) nanocomposite membrane at 60°C under 20% relative humidity (RH) was 17.06 mS cm−1 whereas that of a bare SPEEK membrane under the same conditions was only 4.53 mS cm−1. PEMFCs containing SPEEK/CeO2-ATiO2 (2 wt%) nanocomposite membrane attained a maximum power density of 117 mW cm−2 at a load current density of 371 mA/cm2 at 60°C under 100% RH. In contrast, a PEMFC containing the bare SPEEK membrane delivered a power density of 91 mW cm−2 at a load current of 253 mA cm−2. A single cell open circuit voltage (OCV) test to examine the durability of membranes revealed that a PEMFC with an SPEEK/CeO2-ATiO2 (2 wt%) membrane showed excellent stability with an OCV decay of 0.925 mV h−1 at 60°C under 30% RH, whereas that of a PEMFC with a bare SPEEK membrane was 3.437 mV h−1 under identical conditions. Based on the abovementioned results, it is found that the SPEEK/CeO2-ATiO2 nanocomposite membranes overcome the durability issues of pristine SPEEK membranes and show enhanced electrochemical performance under a harsh PEMFC environment. Highlights CeO2-ATiO2 was utilized as a bifunctional filler to fabricate composite membrane. Integration of CeO2-ATiO2 improved the proton conductivity of sulfonated poly(ether ether ketone) (SPEEK) under low relative humidity. Addition of CeO2-ATiO2 to SPEEK resulted in improved physiochemical and thermomechanical properties. Optimized SPEEK/CeO2-ATiO2 (2 wt%) exhibited improved proton exchange membrane fuel cell performance while retaining excellent durability compared to pristine SPEEK.