Simultaneous improvement of power density and durability of sulfonated poly(ether ether ketone) membrane by embedding CeO2-ATiO(2): A comprehensive study in low humidity proton exchange membrane fuel cells

Abstract

Herein, we describe the incorporation of cerium oxide-coated amine-functionalized titania nanorods (CeO2-ATiO(2)) 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 ATiO(2) nanorods with CeO2. A simple solution casting method was employed to incorporate CeO2-ATiO(2) 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-ATiO(2) composite membranes. The presence of ATiO(2) improved proton conductivity while CeO2 alleviated the chemical degradation of the membrane by scavenging free radicals. The proton conductivity of an SPEEK/CeO2-ATiO(2) (2 wt%) nanocomposite membrane at 60 degrees 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-ATiO(2) (2 wt%) nanocomposite membrane attained a maximum power density of 117 mW cm(-2) at a load current density of 371 mA/cm(2) at 60 degrees 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-ATiO(2) (2 wt%) membrane showed excellent stability with an OCV decay of 0.925 mV h(-1) at 60 degrees 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-ATiO(2) nanocomposite membranes overcome the durability issues of pristine SPEEK membranes and show enhanced electrochemical performance under a harsh PEMFC environment. Highlights CeO2-ATiO(2) was utilized as a bifunctional filler to fabricate composite membrane. Integration of CeO2-ATiO(2) improved the proton conductivity of sulfonated poly(ether ether ketone) (SPEEK) under low relative humidity. Addition of CeO2-ATiO(2) to SPEEK resulted in improved physiochemical and thermomechanical properties. Optimized SPEEK/CeO2-ATiO(2) (2 wt%) exhibited improved proton exchange membrane fuel cell performance while retaining excellent durability compared to pristine SPEEK.