Simultaneous improvement of power density and durability of sulfonated poly(ether ether ketone) membrane by embedding CeO₂-ATiO₂: A comprehensive study in low humidity proton exchange membrane fuel cells

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.