No abstract

Polymer electrolyte membrane fuel cells can generate high power densities with low local emissions of pollutants. Optimal ionomer-Pt/C catalyst interactions in the electrodes enable the efficient generation and transport of ions and electrons required for high fuel cell performances. Critical durability issues involve agglomeration of the Pt/C nanoparticles (Pt/C NPs) and ionomer during discharging. Our novel approach involves ionomer cross-linking immobilization for the fabrication of durable catalyst layers for application in alkaline anion exchange membrane fuel cells (AEMFCs). Pt/C NP catalysts are employed alongside a poly­(2,6-dimethyl-p-phenylene oxide)-(PPO)-based quaternary ammonium ionomer (containing terminal styrenic side-chain groups) to form porous catalyst layers. Following thermally initiated cross-linking of the terminal vinyl groups, an interconnected ionomer network forms conductive shells around the Pt/C aggregates. Ex situ catalytic activity and in situ durability tests demonstrate that this immobilization strategy inhibits Pt/C NP coalescence without sacrificing catalyst layer porosity. An initial demonstration of an H2/O2 AEMFC containing the new CBQPPO@Pt/C cathode shows that high peak power densities can be achieved (1.02 W cm–2 at 70 °C, raising to 1.37 W cm–2 with additional 0.1 MPa back-pressurization).

Bipolar membrane (BPM) has been used commercially in electrodialysis separation processes for the generation of acid and base from aqueous salt solutions and electrochemical water splitting processes for hydrogen generation. Research advances have demonstrated that, upon a sufficient applied reverse bias, water molecules at the junction zone of the BPM can dissociate into protons (H + ) and hydroxide anions (OH − ). Therefore, a stable and catalytic active junction for rapid water dissociation is highly desired, but it still remains a challenge for current bipolar membrane designs. Here, we demonstrate a versatile strategy for fabricating a thin metal−polymer coordination complex junction-based bipolar membrane. The complex used consists of polyethylenimine (PEI) that coordinate to Fe(III) centers through the amine−iron interaction (Fe(III)@PEI). The unique coordination interaction enables to promote water dissociation and suppress catalyst leakage issue. In addition, to prevent junction layer dehydration from highly efficient water dissociation, the cation-exchange membrane containing porous water channels is utilized to sufficiently replenish the water molecules consumed at the junction zone. Notably, under a current density of 320 mA cm −2 , Fe(III)@PEI-based BPM exhibits a voltage of 1.88 V, which is 56 and 36% lower than PEI-based BPM and FeCl 3 -based BPM, respectively. Moreover, during a constant current density operation at 60 mA cm −2 , Fe(III)@PEI-based BPM exhibits a much lower voltage increasing speed (5.93 mV h −1 ) than the FeCl 3 -based BPM (32.64 mV h −1 ), indicating the improved durability of the metal−polymer coordination complex junction.