Anion-exchange membrane (AEM) fuel cells (AEMFCs) and water electrolyzers (AEMWEs) have gained strongattention of the scientific community as an alternative to expensive mainstream fuel cell and electrolysis technologies. However, in the high pH environment of the AEMFCs and AEMWEs, especially at low hydration levels, the molecular structure of most anion-conducting polymers breaks down because of the strong reactivity of the hydroxide anions with the quaternary ammonium (QA) cation functional groups that are commonly used in the AEMs and ionomers. Therefore, new highly stable QAs are needed to withstand the strong alkaline environment of these electrochemical devices. In this study, a series of isoindolinium salts with different substituents is prepared and investigated for their stability under dry alkaline conditions. We show that by modifying isoindolinium salts, steric effects could be added to change the degradation kinetics and impart significant improvement in the alkaline stability, reaching an order of magnitude improvement when all the aromatic positions are substituted. Density functional theory (DFT) calculations are provided in support of the high kinetic stability found in these substituted isoindolinium salts. This is the first time that this class of QAs has been investigated. We believe that these novel isoindolinium groups can be a good alternative in the chemical design of AEMs to overcome material stability challenges in advanced electrochemical systems.
Non-platinum group metal (non-PGM) oxygen reduction reaction (ORR) catalysts have been widely reported, but their application in proton exchange membrane fuel cells (PEMFCs) is challenging because of their poor performance in acidic environments. Here, [BMIM][NTf₂] ionic liquid (IL) modification of microporous ZnCoNC catalysts (derived from ZIF-ZnCo) is investigated to study their behavior in PEMFCs and to elucidate the catalytic mechanisms in practical operation. The high O₂ solubility of ILs enhances the utilization of active sites with porous ZnCoNC, and their hydrophobic nature facilitates the water transport during fuel cell operation. The half-cell measurement in aqueous HClO₄ shows that with the 20 wt % IL modification, the electron-transfer number increases from 2.58 to 3.88, approaching the desired 4-electron-transfer ORR. The power density obtained shows 140% improvement in single-cell PEMFC tests. The catalyst also yields an interesting performance in alkaline anion-exchange membrane fuel cells.
In anion exchange membrane fuel cells, catalytic reactions occur at a well-defined three-phase interface, wherein conventional heterogeneous catalyst layer structures exacerbate problems, such as low catalyst utilization and limited mass transfer. We developed a structural engineering strategy to immobilize a molecular catalyst tetrakis(4-methoxyphenyl)porphyrin cobalt(II) (TMPPCo) on the side chains of an ionomer (polyfluorene, PF) to obtain a composite material (PF-TMPPCo), thereby achieving a homogeneous catalysis environment inside ion-flow channels, with greatly improved mass transfer and turnover frequency as a result of 100 % utilization of the catalyst molecules. The unique structure of the homogeneous catalysis system comprising interconnected nanoreactors exhibits advantages of low overpotential and high fuel-cell power density. This strategy of reshaping of the catalyst layer structure may serve as a new platform for applications of many molecular catalysts in fuel cells.