The preparation and photophysical properties of two heavier main group element analogues of boron-dipyrromethene (BODIPY) chromophores are described. Specifically, we have prepared dipyrrin complexes of dichlorogallate (GADIPY) or phenylphosphenium (PHODIPY) units. Whereas cationic PHODIPY is labile, decomposing to a phosphine over time, GADIPY is readily prepared in good yield as a crystalline solid having moderate air- and water-stability. Crystallographically characterized GADIPY displays intense green photoluminescence (λem = 505 nm, Φem = 0.91 in toluene). These inaugural heavier main group element analogues of BODIPY offer a glimpse into the potential for elaboration to a panoply of chromophores with diverse photophysical properties.

Perfluorosulfonic acid (PFSA) ionomers are ubiquitous as proton-exchange membranes (PEMs) in vanadium redox flow batteries (VRFBs), as they provide high proton conductivity and robust chemical stability. However, traditional PFSA ionomers suffer from high vanadium ion crossover, i.e., low ion selectivity, which reduces the efficiency and lifetime of the battery. Herein, a novel method to fabricate PFSA nanocomposites containing fluorocarbon-decorated silica nanoparticles is presented. These composite ionomers exhibit drastically reduced vanadium ion permeability and an almost two orders of magnitude increase in proton selectivity when compared to the current benchmark commercial ionomer. Small-angle neutron scattering data suggest that the nanostructures of these nanocomposites are drastically different from their pristine counterpart, where the periodic spacing of the hydrophobic domains is significantly reduced, while changes to the ionic structure were seen to be minimal. This work suggests that composite PEMs containing a secondary phase that alters the hydrophobic, nonion-conducting phase of the ionomer may prove to be a fruitful fabrication route to produce ionomer membranes with enhanced performance for use in VRFBs.

Herein, we present a systematic investigation of the impact of silica nanoparticle (SiNP) size and surface chemistry on the nanoparticle dispersion state and the resulting morphology and vanadium ion permeability...

Hydrogen isotope separation is vital for multiple application areas including nuclear energy sectors and nuclear weapons, and is fundamentally interesting. Two-dimensional (2-D) materials such as monolayer graphene have been demonstrated in the past to selectively transport ions including hydrogen isotopes through them which provides a pathway for membrane-based isotope separation. Recent studies have shown that monolayer graphene and other 2-D materials embedded in membrane electrode assemblies (MEAs) prepared from proton exchange membranes (PEMs) such as Nafion® can selectively transport protons at rates up to 14 times higher than deuterons. The mechanism for this unusually high isotope selectivity is still under study and is thought to involve transport at localized defects sites with one or more chemical steps having a high kinetic isotope effect. The long-term stability of electrochemical hydrogen isotope separation using monolayer graphene-based membranes is crucial for the graphene to become a good sieving layer candidate for large-scale hydrogen isotope separation. The focus of this study is on the long-term stability of separating characteristics of graphene layers embedded in MEAs that actively pump protons and deuterons through them over an extended period of time. Initial results suggest that graphene embedded within Nafion sandwiches in their current form have a high isotope selectivity initially but that isotope selectivity can diminish as current is passed through the sandwich structures for extended time periods. Findings from chronoamperometry experiments performed on graphene-embedded MEAs while interchanging H2 and D2 gas feeds in symmetric electrochemical H/D pump cells, and potential factors affecting separation capability over long periods of time, will be discussed during the talk.

Graphene and related two-dimensional (2D) materials are being intensively studied for use in membrane separators. The ultrathin nature of 2D materials combined with the opportunities they afford for intentional creation of nanometer-sized pores having controllable size and chemical character could allow for membrane separations with high flux and also high selectivity. Proton transport through graphene is especially interesting because it may occur through the intact pristine graphene rather than through defects / pores. Other cations, for example lithium or sodium, may pass through graphene but that transport is through to occur through defects / pores. This presentation will focus on selective cation transport through graphene layers that are embedded between Nafion membranes. Ion transmission through graphene is measured using a four-electrode cell in which two Luggin capillaries sense the potential difference that develops across the membrane in response to an ion current that is driven by a pair of platinum wire drive electrodes. Proton transmission in this cell configuration occurs more than 100 times faster than transport of any other ion. This difference is thought to reflect the different mechanisms by which protons and other cations pass though graphene. The lecture will discuss defect characterization in CVD graphene films, and will consider the role of defects, which are in fact nanopores, in allowing for selective transport of ions through graphene.