Albert S. Lee

Heteroepitaxially Grown Zeolitic Imidazolate Framework Membranes with Unprecedented Propylene/Propane Separation Performances

Propylene/propane separation is one of the most challenging separations, currently achieved by energy-intensive cryogenic distillation. Despite the great potential for energy-efficient membrane-based separations, no commercial membranes are currently available due to the limitations of current polymeric materials. Zeolitic imidazolate framework, ZIF-8, with the effective aperture size of ∼4.0 Å, has been shown to be very promising for propylene/propane separation. Despite the extensive research on ZIF-8 membranes, only a few reported ZIF-8 membranes have displayed good propylene/propane separation performances presumably due to the challenges of controlling the microstructures of polycrystalline membranes. Here we report the first well-intergrown membranes of ZIF-67 (Co-substituted ZIF-8) by heteroepitaxially growing ZIF-67 on ZIF-8 seed layers. The ZIF-67 membranes exhibited impressively high propylene/propane separation capabilities. Furthermore, when a tertiary growth of ZIF-8 layers was applied to heteroepitaxially grown ZIF-67 membranes, the membranes exhibited unprecedentedly high propylene/propane separation factors of ∼200 possibly due to enhanced grain boundary structure.

Hybrid ionogel electrolytes for high temperature lithium batteries

Hybrid ionogels fabricated using 1 M LiTFSI in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI) crosslinked with ladder-like structured poly(methacryloxypropyl)silsesquioxane (LPMASQ) were investigated as high temperature ionogel electrolytes for lithium ion batteries. In addition to the exceedingly low crosslinker concentration (∼2 wt%) required to completely solidify the ionic liquids, which provided high ionic conductivities comparable to the liquid state ionic liquid, these hybrid ionogels exhibited superior thermal stabilities (>400 °C). Rigorous lithium ion battery cells fabricated using these hybrid ionogels revealed excellent cell performance at various C-rates at a variety of temperatures, comparable with those of neat liquid electrolytes. Moreover, these hybrid ionogels exhibited excellent cycling performance during 50 cycles at 90 °C, sustaining over 98% coulombic efficiency. Highly advantageous properties of these hybrid ionogels, such as high ionic conductivity in the gel state, thermal stability, excellent C-rate performance, cyclability and non-flammability, offer opportunities for applications as high temperature electrolytes.

Novel polysilsesquioxane hybrid polymer electrolytes for lithium ion batteries

A novel inorganic–organic hybrid crosslinker was prepared through synthesis of a fully condensed, high molecular weight ladder-like poly(methacryloxypropyl)silsesquioxane (LPMASQ) in one pot with a facile, base-catalysed system. The fully condensed LPMASQ revealed good thermal (∼380 °C) and electrochemical stability (∼5.0 V) due to the absence of uncondensed silanol groups. LPMASQ also revealed good solubility in various organic solvents and fully gelated 1 M LiPF6 in ethyl carbonate–diethyl carbonate (EC–DEC, 3/7, v/v) electrolyte solution through fast thermal and photocuring even at a very low concentration of 2 wt%. These observations were attributed to the polymeric nature of LPMASQ containing over one hundred methacryl moieties on the rigid double-stranded siloxane backbone. To the best of our knowledge, formation of a gel polymer electrolyte with 2 wt% gelator is the smallest gelation concentration that has ever been reported. This leads to high ionic conductivity (∼6.0 mS cm−1), excellent Coulombic efficiency and battery cell performance, comparable with those of the neat liquid electrolyte. The small crosslinker content, thermal and electrochemical stability, fast thermal and photocuring and facile processing of the LPMASQ based GPEs, as well as excellent Li battery cell performances strongly hold great promise for future industrial battery applications.

Ionic block copolymer doped reduced graphene oxide supports with ultra-fine Pd nanoparticles: strategic realization of ultra-accelerated nanocatalysis

We synthesized an ultra-fine Pd nanocatalyst supported by ionic block copolymer doped reduced graphene oxide (Pd-PIBrGO) for ultra-accelerated nanocatalysis. This hybrid catalyst exhibited exceptionally advanced catalytic performance for the reduction of methylene blue using miniscule quantities of Pd-PIBrGO due to facilitated diffusion of reagents, resulting in full reduction within a few seconds and showing a 280-fold increase of the rate constant over Pd-rGO without ionic block copolymers.

Rational molecular design of PEOlated ladder-structured polysilsesquioxane membranes for high performance CO2 removal

Poly(methoxy(polyethyleneoxy)propyl-co-methacryloxypropyl) silsesquioxane membranes with different copolymer ratios were successfully fabricated via UV-induced crosslinking with mechanical stability. By selectively introducing polyethylene oxide (PEO) groups covalently bound to the ladder-structured polysilsesquioxane, we effectively suppressed the PEO crystallization, allowing for excellent CO2/H2 and CO2/N2 separation under single as well as mixed gas conditions.

Molybdenum-Doped PdPt@Pt Core-Shell Octahedra Supported by Ionic Block Copolymer-Functionalized Graphene as a Highly Active and Durable Oxygen Reduction Electrocatalyst.

Development of highly active and durable electrocatalysts that can effectively electrocatalyze oxygen reduction reactions (ORR) still remains one important challenge for high-performance electrochemical conversion and storage applications such as fuel cells and metal-air batteries. Herein, we propose the combination of molybdenum-doped PdPt@Pt core-shell octahedra and the pyrene-functionalized poly(dimethylaminoethyl methacrylate)-b-poly[(ethylene glycol) methyl ether methacrylate] ionic block copolymer-functionalized reduced graphene oxide (Mo-PdPt@Pt/IG) to effectively augment the interfacial cohesion of both components using a tunable ex situ mixing strategy. The rationally designed Mo-PdPt@Pt core-shell octahedra have unique compositional benefits, including segregation of Mo atoms on the vertexes and edges of the octahedron and 2-3 shell layers of Pt atoms on a PdPt alloy core, which can provide highly active sites to the catalyst for ORR along with enhanced electrochemical stability. In addition, the ionic block copolymer functionalized graphene can facilitate intermolecular charge transfer and good stability of metal NPs, which arises from the ionic block copolymer interfacial layer. When the beneficial features of the Mo-PdPt@Pt and IG are combined, the Mo-PdPt@Pt/IG exhibits substantially enhanced activity and durability for ORR relative to those of commercial Pt/C. Notably, the Mo-PdPt@Pt/IG shows mass activity 31-fold higher than that of Pt/C and substantially maintains high activities after 10 000 cycles of intensive durability testing. The current study highlights the crucial strategies in designing the highly active and durable Pt-based octahedra and effective combination with functional graphene supports toward the synergetic effects on ORR.

Defect-induced ripening of zeolitic-imidazolate framework ZIF-8 and its implication to vapor-phase membrane synthesis

We report for the first time that ZIF-8 crystals undergo an Ostwald-ripening-like process without degradation in the presence of a ligand vapor. The ripening process is dependent on the defect density of the crystals: the more defective the more amenable to the ripening. The process was adapted to synthesize ultra-thin ZIF-8 membranes by vapor-phase secondary growth.

Fabrication of functional nanosized patterns with UV-curable polysilsesquioxane on photovoltaic protective glass substrates using hybrid nano-imprint lithography

UV-curable polysilsesquioxane materials were used to incorporate moth-eye structures on photovoltaic (PV) protective glass. These patterns were formed using a hybrid nanoimprint lithography technique and annealed at 100 °C to evaporate the solvent (xylene). Compared to the bare, un-patterned PV protective glass, the PV protective glass patterned on both sides had superior optical properties. Transmittance of the PV protective glass patterned on both sides increased by up to 3.13% and reflectance decreased by up to 3.42%, and the transmittance was increased for all angles of incidence. Furthermore, the JSC of devices with the PV protective glass patterned on both sides increased by up to 3.15%. Finally, a monitoring system was set up to measure electricity generated by PV modules. The efficiency of the PV module with PV protective glass patterned on both sides was enhanced by up to 12.16% compared with that of the PV module with un-patterned PV protective glass.

Facilitated Ion Transport in Smectic Ordered Ionic Liquid Crystals

A novel ionic mixture of an imidazolium-based room-temperature ionic liquid containing ethylene-oxide-functionalized phosphite anions is fabricated, which, when doped with lithium salt, self-assembles into a smectic-ordered ionic liquid crystal through Coulombic interactions between the ion species. Interestingly, the smectic order in the ionic-liquid-crystal ionogel facilitates ionic transport.

Lithium Dendrite Suppression with UV-Curable Polysilsesquioxane Separator Binders

For the first time, an inorganic-organic hybrid polymer binder was used for the coating of hybrid composites on separators to enhance thermal stability and to prevent formation of lithium dendrite in lithium metal batteries. The fabricated hybrid-composite-coated separators exhibited minimal thermal shrinkage compared with the previous composite separators (<5% change in dimension), maintenance of porosity (Gurley number ∼400 s/100 cm(3)), and high ionic conductivity (0.82 mS/cm). Lithium metal battery cell examinations with our hybrid-composite-coated separators revealed excellent C-rate and cyclability performance due to the prevention of lithium dendrite growth on the lithium anode even after 200 cycles under 0.2-5C (charge-discharge) conditions. The mechanism for lithium dendrite prevention was attributed to exceptional nanoscale surface mechanical properties of the hybrid composite coating layer compared with the lithium metal anode, as the elastic modulus of the hybrid-composite-coated separator far exceeded those of both the lithium metal anode and the required threshold for lithium metal dendrite prevention.