Zongyu Li

Zwitterionic microcapsules as water reservoirs and proton carriers within a Nafion membrane to confer high proton conductivity under low humidity.

Zwitterionic microcapsules (ZMCs) based on sulfobetaine with tunable hierarchical structures, superior water retention properties, and high proton conduction capacities are synthesized via precipitation polymerization. The incorporation of ZMCs into a Nafion matrix renders the composite membranes with significantly enhanced proton conductivity especially under low humidity. The composite membrane with 15 wt % ZMC-I displayed the highest proton conductivity of 5.8 × 10(-2) S cm(-1) at 40 °C and 20% relative humidity after 90 min of testing, about 21 times higher than that of the Nafion control membrane. The increased proton conductivity is primarily attributed to the versatile roles of ZMCs as water reservoirs and proton conductors for rendering a stable water environment and an additional proton conduction pathway within the membranes. This study may contribute to the rational design of water-retaining and proton-conducting materials.

Functionalized carbon nanotube via distillation precipitation polymerization and its application in nafion-based composite membranes.

The objective of this study is to develop a novel approach to in situ functionalizing multiwalled carbon nanotubes (MWCNTs) and exploring their application in Nafion-based composite membranes for efficient proton conduction. Covalent grafting of acrylate-modified MWCNTs with poly(methacrylic acid-co-ethylene glycol dimethacrylate), poly(vinylphosphonic acid-co-ethylene glycol dimethacrylate), and sulfonated poly(styrene-co-divinylbenzene) was achieved via surface-initiated distillation precipitation polymerization. The formation of core-shell structure was verified by TEM images, and polymer layers with thickness around 30 nm were uniformly covered on the MWCNTs. The graft yield reached up to 93.3 wt % after 80 min of polymerization. The functionalized CNTs (FCNTs) were incorporated into the Nafion matrix to prepare composite membranes. The influence of various functional groups (-COOH, -PO3H2, and -SO3H) in FCNTs on proton transport of the composite membranes was studied. The incorporation of FCNTs afforded the composite membranes significantly enhanced proton conductivities under reduced relative humidity. The composite membrane containing 5 wt % phosphorylated MWCNTs (PCNTs) showed the highest proton conductivity, which was attributed to the construction of lower-energy-barrier proton transport pathways by PCNTs, and excellent water-retention and proton-conduction properties of the cross-linked polymer in PCNTs. Moreover, the composite membranes exhibited an enhanced mechanical stability.

MoO2–CoO coupled with a macroporous carbon hybrid electrocatalyst for highly efficient oxygen evolution

Cost-effective electrocatalysts for oxygen evolution reactions are attractive for energy conversion and storage processes. A high-performance oxygen evolution reaction (OER) electrocatalyst composed of 3D ordered microporous carbon and a MoO2 skeleton modified by cobalt oxide nanoparticles (MoO2-CoO-Carbon) is produced through a template method. This unique 3DOM structure finely combines the larger surface area of the 3D carbon skeleton and MoO2 as well as stablizes anchoring sites for CoO nanocrystals on the skeleton. The synergistic effect between the catalytic activity between MoO2 and CoO as well as the enhanced electron transport arising from the carbon skeleton contributed to superior electrocatalytic OER properties of MoO2-CoO-Carbon. The M200-C-Carbon hybrid with an overpotential as low as 0.24 V is among the best reported Mo-based OER catalysts. Moreover, the turnover frequency at an overpotential of 0.35 V is 6 times as high as that of commercial RuO2.

A Bi2Te3@CoNiMo composite as a high performance bifunctional catalyst for hydrogen and oxygen evolution reactions

Hydrogen generated renewably by using solar energy has attracted increasing interest in the renewable energy research community. Hence, efficient electrocatalysts are in demand to reduce costs and energy consumption for oxygen and hydrogen evolution reaction (OER and HER) activity. Bismuth telluride (Bi2Te3)-based materials, as topological insulators (TIs), have been used to explore the fundamental properties of TIs in recent years, but investigation as functional materials for water splitting applications is still quite limited. In this work, electrocatalysts based on Bi2Te3 nanosheets have been fabricated, and the HER performance was investigated to further enhance OER electrocatalytic properties, with certain transition metals (Co, Ni, and Mo) selected to provide effective electrocatalytic sites. Therefore, the bifunctional catalyst Bi2Te3@CoNiMo was designed for synthesis by a solvothermal and chemical deposition route. The catalyst electrode, Bi2Te3@CoNiMo loaded on Ni foam, exhibits higher activity towards both the oxygen and the hydrogen evolution reactions than some traditional metallic catalysts in alkaline electrolytes. The difference in the HER and OER metrics (ΔE = 1.41 V) is comparable to the theoretical value (1.23 V), so that this reaction can be easily driven by a solar cell.

Enhanced proton conductivity of proton exchange membranes by incorporating phosphorylated hollow titania spheres

Phosphorylated hollow titania spheres (PHTS) with a superior water retention property are synthesized via a soft-template method and introduced into a sulfonated poly(ether ether ketone) (SPEEK) matrix to fabricate SPEEK/PHTS hybrid membranes. The incorporation of PHTS renders hybrid membranes with higher water uptake but lower swelling degree. The increased water retention capacity and additional proton transfer sites in the organic–inorganic interfacial zones lead to an enhancement in membrane proton conductivity. The highest proton conductivity (σ) of 0.228 S cm−1 at 70 °C under 100% RH for the hybrid membrane with 20 wt% of PHTS is achieved, which is two orders of magnitude higher than the pristine SPEEK membrane. Moreover, the PHTS fillers also prolong the tortuous pathways for methanol transport, conferring the hybrid membranes lower methanol permeability (P) in the range of 3.8–4.4 × 10−7 cm2 s−1. The maximum selectivity (σ/P) of as-prepared hybrid membranes is 2.09 × 105 S s cm−3, twice higher than a pristine SPEEK membrane.

Highly Hydroxide-Conductive Nanostructured Solid Electrolyte via Pre-Designed Ionic Nanoaggregates

The creation of interconnected ionic nanoaggregates within solid electrolytes is a crucial yet challenging task for fabricating high-performance alkaline fuel cells. Herein, we present a facile and generic approach to embedding ionic nanoaggregates via predesigned hybrid core-shell nanoarchitecture within nonionic polymer membranes as follows: (i) synthesizing core-shell nanoparticles composed of SiO2/densely quaternary ammonium-functionalized polystyrene. Because of the spatial confinement effect of the SiO2 core, the abundant hydroxide-conducting groups are locally aggregated in the functionalized polystyrene shell, forming ionic nanoaggregates bearing intrinsic continuous ion channels; (ii) embedding these ionic nanoaggregates (20-70 wt %) into the polysulfone matrix to construct interconnected hydroxide-conducting channels. The chemical composition, physical morphology, amount, and distribution of the ionic nanoaggregates are facilely regulated, leading to highly connected ion channels with high effective ion mobility comparable to that of the state-of-the-art Nafion. The resulting membranes display strikingly high hydroxide conductivity (188.1 mS cm-1 at 80 °C), which is one of the highest results to date. The membranes also exhibit good mechanical properties. The independent manipulation of the conduction function and nonconduction function by the ionic nanoaggregates and nonionic polymer matrix, respectively, opens a new avenue, free of microphase separation, for designing high-performance solid electrolytes for diverse application realms.