Guangwei He - Academia.edu (original) (raw)

Papers by Guangwei He

Chemical Research in Chinese Universities

Angewandte Chemie International Edition, 2021

Fabricating covalent organic frameworks (COFs) membranes with tight structure, which can fully ut... more Fabricating covalent organic frameworks (COFs) membranes with tight structure, which can fully utilize well-defined framework structure and thus achieve superior conduction performance, remains a grand challenge. Herein, through molecular precursor engineering of COFs, we reported the fabrication of tight COFs membrane with the ever-reported highest hydroxide ion conductivity over 200 mS cm-1 at 80 °C, 100% RH. Six quaternary ammonium-functionalized COFs were synthesized by assembling functional hydrazides and different aldehyde precursors. In an organic-aqueous reaction system, the impact of the aldehyde precursors with different size, electrophilicity and hydrophilicity on the reaction-diffusion process for fabricating COFs membranes was elucidated. Particularly, more hydrophilic aldehydes were prone to push the reaction zone from the interface region to the aqueous phase of the reaction system, the tight membranes were thus fabricated via phase-transfer polymerization process, conferring around 4~8 times the anion conductivity over the loose membranes via interfacial polymerization process.

ACS Nano, 2021

Predictable and tunable etching of angstrom-scale nanopores in single-layer graphene (SLG) can al... more Predictable and tunable etching of angstrom-scale nanopores in single-layer graphene (SLG) can allow one to realize high-performance gas separation even from similar-sized molecules. We advance toward this goal by developing two etching regimes for SLG where the incorporation of angstromscale vacancy defects can be controlled. We screen several exposure profiles for the etchant, controlled by a multipulse millisecond treatment, using a mathematical model predicting the nucleation and pore expansion rates. The screened profiles yield a narrow pore-size-distribution (PSD) with a majority of defects smaller than missing 16 carbon atoms, suitable for CO 2 / N 2 separation, attributing to the reduced pore expansion rate at a high pore density. Resulting nanoporous SLG (N-SLG) membranes yield attractive CO 2 permeance of 4400 ± 2070 GPU and CO 2 /N 2 selectivity of 33.4 ± 7.9. In the second etching regime, by limiting the supply of the etchant, the nanopores are allowed to expand while suppressing the nucleation events. Extremely attractive carbon capture performance marked with CO 2 permeance of 8730 GPU, and CO 2 /N 2 selectivity of 33.4 is obtained when CO 2-selective polymeric chains are functionalized on the expanded nanopores. We show that the etching strategy is uniform and scalable by successfully fabricating high-performance centimeter-scale membrane.

Advanced Materials, 2021

Single-layer graphene containing molecular-sized in-plane pores is regarded as a promising membra... more Single-layer graphene containing molecular-sized in-plane pores is regarded as a promising membrane material for high-performance gas separations due to its atomic thickness and low gas transport resistance. However, typical etching-based pore generation methods cannot decouple pore nucleation and pore growth, resulting in a trade-off between high areal pore density and high selectivity. In contrast, intrinsic pores in graphene formed during chemical vapor deposition are not created by etching. Therefore, intrinsically porous graphene can exhibit high pore density while maintaining its gas selectivity. In this work, the density of intrinsic graphene pores is systematically controlled for the first time, while appropriate pore sizes for gas sieving are precisely maintained. As a result, single-layer graphene membranes with the highest H2 /CH4 separation performances recorded to date (H2 permeance > 4000 GPU and H2 /CH4 selectivity > 2000) are fabricated by manipulating growth temperature, precursor concentration, and non-covalent decoration of the graphene surface. Moreover, it is identified that nanoscale molecular fouling of the graphene surface during gas separation where graphene pores are partially blocked by hydrocarbon contaminants under experimental conditions, controls both selectivity and temperature dependent permeance. Overall, the direct synthesis of porous single-layer graphene exploits its tremendous potential as high-performance gas-sieving membranes.

Accounts of Materials Research, 2021

Carbon, 2021

The study of the nanometer-scale vacancy defects (nanopores) in graphene by transmission electron... more The study of the nanometer-scale vacancy defects (nanopores) in graphene by transmission electron microscopy (TEM) is severely hindered by the presence of polymeric residues originating from the graphene-transfer-step to the TEM grid. The state-of-the-art transfer strategies yield contamination-free pristine graphene specimens but do not work well for the nanoporous graphene. This is because of the relatively high energy of the vacant nanopores which makes it difficult to remove the residues without altering the structure of nanoporous graphene. Herein, we present a novel strategy to fabricate a sub-100-nm-thick lacey polymer film hosting see-through windows (10e900 nm) by using a facile nonsolvent-induced phase separation (NIPS). The polymer film is transformed into a lacey carbon film that reinforces graphene and allows residue-free transfer to the TEM grid as one avoids the direct contact between the polymer and the nanopores within a window. Finally, atmospheric-, graphene-synthesis-, and transfer-bath-related contaminants are removed by annealing the specimen inside an activated carbon bed at 900 C in a reducing atmosphere. The method results in samples with large contamination-free areas which are easy to find during aberration-corrected high-resolution TEM (AC-HRTEM) imaging, enabling high throughput structural analysis of graphene nanopores.

Advanced Functional Materials, 2020

Advanced Materials, 2020

The emergence of all-organic frameworks is of fundamental significance, and designing such struct... more The emergence of all-organic frameworks is of fundamental significance, and designing such structures for anion conduction holds great promise in energy conversion and storage applications. Herein, inspired by the efficient anion transport within organisms, a de novo design of covalent organic frameworks (COFs) toward ultrafast anion transport is demonstrated. A phase-transfer polymerization process is developed to acquire dense and ordered alignment of quaternary ammonium-functionalized side chains along the channels within the frameworks. The resultant self-standing COFs membranes exhibit one of the highest hydroxide conductivities (212 mS cm-1 at 80 °C) among the reported anion exchange membranes. Meanwhile, it is found that shorter, more hydrophilic side chains are favorable for anion conduction. The present work highlights the prospects of all-organic framework materials as the platform building blocks in designing ion exchange membranes and ion sieving membranes.

Journal of Materials Chemistry A, 2018

Synergistic manipulation in intra- and inter-laminate of layered double hydroxide results in a hi... more Synergistic manipulation in intra- and inter-laminate of layered double hydroxide results in a highly conductive and robust anion conductor.

Solid State Ionics, 2019

Abstract This study presents a generic method to increase the hydroxide conductivity of anion exc... more Abstract This study presents a generic method to increase the hydroxide conductivity of anion exchange membranes by tuning the microphase separation structure. Graphene oxide was functionalized with macromolecular brushes for the first time by a precipitation polymerization method. Densely-functionalized imidazolium groups were aligned in the configuration of macromolecular brushes to act as hydroxide-conductive groups, which endow the functionalized graphene oxide with a high ion exchange capacity value of 3.05 mmol g−1. Polymer-inorganic composite membrane for anion exchange membrane fuel cell was fabricated by incorporating the imidazolium-functionalized graphene oxide into imidazolium-functionalized bisphenol A-type polysulfone. The dense imidazolium groups manipulated the aggregation of conductive groups at the polymer/filler interfaces to induce the well-defined microphase structure of composite membranes, constructing low-resistance channels for ionic transport. The activation energy of hydroxide transport in composite membranes was reduced to 25.17–13.62 kJ mol−1, in comparison with 28.63 kJ mol−1 for control membrane. The hydroxide conductivity of composite membrane was elevated to 22.02 mS cm−1 at 30 °C, which is 2.10 times of that for control membrane. The maximum power density of single fuel cell of 78.7 mW cm−2 at 60 °C was thus achieved.

ACS Sustainable Chemistry & Engineering, 2018

Metal–organic frameworks or MOFs have witnessed a phenomenal rise owing to a highly tunable synth... more Metal–organic frameworks or MOFs have witnessed a phenomenal rise owing to a highly tunable synthetic chemistry allowing flexibility in the selection of its constituents, namely metal nodes and linkers. Combined with their superior adsorption and diffusion properties, MOFs have become one of the most promising nanoporous materials for the fabrication of high-performance membranes. Polycrystalline MOF membranes have yielded one of the best gas separation performances, and are expected to replace or partially substitute thermally driven separation processes. In this respect, we present our perspective on the crystal engineering of MOF films that offers control over nucleation and growth of MOFs, film morphology, lattice defects, and therefore the separation performance of the resulting MOF films.

Journal of Membrane Science, 2018

Abstract Organic polymeric microspheres grafted with ionic brushes are fillers incorporated into ... more Abstract Organic polymeric microspheres grafted with ionic brushes are fillers incorporated into imidazolium functionalized polysulfone (ImPSF) forming a composite membrane. The ionic brushes create continuous and bulky hydrophilic phases in the ImPSF forming a composite membrane with the aggregation of hydrophilic groups at the brush/polymer interfaces. The hydrophilic phases promote ionic transport with decreased activation energies from 14.45 to 11.42 kJ mol−1 and increased effective ionic mobility from 0.84 × 10−4 to 2.19 × 10−4 cm2 s−1 V−1 compared to ImPSF with no brushes. The composite membrane shows increased hydroxide conductivities (up to 38.33 S cm−1 at 30 °C and 64.58 S cm−1 at 60 °C), which is 2.66 times and 2.01 times of the hydroxide conductivity of ImPSF membrane at the same conditions, respectively. Stability of the composite membrane is increased by replacing the imidazolium groups of polymer matrix and organic microsperes with more stable quaternary ammonium groups, such as N,N-dimethylhexylamine (DMHA). The residual hydroxide conductivity ratio of the composite membrane-DMHA is 83.4% after treating by 2.0 M aqueous NaOH at 80 °C for 96 h (vs. only 28.6% for the composite membrane with imidazolium groups under the same conduction). Meanwhile, the doubling increment of hydroxide conductivity in the composite membrane vs. the control membrane can be still retained (23.87 mS cm−1 for the composite membrane-DMHA vs. 8.97 mS cm−1 for the control membrane-DMHA).

Nature communications, Jan 6, 2018

The single-layer graphene film, when incorporated with molecular-sized pores, is predicted to be ... more The single-layer graphene film, when incorporated with molecular-sized pores, is predicted to be the ultimate membrane. However, the major bottlenecks have been the crack-free transfer of large-area graphene on a porous support, and the incorporation of molecular-sized nanopores. Herein, we report a nanoporous-carbon-assisted transfer technique, yielding a relatively large area (1 mm), crack-free, suspended graphene film. Gas-sieving (H/CH selectivity up to 25) is observed from the intrinsic defects generated during the chemical-vapor deposition of graphene. Despite the ultralow porosity of 0.025%, an attractive H permeance (up to 4.1 × 10 mol m s Pa) is observed. Finally, we report ozone functionalization-based etching and pore-modification chemistry to etch hydrogen-selective pores, and to shrink the pore-size, improving H permeance (up to 300%) and H/CH selectivity (up to 150%). Overall, the scalable transfer, etching, and functionalization methods developed herein are expected t...

International Journal of Hydrogen Energy, 2015

ABSTRACT Two kinds of polymeric ellipsoidal microcapsules (EMCs) with different functional groups... more ABSTRACT Two kinds of polymeric ellipsoidal microcapsules (EMCs) with different functional groups (phosphoric acid groups and imidazole groups) were synthesized via precipitation polymerization and incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to prepare hybrid membranes. The structure, thermal stability and composition of EMCs were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The quasi-one dimensional structure endowed EMCs with high water uptake and water retention. Especially, for the hybrid membranes filled with 5 wt.% phosphoric acid-functionalized polymeric EMCs, water uptake was increased from 19.0% for pristine SPEEK membranes to 58.2%, and the water retention was 15.1% after 180 min testing at 40 °C and 20% RH, which is threefold and ninefold higher than those of pristine SPEEK membranes, respectively. Particularly, the proton conductivity at low RH was still up to 3.51 × 10−3 S/cm after 60 min testing. The results manifested that the ellipsoidal microcapsules, as a new kind of filler, had great potential in enhancing the water retention and low-humidity proton conductivity of proton exchange membranes.

Angewandte Chemie International Edition, 2017

Achieving high membrane performance in terms of gas permeance and carbon dioxide selectivity is a... more Achieving high membrane performance in terms of gas permeance and carbon dioxide selectivity is an important target in carbon capture. Aiming to manipulate the channel affinity towards CO2 to implement efficient separations, gas separation membranes containing CO2 -philic and non-CO2 -philic nanodomains in the interlayer channels of graphene oxide (GO) were formed by intercalating poly(ethylene glycol) diamines (PEGDA). PEGDA reacts with epoxy groups on the GO surface, constructing CO2 -philic nanodomains and rendering a high sorption capacity, whereas unreacted GO surfaces give non-CO2 -philic nanodomains, rendering low-friction diffusion. Owing to the orderly stacking of nanochannels through cross-linking and the heterogeneous nanodomains with moderate CO2 affinity, a GO-PEGDA500 membrane exhibits a high CO2 permeance of 175.5 GPU and a CO2 /CH4 selectivity of 69.5, which is the highest performance reported for dry-state GO-stacking membranes.

Electrochimica Acta, 2017

In this study, a well-designed polysulfone with dense phenyl groups surrounding its backbone (des... more In this study, a well-designed polysulfone with dense phenyl groups surrounding its backbone (designated as P(ES1-co-ES2)) was synthesized and then modified with abundant quaternary ammoniums (QA). The QA functionalized P(ES1-co-ES2) was added to QA functionalized poly (ether ether ketone) with N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) as crosslinking reagent to fabricate anion exchange imembranes (AEM). The incorporation of abundant QA groups substantially increased the ion exchange capacity of the blend membranes. Meanwhile, the densely QA functionalized P(ES1-co-ES2) acted as “hydroxide ion wires” in blend membranes, constructing efficient ion channels for high-speed ion transfer. High hydroxide conductivity up to 215.4 mS cm−1 at 90 °C and the maximum power density of single fuel cell up to 137.2 mW cm−2 at 60 °C were thus achieved. In addition, the strong covalent interaction caused by TMHDA led to significantly enhanced physical stability (anti-swelling, tensile strength and elongation etc.), while the steric hindrance by the long aliphatic chain of TMHDA enhanced the chemical stability of the blend membranes. This study presents a novel AEM with simultaneously enhanced hydroxide conductivity, physical and chemical stabilities.

ACS applied materials & interfaces, Jan 23, 2017

Nafion, as a state-of-the-art solid electrolyte for proton exchange membrane fuel cells (PEMFCs),... more Nafion, as a state-of-the-art solid electrolyte for proton exchange membrane fuel cells (PEMFCs), suffers from drastic decline in proton conductivity with decreasing humidity, which significantly restricts the efficient and stable operation of the fuel cell system. In this study, the proton conductivity of Nafion at low relative humidity (RH) was remarkably enhanced by incorporating multifunctional graphene oxide (GO) nanosheets as multifunctional fillers. Through surface-initiated atom transfer radical polymerization of sulfopropyl methacrylate (SPM) and poly(ethylene glycol) methyl ether methacrylate, the copolymer-grafted GO was synthesized and incorporated into the Nafion matrix, generating efficient paths at the Nafion-GO interface for proton conduction. The Lewis basic oxygen atoms of ethylene oxide (EO) units and sulfonated acid groups of SPM monomers served as additional proton binding and release sites to facilitate the proton hopping through the membrane. Meanwhile, the hy...

ACS applied materials & interfaces, Jan 9, 2017

The creation of interconnected ionic nanoaggregates within solid electrolytes is a crucial yet ch... more 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 pre-designed hybrid core-shell nanoarchitecture within nonionic polymer membranes: i) synthesizing core-shell nanoparticles composed of SiO2/densely quaternary ammonium functionalized polystyrene. Due to 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 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...