Browsing by Author "Guo, Dong"
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- Block copolymer derived uniform mesopores enable ultrafast electron and ion transport at highmass loadingsLiu, Tianyu; Zhou, Zhenping; Guo, Yichen; Guo, Dong; Liu, Guoliang (Nature Research, 2019)High mass loading and fast charge transport are two crucial but often mutually exclusive characteristics of pseudocapacitors. On conventional carbon supports, high mass loadings inevitably lead to sluggish electron conduction and ion diffusion due to thick pseudocapacitive layers and clogged pores. Here we present a design principle of carbon supports, utilizing self-assembly and microphase-separation of block copolymers. We synthesize porous carbon fibers (PCFs) with uniform mesopores of 11.7 nm, which are partially filled with MnO2 of <2 nm in thickness. The uniform mesopores and ultrathin MnO2 enable fast electron/ion transport comparable to electrical-double-layer-capacitive carbons. At mass loadings approaching 7mg cm−2, the gravimetric and areal capacitances of MnO2 (~50% of total mass) reach 1148 F g−1 and 3141 mF cm−2, respectively. Our MnO2-coated PCFs outperform other MnO2-based electrodes at similar loadings, highlighting the great promise of block copolymers for designing PCF supports for electrochemical applications.
- Block Copolymer-Derived Porous Carbon Fibers Enable High MnO2 Loading and Fast Charging in Aqueous Zinc-Ion BatteryGuo, Dong; Zhao, Wenqi; Pan, Fuping; Liu, Guoliang (Wiley-V C H Verlag, 2022-04)Rechargeable aqueous Zn MnO2 batteries are promising for stationary energy storage because of their high energy density, safety, environmental benignity, and low cost. Conventional gravel MnO2 cathodes have low electrical conductivity, slow ion (de-)insertion, and poor cycle stability, resulting in poor recharging performance and severe capacity fading. To improve the rechargeability of MnO2, strategies have been devised such as depositing micrometer-thick MnO2 on carbon cloth and blending nanostructured MnO2 with additives and binders. The low electrical conductivity of binders and sluggish ion (de)insertion in micrometer-thick MnO2, however, still limit the fastcharging performance. Herein, we have prepared porous carbon fiber (PCF) supported MnO2 cathodes (PCF@MnO2), comprised of nanometer-thick MnO2 uniformly deposited on electrospun block copolymer-derived PCF that have abundant uniform mesopores. The high electrical conductivity of PCF, fast electrochemical reactions in nanometer-thick MnO2, and fast ion transport through porous nonwoven fibers contribute to a high rate capability at high loadings. PCF@MnO2, at a MnO2 loading of 59.1 wt%, achieves a MnO2-based specific capacity of 326 and 184 mAhg(-1) at a current density of 0.1 and 1.0 Ag-1, respectively. Our approach of block copolymer-based PCF as a support for zinc-ion cathode inspires future designs of fastcharging electrodes with other active materials.
- Block Copolymer-derived Porous Polyimides and Carbon for High-Performance Energy StorageGuo, Dong (Virginia Tech, 2022-05-12)Block copolymer-derived nanoporous materials are featured with microstructures defined by the microphase separation of constituent blocks, enabling various applications in energy storage. Dictated by the molecular weights and volume fractions of constituent blocks, the microphase separation forms nanoscale microstructures of 1-100 nm. Selective removal of a sacrificial phase produces nanopores with tailored pore width, continuity, and tortuosity. The remaining phase customizes the properties of resulting nanoporous materials, including specific surface area, electrical conductivity/insulation, and mechanical performance. Therefore, block copolymer-derived porous materials are felicitous for use in high-performance energy storage. This dissertation presents the utilization of block copolymers to derive nanoporous materials: i) high-modulus polyimide separators for lithium-metal batteries, and ii) high-surface-area carbon electrodes for fast-charging zinc-ion batteries. In lithium-metal batteries, the dendritic growth of lithium leads to deteriorating performance and severe safety concerns. Suppressing lithium dendrites is imperative to guarantee both high performance and safe cycling. Mesoporous polyimide separators are promising for dendrite suppression: i) the mesopores are smaller than the width of lithium dendrites, preventing lithium dendrites from penetrating the separator. ii) The high-modulus polyimide ceases the growth of lithium dendrites. Herein, this dissertation reports a mesoporous polyimide separator produced by thermalizing polylactide-b-polyimide-b-polylactide at 280 °C. The mesoporous polyimide separator exhibits a median pore width of 21 nm and a storage modulus of 1.8 GPa. When serving as a dendrite-suppressing separator in lithium-metal batteries, the mesoporous polyimide separator enables safe cycling for 500 hours at a current density of 4 mA/cm2. In zinc-ion batteries, developing cathodes compatible with fast charging remains a challenge. Conventional MnO2 gravel cathodes suffer from low electrical conductivity and slow ion (de-)insertion, resulting in poor recharging performance. In this dissertation, porous carbon fiber (PCF) supported MnO2 (PCF@MnO2), comprising nanometer-thick MnO2 deposited on block copolymer-derived PCF, serves as a fast-charging cathode. The high electrical conductivity of PCF and fast ion (de-)insertion in nanometer-thick MnO2 both contribute to a high rate capability. The PCF@MnO2 cathode, with a MnO2 loading of 59.1 wt%, achieves a MnO2-based specific capacity of 326 and 184 mAh/g at a current density of 0.1 and 1.0 A/g, respectively. This dissertation investigates approaches to utilizing block copolymers-derived nanoporous materials for high-performance energy storage. Those approaches are envisaged to inspire the design of block copolymer-derived nanoporous materials, and advance the development of "beyond Li-ion" energy storage.
- Stereoselective photoredox ring-opening polymerization of O-carboxyanhydridesFeng, Quanyou; Yang, Lei; Zhong, Yongliang; Guo, Dong; Liu, Guoliang; Xie, Linghai; Huang, Wei; Tong, Rong (Nature, 2018-04-19)Biodegradable polyesters with various tacticities have been synthesized by means of stereoselective ring-opening polymerization of racemic lactide and β-lactones but with limited side-chain groups. However, stereoselective synthesis of functional polyesters remains challenging from O-carboxyanhydrides that have abundant pendant side-chain functional groups. Herein we report a powerful strategy to synthesize stereoblock polyesters by stereoselective ring-opening polymerization of racemic O-carboxyanhydrides with the use of photoredox Ni/Ir catalysts and a selected Zn complex with an achiral ligand. The obtained stereoblock copolymers are highly isotactic with high molecular weights ( > 70 kDa) and narrow molecular weight distributions (Mw/Mn < 1.1), and they display distinct melting temperatures that are similar to their stereocomplex counterparts. Furthermore, in one-pot photoredox copolymerization of two different O-carboxyanhydrides, the use of such Zn complex mediates kinetic resolution of the comonomers during enchainment and shows a chirality preference that allows for the synthesis of gradient copolymers.