Ji-Sen Li

Polyoxometalate-Incorporated Metallapillararene/Metallacalixarene Metal-Organic Frameworks as Anode Materials for Lithium Ion Batteries

A series of remarkable crystalline compounds containing metallapillararene/metallacalixarene metal-organic frameworks (MOFs), [Ag5(pyttz)3·Cl·(H2O)][H3SiMo12O40]·3H2O (1), [Ag5(trz)6][H5SiMo12O40] (2), [Ag5(trz)6][H5GeMo12O40] (3), and [Ag5(trz)6][H4PW12O40] (4) (pyttz = 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, trz = 1,2,4-triazole), have been obtained by using a simple one-step hydrothermal reaction of silver nitrate, pyttz for 1 and trz for 2-4, and Keggin type polyoxometalates (POMs). Crystal analysis reveals that Keggin POMs have been successfully incorporated in the windows of the metallapillararene/metallacalixarene MOFs in compounds 1-4. In addition, the Keggin silicomolybdenate-based hybrid compounds 1 and 2 were used as anode materials in lithium ion batteries (LIBs), which exhibited promising electrochemical performance with the first discharge capacities of 1344 mAh g-1 for 1 and 1452 mAh g-1 for 2, and this stabilized at 520 mAh g-1 for 1 and 570 mAh g-1 for 2 after 100 cycles at a current density of 100 mA g-1. The performances are better than that of (NBu4)4[SiMo12O40] matrix and commercial graphite anodes.

In situ-generated Co@nitrogen-doped carbon nanotubes derived from MOFs for efficient hydrogen evolution under both alkaline and acidic conditions

Electrocatalytic water splitting producing hydrogen is of great importance for renewable energy storage and conversion technologies. In recent years, low-cost and high-efficiency electrocatalysts for the hydrogen evolution reaction (HER) have attracted a lot of attention. Herein, we report that in situ-generated Co@nitrogen-doped carbon nanotubes (Co@NCNTs) derived from metal–organic frameworks (MOFs) were fabricated by a facile method and corresponding HER activities were investigated in detail. Among these hybrids, the Co@NCNTs-800 hybrid shows outstanding electrocatalytic activity and stability, which is one of the best Co-based electrocatalysts for the HER under both alkaline and acidic conditions reported to date, benefiting from the synergistic effect from Co nanoparticles, N dopants, and CNTs. Most importantly, this work paves a new way for designing novel, efficient, and inexpensive HER electrocatalysts derived from MOFs as promising alternatives to Pt or Pt-based materials.

Confined Molybdenum Phosphide in P-Doped Porous Carbon as Efficient Electrocatalysts for Hydrogen Evolution

Highly efficient electrocatalysts for hydrogen evolution reactions (HER) are crucial for electrochemical water splitting, where high-cost and low-abundance Pt-based materials are the benchmark catalysts for HER. Herein, we report the fabrication of MoP nanoparticles confined in P-doped porous carbon (MoP@PC) via a metal-organic framework-assisted route for the first time. Remarkably, due to the synergistic effects of MoP nanocrystals, P dopant, and porous carbon, the resulting MoP@PC composite exhibits superior HER catalytic activity with an onset overpotential of 97 mV, a Tafel slope of 59.3 mV dec-1, and good long-term durability, which compares to those of most reported MoP-based HER catalysts. Most importantly, the work opens a new route in the development of high-performance nonprecious HER electrocatalysts derived from MOFs.

Fabrication and electrochemical performance of unprecedented POM-based metal–carbene frameworks

Unprecedented polyoxometalate based metal–carbene frameworks (POM-based MCFs) [Cu10(H3trz)4(Htrz)4](HPW12O40) (1) and [Cu10(H3trz)4(Htrz)4](H2SiW12O40) (2) have been fabricated via a hydrothermal reaction between 1,2,4-triazole and Cu(CH3COO)2 with the saturated Keggin polyoxoanion [PW12O40]3−/[SiW12O40]4− as a template for the first time. Single crystal X-ray diffraction analysis reveals the successful encapsulation of Keggin POMs into the three-dimensional POM-based MCFs with lvt-a topology based on their effective coordination with Cu ions. Interestingly, these novel 3D POM-based MCFs exhibit good electrochemical performance in lithium-ion batteries (LIBs) as anode materials, with first discharge capacities of ca. 1620 and 1245 mA h g−1 for 1 and 2, respectively, at a current density of 100 mA g−1, and stabilized discharge capacities of ca. 570 mA h g−1 for 1 and 426 mA h g−1 for 2 after 100 cycles. This, in combination with their high thermal stability, suggests their good LIB application potential.

Facile synthesis of FeCo alloys encapsulated in nitrogen-doped graphite/carbon nanotube hybrids: efficient bi-functional electrocatalysts for oxygen and hydrogen evolution reactions

The development of highly efficient and durable non-noble metal catalysts for full water splitting has attracted tremendous attention in recent years. Herein, for the first time, we present a facile synthesis of FeCo alloys encapsulated in a nitrogen-doped graphite/carbon nanotube (FeCo@NG/NCNT) hybrid using MOFs as precursors. Impressively, due to the synergistic interplay between FeCo alloys and NG/NCNTs, the resultant hybrid as a bi-functional electrocatalyst demonstrates an outstanding electrocatalytic performance for both oxygen and hydrogen evolution reactions in alkaline electrolytes. Most importantly, this work paves a new route in rationally designing and developing high-efficienct and stable bifunctional electrocatalysts for overall water splitting.

Assembly of Multifold Helical Polyoxometalate-Based Metal–Organic Frameworks as Anode Materials in Lithium-Ion Batteries

For exploring the multifold helical fabrication of polyoxometalate (POM)-based hybrid compounds, four POM-based crystalline compounds with different meso-helices, H3[Ag27(trz)16(H2O)6][SiW12O40]2·5H2O (1), H[Ag27(trz)16(H2O)4][PW12O40]2·2H2O (2), [Ag23(trz)14(H2O)2][HSiW12O40] (3), and [Ag23(trz)14(H2O)2][PW12O40] (4), were successfully isolated by using the delicate 1,2,3-triazole ligand and silver ions in this work. Crystal analysis reveals that compounds 1 and 2 and compounds 3 and 4 are isomorphous and display 2-/4-fold mixed meso-helices and simple 2-fold meso-helices, respectively. In addition, due to the reversible multielectron redox behavior and electron storage functions of POMs, compounds 1 and 3 were studied as anode materials in lithium-ion batteries (LIBs). Compounds 1 and 3 show very high lithiation capacities (1356 and 1140 mAh g-1, respectively) in the initial cycle, which are much higher than those of (NBu4)4[SiW12O40] and commercial graphite at the current density of 100 mA g-1. More importantly, both compounds also show good stable performance after 100 cycles.