Yu-Jia Tang

Porous Molybdenum‐Based Hybrid Catalysts for Highly Efficient Hydrogen Evolution

We have synthesized a porous Mo-based composite obtained from a polyoxometalate-based metal-organic framework and graphene oxide (POMOFs/GO) using a simple one-pot method. The MoO2 @PC-RGO hybrid material derived from the POMOFs/GO composite is prepared at a relatively low carbonization temperature, which presents a superior activity for the hydrogen-evolution reaction (HER) in acidic media owing to the synergistic effects among highly dispersive MoO2 particles, phosphorus-doped porous carbon, and RGO substrates. MoO2 @PC-RGO exhibits a very positive onset potential close to that of 20 % Pt/C, low Tafel slope of 41 mV dec(-1) , high exchange current density of 4.8×10(-4)  A cm(-2) , and remarkable long-term cycle stability. It is one of the best high-performance catalysts among the reported nonprecious metal catalysts for HER to date.

Heteroatoms ternary-doped porous carbons derived from MOFs as metal-free electrocatalysts for oxygen reduction reaction

The nitrogen (N), phosphorus (P) and sulphur (S) ternary-doped metal-free porous carbon materials have been successfully synthesized using MOFs as templates (denoted as NPS-C-MOF-5) for oxygen reduction reaction (ORR) for the first time. The influences of porous carbons from carbonizing different MOFs and carbonization temperature on ORR have been systematically investigated. Due to the synergistic effect of N, P and S ternary-doping, the NPS-C-MOF-5 catalyst shows a higher onset potential as a metal-free electrocatalyst for ORR among the currently reported metal-free electrocatalysts, very close to the commercial Pt-C catalyst. In particular, the kinetic limiting current density of NPS-C-MOF-5 catalyst at −0.6 V is up to approximate −11.6 mA cm−2, which is 1.2 times higher than that of the commercial Pt-C catalyst. Furthermore, the outstanding methanol tolerance and excellent long-term stability of NPS-C-MOF-5 are superior to those of the commercial Pt-C catalyst for ORR in alkaline media.

Metal–organic framework templated nitrogen and sulfur co-doped porous carbons as highly efficient metal-free electrocatalysts for oxygen reduction reactions

A novel MOF-templated nitrogen and sulphur co-doped porous material has been synthesized as an efficient electrocatalyst for oxygen reduction reactions (ORRs) for the first time. The representative NS(3 : 1)–C-MOF-5 catalyst shows the highest onset potential, and is even comparable to commercial Pt–C catalyst, due to the synergistic effect of N and S co-doping.

Polyoxometalate-based metal–organic framework-derived hybrid electrocatalysts for highly efficient hydrogen evolution reaction

The design and fabrication of electrocatalysts for HER, with superior activity and stability, still remain a significant challenge for clean and renewable energy technologies. Here we have synthesized Fe3C/Mo2C-containing N, P co-doped graphitic carbon derived from POM@MOF-100 (Fe) (denoted as Fe3C/Mo2C@NPGC) via a “killing three birds with one stone” strategy. The Fe3C/Mo2C@NPGC catalyst demonstrates excellent electrocatalytic activity and stability towards HER with a low onset overpotential of 18 mV (vs. RHE), small Tafel slope of 45.2 mV dec−1, as well as long-term durability for 10 h, which is one of the best non-noble metal HER catalysts in acidic media reported so far. Most importantly, this work opens up exciting opportunities for fabricating novel and highly efficient electrocatalysts to replace Pt or Pt-based catalysts utilizing POM-based metal–organic frameworks (MOFs) as precursors.

Coralloid Co2P2O7 Nanocrystals Encapsulated by Thin Carbon Shells for Enhanced Electrochemical Water Oxidation

Core-shell nanohybrids containing cheap inorganic nanocrystals and nanocarbon shells are promising electrocatalysts for water splitting or other renewable energy options. Despite that great progress has been achieved, biomimetic synthesis of metal phosphates@nanocarbon core-shell nanohybrids remains a challenge, and their use for electrocatalytic oxygen evolution reaction (OER) has not been explored. In this paper, novel nanohybrids composed of coralloid Co2P2O7 nanocrystal cores and thin porous nanocarbon shells are synthesized by combination of the structural merits of supramolecular polymer gels and a controllable thermal conversion technique, i.e., temperature programmable annealing of presynthesized supramolecular polymer gels that contain cobalt salt and phytic acid under a proper gas atmosphere. Electrocatalytic tests in alkaline solution show that such nanohybrids exhibit greatly enhanced electrocatalytic OER performance compared with that of Co2P2O7 nanostructure. At a current density of 10 mA cm(-2), their overpotential is 0.397 V, which is much lower than that of Co2P2O7 nanostructures, amorphous Co-Pi nanomaterials, Co(PO3)2 nanosheets, Pt/C, and some reported OER catalysts, and close to that of commercial IrO2. Most importantly, both of their current density at the overpotential over 0.40 V and durability are superior to those of IrO2 catalyst. As revealed by a series of spectroscopic and electrochemical analyses, their enhanced electrocatalytic performance results from the presence of thin porous nanocarbon shells, which not only improve interfacial electron penetration or transfer dynamics but also vary the coordination environment and increase the number of active 5-coordinated Co(2+) sites in Co2P2O7 cores.

Carbon nanodots functional MOFs composites by a stepwise synthetic approach: enhanced H2 storage and fluorescent sensing

Metal–organic frameworks (MOFs) hybrid composites, combining the advantages of both MOFs and nanoparticles, may exhibit unprecedented properties. Herein, carbon nanodots (Cdots) functional UMCM-1 composites (Cdots@UMCM-1a) were successfully synthesized by a stepwise synthetic approach for the first time. The hybrids retain the intact structure of MOFs with high luminescence and longer stability. Due to the interactions between polar functional groups at the surface of the Cdots and H2 molecules, Cdots@UMCM-1a efficiently enhanced H2 storage capacity. Most importantly, Cdots@UMCM-1a exhibited highly fluorescent sensing for nitroaromatic explosives owing to the double effect of porous MOFs and fluorescent Cdots. This work will pave new avenues for the fabrication of novel and multifunctional MOFs composites.

Phenyl Groups Result in the Highest Benzene Storage and Most Efficient Desulfurization in a Series of Isostructural Metal–Organic Frameworks

A series of isoreticular metal-organic frameworks (MOFs; NENU-511-NENU-514), which all have high surface areas and strong adsorption capacities, have been successfully constructed by using mixed ligands. NENU-513 has the highest benzene capacity of 1687 mg g(-1) at 298 K, which ranks as the top MOF material among those reported up to now. This NENU series has been used for adsorptive desulfurization because of its permanent porosity. The results indicate that this series has a higher adsorptive efficiency in the removal of organosulfur compounds than other MOF materials, especially NENU-511, which has the highest adsorptive efficiency in the ambient atmosphere. This study proves that the design and synthesis of targeted MOFs with higher surface areas and with functional groups present is an efficient method to enhance benzene-storage capacity and the adsorption of organosulfur compounds.

Efficient Electrocatalyst for the Hydrogen Evolution Reaction Derived from Polyoxotungstate/Polypyrrole/Graphene

Efficient hydrogen evolution reaction (HER) from water by electrocatalysis using cost-effective materials is critical to realize the clean hydrogen production. Herein, with controlling the structure and composition of polyoxotungstate/conductive polypyrrole/graphene (PCG) precursor precisely and followed by a temperature-programmed reaction, we developed a highly active and stable catalyst: NC@Wx C/NRGO (NC: nitrogen-doped porous carbon, NRGO: nitrogen-doped reduced graphene oxide). The composite presents splendid performance towards HER in acidic media, with a small onset overpotential of 24 mV versus RHE (reversible hydrogen electrode), a low Tafel slope of 58.4 mV dec-1 , a low overpotential of 100 mV at 10 mA cm-2 , and remarkable long-term cycle stability. This is one of the highest HER catalysts among the tungsten carbide-based materials ever reported.

Bimetallic Carbides-Based Nanocomposite as Superior Electrocatalyst for Oxygen Evolution Reaction

The development of highly efficient and low-cost oxygen evolution electrocatalysts is extremely imperative for the new energy technology. Transition metal carbides have been investigated as remarkable hydrogen evolution reaction (HER) electrocatalysts but undesired oxygen evolution reaction (OER) electrocatalysts and need further study. Here, a cobalt-molybdenum-based bimetallic carbide coated by N-doped porous carbon and anchored on N-doped reduced graphene oxide film (Co6Mo6C2/NCRGO) is synthesized by directly carbonizing the Co-doped polyoxometalate/conductive polymer/graphene oxide (Co-PCG) precursors. The precise control of the Co/Mo molar ratio in the Co-PCG precursor is of critical importance to synthesize pure phase bimetallic carbide of Co6Mo6C2. As the highly active and robust OER electrocatalyst, the Co6Mo6C2/NCRGO composite exhibits excellent activity in alkaline solution, affording a low overpotential of 260 mV versus RHE at 10 mA cm-2, a small Tafel slope of 50 mV dec-1, as well as long-term stability. The superior OER performances are strongly associated with the active Co6Mo6C2 particles, polypyrrole (PPy)-derived N-doped porous carbon, and the conductive RGO films. Remarkably, it is the first evidence that the bimetallic carbides were used as the OER catalysts with such high OER activity.

Highly active Co–Mo–C/NRGO composite as an efficient oxygen electrode for water–oxygen redox cycle

The slow kinetics of the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) have hindered energy conversion and storage greatly. Design of a new class of low-cost and highly efficient electrocatalysts for the water–oxygen redox cycle (WORC) system including OER and ORR is considered a huge challenge. Controlled synthesis of unique and stable precursors as a perfect platform to synthesize target products with diverse compositions are of vital importance. Herein, we synthesized a metal/metal carbide-based composite (denoted as Co–Mo–C/NRGO-1) by directly carbonizing Co-doped polyoxometalate/conductive polymer/graphene precursor (Co-PCG) as an efficient bi-functional electrocatalyst. The resulting Co–Mo–C/NRGO-1 composite exhibited superior electrocatalytic activity for OER with an ultra-low Tafel slope of 42 mV dec−1, a small overpotential of 330 mV vs. RHE at the current density of 10 mA cm−2 and long-term stability in alkaline medium. The ORR performance was also investigated with a positive onset potential (∼−95 mV vs. Ag/AgCl), remarkable stability over 30 000 s and good tolerance to methanol crossover. Most importantly, the OER performance of Co–Mo–C/NRGO-1 was the best among all the reported carbide-based materials and was comparable to the best OER electrodes.