Yonghua Du

Post-synthesis modification of a metal–organic framework to construct a bifunctional photocatalyst for hydrogen production

To construct photocatalytically active MOFs, various strategies have recently been developed. We have synthesized and characterized a new metal–organic framework (MOF-253-Pt) material through immobilizing a platinum complex in 2,2′-bipyridine-based microporous MOF (MOF-253) using a post-synthesis modification strategy. The functionalized MOF-253-Pt serves both as a photosensitizer and a photocatalyst for hydrogen evolution under visible-light irradiation. The photocatalytic activity of MOF-253-Pt is approximately five times higher than that of the corresponding complex. The presence of the short Pt⋯Pt interactions in the framework was revealed with extended X-ray absorption fine structure (EXAFS) spectroscopy and low temperature luminescence. These interactions play an important role in improving the photocatalytic activity of the resulting MOF.

Nitrogen-doped cobalt phosphate@nanocarbon hybrids for efficient electrocatalytic oxygen reduction

The development of efficient non-noble metal electrocatalysts for the oxygen reduction reaction (ORR) is still highly desirable before non-noble metal catalysts can replace platinum catalysts. Herein, we have synthesized a new type of ORR catalyst, Co3(PO4)2C-N/rGOA, containing N-coordinated cobalt phosphate, through the thermal treatment of a phosphonate-based metal–organic framework (MOF). Co3(PO4)2C-N/rGOA exhibits not only a comparable onset potential and half-wave potential but also superior stability to the commercial Pt/C catalyst for the ORR in alkaline solutions (0.1 and 1.0 M KOH). A combination of structural characterization (e.g., XPS, HRTEM, XANES, and EXAFS) and electrochemical analysis shows that the high ORR activity of the Co3(PO4)2C-N/rGOA catalyst should be attributed to the co-existence of N-doped graphitic carbon and the cobalt phosphate with Co–N species that boost the activity of the cobalt phosphate. These findings open an avenue for exploring the use of phosphonate-based MOFs for energy conversion and storage applications.

XAFCA: a new XAFS beamline for catalysis research

A new X-ray absorption fine-structure (XAFS) spectroscopy beamline for fundamental and applied catalysis research, called XAFCA, has been built by the Institute of Chemical and Engineering Sciences, and the Singapore Synchrotron Light Source. XAFCA covers the photon energy range from 1.2 to 12.8u2005keV, making use of two sets of monochromator crystals, an Si (111) crystal for the range from 2.1 to 12.8u2005keV and a KTiOPO4 crystal [KTP (011)] for the range between 1.2 and 2.8u2005keV. Experiments can be carried out in the temperature range from 4.2 to 1000u2005K and pressures up to 30u2005bar for catalysis research. A safety system has been incorporated, allowing the use of flammable and toxic gases such as H2 and CO.

Preparation of High‐Percentage 1T‐Phase Transition Metal Dichalcogenide Nanodots for Electrochemical Hydrogen Evolution

Nanostructured transition metal dichalcogenides (TMDs) are proven to be efficient and robust earth-abundant electrocatalysts to potentially replace precious platinum-based catalysts for the hydrogen evolution reaction (HER). However, the catalytic efficiency of reported TMD catalysts is still limited by their low-density active sites, low conductivity, and/or uncleaned surface. Herein, a general and facile method is reported for high-yield, large-scale production of water-dispersed, ultrasmall-sized, high-percentage 1T-phase, single-layer TMD nanodots with high-density active edge sites and clean surface, including MoS2 , WS2 , MoSe2 , Mo0.5 W0.5 S2 , and MoSSe, which exhibit much enhanced electrochemical HER performances as compared to their corresponding nanosheets. Impressively, the obtained MoSSe nanodots achieve a low overpotential of -140 mV at current density of 10 mA cm-2 , a Tafel slope of 40 mV dec-1 , and excellent long-term durability. The experimental and theoretical results suggest that the excellent catalytic activity of MoSSe nanodots is attributed to the high-density active edge sites, high-percentage metallic 1T phase, alloying effect and basal-plane Se-vacancy. This work provides a universal and effective way toward the synthesis of TMD nanostructures with abundant active sites for electrocatalysis, which can also be used for other applications such as batteries, sensors, and bioimaging.

Improved Reversibility of Fe3+/Fe4+ Redox Couple in Sodium Super Ion Conductor Type Na3Fe2(PO4)3 for Sodium-Ion Batteries

The methodology employed here utilizes the sodium super ion conductor type sodium iron phosphate wrapped with conducting carbon network to generate a stable Fe3+ /Fe4+ redox u2009 couple, thereby exhibiting higher operating voltage and energy density of sodium-ion batteries. This new class of sodium iron phosphate wrapped by carbon also displays a cycling stability with >96% capacity retention after 200 cycles.

Metal–organic framework immobilized cobalt oxide nanoparticles for efficient photocatalytic water oxidation

Water oxidation reactions driven by visible light play an important role in solar fuel production. Recently, catalysts based on earth abundant elements, such as cobalt oxides, have been studied extensively. Out of many factors, the catalyst particle size certainly affects the photocatalytic activity. To reduce the catalyst particle size below 5 nm without encountering agglomeration, a practical approach is to adopt a proper substrate to immobilize the catalyst nanoparticles. Herein, we utilized MIL-101, a highly porous and robust metal–organic framework (MOF), to immobilize cobalt oxide nanoparticles by a simple and facile method involving double solvent impregnation followed by a mild heat treatment. With cobalt loading in the range of 1.4–4.9 wt%, ultra small cobalt oxide nanoparticles (2–3 nm) have been successfully immobilized in the cages of MIL-101 with a good dispersion and narrow size distribution. Photocatalytic and electrochemical studies have indicated that the resultant cobalt oxide nanoparticles embedded in the MOF are highly efficient and stable water oxidation catalysts. A high turnover frequency (TOF) of 0.012 s−1 per cobalt atom and oxygen yield of 88% were obtained under the optimized conditions in the [Ru(bpy)3]2+–Na2S2O8 system. The MIL-101 support plays the roles of confining the size of catalyst nanoparticles and promoting charge transfer, leading to an enhanced photocatalytic performance.

A Highly Efficient Oxygen Evolution Catalyst Consisting of Interconnected Nickel–Iron‐Layered Double Hydroxide and Carbon Nanodomains

In this work, a one-pot solution method for direct synthesis of interconnected ultrafine amorphous NiFe-layered double hydroxide (NiFe-LDH) (<5 nm) and nanocarbon using the molecular precursor of metal and carbon sources is presented for the first time. During the solvothermal synthesis of NiFe-LDH, the organic ligand decomposes and transforms to amorphous carbon with graphitic nanodomains by catalytic effect of Fe. The confined growth of both NiFe-LDH and carbon in one single sheet results in fully integrated amorphous NiFe-LDH/C nanohybrid, allowing the harness of the high intrinsic activity of NiFe-LDH due to (i) amorphous and distorted LDH structure, (ii) enhanced active surface area, and (iii) strong coupling between the active phase and carbon. As such, the resultant NiFe-LDH/C exhibits superior activity and stability. Different from postdeposition or electrostatic self-assembly process for the formation of LDH/C composite, this method offers one new opportunity to fabricate high-performance oxygen evolution reaction and possibly other catalysts.

Activation of the MoSe2 basal plane and Se-edge by B doping for enhanced hydrogen evolution

We demonstrate by both calculation and experiments the effective B doping-induced activation of both the basal plane and Se-edge in vertically aligned MoSe2 flakes, and the disruptive enhancement in the electrocatalytic hydrogen evolution reaction. The B doping boosts drastically the catalytic activity of MoSe2 for the hydrogen evolution reaction compared to the undoped one, characterized by a low overpotential (84 mV) and Tafel slope (39 mV s−1), which are comparable to those of the best Pt/C electrode. The realization of activation for both the basal plane and Se-edge by B doping in MoSe2 shows an innovative pathway towards the activity enhancement of TMDs for electrocatalysts and energy storage.

Preparation of 1T′-Phase ReS2xSe2(1-x) (x = 0–1) Nanodots for Highly Efficient Electrocatalytic Hydrogen Evolution Reaction

As a source of clean energy, a reliable hydrogen evolution reaction (HER) requires robust and highly efficient catalysts. Here, by combining chemical vapor transport and Li-intercalation, we have prepared a series of 1T-phase ReS2 xSe2(1- x) ( x = 0-1) nanodots to achieve high-performance HER in acid medium. Among them, the 1T-phase ReSSe nanodot exhibits the highest hydrogen evolution activity, with a Tafel slope of 50.1 mV dec-1 and a low overpotential of 84 mV at current density of 10 mA cm-2. The excellent hydrogen evolution activity is attributed to the optimal hydrogen absorption energy of the active site induced by the asymmetric S vacancy in the highly asymmetric 1T crystal structure.

Encapsulating porous SnO2 into a hybrid nanocarbon matrix for long lifetime Li storage

To overcome the low conductivity and large volume variation of metal oxide anodes, the electrode microstructure design for these metal oxides appeared to be the most promising strategy for achieving the desired Li storage performance. In this article, we report on a rational design of the carbon/SnO2 microstructure, in which porous SnO2 nanoparticles are encapsulated into the graphene matrix and additional carbon coating layer. As an anode material for LIBs, the as-prepared G@p-SnO2@C composite exhibited an ultra-long cycling life up to 1800 cycles. It can sustain high specific capacities of 602 and 418 mA h g−1 at 1.5 A g−1 after 1000 and 1800 cycles, respectively. The excellent battery performance could be attributed to the unique architecture of this composite, which enhances electrical conductivity, provides sufficient interior void space to accommodate the volume variation of SnO2, mitigates the aggregation, and preserves the integrity of electrodes during cycling.