Chungui Tian

Nitrogen-doped graphene supported Pd@PdO core-shell clusters for C-C coupling reactions

The introduction of nitrogen significantly decreases the metal particle size and improves the performance of metal-based graphene-supported catalysts. In this work, the density functional theory is used to understand the interaction between nitrogen-doped graphene and Pd@PdO clusters. Experiments show that small size Pd@PdO clusters (1–2 nm) can be grown uniformly on nitrogen-doped graphene sheets by a facile oxidation-reduction method. The nanoscale interaction relationship between nitrogen-doped graphene and Pd@PdO clusters is investigated through X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectra (XAS). The composite catalysts are applied in Suzuki-Miyaura reactions giving high yields and good structural stability. These results have potential impact in design and optimization of future high performance catalyst materials for cross coupling reactions.

From graphite to porous graphene-like nanosheets for high rate lithium-ion batteries

Graphene nanosheets possess a promising potential as electrodes in Li-ion batteries (LIBs); consequently, the development of low-cost and high-productivity synthetic approaches is crucial. Herein, porous graphene-like nanosheets (PGSs) have been synthesized from expandable graphite (EG) by initially intercalating phosphoric acid, and then performing annealing to enlarge the interlayer distance of EG, thus facilitating the successive intercalation of zinc chloride. Subsequently, the following pyrolysis of zinc chloride in the EG interlayer promoted the formation of the porous PGS structure; meanwhile, the gas produced during the formation of the porous structure could exfoliate the EG to graphene-like nanosheets. The synthetic PGS material used as LIB anode exhibited superior Li+ storage performance, showing a remarkable discharge capacity of 830.4 mAh·g-1 at 100 mA·g-1, excellent rate capacity of 211.6 mAh·g-1 at 20,000 mA·g-1, and excellent cycle performance (near 100% capacity retention after 10,000 cycles). The excellent rate performance is attributed to the Li+ ion rapid transport in porous structures and the high electrical conductivity of graphene-like nanosheets. It is expected that PGS may be widely used as anode material for high-rate LIBs via this facile and low-cost route by employing EG as the raw material.

Small-sized tungsten nitride anchoring into a 3D CNT-rGO framework as a superior bifunctional catalyst for the methanol oxidation and oxygen reduction reactions

The application of direct methanol fuel cells (DMFC) is hampered by high cost, low activity, and poor CO tolerance by the Pt catalyst. Herein, we designed a fancy 3D hybrid by anchoring tungsten nitride (WN) nanoparticles (NPs), of about 3 nm in size, into a 3D carbon nanotube-reduced graphene oxide framework (CNT-rGO) using an assembly route. After depositing Pt, the contacted and strongly coupled Pt–WN NPs were formed, resulting in electron transfer from Pt to WN. The 3D Pt–WN/CNT-rGO hybrid can be used as a bifunctional electrocatalyst for both methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). In MOR, the catalysts showed excellent CO tolerance and a high mass activity of 702.4 mA·mgPt–1, 2.44 and 3.81 times higher than those of Pt/CNT-rGO and Pt/C(JM) catalysts, respectively. The catalyst also exhibited a more positive onset potential (1.03 V), higher mass activity (151.3 mA·mgPt–1), and better cyclic stability and tolerance in MOR than ORR. The catalyst mainly exhibited a 4e-transfer mechanism with a low peroxide yield. The high activity was closely related to hybrid structure. That is, the 3D framework provided a favorable path for mass-transfer, the CNT-rGO support was favorable for charge transfer, and strongly coupled Pt–WN can enhance the catalytic activity and CO-tolerance of Pt. Pt–WN/CNT-rGO represents a new 3D catalytic platform that is promising as an electrocatalyst for DMFC because it can catalyze both ORR and MOR in an acidic medium with good stability and highly efficient Pt utilization.

Synergistic Effect of Tungsten Nitride and Palladium for the Selective Hydrogenation of Cinnamaldehyde at the C=C bond

Herein, a series of catalysts made of Pd–WN on various supports was synthesized by modifying supports with small‐size WN NPs firstly and loading Pd subsequently. Their catalytic performances were evaluated for selective hydrogenation of cinnamaldehyde (CAL) to hydrocinnamaldehyde (HALD). Interestingly, it was found the synergistic effect between Pd and WN can improve conversion and selectivity of CAL to HALD. Among these catalysts, Pd–WN/SBA‐15 shows best performance with highest conversion (99u2009%) and selectivity to HALD (97u2009%), which is superior to commercial 5u2009% Pd/C catalyst. The hydrogenation kinetics of Pd–WN/SBA‐15 has been adequately represented by a standard pseudo‐first‐order approximation, and it discloses that the existence of WN can effectively decrease the activation energy (23.2u2005kJu2009mol−1). The synergistic effect of Pd and WN results in enriching the electron density of Pd, increasing the ratio of surface Pd0 and decreasing the size of Pd on the Pd–WN/SBA‐15 catalyst.

An effective poly(p-phenylenevinylene) polymer adhesion route toward three-dimensional nitrogen-doped carbon nanotube/reduced graphene oxide composite for direct electrocatalytic oxygen reduction

Heteroatom-doped nanocarbons have excellent potential for use in the oxygen reduction reaction (ORR). However, construction of three-dimensional (3D) N-doped carbon materials with good electrocatalytic performance remains a challenge. Herein, a poly(p-phenylenevinylene) (PPV)-precursor adhesion route was developed for construction of 3D N-doped reduced graphene oxide-PPV calcined-carbon nanotubes (N-RGO-PPV(c)-CNTs). In the synthesis, the PPV-precursor plays the role of a “glue” for strong adhesion of the RGO and CNTs. At high temperature, PPV can undergo transformation from the glassy state to a viscous state. Thus, the N-RGO-PPV(c)-CNT composite with multi-porous structure and ridge-like folded graphene flakes could be formed during nitridation at high temperature, which was favorable for production of more active sites for the ORR. As an ORR catalyst, the N-RGO-PPV(c)-CNT composites exhibited superior catalytic activity in alkaline electrolyte. The obtained onset potential (Eonset) of 0.92 V and catalytic current density of 5.7 mA·cm–2 at 0.6 V (vs. RHE) are comparable to those of the 20% Pt/C composite (0.98 V and 5.2 mA·cm–2). The electron transfer number for the N-RGO-PPV(c)-CNT catalyst was about 3.99, which is close to that of the 20% Pt/C (4.01) catalyst. Notably, the optimal N-RGO-PPV(c)-CNT catalyst shows better durability and methanol tolerance than commercial 20% Pt/C. The good performance of the N-RGO-PPV(c)-CNT catalyst for the ORR may be attributed to the synergistic effects of the unique 3D structure for effective mass-transfer, the effective N-doping for production of more active sites, and the good contact between the RGO and CNTs for easy charge-transfer.

Inorganic acid-derived hydrogen-bonded organic frameworks to form nitrogen-rich carbon nitrides for photocatalytic hydrogen evolution

Hydrogen-bonded organic framework (HOF) materials, which feature unique structures, are generally used for gas separation. To fabricate HOF-like precursors with diverse morphologies and further extend their application to hydrogen evolution, melamine has been reacted with inorganic acids (H2SO4, HNO3 and HCl) in this work. After calcining, the framework structure can maintain its major features while being converted into porous nitrogen–rich carbon nitrides. Moreover, the influence of different acid radicals on the “N-rich effect” was also investigated. The results show that the reaction procedure enriches the nitrogen content in all the newly synthesized carbon nitride products compared with bulk carbon nitride. This enrichment is attributed to the preferential formation of high-N-ratio triazine over heptazine. The carbon nitrides prepared from the HOF precursors contain more active sites [N-(C)3] and tune the bandgap by stabilizing the energy level of the conduction band. Moreover, heterogeneous sulfur doping using H2SO4 is another key factor in changing the energy-level structure. Thus, our method provides a feasible way to prepare graphite carbon nitride materials with preeminent photocatalytic activity.

Self-supported Ni6MnO8 3D mesoporous nanosheet arrays with ultrahigh lithium storage properties and conversion mechanism by in-situ XAFS

Murdochite-type Ni6MnO8 three-dimensional mesoporous nanosheet arrays grown on carbon cloth (NMO-SA/CC) are synthesized using an in-situ growth strategy. As self-supported binder-free anodes for LIBs, the NMO-SA/CC hierarchical nanostructures exhibit ultrahigh capacity, excellent cycling stability, and good rate capability. The excellent lithium storage performance can be ascribed to the perfect electrical contact between NMO-SA and CC. The mesopores in the thin nanosheet can maximize the electrode contact with the electrolyte by decreasing the Li+ diffusion path. Moreover, these effects relieve the pulverization and agglomeration that originate from the large volume variations during the Li+ intercalation/deintercalation cycles. The in-situ X-ray absorption fine structure (XAFS) spectrum recorded during the initial lithiation/delithiation processes reveals the conversion reaction process.

Cobalt-vanadium bimetal-based nanoplates for efficient overall water splitting

The development of effective and low-cost catalysts for overall water splitting is essential for clean production of hydrogen from water. In this paper, we report the synthesis of cobalt-vanadium (Co-V) bimetal-based catalysts for the effective water splitting. The Co2V2O7·xH2O nanoplates containing both Co and V elements were selected as the precursors. After the calcination under NH3 atmosphere, the Co2VO4 and Co/VN could be obtained just by tuning the calcination temperature. Electrochemical tests indicated that the Co-V bimetal-based materials could be used as active hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalyst by regulating their structure. The Co/VN showed good performance for HER with the onset potential of 68 mV and can achieve a current density of 10 mA cm−2 at an overpotential of 92 mV. Meanwhile, the Co2VO4 exhibited the obvious OER performance with overpotential of 300 mV to achieve a current density of 10 mA cm−2. When the Co2VO4 and Co/VN were used as the anode and cathode in a two-electrode system, respectively, the cell needed a voltage of 1.65 V to achieve 10 mA cm−2 together with good stability. This work would be indicative to constructing Co-V bimetalbased catalysts for the catalytic application.摘要开发高效的全解水催化剂对于使用清洁水为原料制氢十分必要. 本文设计合成了钴-钒基双金属纳米片用作分解水的有效催化剂.合成中采用Co2V2O7·xH2O作为前驱体, 在氨气氛围下可控热处理获得组成可调的钴-钒基双金属(Co2VO4和Co/VN)纳米片. 电化学测试结果表明Co-V双金属基催化剂可作为活性的产氧和产氢催化剂. Co/VN具有较好的HER性能, 起始电位为68 mV, 电流密度为10 mA cm−2时电压为92 mV. 而Co2VO4具有较好的OER性能, 电流密度为10 mA cm−2时电压为300 mV. 使用Co/VN和Co2VO4分别作为阴极和阳极构建两电极电解池, 当电压为1.65 V时, 电流密度即可达到10 mA cm−2. 因此, 组分可调的Co-V双金属纳米片在催化领域中具有很好的应用

A general strategy toward the large-scale synthesis of the noble metal-oxide nanocrystal hybrids with intimate interfacial contact for the catalytic reduction of p-nitrophenol and photocatalytic degradation of pollutants

The construction of noble metal-oxide nanocrystal hybrids (MOHs) with good interface contact, broadly tunable composition and high yield is critical for their application in the advanced fields. In this paper, a general route was developed for constructing MOHs with intimate interfacial contact based on the coordination of an organic agent with multiple kinds of metal precursors. In the synthesis, critic acid, desirable sources for metal nanoparticles (NPs; for example, Ag+ salts), oxides (for example, Zn2+ salts) and ethylene glycol were dissolved in water. After heating at low temperature to produce the precursor gels and subsequent calcination under air, one kind of the ions (Zn2+) was transformed into an oxide (ZnO) in company with the reduction of another ion (Ag+) to generate metal NPs (Ag). Benefitting from the uniform distribution of Ag and Zn precursor in the gels, the Ag/ZnO composites with good interface contact were finally formed. The Ag/ZnO hybrids can be used as effective catalysts for the catalytic reduction of p-nitrophenol and photocatalytic degradation of pollutants. Under optimized conditions, the Ag/ZnO showed a rate approximately 1.5 times higher than that of Degussa P25 TiO2 for the degradation of rhodamine B. The OH· radicals and ·O2− play predominant roles in the photocatalytic reaction. The Ag/ZnO can also act as an effective catalyst for the reduction of p-nitrophenol with good reuse performance. The present route is also suitable to construct MOHs with other components (Pt/TiO2, Pt/ZnO, etc.). The route is promising to produce MOHs due to the virtues of the easy synthesis process and high yields.