Li An

A metal–organic framework route to in situ encapsulation of Co@Co3O4@C core@bishell nanoparticles into a highly ordered porous carbon matrix for oxygen reduction

Rational design of non-noble metal catalysts with an electrocatalytic activity comparable or even superior to Pt is extremely important for future fuel cell-based renewable energy devices. Herein, we demonstrate a new concept that a metal–organic framework (MOF) can be used as a novel precursor to in situ encapsulate Co@Co3O4@C core@bishell nanoparticles (NPs) into a highly ordered porous carbon matrix (CM) (denoted as Co@Co3O4@C–CM). The central cobalt ions from the MOF are used as a metal source to produce Co metal cores, which are later transformed into a fancy Co@Co3O4 nanostructure via a controlled oxidation. The most notable feature of our Co@Co3O4@C–CM is that the highly ordered CM can provide much better transport pathways than the disordered pure MOF derived nanostructure that can facilitate the mass transport of O2 and an electrolyte. As a result, the well-designed Co@Co3O4@C–CM derived from the MOF shows almost identical activity but superior stability and methanol tolerance for the ORR relative to the commercial Pt/C in alkaline medium. Our work reports a novel Co@Co3O4@C nanostructure from a MOF for the first time and also reveals the important role of the introduction of a highly ordered carbon matrix into the MOF derived catalyst in enhancing the ORR activity and stability. To the best of our knowledge, the Co@Co3O4@C–CM is the most efficient non-noble metal nanocatalyst ever reported for the ORR.

Well-defined carbon polyhedrons prepared from nano metal–organic frameworks for oxygen reduction

We report a nanostructured electrocatalyst engineered from molecular design and morphology evolution. Using a typical Co-based metal–organic framework, ZIF-67, nanocrystals were precisely synthesized with tunable size and morphology. Nitrogen-doped carbon nano polyhedrons decorated with cobalt nanoparticles were fabricated via pyrolysis of ZIF-67 and the carbonized products inherited the nano-size and shape of the MOF precursor. The intense effect of size on the electrocatalytic activity and transport properties was systematically investigated. The catalyst derived from the smallest MOF (300 nm), exhibited superior performance towards oxygen reduction with an onset potential of 0.86xa0V and a half-wave potential of 0.71xa0V in acidic solution, which are comparable to the best carbon-based oxygen reduction reaction (ORR) catalysts. This work will pave the way for the development of MOF-derived energy materials in various fields such as fuel cells and Li-air batteries, and opens new avenues for the design of MOFs in electrochemical applications.

Functional Zeolitic-Imidazolate-Framework-Templated Porous Carbon Materials for CO2 Capture and Enhanced Capacitors

Three types of zeolitic imidazolate frameworks (ZIFs) with different topological structures and functional imidazolate-derived ligands, namely, ZIF-8, ZIF-68, and ZIF69, have been directly carbonized to prepare porous carbon materials at 1000 °C. These as-synthesized porous carbon materials were activated with fused KOH to increase their surface areas and pore volumes for use in gas storage and supercapacitors. The relationship between the local structure of the products and the composition of the precursors has been investigated in detail. The BET surface areas of the resultant activated carbon materials are 2437 (CZIF8a), 1861 (CZIF68a), and 2264 m(2) g(-1) (CZIF69a). CZIF8a exhibits the highest H2 -storage capacities of 2.59 wt.% at 1 atm and 77 K, whereas CZIF69a has the highest CO2 uptake of 4.76 mmol g(-1) at 1 atm and 273 K, owing to its local structure and pore chemical environment. The specific capacities are calculated from the CV curves. CZIF69a exhibits the highest supercapacitor performance of 168 F g(-1) at a scan speed of 5 mV s(-1). These results indicate that the functional chloride group on the benzimidazolate ligand plays a very important role in improving the surface area, pore volume, and, therefore, CO2-capture and supercapacitor properties of the corresponding porous carbon materials.

Supported sub-5nm Pt–Fe intermetallic compounds for electrocatalytic application

Supported chemically ordered Pt–Fe intermetallic compounds have been prepared through a straightforward two-stage approach. By taking advantage of this straightforward two-stage synthesis, we have for the first time successfully obtained supported Pt3Fe1 and Pt1Fe1 intermetallic nanoparticles with a mean size of less than 5 nm, a narrow size distribution and good dispersion. The nanoparticles of supported intermetallic Pt3Fe1 and Pt1Fe1 compounds showed superior electrocatalytic activities towards the oxygen reduction reaction (ORR). The ORR enhancement in supported electrocatalysts made from Pt–Fe intermetallic compounds may be attributed to their geometric and electronic structure. Accelerated durability tests (ADT) show that Pt3Fe1/C has better durability, the electrochemical surface area (ECSA) values of commercial Pt/C decreased by 49% after 5000 cycles, but Pt1Fe1/C showed a reduction in the ECSA value of 3% after 5000 cycles.

A novel CoN electrocatalyst with high activity and stability toward oxygen reduction reaction

Carbon-supported CoN (CoN/C) nanoparticles have been synthesized by heating at reflux in the solution of o-xylene and subsequent thermal annealing under a NH3 reducing atmosphere. The as-prepared CoN/C composite exhibited high oxygen reduction reaction (ORR) activity and excellent stability as a new efficient non-precious metal electrocatalyst.

A New Route Toward Improved Sodium Ion Batteries: A Multifunctional Fluffy Na0.67FePO4/CNT Nanocactus

To improve the performance of energy storage systems, the rational design of new electrode configurations is a strategic initiative. Here, we present a novel monodisperse fluffy alluaudite Na0.67FePO4, prepared by a modified solvothermal method, as promising electrode for sodium ion battery. This porous Na0.67FePO4 with nanocactus-like morphology is composed by nanorods within an open three-dimensional structure. This unique nanocactus-based morphology offers three important advantages when used as electrode for sodium ion battery: (i) provides an open frame structure for a large Na+ ions transport; (ii) reduces the sodium ion and electron transport path by ≈20 nm; (iii) offers a large surface area for a more efficient interface between the electrode and the electrolyte. The electrochemical investigation revealed that this fluffy Na0.67FePO4 nanocactus exhibits the high discharge capacity of 138 mAh g(-1). Moreover, a battery with a Na0.67FePO4/CNT hybrid electrode delivered a discharge capacity as high as ≈143 mAh g(-1), coupled to an excellent stable cyclability (no obvious capacity fading over 50 cycles at a current rate of 5 mA g(-1)). This enhanced mechanism was studied by means of absorption measurements and ex situ XAFS characterizations. Results of the characterization of the Na0.67FePO4 suggests that the outstanding performance can be associated with the unique fluffy nanocactus morphology.

Nano-Intermetallic AuCu3 Catalyst for Oxygen Reduction Reaction: Performance and Mechanism

This paper introduces a new approach for catalyst design using the non-precious metal Cu as one of the catalytic active centers. This differs from previous studies that considered precious metals to be responsible for the catalytic reaction in precious alloys. Intermetallic AuCu3/C nanoparticles with a diameter of 3 nm were developed for the first time, with uniform dispersion and a narrow size distribution. The ca. 3 nm as-synthesised AuCu3/C showed superior catalytic performance for oxygen reduction reactions (ORR) in alkaline solutions, with comparable half-wave potential and 1.5 times mass current density of commercial Pt/C at 0.80 V (vs. reversible hydrogen electrode (RHE)). The advanced catalytic activities are mainly attributed to the synergetic effects of electro-active atomic Au and Cu on the particle surface, in which Cu helps to activate the O2 molecule and Au benefits OH(-) desorption. The excellent durability and methanol tolerance exhibited in alkaline solutions provide another advantage for AuCu3/C to be considered as a potential alternative cathode catalyst in alkaline fuel cells.

Electrocatalytic Dechlorination of Atrazine Using Binuclear Iron Phthalocyanine as Electrocatalysts

The electrochemical reduction approach has been suggested as a promising method for detoxification of chlorine-containing aromatic hydrocarbons. In this study, the electrocatalytic dechlorination of atrazine was studied by using a non-noble catalyst, binuclear iron phthalocyanine coated onto multi-walled carbon nanotubes (bi-FePc/MWNT). Both experimental and theoretical results indicate that dechlorination of atrazine occurs rapidly on bi-FePc/MWNT electrode. The reaction depends on the adsorption of the chlorinated organic compound on the electrode surface and the reaction rate with hydroxy. By liquid chromatography–tandem mass spectrometer technique, the dechlorination product of atrazine can be assigned to 2-hydroxy-4-ethylamino-6-isopropylamino-1,3,5-triazine, which could be disposed by more convenient and economic biodegradation method.

Durability Enhancement of Intermetallics Electrocatalysts via N-anchor Effect for Fuel Cells

Insufficient durability and catalytic activity of oxygen reduction reaction (ORR) electrocatalyst are key issues that have to be solved for the practical application of low temperature fuel cell. This paper introduces a new catalyst design strategy using N-anchor to promote the corrosion resistance of electrocatalyst. The as-synthesized N-Pt3Fe1/C shows a high electrocatalytic activity and a superior durability towards ORR. The kinetic current density of N-Pt3Fe1/C as normalized by ECSA is still as high as 0.145u2005mA cm−2 and only 7% loss after 20000 potential cycles from 0.6 to 1.2u2005V (vs. NHE) in O2-bubbling perchloric acid solution, whereas Pt3Fe1/C shows 49% loss under the same tests. The N-anchor approach offers novel opportunities for the development of ORR catalyst with excellent electrochemical properties.

A highly active and durable iron/cobalt alloy catalyst encapsulated in N-doped graphitic carbon nanotubes for oxygen reduction reaction by a nanofibrous dicyandiamide template

Exploration of competitive electrocatalysts to replace Pt-based catalysts for oxygen reduction reaction (ORR) in fuel cells is one of the most promising strategies to confront the energy and environmental crises. Herein, we highlighted an FeCo alloy catalyst encapsulated in N-doped graphitic carbon nanotubes (FeCo@N-GCNT-FD) as a highly efficient non-precious electrocatalyst for the ORR. The FeCo@N-GCNT-FD catalyst exhibits a positive onset (0.96 V vs. RHE) and half-wave potential (0.88 V vs. RHE) as well as 5.6 times the specific activity of commercial Pt/C at 0.70 V in alkaline media. The excellent catalytic behavior of FeCo@N-GCNT-FD is attributed to the structural properties, including a large surface area, and the synergistic effect of FeCo alloy and N-GCNT, which guarantee a large number of accessible catalytic sites and rapid mass-transfer kinetics. Theoretical calculations further confirm that the strong synergistic and electronic effects, especially the FeCo-NG sites, provide a favorable local coordination environment and electronic structure and a lower oxygen absorbance energy. The improvement of ORR activity and durability of the catalyst by the synergistic and electronic effects between the metal and carbon provides a versatile approach for tuning the catalytic performance of non-noble electrocatalysts.