The development of efficient and low-cost hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalysts for renewable-energy conversion techniques is highly desired. A kind of hollow polyhedral cobalt phosphide (CoP hollow polyhedron) is developed as efficient bifunctional electrocatalysts for HER and OER templated by Co-centered metal-organic frameworks. The as-prepared CoP hollow polyhedron, which have large specific surface area and high porosity providing rich catalytic active sites, show excellent electrocatalytic performances for both HER and OER in acidic and alkaline media, respectively, with onset overpotentials of 35 and 300 mV, Tafel slopes of 59 and 57 mV dec(-1), and a current density of 10 mA cm(-2) at overpotentials of 159 and 400 mV for HER and OER, respectively, which are remarkably superior to those of particulate CoP (CoP particles) and comparable to those of commercial noble-metal catalysts. In addition, the CoP hollow polyhedron also show good durability after long-term operations.
Carbon coated hollow mesoporous FeP microcubes derived from Prussian blue were superior in catalytic activity and durability toward electrochemical hydrogen evolution with an overpotential of 115 mV to drive 10 mA cm−2.
Converting light hydrocarbons such as methane, ethane, propane, and cyclohexane into value-added chemicals and fuelp roducts by meanso fd irectC ÀHf unctionalization is an attractive methodi nt he petrochemical industry. As they emerge as ar elatively new class of porous solidm aterials, metal-organic frameworks (MOFs) are appealing as single-site heterogeneous catalysts or catalytic supports for CÀHb ond activation. In contrast to the traditional microporous and mesoporous materials, MOFs feature high porosity, functional tunability,a nd molecular-level characterization for the study of structure-property relationships.T hese virtues make MOFs ideal platforms to develop catalysts for CÀHa ctivation with high catalytic activity,s electivity,a nd recyclability under relativelym ild reactionc onditions. This review highlightst he research aimed at the implementation of MOFs as single-site heterogeneousc atalysts for CÀHb ond activation.I tp rovidesi nsight into the rational design and synthesis of three types of stable MOF catalysts for CÀH bond activation,t hat is, i) metal nodes as catalytic sites, ii)the incorporation of catalytic sites into organic struts, and iii)the incorporation of catalytically active guest species into pores of MOFs. Here, the rational design and synthesis of MOF catalystst hat lead to the distinct catalytic property for CÀHb ond activation are discussed alongw ith the post-synthesis of MOFs, intriguing functions with MOF catalysts, and microenvironments that lead to the distinct catalytic properties of MOF catalysts.
The oxygen reduction reaction (ORR) plays a more and more important part in many research and engineering fields, such as energy conversion (including fuel cells and metal-air batteries), [1] corrosion prevention, [2] and biosensing.[3] These applications are rising rapidly and the activity of electrocatalysts for ORR has a pronounced effect on their performances.[4] Generally, we expect the ORR process to proceed in an efficient four-electron-transfer pathway with the formation of H 2 O as the end product.[5] However, the two-electron-transfer process often coexists with and this significantly decreases the catalytic efficiency. Noble metal-based electrocatalysts (mainly Pt and its alloys) have been regarded as best catalysts for ORR in fuel cells; [4,[6][7][8] however, the ORR kinetics on Pt-based electrodes is sluggish and they still suffer from multiple problems, for instance, the crossover effects, CO poisoning, and poor stability after long-term operation.[9] Furthermore, the high usage cost of Pt due to its limited natural reserves has greatly hindered the large-scale commercialization of fuel cells. [10] Therefore, finding efficient and low-cost non-noble metal electrocatalysts for ORR is essential.In the efforts to explore cost-effective and methanol-tolerant non-noble or non-Pt cathode catalysts for fuel cells, [5,[11][12][13] transition-metal chalcogenides, [14] oxides, [15] and nitrides [16] have been extensively investigated in recent years. Among them, transition-metal nitrides, particularly titanium nitride (TiN), are promising materials due to their high conductivity, chemical stability, and simple synthesis conditions; they showed good performances in a variety of fields including dye-sensitized solar cells, [17] Li-air batteries, [18,19] supercapacitors, [20] and biosensing. [21] In addition, nitrogen-doped graphene (NG) has also generated a great deal of interest for its unique structure and electron-transfer properties. [22][23][24][25] The nitrogen atoms in NG frameworks can create net positive charge on adjacent carbon atoms, so that electrons are attracted more easily, thus in favor of the adsorption of oxygen and the ORR process.[21] Furthermore, both materials are low-cost and widely available compared to noble metals and quite stable in alkaline media, [19,23] thus suitable for replacement of Pt-based electrocatalysts for ORR in fuel cells. Till now, there have been few reports on the combination of TiN and NG for applications in energy conversion and storage, only some concerning lithium-ion batteries, [26] electrochemical capacitors, [27] and dye-sensitized solar cells. [28,29] The composites in them showed average performances; however, some of the synthetic methods are a little complicated, requiring hydrolysis or two-step calcination resulting in large amounts of time and energy consumption. Besides, the interactions between the two components and the mechanism by which the performances of the hybrid were improved have not discussed sufficiently.In this study, through facile grain n...
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