Hai-Xia Zhong

ZIF‐8 Derived Graphene‐Based Nitrogen‐Doped Porous Carbon Sheets as Highly Efficient and Durable Oxygen Reduction Electrocatalysts

Nitrogen-doped carbon (NC) materials have been proposed as next-generation oxygen reduction reaction (ORR) catalysts to significantly improve scalability and reduce costs, but these alternatives usually exhibit low activity and/or gradual deactivation during use. Here, we develop new 2D sandwich-like zeolitic imidazolate framework (ZIF) derived graphene-based nitrogen-doped porous carbon sheets (GNPCSs) obtained by in situ growing ZIF on graphene oxide (GO). Compared to commercial Pt/C catalyst, the GNPCSs show comparable onset potential, higher current density, and especially an excellent tolerance to methanol and superior durability in the ORR. Those properties might be attributed to a synergistic effect between NC and graphene with regard to structure and composition. Furthermore, higher open-circuit voltage and power density are obtained in direct methanol fuel cells.

Integrated Three-Dimensional Carbon Paper/Carbon Tubes/Cobalt-Sulfide Sheets as an Efficient Electrode for Overall Water Splitting

The development of an efficient catalytic electrode toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of great significance for overall water splitting associated with the conversion and storage of clean and renewable energy. In this study, carbon paper/carbon tubes/cobalt-sulfide is introduced as an integrated three-dimensional (3D) array electrode for cost-effective and energy-efficient HER and OER in alkaline medium. Impressively, this electrode displays superior performance compared to non-noble metal catalysts reported previously, benefiting from the unique 3D array architecture with increased exposure and accessibility of active sites, improved vectorial electron transport capability, and enhanced release of gaseous products. Such an integrated and versatile electrode makes the overall water splitting proceed in a more direct and smooth manner, reducing the production cost of practical technological devices.

In Situ Coupling of Strung Co4N and Intertwined N-C Fibers toward Free-Standing Bifunctional Cathode for Robust, Efficient, and Flexible Zn-Air Batteries.

Flexible power sources with high energy density are crucial for the realization of next-generation flexible electronics. Theoretically, rechargeable flexible zinc-air (Zn-air) batteries could provide high specific energy, while their large-scale applications are still greatly hindered by high cost and resources scarcity of noble-metal-based oxygen evolution reaction (OER)/oxygen reduction reaction (ORR) electrocatalysts as well as inferior mechanical properties of the air cathode. Combining metallic Co4N with superior OER activity and Co-N-C with perfect ORR activity on a free-standing and flexible electrode could be a good step for flexible Zn-air batteries, while lots of difficulties need to be overcome. Herein, as a proof-of-concept experiment, we first propose a strategy for in situ coupling of strung Co4N and intertwined N-C fibers, by pyrolyzation of the novel pearl-like ZIF-67/polypyrrole nanofibers network rooted on carbon cloth. Originating from the synergistic effect of Co4N and Co-N-C and the stable 3D interconnected conductive network structure, the obtained free-standing and highly flexible bifunctional oxygen electrode exhibits excellent electrocatalytic activity and stability for both OER and ORR in terms of low overpotential (310 mV at 10 mA cm(-2)) for OER, a positive half-wave potential (0.8 V) for ORR, and a stable current density retention for at least 20 h, and especially, the obtained Zn-air batteries exhibit a low discharge-charge voltage gap (1.09 V at 50 mA cm(-2)) and long cycle life (up to 408 cycles). Furthermore, the perfect bendable and twistable and rechargeable properties of the flexible Zn-air battery particularly make it a potentially power portable and wearable electronic device.

An Efficient Three-Dimensional Oxygen Evolution Electrode†

The challenges of meeting the rapidly increasing global energy demand and developing carbon-neutral economy require untiring efforts to exploit and store abundant but diffuse renewable energy sources. Among many innovative approaches, the efficient production of hydrogen serving as fuel, through electricity-driven water splitting, seems promising and appealing. However, the overall efficiency of the reaction is largely impeded by the kinetically sluggish oxygen evolution reaction (OER), imposing serious overpotential requirement. Although precious metal oxides, such as RuO2 and IrO2, are considered to be the most active OER electrocatalysts, they are not suitable for large-scale applications because of their scarcity and high costs. In response, non-noble transition-metal-based catalysts, especially nickel (Ni), are becoming focus of growing research interests because of their earth-abundant nature and theoretically high catalytic activity. 6] Currently, these non-noble transition-metal-based OER catalysts are usually prepared as thin films from precursor solution containing metal cations by electrodeposition, sputtering, dip-coating, and spin-coating methods on two-dimensional (2D) planar substrates. Although significant improvements have been achieved, the activity and stability of the catalyst layer should be further enhanced by optimizing the structural, mechanical, and electrical contact between the catalyst and the substrates. Compared to the conventional 2D planar architecture, electrodes based on 3D porous materials might improve the activity by increasing the electroactive surface area of the catalysts. Taking the advantages of a comparatively high surface area, high electron conductivity, and low costs, Ni foam is generally chosen to serve as template, support, as well as current collector for battery and supercapacitor. However, the Ni foam cannot be directly used as OER electrode because of its intrinsic instability under the OER experimental condition. In response, constructing protective and conductive interlayers, such as porous carbon, to bridge the outermost oxygen evolution catalyst (OEC) layer and the innermost 3D conductive Ni backbone could be a promising strategy. Other than traditional templates such as mesoprous silica and zeolites, zeolite imidazolate framework (ZIF-8) possesses a high carbon content, high chemical and thermal stability, large Brunauer–Emmett–Teller (BET) surface area, and oxygen-free character, making it a novel and promising template for porous carbon synthesis. To design an efficient OER catalyst with these factors in mind, herein, we first develop a unique approach to fabricate a 3D Ni foam/porous carbon/anodized Ni (NF/PC/AN) electrode, wherein homogeneous coating of the 3D Ni framework with porous carbon membrane plays a key role, which is derived from ZIF-8 and subsequently employed as difunctional interlayer to both protect the inner instable Ni foam and support the outermost Ni OEC layer. It is also the first report that the Ni-based OEC is in situ generated from anodization of the innermost Ni foam skeleton and then penetrated into the voids and finally covered the surface of the porous carbon membrane. Interestingly, the performance of this novel NF/PC/AN electrode is very good for OER, which is considered to be the synergy of the high activity of AN and the high conductivity and stability of the electrode. Briefly, the facile and scalable fabrication process of the 3D NF/PC/AN electrode (see Scheme S1 in the Supporting Information) is described as follows. The Ni foam is first treated with an acid solution containing polyvinylpyrrolidone (PVP) to remove the possible oxide layer and enhance the affinity of the surface. Then, the Ni foam is immersed in methanolic solution of zinc nitrate and 2-methylimidazole to deposit a ZIF-8 membrane. Next, the as-prepared Ni foam/ ZIF-8 is converted to Ni foam/porous carbon under the treatments of calcination in Ar atmosphere and etching the possible Zn species with acid. Finally, anodization is carried out at a constant potential to obtain a 3D NF/PC/AN electrode which can be in situ applied to test the OER activity. The morphology of ZIF-8 supported on a Ni foam skeleton is characterized by scanning electron microscopy (SEM). As shown in Figure 1a,b, the surface of the obtained Ni foam/ZIF-8 is quite different from that of a bare Ni foam (Figure S1), revealing the success of depositing a ZIF-8 membrane on a Ni foam. The ZIF-8 membrane is composed of well intergrown polyhedral crystals with sizes of about 0.2 mm. And no obvious defects such as cracks are observed, indicating the continuous formation of the membrane on the homogeneous support of Ni foam. From the cross-sectional view (Figure 1c), the thickness of the ZIF-8 membrane is measured to be about 4.5 mm. The carbonization of the ZIF-8 membrane is carried out by calcinating the Ni foam/ZIF-8 at 800 8C for 5 h at a heating rate of 3 8Cmin 1 in Ar atmosphere. Although the carbonization temperature is close to the [*] J. Wang, H. X. Zhong, Y. L. Qin, Prof. X. B. Zhang State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry Chinese Academy of Sciences, Changchun, 130022 (P.R. China) E-mail: xbzhang@ciac.jl.cn Homepage: http://energy.ciac.jl.cn

Artificial Protection Film on Lithium Metal Anode toward Long-Cycle-Life Lithium-Oxygen Batteries

An artificial while very stable solid electrolyte interphase film is formed on lithium metal using an electrochemical strategy. When this protected Li anode is first used in a Li-O2 battery, the film formed on the anode can effectively suppress the parasitic reactions on the Li anode/electrolyte interface and significantly enhance the cycling stability of the Li-O2 battery.

Synergistic Effect between Metal-Nitrogen-Carbon Sheets and NiO Nanoparticles for Enhanced Electrochemical Water-Oxidation Performance

Identifying effective means to improve the electrochemical performance of oxygen-evolution catalysts represents a significant challenge in several emerging renewable energy technologies. Herein, we consider metal-nitrogen-carbon sheets which are commonly used for catalyzing the oxygen-reduction reaction (ORR), as the support to load NiO nanoparticles for the oxygen-evolution reaction (OER). FeNC sheets, as the advanced supports, synergistically promote the NiO nanocatalysts to exhibit superior performance in alkaline media, which is confirmed by experimental observations and density functional theory (DFT) calculations. Our findings show the advantages in considering the support effect for designing highly active, durable, and cost-effective OER electrocatalysts.

C and N Hybrid Coordination Derived Co–C–N Complex as a Highly Efficient Electrocatalyst for Hydrogen Evolution Reaction

Development of an efficient hydrogen evolution reaction (HER) catalyst composed of earth-abundant elements is scientifically and technologically important for the water splitting associated with the conversion and storage of renewable energy. Herein we report a new class of Co-C-N complex bonded carbon (only 0.22 at% Co) for HER with a self-supported and three-dimensional porous structure that shows an unexpected catalytic activity with low overpotential (212 mV at 100 mA cm(-2)) and long-term stability, better than that of most traditional-metal catalysts. Experimental observations in combination with density functional theory calculations reveal that C and N hybrid coordination optimizes the charge distribution and enhances the electron transfer, which synergistically promotes the proton adsorption and reduction kinetics.

Reactive Multifunctional Template‐Induced Preparation of Fe‐N‐Doped Mesoporous Carbon Microspheres Towards Highly Efficient Electrocatalysts for Oxygen Reduction

A novel in situ replication and polymerization strategy is developed for the synthesis of Fe-N-doped mesoporous carbon microspheres (Fe-NMCSs). This material benefits from the synergy between the high catalytic activity of Fe-N-C and the fast mass transport of the mesoporous microsphere structure. Compared to commercial Pt/C catalysts, the Fe-NMCSs show a much better electrocatalytic performance in terms of higher catalytic activity, selectivity, and durability for the oxygen reduction reaction.

Electrochemical Reduction of N2 under Ambient Conditions for Artificial N2 Fixation and Renewable Energy Storage Using N2 /NH3 Cycle.

Using tetrahexahedral gold nanorods as a heterogeneous electrocatalyst, an electrocatalytic N2 reduction reaction is shown to be possible at room temperature and atmospheric pressure, with a high Faradic efficiency up to 4.02% at -0.2 V vs reversible hydrogen electrode (1.648 µg h-1 cm-2 and 0.102 µg h-1 cm-2 for NH3 and N2 H4 ·H2 O, respectively).

Gelatin-derived sustainable carbon-based functional materials for energy conversion and storage with controllability of structure and component

This synthetic approach produced catalysts with higher catalytic activity and better oxygen-reduction durability. Nonprecious carbon catalysts and electrodes are vital components in energy conversion and storage systems. Despite recent progress, controllable synthesis of carbon functional materials is still a great challenge. We report a novel strategy to prepare simultaneously Fe-N-C catalysts and Fe3O4/N-doped carbon hybrids based on the sol-gel chemistry of gelatin and iron with controllability of structure and component. The catalysts demonstrate higher catalytic activity and better durability for oxygen reduction than precious Pt/C catalysts. The active sites of FeN4/C (D1) and N-FeN2+2/C (D3) are identified by Mössbauer spectroscopy, and most of the Fe ions are converted into D1 or D3 species. The oxygen reduction reaction (ORR) activity correlates well with the surface area, porosity, and the content of active Fe-Nx /C (D1 + D3) species. As an anode material for lithium storage, Fe3O4/carbon hybrids exhibit superior rate capability and excellent cycling performance. The synthetic approach and the proposed mechanism open new avenues for the development of sustainable carbon-based functional materials.