MOF-derived multi-metal embedded N-doped carbon sheets rich in CNTs as efficient bifunctional oxygen electrocatalysts for rechargeable ZABs

The rational design and preparation of bifunctional electrocatalysts with pleasant oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performance is crucial for extensive commercial applications of rechargeable Zn–air batteries (ZABs). Herein, we report a simple method to obtain multi-metal (Fe, Ni, Zn) embedded in N-doped carbon sheets entangled with carbon nanotubes (CNTs) as superior oxygen electrocatalysts (FeNi-NCS-2). The resultant FeNi-NCS-2 exhibits an impressive electrochemical performance, providing a reversible oxygen overpotential as low as 0.758 V. The ZAB with FeNi-NCS-2 as the air cathode shows a promising capacity of 639.71 mAh g^?1 at 20 mA cm^?2, a power density of 109.8 mW cm^?2 and cycling stability of over 130 cycles at 10 mA cm^?2 with an energy efficiency of about 55%, superior to the ZAB based on Pt/C–IrO₂. The satisfactory electrocatalytic performance is mainly due to the Fe, Ni-based nanoparticles protected by graphitic carbon layers, hierarchical porous lamellar structures that promote the accessibility between the active centers and the electrolyte as well as self-growing tangled carbon nanotubes that provide fast transmission channels. This study presents a facile way for the synthesis of highly efficient ORR/OER bifunctional electrocatalysts for high-performance rechargeable ZABs.     

Graphitic carbon-encapsulated cobalt nanoparticles embedded 1D porous hollow carbon nanofibers as advanced multifunctional electrocatalysts for overall water splitting and Zn-air batteries

Physical mixing of monofunctional noble metal catalysts, such as Pt/C or Ru/IrO₂, increases the commercial cost and stability risk of electrodes. Therefore, it is desirable to develop a multifunctional electrocatalyst for zinc-air batteries and integrated electrolytic devices. To develop an effective way to fabricate high-performance multifunctional electrocatalysts by modifying advanced nanostructures, a coaxial electrospinning approach with in-situ synthesis and subsequent carbonization was used to construct a highly integrated three-function catalyst composed of graphitic carbon-encapsulated cobalt nanoparticles embedded into one-dimensional (1D) porous hollow carbon nanofibers (CoNC-HCNFs). Under the synergistic effect of the active material and the advanced nanostructure, the as-prepared CoNC-HCNFs demonstrated an operating overpotential of 186 mV (10 mA cm^?2) for the hydrogen evolution reaction (HER), a half-wave potential of 0.83 V (vs. RHE at 10 mA cm^?2) for the oxygen reduction reaction (ORR), and a potential of 1.58 V (10 mA cm^?2) for the oxygen evolution reaction (OER). With their exceptional multifunctional activities, two CoNC–HCNF-based aqueous zinc-air batteries (ZABs) in series could drive an alkaline water electrolyzer for splitting water. Furthermore, due to the superior mechanical flexibility and rechargeability of the solid-state ZAB, it has great application prospects in powering portable and wearable electronics. This research is expected to offer inspiration for the development of other excellent MOF-based hollow carbon nanofibers and to enable them to be adopted more widely in electrochemical energy conversion and energy storage.     

Co,N co-doped carbon nanosheets coupled with NiCo2O4 as an efficient bifunctional oxygen catalyst for Zn-air batteries

Developing of inexpensive and efficient bifunctional oxygen catalysts is important for the zinc-air batteries (ZABs). Here, a composite of Co, N co-doped carbon nanosheets coupled with NiCo₂O₄ (NiCo₂O₄/CoNC-NS) is developed as oxygen catalyst, which has good bifunctional oxygen catalytic activity and durability. Specifically, the half-wave potential of oxygen reduction reactions (ORR) is 0.849 V, and the overpotential of oxygen evolution reactions (OER) is 1.582 V at a current density of 10 mA cm⁻². And the assembled liquid ZABs based on NiCo₂O₄/CoNC-NS exhibit high open circuit potential (OCP, 1.482 V), high peak power density (148.3 mW cm⁻²) and large specific capacity (699.9 mAh g⁻¹) with long-term stability. Moreover, the further assembled solid ZABs can also provide high OCP (1.401 V), good power density (58.1 mW cm⁻²) and superior stability. This work would provide a good reference for the development of other advanced oxygen catalyst in future.     

Achieving high energy efficiency of alkaline hybrid zinc battery by using the optimized Co–Mn spinel cathode

As a potential candidate in the future energy storage system, Zinc-air batteries (ZABs) are impeded by their insufficient discharge voltages and low charge-discharge efficiencies. Building the alkaline hybrid zinc batteries (AHZBs) combining ZAB and alkaline zinc/cobalt batteries (ZCB) at the battery level can supply an effective strategy to solve these problems. In this work, we fabricate a self-supported Mn–Co spinel electrode (named as MnCo₂O₄) with the porous nanofiber morphology by a facile hydrothermal method and assemble AHZB. Thanks to the large electrochemical active surface area and appropriate ratio of Co²⁺/Co³⁺, the as-prepared MnCo₂O₄ electrode shows both the high bifunctional oxygen catalytic activities for ZABs and metal ion redox properties for ZCBs. AHZB with the self-supported MnCo₂O₄ electrode possesses two voltage platforms in both charge and discharge processes due to the oxygen evolution/reduction reactions (OER/ORR) ZABs and metal ion redox reaction in ZCBs. Besides of the highly power density and excellent cyclic stability, the charge-discharge efficiency of our AHZB with the self-supported MnCo₂O₄ electrode can reach 86.2%, almost being the highest value in the recent works. Our work supplies a viable strategy for developing high-performance ZABs with improved discharge voltage and charge-discharge efficiency.     

Amino functionalized carbon nanotubes supported CoNi@CoO–NiO core/shell nanoparticles as highly efficient bifunctional catalyst for rechargeable Zn-air batteries

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the core reaction processes of rechargeable Zn-air battery (ZAB) cathode. Therefore, exploring a bifunctional catalyst with excellent electrochemical performance, high durability, and low cost is essential for rechargeable ZAB. In this work, amino functionalized carbon nanotubes supported core/shell nanoparticles composed of CoNi alloy core and CoO–NiO shell (CoNi@CoO–NiO/NH₂-CNTs-1) is synthesized through a simple and efficient hydrothermal reaction and calcination method, which shows higher ORR/OER bifunctional catalytic performance than the single metal-based catalyst, such as Ni@NiO/NH₂-CNTs and Co@CoO/NH₂-CNTs. The fabricated bimetallic alloy based catalyst CoNi@CoO–NiO/NH₂-CNTs-3 with the optimized loading content of CoNi@CoO–NiO core/shell nanoparticles, presents the best bifunctional catalytic performance for ORR/OER. Experimental studies reveal that CoNi@CoO–NiO/NH₂-CNTs-3 exhibits the onset potential of 0.956 V and 1.423 V vs. RHE for ORR and OER, respectively. It also exhibits a low overpotential of 377 mV to achieve a 10 mA cm^?2 current density for OER, and positive half-wave potentials of 0.794 V for ORR. And the potential difference between half-wave potential of ORR (E_1/2) and the potential at 10 mA cm^?2 for OER (E_j10) is 0.813 V. In addition, when CoNi@CoO–NiO/NH₂-CNTs-3 is used as an air electrode catalyst of rechargeable ZAB, its maximum power density and open circuit voltage (OCV) can reach 128.7 mW cm^?2 and 1.458 V (The commercially available catalyst of Pt/C–RuO₂ is 88.1 mW cm^?2), which strongly demonstrates that the fabricated catalyst CoNi@CoO–NiO/NH₂-CNTs-3 can be used as a highly efficient bifunctional catalyst for ZABs, and is expected to replace those expensive precious metal electrocatalysts to meet the growing demand for new energy devices.     

Nitrogen-doped carbon confined NiFe–NiFeP nanocubes immobilized on carbon nanotube as an efficient electrocatalyst for oxygen evolution reaction

The future sustainable energy related application, especially Zn-air batteries (ZABs) and electrochemical water splitting to produce hydrogen, are limited by oxygen evolution reaction (OER). Transition metal phosphides have excellent catalytic activity for OER, but their poor conductivity and bad stability still require to be solved. Herein, the nitrogen-doped carbon (NC) confined NiFe–NiFeP nanocubes immobilized on carbon nanotube (CNT) (NiFe–NiFeP@NC/CNT) is fabricated by employing NiFe-Prussian Blue Analogs (NiFe–PBAs) nanocubes and CNT composite as precursor, and subsequent polydopamine (PDA) coating, carbonization and partial phosphorization. Profiting from its unique “nanonecklaces” structure with conductive CNT and ordered NiFe–NiFeP@NC nanocubes, NiFe–NiFeP@NC/CNT provides an efficient electron transfer path and uniformly dispersed active sites for OER process. The optimized NiFe–NiFeP@NC/CNT exhibits a low overpotential of 228 (328) mV at 10 (100) mA cm⁻² and high durability. Furthermore, the NiFe–NiFeP@NC/CNT || Pt/C requires 1.51 V to realize 20 mA cm⁻² for overall water spitting. And the ZAB assembled with NiFe–NiFeP@NC/CNT shows excellent discharge-charge stability for 240 h.     

An efficient metal-free bifunctional oxygen electrocatalyst of carbon co-doped with fluorine and nitrogen atoms for rechargeable Zn-air battery

It is highly critical to explore efficient bifunctional oxygen electrocatalysts for regenerative fuel cells and metal-air batteries. Herein, N, F co-doped carbon material (NF@CB) was synthesized as metal-free efficient bifunctional electrocatalysts by directly pyrolyzing a mixture of carbon black, polytetrafluoroethylene and melamine. Benefiting from the synergistic effects between N and F atoms, NF@CB exhibits a positive half-wave potential (E_1/2) of 0.814 V (vs. RHE) for oxygen reduction reaction, and an operating potential (E₁₀) of 1.609 V at 10 mA cm⁻² for oxygen evolution reaction in alkaline electrolyte. The bifunctional oxygen electrocatalytic activity index (ΔE = E₁₀−E_1/2) is 0.795 V, which is notably better than that of the single N-doped carbon (1.238 V), and similar to that of the commercial Pt/C and RuO₂ mixture catalyst (0.793 V). Impressively, the assembled Zn-air battery (ZAB) with NF@CB as an air-electrode catalyst displays a small charge/discharge voltage gap of 0.852 V at 20 mA cm⁻². Moreover, the NF@CB catalyzed ZAB exhibits good rechargeability and long-lasting cycling stability with over 49 h. This investigation introduces a cheap and simple way to develop highly efficient bifunctional N, F co-doped electrocatalysts.     

Bamboo-like carbonitride nanotubes with multi-type active sites for oxygen reduction reaction in both alkaline and acid mediums

To omni-directionally utilize carbon-based material in nanoscale and improve its catalytic activity for oxygen reduction reaction (ORR), bamboo-like carbonitride nanotubes (bCNTs) with high-density multi-type active sites (CoO@Co–N-bCNT) are facilely synthesized via a multi-step method referring to thermal pyrolysis of Co²⁺ complexed melamine, acid leaching and second annealing. Multi-type active sites including encapsulated Co nanoparticles, intercalated Co/CoO species, Co-N_x coordinated sites and defect-rich surface are present in the as-prepared CoO@Co–N-bCNT electrocatalyst. The types and densities of these active sites are easily tuned via the ratio of melamine to Co²⁺ in precursors and subsequent treatment. Due to the high-density multi-type active sites and bamboo-like tubular structure, CoO@Co–N-bCNT electrocatalyst exhibits high catalytic activity for ORR with high stability in both alkaline and acid electrolytes. Quasi-solid-state zinc air battery (ZAB) assembled with the CoO@Co–N-bCNT as the cathode exhibits open circle voltage of 1.39 V and peak power density of 14.9 mW cm^?2. Two-cell series of quasi-solid-state ZABs can light LED indicator for 7 h, suggesting its promising practical application. The studies provide facile strategy to design the carbon-based electrocatalysts with high performance and tune their active sites.     

A robust bifunctional electrocatalyst for rechargeable zinc-air batteries: NiFe nanoparticles encapsulated in nitrogen-doped carbon nanotubes

Developing high-efficiency, low-cost, and stable bifunctional oxygen electrocatalysts is essential for the commercialization of rechargeable metal-air batteries. Herein, three-dimensional self-assembled microspheres via in situ encapsulation of NiFe alloy nanoparticles (NPs) into N-doping carbon nanotubes (NiFe@NCNTs) have been achieved through pyrolyzing a mixture of nickel-iron alkoxide and melamine. The as-prepared electrocatalyst exhibits outstanding oxygen reduction reaction (ORR) performance with a half-wave potential of 0.79 V and oxygen evolution reaction (OER) activity with a low overpotential of 330 mV at 10 mA cm^?2. The eminent activity of NiFe@NCNTs is ascribed to high dispersion of active sites (zero-dimensional core-shell structure of NiFe@NC) and one-dimensional conductive network (NCNTs). Accordingly, the zinc-air battery assembled with NiFe@NCNTs as the air cathode exhibits a long cycling life of 200 h with a high energy efficiency of 65.6%. This work may shed new light on the design of advanced bifunctional electrocatalysts toward metal-air batteries.     

Y and Fe co-doped LaNiO3 perovskite as a novel bifunctional electrocatalyst for rechargeable zinc-air batteries

Perovskite oxides are widely regarded as the promising air electrode catalytic materials for zinc-air batteries (ZABs). In the present work, A-site Y and B-site Fe co-doped La_0.85Y_0.15Ni_0.7Fe_0.3O₃ perovskite catalyst was prepared by self-propagating high-temperature synthesis, and this material was evaluated as a bifunctional electrocatalyst for ZABs. The effect of co-doping on crystal structure and reaction activities, which can promote oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), was investigated. Results show that Y and Fe co-doping substantially improved the ORR and OER of LaNiO₃. In comparison with LaNiO₃, the ORR performance of La_0.85Y_0.15Ni_0.7Fe_0.3O₃ exhibited a higher limiting current density (3.8 mA cm^?2 at 0.4 V vs. RHE) and more positive onset potential (0.75 V vs. RHE) at 1600 rpm. It also had an excellent OER performance of 1.74 V vs. RHE at 10 mA cm^?2. When La_0.85Y_0.15Ni_0.7Fe_0.3O₃ was used as an air electrode catalyst for ZABs, it exhibited a high power density of 93.6 mW cm^?2, which increased by 84.8% compared with that of LaNiO₃. Moreover, the full cell with La_0.85Y_0.15Ni_0.7Fe_0.3O₃ air electrode catalyst was operated for more than 80 h, maintaining good stability. Therefore, La_0.85Y_0.15Ni_0.7Fe_0.3O₃ can be used as a promising bifunctional air electrode catalyst for ZABs. The characterization analysis reveals that A-site Y and B-site Fe co-doped catalyst transforms crystal structure from trigonal system to cubic system, retain the valence state of Ni³⁺ and increases the contents of O₂^2?/O^?, and these properties are more conducive for LaNiO₃ catalysis.     

Facile synthesis of CO/N-doped carbon nanotubes and the application in alkaline and neutral metal-air batteries

Nonprecious transition metals [e.g., cobalt (Co), iron (Fe), and zinc (Zn)], and nitrogen doped carbon materials are considered to be the most attractive alternatives to precious metal catalysts. Herein, Cobalt decorated nitrogen-doped carbon nanotubes were synthesized via a facile hydrothermal method and calcination. Benefiting from the N-doping, etching of Co nanoparticles to carbon nanotubes and synergistic effect between the components, the as-prepared Co/nitrogen-doped carbon nanotubes (Co-NCNT) displays a half-wave potential of 0.88 V (vs. RHE), a limiting current density of 5.6 mA cm⁻², and electron transfer number of 3.9 in 0.1 M KOH. When applied in metal-air batteries, it delivered maximum power densities of 130.0 mW cm⁻², 117.3 mW cm⁻² and 58.6 mW cm⁻² in alkaline Zn-air, Al-air batteries and neutral Mg-air batteries respectively, outperforming the commercial Pt/C. These demonstrate that the synthesized Co-NCNT is a promising candidate for ORR in metal-air batteries with both alkaline and neutral electrolytes.     

Cu-MOF@Co-MOF derived Co–Cu alloy nanoparticles and N atoms co-doped carbon matrix as efficient catalyst for enhanced oxygen reduction

We prepare a series of N-containing Cu-MOF@Co-MOF core-shell templates by employing two-step feed-in pathway and then step by step calcining these materials to obtain the N-doped carbon layers encapsulated Co–Cu alloy nanoparticles as efficient catalysts for enhanced oxygen reduction. The purpose of Cu-MOF designed as core materials is to increase the number of openly active sites when the templates are calcined at high temperature. During calcining, the Cu atoms facilitate the dispersion of Co on the surface of Co–Cu alloy nanoparticles, which efficiently avoid the agglomeration of Co during carbonization. When being used as cathode oxygen reduction catalysts, the optimal Co–Cu(3:1)@CN-900 material exhibits outstanding performance that can be comparable with the 20 wt% Pt/C catalysts, and the onset potential and half-wave potential of Co–Cu(3:1)@CN-900 is 60 mV and 37 mV higher than that of monometallic Co@CN-900 catalysts, respectively. Moreover, the active sites of Co–Cu(3:1)@CN-900 catalysts are also carefully investigated.     

Tunable Fe/N co-doped 3D porous graphene with high density Fe-Nx sites as the efficient bifunctional oxygen electrocatalyst for Zn-air batteries

Nitrogen-doped transition metal materials display promising potential as bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, Fe/N co-doped three-dimensional (3D) porous graphene (FeN-3D-PG) is prepared via a template method using sodium alginate as the carbon source and low polymerization degree melamine resin as the nitrogen source. The low polymerization degree melamine resin can form complexes with Fe³⁺ in the aqueous solution and further forms high density Fe-N_x active sites during pyrolysis. Meanwhile, the formed 3D porous structure efficiently promotes the uniform distribution of Fe-N_x active sites. The FeN-3D-PG catalyst exhibits pH-independent ORR activity. For OER, the catalyst possesses a low over potential (370 mV at 10 mA cm⁻²) in alkaline electrolyte. The Zn-air batteries (ZABs) using FeN-3D-PG as cathode exhibits a power density up to 212 mW cm⁻², a high specific capacity of 651 mAh g⁻¹, and the charge-discharge stability of 80 h. This work provides new sight to transition metal materials based ZABs with excellent performance.     

Issues of using inorganic proton conductor in the electrodes of polymer electrolyte fuel cells

We clarify the issues to be addressed when inorganic materials are employed in the electrodes of low temperature fuel cells, which conventionally operate around 80 °C. The employed inorganic proton conductor is zirconium sulfophenyl phosphonate (ZrSPP), which is incorporated as an ionomer in the electrode catalyst layers by coating the Pt-supported carbon nanotubes with a ZrSPP layer (ZrSPP–Pt/CNTs). Compared with an MEA with an electrode comprising Nafion and Pt/CNT without a ZrSPP coating, a membrane–electrode assembly (MEA) with an electrode comprising ZrSPP–Pt/CNT exhibits an improved performance at elevated temperatures of 90 °C and 100 °C, illustrating an advantage of the inorganic proton conductors. However, a ZrSPP coating on the Pt/CNTs decreases the cell performance at 80 °C. A detailed in situ analysis using limiting-current measurements reveals that the oxygen transport resistance through the solid ionomers increases by approximately six times with the incorporation of the ZrSPP layer. These results indicate that the mass transport through the inorganic materials should be addressed when they are employed in electrodes.     

Covalent organic polymer derived N–doped carbon confined FeNi alloys as bifunctional oxygen electrocatalyst for rechargeable zinc-air battery

N–doped carbon confined FeNi alloys are promising candidate to noble Pt and IrO₂ or RuO₂ for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable zinc-air batteries. However, it is difficult to control the distribution of transition metals in the precursor and electrocatalyst. Herein, we design a covalent organic polymer to realize the uniform distribution of metal, nitrogen and carbon precursors. The structure of the obtained electrocatalyst is FeNi nanoparticles coated with carbon shells dispersed on N-doped multilayer porous carbon (FeNi@NC). The resultant FeNi@NC delivered a half-wave potential for ORR of 0.878 V and a low potential of 1.59 V to achieve 10 mA cm^?2 for OER, which surpasses commercial platinum/carbon and ruthenium dioxide. The outstanding bifunctional properties of FeNi@NC attribute to the synergistic coupling between N-doped carbon shells and dense FeNi nanoparticles. Moreover, the self-made zinc-air battery with FeNi@NC air-cathode displayed an excellent energy density of 137.7 mW cm^?2 as well as cycling stability (100 h, 200 cycles).     

One-step complexation and self-template strategy to synthesis bimetal Fe/Mn–N doped interconnected hierarchical porous carbon for enhancing catalytic oxygen reduction reaction

Currently, it is still a challenge in the research of fuel cells and zinc-air battery to use a facile method to prepare efficient and low-cost cathode oxygen reduction reaction (ORR) catalysts to replace the precious metal Pt-based catalyst. Herein, we reported a one-step complexation of ethylenediaminetetraacetic acid disodium (EDTA-2Na) with transition metals (M) and self-template strategy to synthesis an bimetal Fe/Mn–N doped interconnected hierarchical porous carbon material for efficient catalytic ORR. In addition to being a carbon source, EDTA-2Na can very well fix M atoms in the carbon precursory by complexation, which is beneficial for M atoms to be anchored in the carbon structure by N atoms, thus forming the M-N_x catalytic active site. During pyrolysis, meanwhile, Na ions in EDTA-2Na not only acted as self-template to form the interconnected porous structure but also separated M atoms from each other, which also suppressed the aggregation and growth of the M atoms. More importantly, the prepared bimetal Fe/Mn–N doped interconnected hierarchical porous carbon (Fe/Mn–NIHPC) showed better catalytic ORR performance (half-wave potentials of 0.86 V vs. RHE) than those prepared by single metal elements (Fe or Mn). And Fe/Mn–NIHPC also exhibited better catalytic ORR activity and durability, compared with the Pt/C (20 wt%) catalyst.     

Investigation on platinum loaded multi-walled carbon nanotubes for hydrogen storage applications

Molecular hydrogen uptake of modified carbon nanotubes is a prospect for efficient hydrogen storage in fuel cell vehicles. In this study, a simple and efficient method to decorate the surface of multi-walled carbon nanotubes (MWNT) with platinum nanoparticles is presented. To load the Pt nanoparticles, hexachloroplatinic acid (H₂PtCl₆·6H₂O) is used as a precursor. Surface morphology of these Pt loaded MWNT is observed using Scanning and Transmission Electron Microscopy. Both samples are also characterized by X-Ray Diffraction. Thermal Gravimetric Analysis results indicate that both as purchased MWNT and Pt loaded MWNT have decomposition temperature higher than 500 °C in air. N₂ adsorption experiments yields a BET area of the sample close to 500 m²/g. This MWNT/Pt sample was reduced in 10% of H₂ in Ar, flowing at 900 °C in a tubular furnace for 1 h before hydrogen adsorption measurements. Hydrogen uptake of MWNT/Pt was measured at 2.5 MPa and 77 K. This hydrogen uptake isotherm is also compared with measurements at ambient temperature.     

Facile synthesis of carbon nanosheet arrays decorated with chromium-doped Co nanoparticles as advanced bifunctional catalysts for Zn-air batteries

The development of low-cost electrochemical catalytic nanomaterials for efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through structural and composition control is a great challenge. Herein, a 3D hybrid structure is designed by an in-situ approach for growing 2D leaf-like nanosheet arrays on 1D electrospun nanofibers. The resultant catalysts composed of Cr-doped Co nanoparticle decorated N-doped carbon nanosheet and carbon nanofiber are synthesized by subsequent Cr³⁺ impregnation and heat treatment. The excellent properties of the as-prepared cathode benefit from the novel establishment of the 3D structure and the regulating mechanism of the electron density of Co after Cr doping, which simultaneously increases the mass and charge transfer process during the catalytic reaction. Consequently, Cr_0.10-Co@NC exhibits excellent catalytic performance for the ORR (with a half-wave potential of 0.84 V) and OER (with an overpotential of 370 mV). When used in a homemade ZAB for evaluating their practical reversible performance, the device exhibits a higher open-circuit voltage (1.45 V) and a smaller potential gap (0.73 V) with excellent cycle durability of 110 h. This work offers a well-designed structure and development for synthesizing efficient and durable electrocatalysts in electrochemical energy conversion technologies.     

Medulla stachyuri-derived iron and nitrogen co- doped 2D porous carbon-flakes for highly efficient oxygen reduction electrocatalysis and supercapacitors

Iron and nitrogen co-doped two-dimensional (2D) porous carbon-flakes have been fabricated by using foam-like Medulla stachyuri (MS, the stem pith of tetrapanax papyrifer) as both carbon precursor and template and ammonium ferric citrate as iron and nitrogen precursor. The ammonium ferric citrate-impregnated foams are subsequently converted into iron and nitrogen co-doped 2D porous carbon-flakes by pyrolysis at high temperature in an inert atmosphere. The porous carbon-flakes fabricated at 900 °C (MS-Fe-900) possess high surface area (1140.9 m² g⁻¹) and effective Fe/N co-doping (0.22 at.% Fe and 2.02 at.% N). In comparison with Pt/C, MS-Fe-900 exhibits superior ORR activity (E₀ = 968 mV; E_1/2 = 830 mV vs RHE), preferable methanol/CO tolerance and better stability. Furthermore, the MS-Fe-900-based electrode presents high-rate performance (80.1% capacitance retention from 1 to 100 A g⁻¹), and good cycling stability for over 10000 cycles in 6 M KOH electrolyte. This work takes full advantage of the unique structure of biomass and provides a feasible approach to develop cost-efficient and high performance activated carbon materials for ORR electrocatalysis and supercapacitors.     

Synthesis of hollow carbon-incorporated NiCoM (M = Mn,Cu, Zn) layered double hydroxide nanocages for hybrid supercapacitors

Nanostructures and compositions are the most crucial aspects in the design of electrode materials with excellent properties for hybrid supercapacitors (HSCs). In this study, bimetallic CoM-zeolitic imidazolate framework-67 (CoM-ZIF-67, M = Mn, Cu, and Zn) derived nanosheet-constructed hollow carbon-incorporated NiCoM layered double hydroxide nanocages (NiCoM-LDH/C) are successfully synthesized via the thermal annealing and subsequent etching/ion-exchange reaction. As a consequence, the NiCoM-LDH/C materials exhibit significantly improved electrochemical performance. Specifically, the optimized NiCoMn-LDH/C electrode possesses an excellent capacity performance of 888.3 C g^?1 at 1 A g^?1. Moreover, the HSC device assembled by NiCoMn-LDH/C and active carbon delivers a remarkable energy density of 46.5 Wh kg^?1 at a power density of 792.5 W kg^?1 and possesses superior cyclic stability with about 92.05% capacity retention after 5000 cycles. This work may offer a feasible and effective approach for the synthesis of carbon-incorporated ternary layered double hydroxide nanocage materials for high-performance HSC applications.