Novel Graphene Hydrogel/B‐Doped Graphene Quantum Dots Composites as Trifunctional Electrocatalysts for Zn−Air Batteries and Overall Water Splitting

Herein, a facile, one‐step hydrothermal route to synthesize novel all‐carbon‐based composites composed of B‐doped graphene quantum dots anchored on a graphene hydrogel (GH‐BGQD) is demonstrated. The obtained GH‐BGQD material has a unique 3D architecture with high porosity and large specific surface area, exhibiting abundant catalytic active sites of B‐GQDs as well as enhanced electrolyte mass transport and ion diffusion. Therefore, the prepared GH‐BGQD composites exhibit a superior trifunctional electrocatalytic activity toward the oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction with excellent long‐term stability and durability comparable to those of commercial Pt/C and Ir/C catalysts. A flexible solid‐state Zn–air battery using a GH‐BGQD air electrode achieves an open‐circuit voltage of 1.40 V, a stable discharge voltage of 1.23 V for 100 h, a specific capacity of 687 mAh g^?1, and a peak power density of 112 mW cm^?2. Also, a water electrolysis cell using GH‐BGQD electrodes delivers a current density of 10 mA cm^?2 at cell voltage of 1.61 V, with remarkable stability during 70 h of operation. Finally, the trifunctional GH‐BGQD catalyst is employed for water electrolysis cell powered by the prepared Zn–air batteries, providing a new strategy for the carbon‐based multifunctional electrocatalysts for electrochemical energy devices.     

Two‐Step Activated Carbon Cloth with Oxygen‐Rich Functional Groups as a High‐Performance Additive‐Free Air Electrode for Flexible Zinc–Air Batteries

A flexible air electrode (FAE) with both high oxygen electrocatalytic activity and excellent flexibility is the key to the performance of various flexible devices, such as Zn–air batteries. A facile two‐step method, mild acid oxidation followed by air calcination that directly activates commercial carbon cloth (CC) to generate uniform nanoporous and super hydrophilic surface structures with optimized oxygen‐rich functional groups and an enhanced surface area, is presented here. Impressively, this two‐step activated CC (CC‐AC) exhibits superior oxygen electrocatalytic activity and durability, outperforming the oxygen‐doped carbon materials reported to date. Especially, CC‐AC delivers an oxygen evolution reaction (OER) overpotential of 360 mV at 10 mA cm^?2 in 1 m KOH, which is among the best performances of metal‐free OER electrocatalysts. The practical application of CC‐AC is presented via its use as an FAE in a flexible rechargeable Zn–air battery. The bendable battery achieves a high open circuit voltage of 1.37 V, a remarkable peak power density of 52.3 mW cm^?3 at 77.5 mA cm^?3, good cycling performance with a small charge–discharge voltage gap of 0.98 V and high flexibility. This study provides a new approach to the design and construction of high‐performance self‐supported metal‐free electrodes.     

Ice Templated Free‐Standing Hierarchically WS2/CNT‐rGO Aerogel for High‐Performance Rechargeable Lithium and Sodium Ion Batteries

A hybrid nanoarchitecture aerogel composed of WS₂ nanosheets and carbon nanotube‐reduced graphene oxide (CNT‐rGO) with ordered microchannel three‐dimensional (3D) scaffold structure was synthesized by a simple solvothermal method followed by freeze‐drying and post annealing process. The 3D ordered microchannel structures not only provide good electronic transportation routes, but also provide excellent ionic conductive channels, leading to an enhanced electrochemical performance as anode materials both for lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs). Significantly, WS₂/CNT‐rGO aerogel nanostructure can deliver a specific capacity of 749 mA h g^?1 at 100 mA g^?1 and a high first‐cycle coulombic efficiency of 53.4% as the anode material of LIBs. In addition, it also can deliver a capacity of 311.4 mA h g^?1 at 100 mA g^?1, and retain a capacity of 252.9 mA h g^?1 at 200 mA g^?1 after 100 cycles as the anode electrode of SIBs. The excellent electrochemical performance is attributed to the synergistic effect between the WS₂ nanosheets and CNT‐rGO scaffold network and rational design of 3D ordered structure. These results demonstrate the potential applications of ordered CNT‐rGO aerogel platform to support transition‐metal‐dichalcogenides (i.e., WS₂) for energy storage devices and open up a route for material design for future generation energy storage devices.     

3D Hierarchical Porous α‐Fe2O3 Nanosheets for High‐Performance Lithium‐Ion Batteries

To develop a long cycle life and good rate capability electrode, 3D hierarchical porous α‐Fe₂O₃ nanosheets are fabricated on copper foil and directly used as binder‐free anode for lithium‐ion batteries. This electrode exhibits a high reversible capacity and excellent rate capability. A reversible capacity up to 877.7 mAh g^?1 is maintained at 2 C (2.01 A g^?1) after 1000 cycles, and even when the current is increased to 20 C (20.1 A g^?1), a capacity of 433 mA h g^?1 is retained. The unique porous 3D hierarchical nanostructure improves electronic–ionic transport, mitigates the internal mechanical stress induced by the volume variations of the electrode upon cycling, and forms a 3D conductive network during cycling. No addition of any electrochemically inactive conductive agents or polymer binders is required. Therefore, binder‐free electrodes further avoid the uneven distribution of conductive carbon on the current collector due to physical mixing and the addition of an insulator (binder), which has benefits leading to outstanding electrochemical performance.     

Atomic Modulation of FeCo–Nitrogen–Carbon Bifunctional Oxygen Electrodes for Rechargeable and Flexible All‐Solid‐State Zinc–Air Battery

Rational design and exploration of robust and low‐cost bifunctional oxygen reduction/evolution electrocatalysts are greatly desired for metal–air batteries. Herein, a novel high‐performance oxygen electrode catalyst is developed based on bimetal FeCo nanoparticles encapsulated in in situ grown nitrogen‐doped graphitic carbon nanotubes with bamboo‐like structure. The obtained catalyst exhibits a positive half‐wave potential of 0.92 V (vs the reversible hydrogen electrode, RHE) for oxygen reduction reaction, and a low operating potential of 1.73 V to achieve a 10 mA cm^?2 current density for oxygen evolution reaction. The reversible oxygen electrode index is 0.81 V, surpassing that of most highly active bifunctional catalysts reported to date. By combining experimental and simulation studies, a strong synergetic coupling between FeCo alloy and N‐doped carbon nanotubes is proposed in producing a favorable local coordination environment and electronic structure, which affords the pyridinic N‐rich catalyst surface promoting the reversible oxygen reactions. Impressively, the assembled zinc–air batteries using liquid electrolytes and the all‐solid‐state batteries with the synthesized bifunctional catalyst as the air electrode demonstrate superior charging–discharging performance, long lifetime, and high flexibility, holding great potential in practical implementation of new‐generation powerful rechargeable batteries with portable or even wearable characteristic.     

Blood‐Capillary‐Inspired,Free‐Standing,Flexible, and Low‐Cost Super‐Hydrophobic N‐CNTs@SS Cathodes for High‐Capacity,High‐Rate,and Stable Li‐Air Batteries

With the rising demand for flexible and wearable electronic devices, flexible power sources with high energy densities are required to provide a sustainable energy supply. Theoretically, rechargeable, flexible Li‐O₂/air batteries can provide extremely high specific energy densities; however, the high costs, complex synthetic methods, and inferior mechanical properties of the available flexible cathodes severely limit their practical applications. Herein, inspired by the structure of human blood capillary tissue, this study demonstrates for the first time the in situ growth of interpenetrative hierarchical N‐doped carbon nanotubes on the surface of stainless‐steel mesh (N‐CNTs@SS) for the fabrication of a self‐supporting, flexible electrode with excellent physicochemical properties via a facile and scalable one‐step strategy. Benefitting from the synergistic effects of the high electronic conductivity and stable 3D interconnected conductive network structure, the Li‐O₂ batteries obtained with the N‐CNTs@SS cathode exhibit superior electrochemical performance, including a high specific capacity (9299 mA h g^?1 at 500 mA g^?1), an excellent rate capability, and an exceptional cycle stability (up to 232 cycles). Furthermore, as‐fabricated flexible Li‐air batteries containing the as‐prepared flexible super‐hydrophobic cathode show excellent mechanical properties, stable electrochemical performance, and superior H₂O resistibility, which enhance their potential to power flexible and wearable electronic devices.     

MnMoO4 Electrocatalysts for Superior Long‐Life and High‐Rate Lithium‐Oxygen Batteries

Lithium‐oxygen batteries represent a significant scientific challenge for high‐rate and long‐term cycling using oxygen electrodes that contain efficient electrocatalysts. The mixed transition metal oxide catalysts provide the most efficient catalytic activity for partial heterogeneous surface cations with oxygen vacancies as the active phase. They include multiple oxidation states and oxygen vacancies. Here, using a combination of transmission electron microscopy, differential electrochemical mass spectrometry, X‐ray photoelectron spectroscopy, and electrochemical properties to probe the surface of the MnMoO₄ nanowires, it is shown that the intrinsic MnMoO₄ oxygen vacancies on the oxygen electrode are an effective strategy to achieve a high reversibility and high efficiency for lithium‐oxygen (Li‐O₂) batteries. The modified MnMoO₄ nanowires exhibit a highly stable capacity at a fixed capacity of 5000 mA h g_sp^?1 (calculated weight of Super P carbon black) during 50 cycles, a high‐rate capability at a current rate of 3000 mA g_sp^?1 during 70 cycles, and a long‐term reversible capacity during 188 cycles at a fixed capacity of 1000 mA h g_sp^?1. It is demonstrated that this strategy for creating mixed transition metal oxides (e.g., MnMoO₄) may pave the way for the new structural design of electrocatalysts for Li‐O₂ batteries.     

Apically Dominant Mechanism for Improving Catalytic Activities of N‐Doped Carbon Nanotube Arrays in Rechargeable Zinc–Air Battery

The oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in zinc–air batteries (ZABs) require highly efficient, cost‐effective, and stable electrocatalysts as alternatives to high cost and low poison resistant platinum group metals (PGM) catalysts. Although nitrogen‐doped carbon nanotube (NCNT) arrays are now capable of catalyzing ORR efficiently, their hydrophobic surface and base‐growth mode are found to limit the catalytic performance in the practical ZABs. Here, the concept of an apically dominant mechanism in improving the catalytic performance of NCNT by precisely encapsulating CoNi nanoparticles (NPs) within the apical domain of NCNT on the Ni foam (denoted as CoNi@NCNT/NF) is demonstrated. The CoNi@NCNT/NF exhibits a more excellent catalytic performance toward both ORR and OER than that of traditional NCNT derived from the base‐growth method. The ZAB coin cell using CoNi@NCNT/NF as an air electrode shows a peak power density of 127 mW cm^?2 with an energy density of 845 Wh kg_Zn^?1 and rechargeability over 90 h, which outperforms the performance of PGM catalysts. Density functional theory calculations reveal that the ORR catalytic performance of the CoNi@NCNT/NF is mainly attributed to the synergetic contributions from NCNT and the apical active sites on NCNT near to CoNi NPs.     

High Energy and High Power Lithium‐Ion Capacitors Based on Boron and Nitrogen Dual‐Doped 3D Carbon Nanofibers as Both Cathode and Anode

High energy density at high power density is still a challenge for the current Li‐ion capacitors (LICs) due to the mismatch of charge‐storage capacity and electrode kinetics between capacitor‐type cathode and battery‐type anode. In this work, B and N dual‐doped 3D porous carbon nanofibers are prepared through a facile method as both capacitor‐type cathode and battery‐type anode for LICs. The B and N dual doping has profound effect in tuning the porosity, functional groups, and electrical conductivity for the porous carbon nanofibers. With rational design, the developed B and N dual‐doped carbon nanofibers (BNC) exhibit greatly improved electrochemical performance as both cathode and anode for LICs, which greatly alleviates the mismatch between the two electrodes. For the first time, a 4.5 V “dual carbon” BNC//BNC LIC device is constructed and demonstrated, exhibiting outstanding energy density and power capability compared to previously reported LICs with other configurations. In specific, the present BNC//BNC LIC device can deliver a large energy density of 220 W h kg^?1 and a high power density of 22.5 kW kg^?1 (at 104 W h kg^?1) with reasonably good cycling stability (≈81% retention after 5000 cycles).     

NiFe‐Based Metal–Organic Framework Nanosheets Directly Supported on Nickel Foam Acting as Robust Electrodes for Electrochemical Oxygen Evolution Reaction

It is of great significance to develop highly efficient and superior stable oxygen evolution reaction (OER) electrocatalysts for upcoming electrochemical conversion technologies and clean energy systems. Here, an assembled 3D electrode is synthesized by a one‐step solvothermal process using such an original OER electrocatalyst. During the solvothermal process, Ni ions released from Ni foam in acidic solution and Fe ions added exogenously act as metal centers and coordinate with terephthalic acid (TPA) organic molecules by robust coordinate bonds, and finally, NiFe‐based metal–organic framework (MOF) nanosheets in situ grown on Ni foam, i.e., MIL‐53(FeNi)/NF, are prepared. This binder‐free 3D electrode shows superior OER activity with high current density (50 mA cm^?2) at an overpotential of 233 mV, a Tafel slope of 31.3 mV dec^?1, and excellent stability in alkaline aqueous solution (1 m KOH). It is discovered that introduction of Fe into MIL‐53 structure increases electrochemically‐active areas as well as reaction sites, accelerated electron transport capability, and modulated electronic structure to enhance catalytic performance. Besides, first principles calculations show that MIL‐53(FeNi) is more favorable for foreign atoms' adsorption and has increased 3d orbital electron density boosting intrinsic activity. This work elucidates a promising electrode for electrocatalysts and enriches direct application of MOF materials.     

Highly Active Trimetallic NiFeCr Layered Double Hydroxide Electrocatalysts for Oxygen Evolution Reaction

The development of efficient and robust earth‐abundant electrocatalysts for the oxygen evolution reaction (OER) is an ongoing challenge. Here, a novel and stable trimetallic NiFeCr layered double hydroxide (LDH) electrocatalyst for improving OER kinetics is rationally designed and synthesized. Electrochemical testing of a series of trimetallic NiFeCr LDH materials at similar catalyst loading and electrochemical surface area shows that the molar ratio Ni:Fe:Cr = 6:2:1 exhibits the best intrinsic OER catalytic activity compared to other NiFeCr LDH compositions. Furthermore, these nanostructures are directly grown on conductive carbon paper for a high surface area 3D electrode that can achieve a catalytic current density of 25 mA cm^?2 at an overpotential as low as 225 mV and a small Tafel slope of 69 mV dec^?1 in alkaline electrolyte. The optimized NiFeCr catalyst is stable under OER conditions and X‐ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, and elemental analysis confirm the stability of trimetallic NiFeCr LDH after electrochemical testing. Due to the synergistic interactions among the metal centers, trimetallic NiFeCr LDH is significantly more active than NiFe LDH and among the most active OER catalysts to date. This work also presents general strategies to design more efficient metal oxide/hydroxide OER electrocatalysts.     

Direct Growth of Flower‐Like δ‐MnO2 on Three‐Dimensional Graphene for High‐Performance Rechargeable Li‐O2 Batteries

A challenge still remains to develop high‐performance and cost‐effective air electrode for Li‐O₂ batteries with high capacity, enhanced rate capability and long cycle life (100 times or above) despite recent advances in this field. In this work, a new design of binder‐free air electrode composed of three‐dimensional (3D) graphene (G) and flower‐like δ‐MnO₂ (3D‐G‐MnO₂) has been proposed. In this design, graphene and δ‐MnO₂ grow directly on the skeleton of Ni foam that inherits the interconnected 3D scaffold of Ni foam. Li‐O₂ batteries with 3D‐G‐MnO₂ electrode can yield a high discharge capacity of 3660 mAh g^?1 at 0.083 mA cm^?2. The battery can sustain 132 cycles at a capacity of 492 mAh g^?1 (1000 mAh g_carbon ^?1) with low overpotentials under a high current density of 0.333 mA cm^?2. A high average energy density of 1350 Wh Kg^?1 is maintained over 110 cycles at this high current density. The excellent catalytic activity of 3D‐G‐MnO₂ makes it an attractive air electrode for high‐performance Li‐O₂ batteries.     

Trifunctional Electrocatalysis on Dual‐Doped Graphene Nanorings–Integrated Boxes for Efficient Water Splitting and Zn–Air Batteries

Despite the exciting achievements made in synthesis of monofunctional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), or hydrogen evolution reaction (HER), it is challenging to develop trifunctional electrocatalysts for both ORR/OER/HER. Herein, N, O‐codoped graphene nanorings‐integrated boxes (denoted NOGB) are crafted via high‐temperature pyrolysis and following acid etching of hybrid precursors containing polymers and Prussian blue analogue cubes. The electrochemical results signified that the resulting NOGB‐800 (800 refers to pyrolysis temperature) is highly active for trifunctional electrocatalysis of ORR/OER/HER. This can be reasonably attributed to the advanced nanostructures (i.e., the hierarchically porous nanostructures on the hollow nanorings) and unique chemical compositions (i.e., N, O‐codoped graphene). More attractively, the rechargeable Zn–air battery based on NOGB‐800 displays maximum power density of 111.9 mW cm^?2 with small charge–discharge potential of 0.72 V and excellent stability of 30 h, comparable with the Pt/C+Ir/C counterpart. The NOGB‐800 could also be utilized as bifunctional electrocatalysts for overall water splitting to yield current density of 10 mA cm^?2 at a voltage of 1.65 V, surpassing most reported electrocatalysts. Therefore, the NOGB‐800 is a promising candidate instead of precious metal–based electrocatalysts for the efficient Zn–air battery and water splitting.     

Hybrid and Aqueous Lithium‐Air Batteries

Lithium‐air (Li‐air) batteries have become attractive because of their extremely high theoretical energy density. However, conventional Li‐air cells operating with non‐aqueous electrolytes suffer from poor cycle life and low practical energy density due to the clogging of the porous air cathode by insoluble discharge products, contamination of the organic electrolyte and lithium metal anode by moist air, and decomposition of the electrolyte during cycling. These difficulties may be overcome by adopting a cell configuration that consists of a lithium‐metal anode protected from air by a Li⁺‐ion solid electrolyte and an air electrode in an aqueous catholyte. In this type of configuration, a Li⁺‐ion conducting “buffer” layer between the lithium‐metal anode and the solid electrolyte is often necessary due to the instability of many solid electrolytes in contact with lithium metal. Based on the type of buffer layer, two different battery configurations are possible: “hybrid” Li‐air batteries and “aqueous” Li‐air batteries. The hybrid and aqueous Li‐air batteries utilize the same battery chemistry and face similar challenges that limit the cell performance. Here, an overview of recent developments in hybrid and aqueous Li‐air batteries is provided and the factors that influence their performance and impede their practical applications, followed by future directions are discussed.     

High‐Performance Fiber‐Shaped All‐Solid‐State Asymmetric Supercapacitors Based on Ultrathin MnO2 Nanosheet/Carbon Fiber Cathodes for Wearable Electronics

Flexible fiber‐shaped supercapacitors have shown great potential in portable and wearable electronics. However, small specific capacitance and low operating voltage limit the practical application of fiber‐shaped supercapacitors in high energy density devices. Herein, direct growth of ultrathin MnO₂ nanosheet arrays on conductive carbon fibers with robust adhesion is exhibited, which exhibit a high specific capacitance of 634.5 F g^?1 at a current density of 2.5 A g^?1 and possess superior cycle stability. When MnO₂ nanosheet arrays on carbon fibers and graphene on carbon fibers are used as a positive electrode and a negative electrode, respectively, in an all‐solid‐state asymmetric supercapacitor (ASC), the ASC displays a high specific capacitance of 87.1 F g^?1 and an exceptional energy density of 27.2 Wh kg^?1. In addition, its capacitance retention reaches 95.2% over 3000 cycles, representing the excellent cyclic ability. The flexibility and mechanical stability of these ASCs are highlighted by the negligible degradation of their electrochemical performance even under severely bending states. Impressively, as‐prepared fiber‐shaped ASCs could successfully power a photodetector based on CdS nanowires without applying any external bias voltage. The excellent performance of all‐solid‐state ASCs opens up new opportunity for development of wearable and self‐powered nanodevices in near future.     

Alkaline Polymer Membrane‐Based Ultrathin,Flexible, and High‐Performance Solid‐State Zn‐Air Battery

The increasing demand for portable and wearable electronics requires lightweight, thin, and highly flexible power sources, for example, flexible zinc‐air batteries (ZABs). The so‐far reported flexible ZAB devices mostly remain bulky, with a design consisting of two relatively thick substrates (e.g., carbon cloths and/or metal foams) and a gel electrolyte‐coated separator in between. Herein, an ultrathin (≈0.2 mm) solid‐state ZAB with high flexibility and performance is introduced by directly forming self‐standing active layers on each surface of an alkaline polymer membrane through an ink‐casting/hot‐pressing approach. A Fe/N‐doped 3D carbon with hierarchic pores and an interconnected network structure is used as cathode electrocatalyst, so that the backing gas‐diffusion layer (e.g., carbon cloth) can be abandoned. What is further, a microstructure‐modulating method to significantly increase the FeN₄ active sites for oxygen reduction reaction is developed, thus significantly boosting the performance of the ZAB. The assembled solid‐state ZAB manifests remarkable peak power density of 250 mW cm^?3 and high capacity of 150.4 mAh cm^?3 at 8.3 mA cm^?3, as well as excellent flexibility. The new design should provide valuable opportunity to the portable and wearable electronics.     

Three‐Dimensional Smart Catalyst Electrode for Oxygen Evolution Reaction

A multifunctional catalyst electrode mimicking external stimuli–responsive property has been prepared by the in situ growth of nitrogen (N)‐doped NiFe double layered hydroxide (N–NiFe LDH) nanolayers on a 3D nickel foam substrate framework. The electrode demonstrates superior performance toward catalyzing oxygen evolution reaction (OER), affording a low overpotential of 0.23 V at the current density of 10 mA cm^?2, high Faradaic efficiency of ≈98%, and stable operation for >60 h. Meanwhile, the electrode can dynamically change its color from gray silver to dark black with the OER happening, and the coloration/bleaching processes persist for at least 5000 cycles, rendering it a useful tool to monitor the catalytic process. Mechanism study reveals that the excellent structural properties of electrode such as 3D conductive framework, ultra thickness of N–NiFe LDH nanolayer (≈0.8 nm), and high N‐doping content (≈17.8%) make significant contribution to achieving enhanced catalytic performance, while N–NiFe LDH nanolayer on electrode is the main contributor to the stimuli‐responsive property with the reversible extraction/insertion of electrons from/into N–NiFe LDH leading to the coloration/bleaching processes. Potential application of this electrode has been further demonstrated by integrating it into a Zn–air battery device to identify the charging process during electrochemical cycling.     

Chemically Exfoliating Biomass into a Graphene‐like Porous Active Carbon with Rational Pore Structure,Good Conductivity,and Large Surface Area for High‐Performance Supercapacitors

Active carbons have unique physicochemical properties, but their conductivities and surface to weight ratios are much poorer than graphene. A unique and facile method is innovated to chemically process biomass by “drilling” holes with H₂O₂ and exfoliating into graphene‐like nanosheets with HAc, followed by carbonization at a high temperature for highly graphitized activated carbon with greatly enhanced porosity, unique pore structure, high conductivity, and large surface area. This graphene‐like carbon exhibits extremely high specific capacitance (340 F g^?1 at 0.5 A g^?1) and high specific energy density (23.33 to 16.67 W h kg^?1) with excellent rate capability and long cycling stability (remains 98% after 10 000 cycles), which is much superior to all reported carbons including graphene. Synthesis mechanism for deriving biomass into porous graphene‐like carbons is discussed in detail. The enhancement mechanism for the porous graphene‐like carbon electrode reveals that rationally designed meso‐ and macropores are very critical in porous electrode performance, which can network micropores for diffusion freeways, high conductivity, and high utilization. This work has universal significance in producing highly porous and conductive carbons from biomass including biowastes for various energy storage/conversion applications.     

Seamlessly Conductive 3D Nanoarchitecture of Core–Shell Ni‐Co Nanowire Network for Highly Efficient Oxygen Evolution

Electrochemical splitting of water is an attractive way to produce hydrogen fuel as a clean and renewable energy source. However, a major challenge is to accelerate the sluggish kinetics of the anodic half‐cell reaction where oxygen evolution reaction (OER) takes place. Here, a seamlessly conductive 3D architecture is reported with a carbon‐shelled Ni‐Co nanowire network as a highly efficient OER electrocatalyst. Highly porous and granular Ni‐Co nanowires are first grown on a carbon fiber woven fabric utilizing a cost‐effective hydrothermal method and then conductive carbon shell is coated on the Ni‐Co nanowires via glucose carbonization and annealing processes. The conductive carbon layer surrounding the nanowires is introduced to provide a continuous pathway for facile electron transport throughout the whole of the integrated 3D catalyst. This 3D hierarchical structure provides several synergistic effects and beneficial functions including a large number of active sites, easy accessibility of water, fast electron transport, rapid release of oxygen gas, enhanced electrochemical durability, and stronger structural integrity, resulting in a remarkable OER activity that delivers an overpotential of 302 mV with a Tafel slope of 43.6 mV dec^?1 at a current density of 10 mA cm^?2 in an alkaline medium electrolyte (1 m KOH).     

Enhanced Cathodic Oxygen Reduction and Power Production of Microbial Fuel Cell Based on Noble‐Metal‐Free Electrocatalyst Derived from Metal‐Organic Frameworks

Microbial fuel cell (MFC) can generate electricity from organic substances based on anodic electrochemically active microorganisms and cathodic oxygen reduction reaction (ORR), thus exhibiting promising potential for harvesting electric energy from organic wastewater. The ORR performance is crucial to both power production efficiency and overall cost of MFC. A new type of metal‐organic‐framework‐derived electrocatalysts containing cobalt and nitrogen‐doped carbon (CoNC) is developed, which is effective to enhance activity, selectivity, and stability toward four‐electron ORR in pH‐neutral electrolyte. When glucose is used as the substrate, the maximum power density of 1665 mW m^?2 is achieved for the optimized CoNC pyrolyzed at 900 °C, which is 39.8% higher than that of 1191 mW m^?2 for commercial Pt/C catalyst in the single‐chamber MFC. The improved performance of CoNC catalyst can be attributed to large surface area, microporous nature, and the involvement of nitrogen‐coordinated cobalt species. These properties enable the efficient ORR by increasing the active sites and enhancing mass transfer of oxygen and protons at “water‐flooding” three‐phase boundary where ORR occurs. This work provides a proof‐of‐concept demonstration of a noble‐metal‐free high‐efficiency and cost‐effective ORR electrocatalyst for effective recovery of electricity from biomass materials and organic wastewater in MFC.