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The traditional air cathode in microbial fuel cell (MFC) usually consists of catalyst layer (CL), supporting layer (SL) and conductive gas diffusion layer (GDL), the overall MFC performance is inevitably affected by the additional and expensive adhesives and conductive agents. Here, we developed an integrated air cathode in MFC without any additional SL, GDL or adhesives. The integrated air cathode was self-supporting nitrogen-doped reduced graphene oxide@carbon nanofiber (N-rGO@CNF) hybrid membranes fabricated by electrospinning with subsequent heat-treatment under ammonia atmosphere. The as-fabricated N-rGO@CNFs possessed far superior MFC performance and oxygen reduction reaction (ORR) activity to the pristine nitrogen-doped carbon nanofibers (NCNF) and commercial activated carbon (CAC). The amount of rGO embedded into CNF had prominent influence on their ORR activities and MFC performances. N-5-rGO@CNF had the lowest resistance and the maximal exchange current density, exhibiting desirable oxygen reduction performance via a four-electron pathway. The maximum power density of N-5-rGO@CNF can reach 826 mW m−2 in MFC, which is approximately 9, 2.53 and 1.82 times of pristine NCNF, CAC and Pt/C with values of 91, 327 and 454 mW m−2. The outstanding performance of the integrated air-cathodes originates from the integrality, brevity and hybrid composition of the electrospun nanofiber membrane. The appropriate embedded rGO not only improves the bulk conductivity of the rGO@CNF to promote ion adsorption, but also provides vacancies to accommodate ions, the doped nitrogen atoms facilitate O 2 adsorption and/or subsequent O–O bond breaking, thus improving the electrochemical performance of N-rGO@CNF in MFC. [Display omitted] • An integrated N-rGO@CNF air cathodes with high-efficiency were developed via electrospinning. • The integrated air cathodes showed excellent catalytic performance in Microbial Fuel Cells. • The optimal air cathode (N-5-rGO@CNF) had maximum power density of 20650 mW m−3. • N-5-rGO@CNF exhibited ideal oxygen reduction reaction via a four-electron pathway. [ABSTRACT FROM AUTHOR]

Rational design and modulation of oxygen electrocatalytic microenvironment are crucial for achieving high performance in rechargeable Zn-air batteries (RZABs). We report a high-efficiency bifunctional electrocatalyst based on S, N codoped carbon fibers confining carbon nanocapsules attached with Co 9 S 8 nanoparticles to customize the oxygen electrocatalytic microenvironment. The inner carbon nanocapsules function as a "gas buffer", while the outer fiber skeleton acts as a self-supporting structure, which jointly refine the oxygen electrocatalytic microenvironment and improve accessibility of the active sites. Such a unique nanostructure proves advantageous for O 2 adsorption/diffusion and mitigation of local pH changes during oxygen reduction reaction, and favors the release of generated O 2 and the transfer of interfacial electron during the oxygen evolution reaction as well. The constructed liquid RZABs deliver a large peak power density (280 mW cm−2) and robust cyclability (1200 h at 10 mA cm−2), and the assembled quasi-solid state flexible RZABs further indicate long-term durability. [Display omitted] • S, N codoped carbon fibers confining carbon nanocapsules attached with Co 9 S 8 NPs are constructed. • DFT confirms the curved structures can optimize the free energy of Co 9 S 8 for intermediates. • CNC/Co 9 S 8 @SNCF exhibits outstanding pH-universal ORR performance and OER activity. • The Zn-air battery shows a large peak power density (280 mW cm−2) and robust cyclability (1200 h at 10 mA cm−2). [ABSTRACT FROM AUTHOR]

Rational design of highly effective and low-cost oxygen reduction reaction (ORR) electrocatalysts to replace Pt-based catalysts is still a significant challenge for rechargeable zinc-air batteries. Hence, Fe, N co-doped one-dimensional carbon nanofibers with Fe 4 N species (Fe/N-CNFs) are synthesized through the electrospun technique combining with the "rapid calcination under vacuum" method. Benefitting from the one-dimensional structure obtained by the electrospun technique, the as-synthesized Fe/N-CNFs electrocatalyst with mesoporous exhibits a relatively large specific surface area of 624.12 m2 g−1. Notably, the intrinsic activity of Fe 4 N species as well as the large specific surface area can endow the resulting Fe/N-CNFs with a positive half-wave potential of 0.88 V compared with 20 wt% Pt/C (0.86 V) for ORR. The Fe/N-CNFs also exhibits better long-term stability than 20 wt% Pt/C. Furthermore, the rechargeable zinc-air battery constructed with Fe/N-CNFs as the cathode shows a high open-circuit voltage of 1.51 V, a peak power density of 135 mW cm−2 and an excellent cycle life for 55 h. The as-synthesized electrocatalyst is promising to replace the precious metal catalysts for rechargeable zinc-air batteries. Unlabelled Image • Fe, N co-doped carbon nanofibers (Fe/N-CNFs) with Fe 4 N species were synthesized. • The "rapid calcination under vacuum" was reported for the preparation of Fe/N-CNFs. • The one-dimensional structure of Fe/N-CNFs provides a large specific surface area. • The Fe/N-CNFs exhibits more excellent ORR activity than commercial 20 wt% Pt/C. • The Fe/N-CNFs endows zinc-air batteries with comparable performances to 20 wt% Pt/C. [ABSTRACT FROM AUTHOR]

A novel one step method was developed to dope nitrogen (N), sulfur (S) and carbon (C) in the Fe nanoparticles-dispersed carbon nanofibers (CNFs) grown over carbide-derived carbon (CDC), using thiourea as the single source of N, S and C. The synthesized N/S-Fe-CNF/CDC electrode was successfully used in a microbial fuel cell (MFC). When tested as the oxygen reduction reaction (ORR) catalyst, the electrode achieved a high current density (2.261 ± 0.002 mA/cm2), high OCP (0.611 ± 0.005 V), high stability upto 400 cycles, response time of ∼11 s, electron transfer number in the range 3.73–4.03, and Tafel slopes of −0.0627 and −0.183 V/dec at low and high current densities, respectively. A first order kinetics and a 4e− pathway were deduced from the ORR analysis. Notably, the fabricated MFC based on the prepared electrode produced a high current density of 1.3887 ± 0.002 mA/cm2, high OCP of 0.626 ± 0.005 V and maximum power density of 0.238 ± 0.002 mW/cm2, attributed to the synergistic effects of heteroatoms, Fe nanoparticles, and CNFs. Image 1 • Thiourea was used as the single source of heteroatoms (N, S) and carbon in Fe-CDC. • N/S-Fe-CNF/CDC-based MFC generated high OCP and power density. • Synergy of N, S, Fe, and graphitic CNFs resulted in the high performance of MFC. [ABSTRACT FROM AUTHOR]

An efficient, robust and low-cost bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential to high-performance zinc-air batteries (ZABs). Metal-nitrogen-carbon (M-N-C) systems have attracted considerable attention recently. Herein, a novel Co-N x -enriched electrospun porous carbon nanofibrous bifunctional electrocatalyst (Co-N x /EPCF) is prepared by electrospinning with cobalt nitrate and SiO 2 , followed by carbonization and acid etching. The catalyst displays an outstanding electrocatalytic activity of reversible oxygen overpotential (ΔE = E j = 10 - E 1/2 = 0.87 V), as well as a high stability. The first-principal calculation reveals that the Co–N–C structure has better ORR paths than that of Co cluster. Furthermore, based on the electrocatalyst, the assembled flexible ZABs possess a power density of 81 mW cm−2, a capacity of 807 mAh g zn −1, and 111 stability cycles. The study provides a novel strategy to prepare high-performance bifunctional catalysts for wearable power sources. [Display omitted] • Electrospun porous carbon nanofibers are prepared by hard template method. • Co-N x -enriched catalyst drives energy-efficient ORR/OER kinetics with ΔE = 0.87 V. • Flexible ZABs achieve a power density of 81 mW cm−2 and a cycle time of 37 h. [ABSTRACT FROM AUTHOR]

The in-situ immobilization of Co/MnO hetero-nanoparticles onto N,S co-doped carbon nanotubes/nanofiber-integrated hierarchical branched superstructures demonstrates excellent oxygen reduction electrocatalytic activity, stability and performs robust cycling stability. [Display omitted] • The Co/MnO hetero-nanoparticles were immobilized onto carbon nanofibers. • The heterojunctions cause electronic redistribution and create more active sites. • The "branches"/"trunk"-structure could accelerate electrolyte and mass transport. • The Co/MnO@N,S-C NT/NFs-equipped Zn-air battery shows superior cycling stability. Electronic regulation via interfacial formation is identified as a versatile strategy to improve the electrocatalytic activity. Herein, we report a feasible electrospinning-pyrolysis approach for the in-situ immobilization of Co/MnO hetero-nanoparticles onto N,S co-doped carbon nanotubes/nanofiber-integrated hierarchical branched superstructures (abbreviated as Co/MnO@N,S-C NT/CNFs hereafter). The simultaneous realization of interfacial engineering and nanocarbon hybridization renders the fabricated Co/MnO@N,S-C NT/CNFs with abundant firmly anchored active sites, modified electronic configuration, improved electric conductivity, efficient mass transport pathways, and significantly reinforced stability. Profiting from the compositional synergy and architectural advantages, the Co/MnO@N,S-C NT/CNFs exhibit outstanding ORR activity, superior tolerance to methanol, and excellent long-term stability in KOH electrolyte. More encouragingly, as a proof-of-concept demonstration, the rechargeable aqueous and flexible all-solid-state Zn-air batteries using Co/MnO@N,S-C NT/NFs + RuO 2 as the air-cathode afford higher power densities, larger specific capacities and superb cycling stability, outperforming the state-of-the-art Pt/C + RuO 2 counterparts. This work demonstrates the great contribution of heterointerfaces for oxygen electrocatalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel electrode was fabricated by electrospinning PAN blended with ZIF-67. • The ZIF-67/CNFs electrode showed excellent electrocatalytic activities for ORR. • MFCs with ZIF-67/CNFs cathode had a maximum power density of 1.191±0.017 W m−2. • Geobacter was the highest proportion of microbial in ZIF-67/CNFs-MFC. In this study, the zeolitic imidazolate framework-67 (ZIF-67) and electrospinning polyacrylonitrile membrane were combined to prepare electrospinning carbon nanofibers composite cathode (ZIF-67/CNFs) which could enhance the oxygen reduction reaction (ORR) performance of microbial fuel cells (MFCs) cathode. The optimum electrode 3 wt% ZIF-67/CNFs revealed the excellent ORR performance with a half-wave potential of −0.03 V vs. Ag/AgCl, which was more positive than Pt/C-CC (-0.09 V vs. Ag/AgCl). The highest output voltage (607±9 mV) and maximum power density (1.191±0.017 W m−2) were obtained when the prepared ZIF-67/CNFs electrode was applied to the cathode of MFC (ZIF-67/CNFs-MFC). In addition, ZIF-67/CNFs-MFC showed the best pollutant removal effect. Geobacter was the highest proportion of microbial in ZIF-67/CNFs-MFC. The results have shown that the application of ZIF-67/CNFs electrode to MFC cathode is promising. [ABSTRACT FROM AUTHOR]

[Display omitted] • Developed a new type of Fe 3 C-N-C nanofibers as oxygen reduction catalyst. • Dicyandiamide can increase specific surface area and generate active sites for ORR. • Synergistic effect between N-doped carbon and Fe 3 C can enhance the ORR performance. • Zn-air battery with Fe 3 C-N-C-0.5 delivers high power density and cycling stability. Slow oxygen reduction reaction (ORR) kinetic at the cathode side of Zn-air batteries seriously hinder its large-scale applications. Here, dicyandiamide (DCD) was used to synthesis high specific surface area ORR electrocatalysts by electrospun. The as-synthesized Fe 3 C nanoparticles decorated N-doped carbon nanofibers exhibit comparable performance to commercial Pt/C catalysts. Rechargeable Zn–air batteries with the catalyst exhibits higher power density and cycling stability compared to the commercial Pt/C catalyst. This work has demonstrated a new way to prepare highly efficient and stable ORR electrocatalysts for rechargeable Zn-air batteries. [ABSTRACT FROM AUTHOR]

Developing transition-metal based bifunctional electrocatalysts to efficiently drive oxygen evolution reaction and oxygen reduction reaction is an urgent demand for the implementation of rechargeable Zn-air batteries. Transition-metal sulfides are emerging as alternatives to precious metal-based electrocatalysts, however, their bifunctional activities are usually restricted by inferior electrical conductivities and limited electrochemical active sites. Herein, we highlight a novel metal-organic frameworks derived nitrogen-doped carbon nanofiber coupled FeS 2 –CoS 2 (FeS 2 –CoS 2 /NCFs) by a combination of electrospinning and atomic-layer-deposition approach. Benefiting from the large exposed surface active sites of hierarchical structure and the abundant interfacial vacancies in FeS 2 –CoS 2 heterointerface, the FeS 2 –CoS 2 /NCFs integrated electrocatalyst delivers a high bifunctional activity together with a good durability in alkaline medium. Notably, the liquid Zn-air battery assembled with this FeS 2 –CoS 2 /NCFs electrode displays a considerable peak power density of 257 mW cm−2, a high specific capacity of 814 mA h g−1 and a long cycling life of 250 h, superior to precious metal based Zn-air batteries. Moreover, the flexible solid-state Zn-air battery using such FeS 2 –CoS 2 /NCFs electrode can stably power LED panels even under twisting state, demonstrating practical potentials in wearable and portable electrochemical devices. Image 1 • Hierarchical FeS 2 –CoS 2 /NCFs with core-shell structure was designed. • FeS 2 –CoS 2 /NCFs displayed efficient bifunctional catalytic activities. • The interfacial vacancies and hierarchical structure increased its activities. • FeS 2 –CoS 2 /NCFs-based batteries exhibited excellent power density and cycling durability. [ABSTRACT FROM AUTHOR]

A highly porous free-standing NiCr-bimetallic catalyst is synthesized by electrospinning and carbonization and is applied as an anode in a direct urea/H 2 O 2 fuel cell for electro-oxidation of urea. It is observed that the morphology of the calcined NiCr catalyst, which has a higher specific surface area, is identical to that of the electrospun NiCr catalyst fiber. Cr-doping at 40% (Cr/Ni) significantly increases the oxidation peak current of the urea oxidation reaction. The addition of carbon nanotubes also considerably enhances the catalytic activity. A direct urea/H 2 O 2 fuel cell, which utilizes the synthesized catalyst (NiCr-CNT@C) as a free-standing anode, exhibits excellent performance with a maximum power density of 48.1 mW cm−2 and an open-circuit voltage of 0.92 V at 80 °C. Thus, the highly porous free-standing NiCr-CNT@C catalyst mat can be employed as an efficient anode material for urea oxidation in urea fuel cells. Image 1 • A freestanding NiCr catalyst mat was synthesized by electrospinning technique. • NiCr bimetal nanoparticles were uniformly embedded in the carbon nanofibers. • The NiCr catalyst featured excellent electro-catalytic activity for urea oxidation. • A urea fuel cell with NiCr catalyst exhibited a power density of 48.1 mW cm−2. [ABSTRACT FROM AUTHOR]

Here, we successfully synthesize three-dimensional (3D) callistemon-like hierarchical networks structural catalysts (CoNC/NCNTs@CNF) in which Co nanoparticles are encapsulated within N-doped carbon nanotubes apexes via electrospinning method combined with two-step pyrolysis process. Benefiting from the unique 3D callistemon-like structure, CoNC/NCNTs@CNF affords adequate surface area (261 m2 g−1) and the enhanced electronic conductivity (even superior to Pt/C and RuO 2). Due to the synergistic effect of the coupling between highly Co–N–C active sites and unique 3D callistemon-like structure, CoNC/NCNTs@CNF was explored as the trifunctional electrocatalysts for oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction. Further, we assemble the catalysts as an air electrode for Zn-air batteries, demonstrating a maximum power density of 260 mW cm−2, and excellent cycling stability even after 43 h at 5 mA cm−2. Thus, this work offers a guide to the design of metal organic frameworks-derived 3D structure materials combined with electrospinning for wider application in renewable energy technologies. Image 1 • A ZIFs-derived callistemon-like 3D structure materials. • 1D carbon nanofibers were supported in situ forming carbon nanotubes. • Co nanoparticles coated with graphitic carbon were precisely encapsulated within the CNT apex. • The resultant catalyst displayed a multifunctional performance for ORR, OER, HER. • Catalyst was further constructed as overall water splitting and Zn-air batteries. [ABSTRACT FROM AUTHOR]