Tuning morphology and structure of Fe–N–C catalyst for ultra-high oxygen reduction reaction activity

Exploring efficient and durable non-precious metal catalysts for oxygen reduction reaction (ORR) has long been pursued in the field of metal-air batteries, fuel cells, and solar cells. Rational design and controllable synthesis of desirable catalysts are still a great challenge. In this work, a novel approach is developed to tune the morphologies and structures of Fe–N–C catalysts in combination with the dual nitrogen-containing carbon precursors and the gas-foaming agent. The tailored Fe–N₁/N₂–C-A catalyst presents gauze-like porous nanosheets with uniformly dispersed tiny nanoparticles. Such architectures exhibit abundant Fe-N_x active sites and high-exposure surfaces. The Fe–N₁/N₂–C-A catalyst shows extremely high half-wave potential (E_1/2, 0.916 V vs. RHE) and large limiting current density (6.3 mA cm⁻²), far beyond 20 wt% Pt/C catalyst for ORR. This work provides a facile morphological and structural regulation to increase the number and exposure of Fe-N_x active sites.     

In-situ synthesis of Fe,N, S co-doped graphene-like nanosheets around carbon nanoparticles with dual-nitrogen-source as efficient electrocatalyst for oxygen reduction reaction

Iron, nitrogen, sulfur co-doped Fe/N/C catalyst (poly-AT/Me–Fe/N/C) with the structure of graphene-like nanosheets around carbon nanoparticles were successfully synthesized for oxygen reduction reaction (ORR). 2-Aminothiazole and melamine were utilized as the dual-nitrogen-source. The results showed that 2-Aminothiazole, as the nitrogen and sulfur source, contributed to in-situ synthesizing graphene-like nanosheets around KJ-600 carbon nanoparticles with high specific surface area (1098 m²/g). Proper method to introduce melamine during the synthesis could increase the content of pyridinic-N and Fe-N_x moieties in the catalyst without changing the morphology. Due to the high surface area and high content of pyridinic-N and Fe-N_x moieties, the obtained poly-AT/Me–Fe/N/C catalyst exhibited high electrochemical activity and stability with the half-wave potential of 0.84 V (RHE) in 0.1 M NaOH solution, which is merely 17 mV lower than commercial Pt/C. The electron transfer number was 3.83, indicating a nearly 4e^? transfer for the ORR with low HO₂^? yield.     

Co2P nanoparticles supported on cobalt-embedded N-doped carbon materials as a bifunctional electrocatalyst for rechargeable Zn-air batteries

Reversible oxygen electrodes with high efficiencies for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are of great significance for a variety of energy conversion devices, such as fuel cells and metal-air batteries. Herein, Co₂P nanoparticles supported on cobalt-embedded N-doped carbon materials (Co₂P/Co–N–C) have been prepared by pyrolysis of cobalt zeolitic imidazolate framework and phosphating post treatment. The optimal Co₂P/Co–N–C composite shows excellent bifunctional electrocatalytic activities for both OER (the potential of 1.65 V at 10 mA cm^?2) and ORR (half-wave potential of 0.82 V). As a practical demonstration, Co₂P/Co–N–C catalyst is used as an air electrode in liquid Zn-air battery, which displays a large open-circuit voltage of 1.50 V, a high peak-power density of 158 mW cm^?2 and excellent reversibility of over 205 h at 5 mA cm^?2. Moreover, the flexible Zn-air battery with Co₂P/Co–N–C exhibits a high open-circuit voltage of 1.46 V and the good flexibility with different angles. This work provides inspiration to explore new strategies for electrochemical energy conversion and storage.     

Effect of synthesis method on the oxygen reduction performance of Co–N–C catalyst

In recent years, Co, N co-doped carbon (Co–N–C) materials as oxygen reduction reaction (ORR) catalysts have attracted great attention because of their good ORR stability as well as decent activity. Co-doped zeolitic imidazolate framework-8 (Co@ZIF-8) as the precursor for synthesizing Co–N–C has attracted great interest recently. Co@ZIF-8 synthesis method may affect the properties of the as-synthesized Co@ZIF-8 precursors, which will surely affect the properties and ORR performance of Co@ZIF-8-derived Co–N–C catalysts. Herein, three methods, viz. room-temperature stirring method, reflux method, and hydrothermal method, were used to synthesize Co@ZIF-8 precursors. Physical characterization shows that the synthesis method has a great influence on the textural properties, composition, and graphitization degree of the as-synthesized Co–N–C catalysts. Electrochemical characterization shows that Co–N–C-R synthesized with reflux method exhibits an onset potential (E_onset) of 0.905 V, a half-wave potential (E_1/2) of 0.792 V and a limiting current density (J_L) of 5.85 mA cm^?2 in acidic media, which are higher than those of Co–N–C–S (E_onset = 0.870 V, E_1/2 = 0.770 V, J_L = 4.71 mA cm^?2) and Co–N–C–H (E_onset = 0.892 V, E_1/2 = 0.785 V, J_L = 4.68 mA cm^?2) synthesized with room-temperature stirring method and hydrothermal method, respectively. The better ORR activity observed on Co–N–C-R can be attributed to its larger graphitization degree and larger mesopore volume. Catalytic stability test shows that Co–N–C-R has negligible activity loss after 5000 potential cycles. This work demonstrates that reflux method is a more suitable method for synthesizing Co–N–C catalysts for ORR.     

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.     

Morphological influence of graphitic carbon nanofibers by N–F dual-doping on Pt electrocatalytic activity and stability for oxygen reduction reaction in polymer electrolyte membrane fuel cells

Morphology of carbon nanofibers significantly effects Pt nanoparticles dispersion and specific interaction with the support, which is an important aspect in the fuel cell performance of the electrocatalysts. This study emphasizes, the defects creation and structural evolution comprised due to N–F co-doping on graphitic carbon nanofibers (GNFs) of different morphologies, viz. GNF-linearly aligned platelets (L), antlers (A), herringbone (H), and their specific interaction with Pt nanoparticle in enhancing the oxygen reduction reaction (ORR). GNFs–NF–Pt catalysts exhibit better ORR electrocatalytic activity, superior durability that is solely ascribed to the morphological evolution and the doped N–F heteroatoms, prompting the charge density variations in the resultant carbon fiber matrices. Amongst, H–NF–Pt catalyst performed outstanding ORR activity with exceptional electrochemical stability, which shows only 20 mV loss in the half-wave potential whilst 100 mV loss for Pt/C catalyst on 20,000 potential cycling. The PEMFC comprising H–NF–Pt as cathode catalyst with minimum loading of 0.10 mg cm^?2, delivers power density of 0.942 W cm^?2 at current density of 2.50 A cm^?2 without backpressures in H₂–O₂ feeds. The H–NF–Pt catalyst owing to its hierarchical architectures, performs well in PEMFC at the minimized catalyst loading with outstanding stability that can significantly decrease total price for the fuel cell.     

Core-shell structured metal organic framework materials derived cobalt/iron–nitrogen Co-doped carbon electrocatalysts for efficient oxygen reduction

Homogeneous dispersion of active sites and abundant pore structure for non-precious metal electrocatalysts are favorable for the oxygen reduction reaction (ORR) activity. Herein, a nitrogen-doped carbon core supported CoFe alloy-nitrogen co-doped carbon shell nanopolyhedron (NC@CoFe,N–CNP) electrocatalyst, which has rich pore structure and uniformly distributed active sites, is prepared through a facile thermal conversion of a ZIF-8 core and Fe,Co-ZIF shell composite precursor (ZIF-8@Fe,Co-ZIF) without any post-treatments. The existence of ZIF-8 core can maintain the structure of the ZIF-8@Fe,Co-ZIF composite controllable, avoiding the damage to the pore structure for fast mass transfer during pyrolysis. Meanwhile, the bi-metal iron and cobalt co-doping shell is more conducive for uniform dispersion of CoFe alloy particles than single one due to the interval effects, which can create various active sites and efficiently promote the ORR activity. As expected, the optimal NC@CoFe,N–CNP electrocatalyst exhibits an excellent catalytic activity with a high onset potential and half-wave potential (0.970 V and 0.865 V) compared to commercial Pt/C (0.934 V and 0.846 V). The kinetic current density of NC@CoFe,N–CNP reached to 7.99 mA cm^?2, which is higher than Pt/C (5.14 mA cm^?2) at 0.85 V. Furthermore, the NC@CoFe,N–CNP electrocatalyst demonstrates better electrochemical stability and anti-poisoning ability.     

Efficient oxygen reduction electrocatalysis on Mn3O4 nanoparticles decorated N-doped carbon with hierarchical porosity and abundant active sites

Transition metal on nitrogen-doped carbons (M-N-C, M = Fe, Co, Mn, etc.) are a group of promising sustainable electrocatalysts toward oxygen reduction reaction (ORR). Compared to its Fe, Co analogues, Mn–N–C possesses the advantage of being inert for catalyzing Fenton reaction, and thus is expected to offer higher durability, but its ORR activity needs essential improvement. Herein, an efficient Mn–N–C ORR catalyst composed of Mn₃O₄ nanoparticles supported on nitrogen-doped carbon was successfully synthesized by pyrolysis of cyanamide/Mn-incorporated polydopamine (PDA) film coated carbon black (CB), where the presence of N-rich cyanamide confers abundant Mn-N_x active sites and rich micropore/mesopores to the catalyst. In an alkaline medium, as-synthesized Mn–N–C electrocatalyst outperforms commercial Pt/C catalyst in terms of onset potential (0.98 V, vs. RHE), half-wave potential (0.868 V, vs. RHE), and limiting current density. Meanwhile, it exhibits excellent durability and resistance to methanol. In a Zinc-air primary battery, it demonstrates better performance as a cathodic catalyst than Pt/C.     

Iron-gelatin aerogel derivative as high-performance oxygen reduction reaction electrocatalysts in microbial fuel cells

Currently, precious based materials are known as highly efficient and widely used catalysts for oxygen reduction reaction (ORR). The expensive price and scarce resource of precious metals have stimulated researchers to explore low-cost and high-performance non-precious metal catalysts. Gelatin is a promising precursor to prepare cost-effective and high-performance catalysts because of abundant micropores and nitrogen self-doping sites after pyrolysis. Herein, we developed a new highly active ORR catalyst (G/C–Fe-2) containing Fe–N coordination sites and Fe/Fe₃C nanoparticles. G/C–Fe-2 exhibited excellent ORR electrocatalytic activity (onset potential: 0.21 V, and limiting current density:7.36 mA cm^?2) and high-performance in air-cathode MFCs (Output voltage: 660 mV, and maximum power density: 560 mW m^?2). It is significant for synthesizing low-cost and high-activity ORR electrocatalysts through this strategy.     

Highly efficient PtCo nanoparticles on Co–N–C nanorods with hierarchical pore structure for oxygen reduction reaction

Developing platinum-based nanoparticles on carbon catalysts with high activity and stability for oxygen reduction reaction (ORR) is of great significance for the practical application of fuel cells. Herein, a synchronous strategy of preparing nano-sized PtCo supported on atomic Co and N co-doped carbon nanorods (PtCo/Co–N–C NR) was developed to replace the conventional method of impregnating Pt sources into ready-made carbon materials, in which metal-organic frameworks (MOFs) with Co and Zn ions of rhombic dodecahedron were first prepared using 2-methylimidazole as building block and then their morphology was transformed into porous nanorods via the reduction of Co ions to Co–B–O complex in the MOFs by NaBH₄; subsequently, Pt was deposited on the Co–Zn MOF nanorods through the displacement reaction of PtCl₆^2- and metallic Co and coordination between MOF and PtCl₆^2-; after pyrolysis and acid-leaching process, highly dispersed PtCo/Co–N–C NR was obtained. Attributed to its unique characteristics of hierarchical pore structure, uniform PtCo alloy nanoparticles with the average size of 7.0 nm and strong supporting interaction effect, the catalyst exhibits high ORR activity and stability with the mass activity of 577.0 mA mg^?1_Pt and specific activity of 1.4 mA cm^?2 at 0.9 V vs RHE in 0.1 M HClO₄, which is about 3.6 times and 3.5 times high than that of commercial Pt/C catalyst respectively. This strategy would provide a flexible route to develop highly active and stable ORR electrocatalysts with various morphologies for optimizing the exposure of active sites.     

Soybean powder enables the synthesis of Fe–N–C catalysts with high ORR activities in microbial fuel cell applications

The development of microbial fuel cells (MFCs) into a new type of carbon-neutral wastewater treatment technology requires efficient and low-cost oxygen reduction reaction catalysts in air cathodes. The use of raw soybean powder was investigated for synthesizing Fe–N–C ORR catalysts in a sacrificial SiO₂ support method. ZnCl₂ etching in the synthesis was found to facilitate the formation of hierarchical porous structures of Fe–N–C catalysts. Fe–N–C(1-1) catalyst synthesized with an optimal soybean/ZnCl₂ mass ratio of 1:1 exhibited the highest ORR activity in air cathodes. The use of the obtained Fe–N–C(1-1) catalyst enables a maximum power production of ~0.480 mW cm⁻² in MFCs, higher than commercial Pt/C (0.438 mW cm⁻²) with the same catalyst loading of 2 mg cm⁻². Long-term MFC operations demonstrated that the Fe–N–C synthesized from raw soybean have high stability and toxic tolerance, indicating that abundant low cost soybean biomass is a potential material for ORR catalyst development in MFC applications.     

Rapeseed meal-based autochthonous N and S-doped non-metallic porous carbon electrode material for oxygen reduction reaction catalysis

The heteroatom-doped porous carbon material as an alternative to commercial Pt/C catalysts in oxygen reduction reaction has attracted extensive attention. In this study, the rapeseed meal-based material (ARM-900) prepared by carbonization with high temperature and activation with ZnCl₂ had a porous structure and was doped with N and S heteroatoms. Compared to commercial Pt/C catalysts (onset potential of 0.95 V vs. RHE and limiting diffusion current of ?5.7 mA cm^?2), ARM-900 demonstrated excellent electrocatalytic performance with an onset potential of 0.98 V vs. RHE and limiting diffusion current of ?8.1 mA cm^?2 in O₂ saturated 0.1 M KOH solution. Meanwhile, ARM-900 had higher durability and more superior methanol tolerance than Pt/C catalyst. The excellent ORR performance of ARM-900 was derived from the formation of abundant pore structure and the doping of the autochthonous N and S heteroatoms. MFCs with ARM-900 as the cathode had the maximum power density of 808 mW/m², which was obviously better than Pt/C (709 mW/m²). This study provided an environment-friendly and effective strategy for the reuse of rapeseed meal and the preparation of N and S-doped non-metallic ORR catalysts.     

Template-assisted polymerization-pyrolysis derived mesoporous carbon anchored with Fe/Fe3C and Fe−NX species as efficient oxygen reduction catalysts for Zn-air battery

Constructing highly efficient and durable non-noble metal modified carbon catalysts for oxygen reduction reaction (ORR) in the whole pH range is essential for energy conversion devices but still remains a challenge. Herein, the Fe/Fe₃C nanoparticles and Fe-N_X species anchored on the interconnected mesoporous carbon materials are fabricated through an economical and facile template-assisted polymerization-pyrolysis strategy. The catalyst exhibits unique features with the electronic interaction between Fe/Fe₃C and Fe−N_X, large specific surface area and high mesoporous structure as well as nitrogen doping in porous carbon skeletons, which can effectively catalyze ORR over the full pH range. In an alkaline electrolyte, the optimized catalyst displays favorable ORR performance with positive onset potential (E_onset = 0.91 V), half-wave potential (E_1/2 = 0.83 V), long-term cycles stability and methanol tolerance, exceeding those for the commercial Pt/C. Furthermore, the prepared catalyst could be directly assembled into the alkaline Zn−air battery that exhibits the open-circuit voltage of 1.44 V, high power density of 96.0 mW cm⁻² and long-term durability. Therefore, the template-assisted polymerization-pyrolysis strategy provides a promising route for designing high-performance non-noble metal decorated ORR electrocatalysts.     

Spherical mesoporous Fe–N–C catalyst for the air cathode of membrane-less direct formate fuel cells

Fe–N–C catalysts with excellent performance regarding the oxygen reduction reaction (ORR) have aroused enormous interest in direct-formate fuel cells (DFFCs). However, their limited mass transfer ability, insufficient ORR active sites, and complex fabrication processes remain significant obstacles to the widespread application of Fe–N–C catalysts. Herein, we propose a simple hydrothermal-annealing method with agarose powders to synthesize a uniform spherical Fe–N–C catalyst (∼3 μm) with well-developed mesopores (Fe/rG@C/H-Agar-900). The resultant Fe/rG@C/H-Agar-900 catalyst possesses rich oxygen-containing functional groups and enhanced interconnected pores, which can significantly boost the content of catalytic sites and facilitate mass transport, resulting in a high content of active sites. In the meantime, the mesopore content of Fe/rG@C/H-Agar-900, which can facilitate the formation of the three-phase gas/electrolyte/catalyst interfaces, was optimized by varying the annealing temperature. As a result, the Fe/rG@C/H-Agar-900 demonstrates a half-wave potential of 0.91 V vs. RHE, nearly four-electron pathway selectivity, excellent durability, and excellent formate tolerance for ORR. Furthermore, when used as the air cathode in membrane-less DFFCs, the Fe/rG@C/H-Agar-900-based device exhibits a remarkable peak power density of 24.5 mW cm⁻², significantly outperforming the 20 wt% commercial Pt/C. This research facilitates the synthesis of an advanced Fe–N–C catalyst and promotes the practical development of membrane-less DFFCs.     

Dual optimization strategy to construct hierarchical reticulated porous framework with enriched Fe-NX active species for the highly efficient oxygen reduction reaction

Proton exchange membrane fuel cells (PEMFCs) are severely restricted by slow cathodic oxygen reduction reaction (ORR) kinetics and expensive noble metal platinum catalysts. In particular, the ORR serves as a key process in electrochemical conversion, which significantly impacts the overall performance of the related devices. Accordingly, we proposed a facile and novel dual-optimization strategy to construct abundant Fe-N_X active site embedded hierarchical reticulated porous structure catalysts. Initially, an extensive encapsulated Fe and Fe–N complexes is created in Fe modified zeolitic-imidazolate-frameworks-8/graphene oxide (Fe-ZIF-8/GO) precursor, subsequently, the thermal melting and restructuring process fosters the structural transformation of the precursor to robust and open nano-porous frameworks. In the meanwhile, the encapsulated Fe in the pores of the precursors and the pre-existing Fe–N coordination structures are converted into new Fe-N_X active sites. This approach realizes the dual optimization of Fe-N_X active site density enhancement and utilization, making the optimal catalyst Fe and N-doped porous carbon/graphene nanosheets-1 (Fe-NPC/GNs-1) exhibits a half-wave potential (E_1/2) of 0.771V under acidic medium, and E_1/2 of 0.917 V toward the ORR in alkaline conditions. The activity and stability under alkaline conditions exceed even that of commercial Pt/C (with negligible potential decay after 10,000 cycles under alkaline conditions), and also showed its capacity to substitute platinum-based catalysts and the potential application in Zn?air batteries.     

Sengon wood-derived RGO supported Fe-based electrocatalyst with stabilized graphitic N-bond for oxygen reduction reaction in acidic medium

This work reports utilised of RGO from Sengon wood biomass to support Fe–N–C noble-free catalyst (Fe–N-RGO), while also attempt to investigate the effect of pyrolysis stage on Fe–N-RGO catalysts with four different nitrogen precursors towards the ORR activity in acidic medium. One- and two-step pyrolysis were performed at 900 °C for 1 h and 2 h respectively to produce Fe–N-RGO. This work revealed that two-step pyrolysis was able to remove the volatile components and hence forming more graphitised, stable graphitic-N and Fe-Nx, synergistically improve the ORR activity with highest onset potential of 0.83 V vs RHE and limiting current density of 5.33 mA cm⁻² reported on Fe-Pani-RGO 2py. An increase in the kinetic on Fe-Pani-RGO 2py with Tafel slope of 74 mV/dec operated at 80 °C was reported. The mesoporous structure on RGO increases the stability by 8% and better methanol tolerance when compared to a benchmark Pt/C catalyst.     

Fe3C nanoparticles decorated Fe/N codoped graphene-like hierarchically carbon nanosheets for effective oxygen electrocatalysis

Hierarchically porous carbon sheets decorated with transition metal carbides nanoparticles and metal-nitrogen coordinative sites have been proposed as the promising non-precious metal oxygen electrocatalysts. In this work, we demonstrate a facile and low-cost strategy to in situ form Fe/N codoped hierarchically porous graphene-like carbon nanosheets abundant in Fe-N_x sites and Fe₃C nanoparticles (Fe–N/C) from pyrolyzing chestnut shell precursor. The as-prepared Fe–N/C samples with abundant Fe-N_x sites and Fe₃C nanoparticles show superior electrocatalytic activity to oxygen reduction reaction (ORR) in the alkaline medium as well as high stability and methanol tolerance due to the integration of multi-factors: the high content of Fe-N_x active sites, the coexistence of Fe₃C, the unique hierarchically porous structure and high conductivity of carbon matrix. The optimal Fe–N/C-2-900 sample exhibits a more positive half-wave potential (−0.122 V vs. Ag/AgCl (3 M) reference electrode) than commercial 20 wt% Pt/C catalyst. This study provides a facile approach to synthesize Fe₃C nanoparticles decorated Fe/N co-doped hierarchically porous carbon materials for effective oxygen electrocatalyst.     

One-step synthesis of carbon-encapsulated nickel phosphide nanoparticles with efficient bifunctional catalysis on oxygen evolution and reduction

As a promising and cost-efficient alternative to noble metal catalysts, transition metal phosphides (TMPs) show highly catalytic performance toward oxygen reduction and evolution reactions (ORR and OER). Mesoporous carbon-coated nickel phosphide (NiP) nanoparticles were successfully synthesized by thermal decomposition at 500 °C under N₂/H₂ (95:5) atmosphere. The NiP/C hybrid exhibits excellent OER/ORR activity. It can generate an OER current density of 10 mA cm^?2 at the overpotential of 0.26 V with a low Tafel slope of 43 mV dec^?1, and produce a limited ORR current density of 5.10 mA cm^?2 at 1600 rpm with a half-wave potential of 0.82 V via a 4-electron pathway. In addition, the OER/ORR catalytic currents remain considerable stable without significant loss for more than 25 h polarization. This work will open up a new avenue to design a bifunctional catalyst with a superior OER/ORR activity and stability, and this cost-efficient strategy will pave the way for the industrial application of the renewable energy technologies.     

Synthesis and electrocatalytic properties of M (Fe,Co),N co-doped porous carbon frameworks for efficient oxygen reduction reaction

The exploitation of high efficiency non-precious metal electrocatalysts towards oxygen reduction reaction (ORR) is great significant for large-scale commercialization of next-generation fuel cells. In this work, we designed and fabricated a series of porous carbazole-based N and M (Co, Fe) doped carbon framework catalysts which were obtained by the pyrolysis of a N-rich hypercrosslinked polymers derived from Friedel–Crafts reaction (abbreviated as TSP-HCP-900) followed by the incorporation of metal into the as-resulted N rich carbon (abbreviated as M-TSP-HCP-900, M = Co, Fe). Based on the high specific surface, excellent porosity, large pyridine nitrogen content and synergistic catalytic effects between the N dopants and metal nanoparticles, the M-TSP-HCP-900 exhibited superior ORR catalytic activity. Among them, the Co-TSP-HCP-900 possesses better electrocatalysis, i.e., a high diffusion limiting current density of 4.74 mA cm^?2, half-wave potential of 0.8 V (vs. RHE, the same below) and onset potential of 0.9 V were found, respectively. In addition, this catalyst also discloses an excellent methanol tolerance, better durability and a biased 4e^? reaction pathway, which are comparable to state-of-the-art Pt/C catalysts. Taking advantage of mentioning above, the M-TSP-HCP-900 may hold great potentials as promising alternative of precious metal catalysts for electrochemical energy conversion and storage.     

Efficient electrocatalyst of Pt–Fe/CNFs for oxygen reduction reaction in alkaline media

Transition metal iron-based catalysts are promising electrocatalysts for oxygen reduction reaction (ORR), and they have the potential to replace noble metal catalysts. The one-dimensional of carbon nanofibers with tubular structure can effectively promote the electrocatalytic activity, which facilitates electron transport. Herein, the Pt–Fe/CNFs were synthesized by electrospinning and subsequent calcination. Benefiting from the advantages of one-dimensional structure, Pt–Fe/CNFs-900 with fast electrochemical kinetics and excellent stability for ORR with excellent onset of 0.99 V, a low Tafel slope of 62 mV dec⁻¹ and high limiting current density of 6.00 mA cm⁻². Long-term ORR testing indicated that the durability of this catalyst was superior to that of commercial Pt/C in alkaline electrolyte. According to RRDE test, the ORR reaction process of Pt–Fe/CNFs-900 was close to four-electron transfer routes.