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.     

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.     

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.     

Ni3S2-MoSx nanorods grown on Ni foam as high-efficient electrocatalysts for overall water splitting

In order to solve the problem of large overpotential in water electrolysis for hydrogen production, transition metal sulfides are promising bifunctional electrocatalysts for hydrogen evolution reaction/oxygen evolution reaction that can significantly reduce overpotential. In this work, Ni₃S₂ and amorphous MoS_x nanorods directly grown on Ni foam (Ni₃S₂-MoS_x/NF) were prepared via one-step solvothermal process, which were used as a high-efficient electrocatalyst for overall water splitting. The Ni₃S₂-MoS_x/NF composite exhibits very low overpotentials of 65 and 312 mV to reach 10 mA cm⁻² and 50 mA cm⁻² in 1.0 M KOH for HER and OER, respectively. Besides, it exhibits a low Tafel slope (81 mV dec⁻¹ for HER, 103 mV dec⁻¹ for OER), high exchange current density (1.51 mA cm⁻² for HER, 0.26 mA cm⁻² for OER), and remarkable long-term cycle stability. This work provides new perspective for further the development of highly effective non-noble-metal materials in the energy field.     

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.     

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.     

Mesoporous nickel-sulfide/nickel/N-doped carbon as HER and OER bifunctional electrocatalyst for water electrolysis

The development of non-precious metal-based highly active bi-functional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is critical factor for making water electrolysis a viable process for large-scale industrial applications. In this study, bi-functional water splitting electrocatalysts in the form of nickel-sulfide/nickel nanoparticles integrated into a three-dimensional N-doped porous carbon matrix, are prepared using NaCl as a porous structure-forming template. Microstructures of the catalytic materials are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and N₂ adsorption-desorption analysis. The most active catalyst synthesized in this study exhibits a low HER overpotential of 70 mV at 10 mA cm⁻² and a low Tafel slope of 45 mV dec⁻¹. In OER, the optimized sample performs better than a state-of-the-art RuO₂ catalyst and produces an overpotential of 337 mV at 10 mA cm⁻², lower than that of RuO₂. The newly obtained materials are also used as HER/OER electrocatalysts in a specially assembled two-electrode water splitting cell. The cell demonstrates high activity and good stability in overall water splitting.     

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.     

Top-down preparation of Ni–Pd–P@graphitic carbon core-shell nanostructure as a non-Pt catalyst for enhanced electrocatalytic reactions

Electrochemical reactions such as the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and methanol oxidation reaction (MOR) are essential for energy conversion applications such as water electrolysis and fuel cells. Furthermore, Pt or Ir-related materials have been extensively utilized as electrocatalysts for the OER, ORR, and MOR. To reduce the utilization of precious metals, innovative catalyst structures should be proposed. Herein, we report a bi-metallic phosphide (Ni₂P and PdP₂) structure surrounded by graphitic carbon (Ni–Pd–P/C) with an enhanced electrochemical activity as compared to conventional electrocatalysts. Despite the low Pd content of 3 at%, Ni–Pd–P/C exhibits a low overpotential of 330 mV at 10 mA cm^?2 in the OER, high specific activity (2.82 mA cm^?2 at 0.8 V) for the ORR, and a high current density of 1.101 A mg^?1 for the MOR. The superior electrochemical performance of Ni–Pd–P/C may be attributed to the synergistic effect of the bi-metallic phosphide structure and core-shell structure formed by graphitic carbon.     

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.     

Boron doping induced electronic reconfiguration of Fe-Nx sites in N-doped carbon matrix for efficient oxygen reduction reaction in both alkaline and acidic media

Developing non-precious metal-based catalysts as the substitution of precious catalysts (Pt/C) in oxygen reduction reaction (ORR) is crucial for energy devices. Herein, a template and organic solvent-free method was adopted to synthesize Fe, B, and N doped nanoflake-like carbon materials (Fe/B/N–C) by pyrolysis of monoclinic ZIF-8 coated with iron precursors and boric acid. Benefiting from introducing B into Fe–N–C, the regulated electron cloud density of Fe-N_x sites enhance the charge transfer and promotes the ORR process. The as-synthesized Fe/B/N–C electrocatalyst shows excellent ORR activity of a half-wave potential (0.90 V vs 0.87 V of Pt/C), together with superior long-term stability (95.5% current density retention after 27 h) in alkaline media and is even comparable to the commercial Pt/C catalyst (with a half-wave potential of 0.74 V vs 0.82 V of Pt/C) in an acidic electrolyte. A Zn-air battery assembled with Fe/B/N–C as ORR catalyst delivers a higher open-circuit potential (1.47 V), specific capacity (759.9 mA h g^?1_Zn at 10 mA cm^?2), peak power density (62 mW cm^?2), as well as excellent durability (5 mA cm^?2 for more than 160 h) compared to those with commercial Pt/C. This work provides an effective strategy to construct B doped Fe–N–C materials as nonprecious ORR catalyst. Theoretical calculations indicate that introduction of B could induce Fe-N_x species electronic configuration and is favorable for activation of OH1 intermediates to promote ORR process.     

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.     

Hollow NH2-MIL-101@TA derived electrocatalyst for enhanced oxygen reduction reaction and oxygen evolution reaction

Non-precious metal-based electrocatalysts with excellent activity and stability are highly desired for the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a tannic acid (TA) etching strategy is used to inhibit the metal aggregation and achieve muti-metal doping. The hollow NH₂-MIL-101@TA derived Fe–N–C catalyst exhibits superior ORR catalytic activity with an E_1/2 of 0.872 V and a maximum output power density of 123.4 mW cm⁻² in Zn-air battery. Since TA can easily chelate with metal ions, Fe/Co–N–C and Fe/Ni–N–C are also synthesized. Fe/Ni–N–C manifests exceptional bifunctional activity with an E_j = 10 of 1.67 V and a potential gap of 0.833 V between E_j = 10 and E_1/2 in alkaline electrolyte, which is 45 mV smaller than Pt/C–IrO₂. The improvement of ORR and OER performance of the catalysts via the simple TA etching and chelation method provides a novel strategy for the design and synthesis of efficient electrocatalysts.     

Porous NiFe alloys synthesized via freeze casting as bifunctional electrocatalysts for oxygen and hydrogen evolution reaction

Binder-free NiFe-based electrocatalyst with aligned pore channels has been prepared by freeze casting and served as a bifunctional catalytic electrode for oxygen and hydrogen evolution reaction (OER and HER). The synergistic effects between Ni and Fe result in the high electrocatalytic performance of porous NiFe electrodes. In 1.0 M KOH, porous Ni₇Fe₃ attains 100 mA cm⁻² at an overpotential of 388 mV with a Tafel slope of 35.8 mV dec⁻¹ for OER, and porous Ni₉Fe₁ exhibits a low overpotential of 347 mV at 100 mA cm⁻² with a Tafel slope of 121.0 mV dec⁻¹ for HER. The Ni₉Fe₁//Ni₉Fe₁ requires a low cell voltage of 1.69 V to deliver 10 mA cm⁻² current density for overall water splitting. The excellent durability at a high current density of porous NiFe electrodes has been confirmed during OER, HER and overall water splitting. The fine electrocatalytic performances of the porous NiFe-based electrodes owing to the three-dimensionally well-connected scaffolds, aligned pore channels, and bimetallic synergy, offering excellent charge/ion transfer efficiency and sizeable active surface area. Freeze casting can be applied to design and synthesize various three-dimensionally porous non-precious metal-based electrocatalysts with controllable multiphase for energy conversion and storage.     

Atomically dispersed Fe-Nx sites doped mesopore-dominated carbon nanodisks towards efficient oxygen reduction

Rational design and synthesis of carbon nanostructures doped with atomically dispersed metal sites is an effective method to improve electrocatalytic oxygen reduction reaction (ORR) performance. Introducing mesopores into substrate carbon materials would help expose more active sites and improve mass/charge transfer in the microenvironments near active sites, thus accelerating ORR. Nonetheless, it is still challenging to construct atomically dispersed metal-nitrogen-carbon with mesoporous structures. Herein, we propose a facile strategy to synthesize atomically dispersed Fe-N_x sites doped mesopore-dominated carbon nanodisks catalysts (Fe–N/CNDs) using functionalized zeolitic imidazole frameworks (ZIF-D). The Fe–N/CNDs-900 catalyst exhibits outstanding ORR activity (E_o = 1.03 V, E_1/2 = 850 mV), as well as excellent long-term durability and methanol-tolerance, ascribed to synergistic effect of the Fe-N_x active sites and the surrounding mesoporous structures. This work presents a promising method to develop highly efficient metal-nitrogen-carbon ORR catalysts using functionalized MOFs.     

Fe2O3 nanoparticles immobilized on N and S codoped C as an efficient multifunctional catalyst for oxygen reduction reaction and overall water electrolysis

Currently, multifunctional electrocatalysts with superior performance are very vital for developing various clean and regenerated energy systems. Herein, an effective multifunctional electrocatalyst comprising Fe₂O₃ nanoparticles immobilized on N and S codoped C has been synthesized via heat-treatment of Fe(II) complex at 800 °C (denoted as Fe₂O₃/NS-C-800). Favorable features including the introduction of maghemite nanoparticles, N/S-codoping effect, and close contact between the Fe₂O₃ nanoparticles and NS-C ender the Fe₂O₃/NS-C-800 with high multifunctional catalytic performance. The onset potential (0.97 V) and half-wave potential (0.81 V) of the Fe₂O₃/NS-C-800 towards oxygen reduction reaction (ORR) are comparable to Pt/C (0.99 and 0.82 V). The Fe₂O₃/NS-C-800 also exhibits high oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity with low OER and HER overpotentials of 0.37 and −0.27 V at 10 mA cm⁻², respectively. In addition, higher ORR, OER and HER stabilities than Pt/C are observed for the Fe₂O₃/NS-C-800. More importantly, the assembled water electrolyzer using the Fe₂O₃/NS-C-800 as the anode and cathode exhibits a high stability at a water electrolysis current density of 10 mA cm⁻². The present study offers a new promising non-noble multifunctional catalyst for future application in renewable energy technologies.     

Iridium-titanium oxides for efficient oxygen evolution reaction in acidic media

Active and highly stable oxygen evolution reaction (OER) electrocatalyst for PEM-based water electrolysis are currently in high demand. Herein, we report a rutile iridium-titanium oxide solid solution (IrTiO_x) through a facile one-step annealing of a Ti-based metal-organic framework precursor. The composite exhibits excellent OER activity and stability in acidic media, with a low overpotential of 296 mV at 10 mA cm⁻² while the OER activity was retained during a 100-h galvanostatic stability test at a constant current of 10 mA cm⁻² in 0.5 M H₂SO₄, outperforming the state-of-the-art IrO₂-based electrocatalysts. We further demonstrate the structure evolution of iridium-titanium oxide during OER operations. In contrast to the initial uniform distribution of Ir and Ti over the entire architecture, after OER stability test, a hollow morphology is formed, in which the particle surface is covered with an IrO_x-rich layer and entire particle becomes hollow. We ascribe the structure evolution to the Ir/Ti leaching and redeposition during the OER operations. We propose that the structure evolution of iridium-titanium oxide during the electrochemical process is responsible for the high OER activity and stability of IrTiO_x.     

Catalytic behavior of Pr1-xBa1+xCo2O6-δ in alkaline medium

In this work, a series of double perovskite oxide materials Pr_1-xBa_1+xCo₂O_6-δ (x = 0.05, 0.10, 0.15, and 0.20) was synthesized using the solid-state route method. Their catalytic activity and stability in 1 M KOH alkaline medium were investigated. The phase formation and structure of the prepared oxides were determined by Powder X-ray diffraction. The morphology of prepared catalysts was confirmed by SEM analysis. The catalytic performance of the prepared catalyst in alkaline solution was investigated using electrochemical measurements for both oxygen evolution reaction (OER) and oxygen reduction reactions (ORR). This series of double perovskite oxide materials exhibit catalytic activity for both OER and ORR. Pr_0.90Ba_1.10Co₂O_6-δ shows wonderful OER activity among all the catalysts with a specific capacitance of 598.40 F/g and double-layer capacitance of 38.94 mF/cm². Power low gives a hint of oxide-ion intercalation pseudocapacitance in the Pr_0.90Ba_1·10Co₂O_6-δ. On the other hand, Pr_0.95Ba_1·10Co₂O_6-δ exhibits potential behavior for ORR. Overall, our findings highlight the combined effects of incorporating Ba into double perovskite PrBaCo₂O_6-δ in its behavior for OER and ORR.     

Porous carbon polyhedrons with exclusive Metal-NX moieties for efficient oxygen reduction reaction

This work has manufactured a series of M-N_X/C (M = Fe, Cu, Ni) ORR catalysts by the pyrolysis of metal tetraphenylporphyrin (MTPP) adsorbed onto N-doped porous carbon polyhedrons (NPCP) derived from ZIF-8. The comprehensive characterization data shows that the prepared M-N_X/C catalysts have hierarchical porous structure with high specific surface area and abundant M-N_X moieties. All prepared M-N_X/C catalysts exhibit good ORR performance. The ORR half-wave potentials E_1/2 of Fe-N_X/C, Cu-N_X/C and Ni-N_X/C catalyst are 0.885, 0.801 and 0.755 V respectively. The rotating ring-disk electrode (RRDE) test reveals that the ORR of Fe-N_X/C is a four electron process. While a two and four electron mixing ORR process are observed for Cu-N_X/C and Ni-N_X/C. In an alkaline medium, E_1/2 of Fe-N_X/C is observed 44 mV higher than that of commercial Pt/C. Also, Fe-N_X/C catalyst has outstanding long-term durability and good methanol resistance.     

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.