High Nitrogen Doping Level Research Articles

Nitrogen-doped mesoporous graphene nanoflakes for high performance ionic liquid supercapacitors

Mesoporous nitrogen-doped graphene nanoflakes (N-GNFs) with high nitrogen doping level of 5.0–10.7 at.% were produced by a facile template CVD synthesis using the mixture of acetonitrile and benzene as a precursor. The pore structure, morphology and physicochemical properties of N-GNFs were characterized by TEM, XPS, Raman spectroscopy, and low-temperature nitrogen physisorption. The electrochemical performance of N-GNFs was tested in electric double-layer capacitor (EDLC) with ionic liquid electrolyte (1.2 M N+Et4TFSI− solution in CH3CN) by cyclic voltammetry, galvanostatic charge-discharge measurements, and electrochemical impedance spectroscopy. With increasing the nitrogen content in N-GNFs their specific capacitance increased and achieved 167 F g−1 at a scan rate of 5 mV s−1. The maximum delivered energy density was 46.3 Wh kg−1, which corresponded to a power density of 0.74 kW kg−1. The high electrochemical performance of N-GNFs was attributed both to the pseudo-capacitance of active nitrogen sites and to the developed mesoporosity. Different tetraalkylammonium bis(trifluoromethylsulfonyl)imide ionic liquids were used to evaluate the cation size effect on the stability and performance of N-GNFs-based EDLCs. In contrast to N+Et4TFSI− and N+Bu4TFSI− electrolytes, the cycling performance of N-GNFs in N+Me4TFSI− was limited because of the electrode degradation resulted from the intercalation of N+Me4 ions between graphene layers and their exfoliation.

A Site-Selective Doping Strategy of Carbon Anodes with Remarkable K-Ion Storage Capacity.

The limited potassium-ion intercalation capacity of graphite hampers development of potassium-ion batteries (PIB). Edge-nitrogen doping is an effective approach to enhance K-ion storage in carbonaceous materials. One shortcoming is the lack of precise control over producing the edge-nitrogen configuration. Here, a molecular-scale copolymer pyrolysis strategy is used to precisely control edge-nitrogen doping in carbonaceous materials. This process results in defect-rich, edge-nitrogen doped carbons (ENDC) with a high nitrogen-doping level (up to 10.5 at %) and a high edge-nitrogen ratio (87.6 %). The optimized ENDC exhibits a high reversible capacity of 423 mAh g-1 , a high initial Coulombic efficiency of 65 %, superior rate capability, and long cycle life (93.8 % retention after three months). This strategy can be extended to design other edge-heteroatom-rich carbons through pyrolysis of copolymers for efficient storage of various mobile ions.

3D interconnected crumpled porous carbon sheets modified with high-level nitrogen doping for high performance lithium sulfur batteries

To enable the theoretically appealing Li–S electrochemistry in battery, the issues of the low conductivity and volume variation of the active materials as well as the intermediates diffusion need to be comprehensively addressed, which calls for rational structure design of multifunctional host material for sulfur. Herein, a novel strategy is proposed to construct 3D graphene-based N-doped porous carbon for Li–S batteries. In this strategy, interconnected macropore channels, abundant mesopores and highly accessible micropores are synergistically integrated into a conductive framework constructed by crumpled carbon sheets, and a high content of N-doping (∼18 at%) is simultaneously achieved. The obtained porous carbon possesses 3D conductive network, interconnected hierarchical porosities as well as large polarized specific surface, which endow the carbon matrix multifaceted structural merits for electrons/ions transfer, sulfur accommodation, and polysulfides immobilization. The obtained carbon sulfur composite exhibits a high reversible capacity of 1280 mA h g−1 at 0.2C, remarkable rate capabilities up to 3C and a prolonged cycling life over 500 cycles at 1C, showing intriguing promise for constructing high energy density Li–S batteries. This strategy provides a new perspective to porosity engineering and surface chemistry modification of carbon-based sulfur hosts and also other electrochemical electrode material.

Nitrogen functionalized carbon nanocages optimized as high-performance anodes for sodium ion storage

Energy storage based on sodium ions is considered to be one of the most promising candidates for large-scale applications. However, designing nanostructured anodes with ultralong cycle life, superior rate capability, and high specific capacitance is still a challenge. Herein, we report that nitrogen functionalized carbon nanocages with optimized structures as anodes in sodium-ion half cells demonstrate a superior capacity of 402 mA h g−1 at 50 mA g−1, excellent rate performance with 101 mA h g−1 at 10 A g−1, and an ultra-long cycle life by retaining 81% of its initial capacity after 5000 cycles at 10 A g−1. It can be observed that carbons with high nitrogen doping level and few-layer graphene domains are proved to be effective for sodium ion storage. Benefiting from the merits of structure and electrochemical performance of nitrogen functionalized carbon nanocages, the sodium-ion capacitors by using identical carbon electrodes achieves a high energy density of 102.5 W h kg−1 and an outstanding cycle life of 100,000 cycles with 74.2% of the capacity retention. This work opens a new opportunity for designing high-performance carbon electrodes with scalable production for next-generation energy storage.

Facile synthesis of MOF-Derived Co@CoNx/bamboo-like carbon tubes for efficient electrocatalytic water oxidation

The development of economical noble metal-free electrocatalysts for oxygen evolution reaction (OER) with high catalytic activity and durability is crucial for the practical applications of many energy storage and conversion technologies. Here, we report a facile and economical synthesis of Co@CoNx/N-doped carbon tubes hybrid (Co@CoNx/NCT hybrid) via one-step pyrolysis of ZIF-67 at a low temperature of 650 °C with the introduction of urea, which functions as both nitrogen source and promoter of carbon tube growth. The resultant Co@CoNx/NCT hybrid exhibits bamboo-like structure with numerous active sites originated from abundant CoNx species, high nitrogen doping level and topological defects, rendering excellent catalytic activities towards OER in alkaline medium. As a result, the as-obtained Co@CoNx/NCT hybrid shows an overpotential of as low as 290 mV at a current density of 10 mA cm−2 with a small Tafel slope of 60 mV dec−1, which outperforms most noble metal-free electrocatalysts and even commercial IrO2. Therefore, the Co@CoNx/NCT hybrid holds great promise for efficient electrocatalytic water oxidation applications.

Densely pillared holey-graphene block with high-level nitrogen doping enabling ultra-high volumetric capacity for lithium ion storage

Developing high volumetric capacity and long cycle-life anode materials for high-performance lithium-ion batteries (LIBs) still remains a great challenge. Herein, densely pillared holey-graphene block with high N-doping (P-NHG) has been successfully synthesized through thermal decomposition of (NH4)6Mo7O24 in-between stacked GO sheets. The dense graphene building block processes a high packing density of 2.53 g cm−3, high nitrogen doping (19.2 at%), numerous holes on the graphene sheet, and ∼5 nm Mo2C nanoparticles as the pillars in-between the graphene sheets, facilitating rapid ion diffusion and storage and ensuring structural stability during Li ion storage. As a result, the P-NHG electrode can deliver high gravimetric capacity of 1221 mAh g−1 and ultrahigh volumetric capacity of 3089 mAh cm−3 at 0.1 A g−1, as well as excellent cyclability (713 mAh g−1/1803 mAh cm−3 after 300 cycles at 0.5 A g−1). The novel design of densely pillared holey-structure materials represents greatly improved properties such as superior cyclability, and high volumetric capacity for LIBs.

Iron-nitrogen dual-doped three-dimensional mesoporous carbons for high-activity electrocatalytic oxygen reduction

To improve the efficiency of oxygen reduction reaction (ORR) on non-precious metal electrocatalyst, designing three-dimensional porous catalysts with abundant exposed active sites, accessible catalytic surface and excellent stability are of significant interest. Herein, we prepared Fe/N co-doped mesoporous carbons (FeNMCs) via a facile aggregation of renewable biomass flour, dicyanamide, colloidal silica and anhydrous ferric chloride, followed by carbonizing at 900°C in N2 atmosphere. The optimal catalyst (FeNMC-2) possesses interconnected uniform mesopores of ∼12.9nm, large surface area of 769.5m2g−1, high nitrogen-doping level and atomically dispersed Fe-Nx active species. The developed porous texture is advantageous for not only promoting the formation of Fe-N coordinated functional species and the accessibility of catalytic sites, but also facilitating the transport of reactants and products during the ORR process. For the ORR, the optimized FeNMC-2 displays excellent electrocatalytic performance, which even outperforms commercial Pt/C. Furthermore, the control experiments verify that the high ORR activity should be ascribed to uniformly dispersed Fe-Nx sites within the framework of 3D porous carbons. The present strategy can be extended to design and prepare other metal, N-co-doped porous carbons with great potentials in energy conversion and storage.

Fe, Cu‐Coordinated ZIF‐Derived Carbon Framework for Efficient Oxygen Reduction Reaction and Zinc–Air Batteries

AbstractZeolitic imidazole frameworks (ZIFs) offer rich platforms for rational design and construction of high‐performance nonprecious‐metal oxygen reduction reaction (ORR) catalysts owing to their flexibility, hierarchical porous structures, and high surface area. Herein, an Fe, Cu‐coordinated ZIF‐derived carbon framework (Cu@Fe‐N‐C) with a well‐defined morphology of truncated rhombic dodecahedron is facilely prepared by introducing Fe2+ and Cu2+ during the growth of ZIF‐8, followed by pyrolysis. The obtained Cu@Fe‐N‐C, with bimetallic active sites, large surface area, high nitrogen doping level, and conductive carbon frameworks, exhibits excellent ORR performance. It displays 50 mV higher half‐wave potential (0.892 V) than that of Pt catalysts in an alkaline medium and comparable performance to Pt catalysts in an acidic medium. In addition, it also has excellent durability and methanol resistance ability in both acidic and alkaline solutions, which makes it one of the best Pt‐free catalysts reported to date for ORR. Impressively, when being employed as a cathode catalyst in zinc–air batteries, Cu@Fe‐N‐C presents a higher peak power density of 92 mW cm−2 than that of Pt/C (74 mW cm−2) as well as excellent durability.

A lightweight carbon nanofiber-based 3D structured matrix with high nitrogen-doping level for lithium metal anodes

Lithium metal is considered to be the most promising anode material for the next-generation rechargeable batteries. However, the uniform and dendrite-free deposition of Li metal anode is hard to achieve, hindering its practical applications. Herein, a lightweight, free-standing and nitrogen-doped carbon nanofiber-based 3D structured conductive matrix (NCNF), which is characterized by a robust and interconnected 3D network with high doping level of 9.5 at%, is prepared by electrospinning as the current collector for Li metal anode. Uniform Li nucleation with reduced polarization and dendrite-free Li deposition are achieved because the NCNF with high nitrogen-doping level and high conductivity provide abundant and homogenous metallic Li nucleation and deposition sites. Excellent cycling stability with high coulombic efficiency are realized. The Li plated NCNF was paired with LiFePO4 to assemble the full battery, also showing high cyclic stability.

Three-dimensional interconnected nitrogen-doped mesoporous carbons as active electrode materials for application in electrocatalytic oxygen reduction and supercapacitors

In this paper, a series of nitrogen-doped mesoporous carbons (NMCs) with three-dimensional (3D) interconnected mesopores have been prepared using flour as carbon source, dicyanamide as nitrogen source and colloidal silica as hard template. The optimized material (NMC-4) prepared with the colloidal silica/flour mass ratio of 4 has a high nitrogen doping level of 5.69 at.% and large specific surface area of 995 m2 g−1 as well as 3D interconnected mesopores (12.9 nm). As the oxygen reduction reaction (ORR) electrocatalyst among various NMCs, NMC-4 exhibits the superior performance and much better stability and methanol crossover with a four-electron dominant reaction pathway compared to commercial 20 wt% Pt/C. Furthermore, as a supercapacitor (SC) electrode material, NMC-4 exhibits a high specific capacitance of 178.5 F g−1 at a current density of 0.5 A g−1 and long cycle life (94.5% capacity retention after 5000 cycles). It also shows a good rate capacity as 76.1% of original specific capacitance remains when the current density increases from 0.5 to 20 A g−1. The high-performance of NMCs results from the synergetic effects of 3D interconnected mesopores, large surface area, and high N-doping level, enabling fast mass transport and electron transfer during the electrochemical process. This work provides a facile and efficient strategy to heteroatom-doped carbons from extensively available biomass, showing great potentials in electrocatalysis, energy storage, and other applications.

Nitrogen-Containing Functional Groups-Facilitated Acetone Adsorption by ZIF-8-Derived Porous Carbon.

Nitrogen-doped porous carbon (ZC) is prepared by modification with ammonia for increasing the specific surface area and surface polarity after carbonization of zeolite imidazole framework-8 (ZIF-8). The structure and properties of these ZCs were characterized by Transmission electron microscopy, X-ray diffraction, N2 sorption, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Through static adsorption tests of these carbons, the sample obtained at 600 °C was selected as an excellent adsorbent, which exhibited an excellent acetone capacity of 417.2 mg g−1 (25 °C) with a very large surface area and high-level nitrogen doping (13.55%). The microporosity, surface area and N-containing groups of the materials, pyrrolic-N, pyridinic-N, and oxidized-N groups in particular, were found to be the determining factors for acetone adsorption by means of molecular simulation with density functional theory. These findings indicate that N-doped microporous carbon materials are potential promising adsorbents for acetone.

Direct production of nitrogen-doped porous carbon from urea via magnesiothermic reduction

With high capacities, as well as controllable morphologies and compositions, doped carbons represent attractive options for metal-ion battery electrode materials. In this work, we demonstrated a facile one-pot, one-step production of nitrogen-doped porous carbon (NPC) from an abundant and inexpensive urea precursor. The unique porous structure composed of an abundance of graphene nanosheets with high nitrogen doping level for the obtained NPC materials resulted in very promising electrochemical performances when used in lithium-ion batteries (LIBs). A high reversible lithium storage capacity of 1781 mAh/g was obtained after 500th cycle, with an enhanced cycling stability and rate capability. The method presented in this work may provide a simple, clean, economical and scalable strategy for production of NPC as a feasible and promising anode material for energy storage applications.

A Thermally Decomposable Template Route to Synthesize Nitrogen-Doped Wrinkled Carbon Nanosheets as Highly Efficient and Stable Electrocatalysts for the Oxygen Reduction Reaction

We successfully developed a thermally decomposable template route to prepare wrinkled carbon nanosheets with a high level of nitrogen functional moieties by direct carbonization of biomass glucose and dicyandiamide as the renewable feedstocks. Confined pyrolysis of glucose within the interlayers of dicyandiamide-derived g-C3N4 as a thermally removable template results in the formation of two-dimensional (2D) wrinkled carbon nanosheets as well as simultaneous high-level nitrogen doping. The textural properties and nitrogen contents could be controlled by adjusting the mass ratio of glucose/dicyandiamide. Among various samples, the sample prepared with the dicyandiamide/glucose mass ratio of 7/1 has optimal activity for the electrocatalytic oxygen reduction (onset potential −0.12 V vs saturated calomel electrode (SCE); limiting current density 4.73 mA/cm2) in 0.1 M KOH solution, the half-wave potential of which is only 67 mV larger than that for 20 wt % Pt/C. Moreover, it demonstrates a highly efficient fou...

SAPO-34 templated growth of hierarchical porous graphene cages as electrocatalysts for both oxygen reduction and evolution

Three-dimensional hierarchical porous graphene materials with unique properties are of significant importance for the exploration of advanced electrocatalysts for both the oxygen reduction and evolution reactions (ORR/OER). Templated chemical vapor deposition is a favorable strategy to fabricate this kind of graphene, but the number of effective templates is limited. Here, silicoaluminophosphate (SAPO-34) zeolite crystals were used as the catalytic templates for the deposition of hierarchical porous graphene. The graphene obtained consisted of micron-size hollow cubes with mesoporous/nanoporous facets, and ultrathin walls, precisely replicating the structure of the cube-like SAPO-34 zeolite particles. A high doping level of nitrogen (6.84 at%) was achieved by subsequent annealing at 700 °C under ammonia before template removal. Because of the unique porosity, abundant defects, and favorable N-doping, the N-doped graphene exhibited considerable reactivity for both ORR and OER.

High Rate Performing in Situ Nitrogen Enriched Spherical Carbon Particles for Li/Na-Ion Cells.

Nitrogen rich, porous spherical carbon particle with the large surface area was synthesized by simple pyrolysis of the amorphous covalent organic framework. The obtained mesoporous spherical carbon particles with dilated interlayer distance (0.377 nm), large surface area (390 m2 g-1) and high level nitrogen doping (10.9%) offer eminent electrochemical performance as an anode for both lithium ion (LIBs) and sodium ion batteries (SIBs). In LIB applications, the synthesized material delivers an average reversible capacity of 820 mAh g-1 after 100 cycles at 0.1 A g-1, superior rate capability of 410 and 305 mAh g-1 at 4.0 and 8.0 A g-1 respectively. In SIBs, the material shows the stable reversible capacity of about 238 mAh g-1 for the studied 500 cycles at 0.5 A g-1. The rate and steady state cycling performance at high current densities are impressive, being as high as 165 mAh g-1 even after 250 cycles at 2.0 A g-1.

Ammonia-Treated Ordered Mesoporous Carbons with Hierarchical Porosity and Nitrogen-Doping for Lithium-Sulfur Batteries

The theoretical specific capacity and energy density of lithium sulfur battery are as high as 1675 mAh/g and 2600 Wh/kg，which is an order of magnitude higher than that of the commercial insertion cathodes. In combination with the natural abundance, low cost and environmental friendliness of sulfur, the Li-S battery becomes a promising candidate for the next generation power source. However，the commercialization of Li-S battery is inhibited by the insulating nature of sulfur and Li2S, the volume expansion, “Shuttle effect” caused by the high solubility of lithium polysulfides in the electrolyte, the severe corrosion of lithium anode and irreversible reaction during the charge/discharge process, which lead to a low utilization rate of sulfur, serious capacity fading, and low Coulombic efficiency of Li-S battery. One of the most effective ways to circumvent these three limitations is to fabricate sulfur/carbon composite cathodes by incorporating sulfur within a variety of carbon materials including porous carbons, carbon nanotubes, graphene nanosheets and many other forms. These carbon hosts can enhance the conductivity of sulfur electrodes and accommodate their volume changes. Furthermore, the weak interactions between carbon and polysulfides also alleviate the dissoluble loss of polysulfide intermediates. In particular, hierarchically porous carbon materials are recently receiving discernable attention. It is believed that the micropores enable better cycle stability due to solvent-restricted lithiation/delithiation of sulfur, while the larger pores (mesopores and macropores) promise high sulfur loading and rapid ion transport. Therefore, both of large capacity and high rate performance may be achieved. Further, the nitrogen doping of carbon materials has been recently demonstrated to be a powerful method for enhancing the overall electrochemical performance of sulfur cathodes. The nitrogen heteroatom with high electronegative improves the carbon conductivity and promotes chemical adsorption of polysulfides, resulting in enhanced sulfur utilization, rate capability, and cyclic stability. For these reasons, it is essential to develop facile and scalable methods to prepare nitrogen-doped carbon materials with hierarchical porosity. However, there is a trade-off between well-developed porosity and high nitrogen-doping level. Generally, current methods that favor high nitrogen contents tend to result in low specific surface area or small pore volume, or vice versa. To produce hierarchical porous carbon materials with both developed porosity and high nitrogen content, we herein introduce a simple and cost-efficient approach using two ease-to-scale-up steps including 1) one-pot aqueous self-assembly route to firstly get nitrogen-doped ordered mesoporous carbons (NOMCs) and then 2) ammonia activation treatment to achieve desirable porosity and nitrogen-doping. For comparison, another important and industrial method, KOH activation, was also used to obtain hierarchically porous carbon. Those gained carbons were then used as the sulfur hosts in the Li-S batteries. The effect of activation conditions on the nitrogen content, specific surface area, and pore size distribution of the hierarchically porous carbons as well as their electrochemical performance were investigated in detail. It clearly exhibits that ammonia activation enables the hierarchically porous carbon with relatively high porosity (specific surface area up to 1565 m2 g−1) and nitrogen content (up to 4.4 wt%). These combined superior properties make them good candidates as the host materials of sulfur cathodes in Li-S batteries with high sulfur loading.

N‐doping Hierarchical Porosity Carbon from Biowaste for High‐Rate Supercapacitive Application

AbstractIn this work, nitrogen‐doped carbon materials with hierarchical porosity were prepared from biowaste of soybean curd residue (SCR) by KOH activation. The morphology, structure and textural properties of the carbon materials are investigated by scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, Raman spectroscopy, and N2 absorption‐desorption isotherms, respectively. The products exhibit high specific surface area of 3431 m2 g−1, high nitrogen doping level, outstanding charge storage capacity of 282 F g−1 at the current density of 0.5 A g−1 and good electrochemical stability over 10000 cycles. Moreover, it still retains 200 F g−1 (71 % of its capacitance at 0.5 A g−1) at 20 A g−1. The findings pave the way for improving charge storage capacity of supercapacitors based on activated carbon and provide a new method to transfer biowaste to effective electrode material.

Dual mesoporous carbon with high nitrogen doping level as an efficient electrode material for supercapacitors

This paper reports a dual mesoporous carbon (NDMC) with high nitrogen doping level derived from the amino production of the sucrose synthesized under hydrothermal condition. The S BET and total pore volume of the reported materials reaches up to 1101 and 1.67 cm3 g−1, the small mesopores center at about 3.22–3.31 nm while the larger mesopores locate at 8.98–12.58 nm. The doping content of the nitrogen heteroatoms is found to be more than 11.6 at.%, and depend on the carbonization temperature. The maximum specific capacitance of the reported materials reaches up to 512 F g−1 due to the additional contribution of pseudo-capacitance induced by the nitrogen heteroatoms doping. The capacitance retention rate is found to be up to 95% after 1000 times cycles. The dual mesoporous structure, high specific area, additional pseudo-capacitance, enhanced wettability and conductivity are found to response for the superior capacitance performance of the reported materials.

Structure of functionalized nitrogen-doped graphene hydrogels derived from isomers of phenylenediamine and graphene oxide based on their high electrochemical performance

Three functionalized N-doped graphene hydrogels were prepared from graphene oxide (GO) and isomers of phenylenediamine through hydrothermal process, which were (1) FONGH prepared with o-phenylenediamine (OPD); (2) FMNGH prepared with m-phenylenediamine (MPD) and (3) FPNGH prepared with p-phenylenediamine (PPD). As-prepared FONGH, FMNGH and FPNGH possessed different microstructures and exhibited different specific surface area: 107.8, 24.3 and 145.2m2g−1. The prepared graphene hydrogels were found with different N contents: FONGH (11.1 at.%)>FPNGH (9.8 at.%)>FMNGH (7.2 at.%). High resolution N 1s spectra of as-prepared hydrogels revealed that OPD facilitated the preparation of graphene with high doping level of nitrogen; while PPD was favorable to preparing N-doped graphene hydrogel with high moieties of amine including -NH2 or N covalent bonded with sp3-C of graphene. As-prepared FONGH, FMNGH and FPNGH exhibited excellent electrochemical performance with high specific capacitance (645, 365.7 and 467Fg−1 at 1Ag−1) and superior cycling stability (97.6%, 83.1% and 91% retention at 20Ag−1 after 1000 cycles). The different microstructures and electrochemical performance of FONGH, FMNGH and FPNGH were caused by different positions of -NH2 groups on the benzene rings of OPD, MPD and PPD. The present work proposes a novel idea to prepare functionalized N-doped graphene with high electrochemical performance.

Pyridinic‐Nitrogen‐Dominated Graphene Aerogels with Fe–N–C Coordination for Highly Efficient Oxygen Reduction Reaction

Here, pyridinic nitrogen dominated graphene aerogels with/without iron incorporation (Fe‐NG and NG) are prepared via a facile and effective process including freeze‐drying of chemically reduced graphene oxide with/without iron precursor and thermal treatment in NH3. A high doping level of nitrogen has been achieved (up to 12.2 at% for NG and 11.3 at% for Fe‐NG) with striking enrichment of pyridinic nitrogen (up to 90.4% of the total nitrogen content for NG, and 82.4% for Fe‐NG). It is found that the Fe‐NG catalysts display a more positive onset potential, higher current density, and better four‐electron selectivity for ORR than their counterpart without iron incorporation. The most active Fe‐NG exhibits outstanding ORR catalytic activity, high durability, and methanol tolerance ability that are comparable to or even superior to those of the commercial Pt/C catalyst at the same catalyst loading in alkaline environment. The excellent ORR performance can be ascribed to the synergistic effect of pyridinic N and Fe‐N x sites (where iron probably coordinates with pyridinic N) that serve as active centers for ORR. Our Fe‐NG can be developed into cost‐effective and durable catalysts as viable replacements of the expensive Pt‐based catalysts in practical fuel cell applications.