Design of Fe and Cu bimetallic integration on N and F co-doped porous carbon material for oxygen reduction reaction

At present, fuel cell is considered to be one of the most ideal application technologies of hydrogen energy. In order to develop fuel cells on a large scale and in a sustainable way, low platinum or non-platinum oxygen reduction catalyst has become a research hotspot. In this work, a kind of doped carbon-based catalyst MPFe₁Cu₁-850 is prepared by high temperature synthesis. The catalyst has an ultra-thin lamellar porous structure. In an acidic medium, the MPFe₁Cu₁-850 displays good oxygen reduction reaction (ORR) activity (ΔE_1/2 = 0.725 V). In addition, it shows better stability (91%) and higher methanol tolerance than that of commercial Pt/C catalyst. In our catalyst MPFe₁Cu₁-850, the contents of nitrogen, iron and copper are 10.31 at.%, 0.51 at.%, and 0.50 at.%, respectively. This work shows that high N content, and the proper ratio of iron to copper (Fe:Cu = 1:1), are conducive to the enhancement of ORR activity.     

Synthesis of hollow Fe,Co, and N-doped carbon catalysts from conducting polymer-metal-organic-frameworks core-shell particles for their application in an oxygen reduction reaction

Oxygen reduction reaction (ORR), one of the key reactions for fuel cells and zinc-air batteries, should be improved for higher performance. Herein, we fabricated hollow Fe, Co, and nitrogen co-doped carbon (H-FeCo-NC) catalyst, which was prepared by carbonization of core-shell particles made of polypyrrole (PPy)-coated polystyrene (PS) spheres as cores and (Zn, Co) bimetallic-zeolitic imidazolate frameworks (ZnCoBZIFs) as shells. PPy was used as a nitrogen and a carbon source. The H-FeCo-NC catalyst had a high surface area of 324.08 m² g^?1 with uniformly distributed Fe and Co species, and excellent ORR performance with the half-wave potential of 0.888 V vs. reversible hydrogen electrode in alkaline media. Furthermore, the H-FeCo-NC catalyst demonstrated exceptional stability, durability, and tolerance to methanol crossover.     

Preparation of iron and nitrogen co-doped carbon material Fe/N-CCM-T for oxygen reduction reaction

In this paper, iron and nitrogen co-doped carbon material with nanotube structure (Fe/N-C_CM-T) was synthesized by pyrolyzing a mixture of Fe salt, chitosan and melamine and displayed high electrocatalytic performance for oxygen reduction reaction (ORR). The structure of the Fe/N-C_CM-T was characterized and their ORR performance in alkaline media was investigated by linear sweep voltammetry, cyclic voltammetry and chronoamperometry. Fe/N-C_CM-T displayed better ORR performance than other carbon materials like Fe/N-C_C-800. The Fe/N-C_CM-800 with a large surface area (302.5 m²/g) especially exhibited the best ORR electrocatalytic performance among the prepared carbon materials, which was also proved by its similar Tafel slope (76 mV decade^?1) to Pt/C catalyst (74 mV decade^?1). Fe/N-C_CM-800 showed similar ORR activity as commercial Pt/C catalyst, but superior tolerance to methanol and stability. Such high ORR performance of the Fe/N-C_CM-T can be attributed to its nanotube structure, high specific surface area (SSA), high graphitic-N and pyridinic-N contents.     

Zr enhanced Fe,N, S co-doped carbon-based catalyst for high-efficiency oxygen reduction reaction

Fe-N_x catalysts have received widespread attention in recent years due to their excellent catalytic performance, hoping to replace platinum for oxygen reduction reactions (ORR). In recent years, more studies have shown that when the catalyst contains two or more metals doped, its catalytic performance will be improved. Herein, using the high temperature pyrolysis method, through the incorporation of the second phase metal (Zr), melamine as the nitrogen source, and thiourea as the sulfur source, a high-activity carbon-based catalyst doped with Fe and Zr bimetals was synthesized. Originating from the strong interaction between Fe species and ZrO₂ clusters and the promotion of O₂ adsorption by ZrO₂ nanoparticles supported on nitrogen-doped carbon, this catalyst has a better ORR electrocatalytic performance than 46% TKK commercial platinum carbon in 0.1 M KOH, exhibiting an onset potential of 1.047 V vs RHE, a half-wave potential of 0.909 V vs RHE. It provides a new idea for the preparation of high-performance bimetallic-doped carbon-based electrocatalysts.     

Composition-tunable PtCu porous nanowires as highly active and durable catalyst for oxygen reduction reaction

To accelerate the commercialization of fuel cells, many efforts have been made to develope highly active and durable Pt-based catalyst for oxygen reduction reaction (ORR). Herein, PtCu porous nanowires (PNWs) with controllable composition are synthesized through an ultrasound-assisted galvanic replacement reaction. The porous structure, surface strain, and electronic property of PtCu PNWs are optimized by tuning composition, which can improve activity for ORR. Electrochemical tests reveal that the mass activity of Pt_0.5Cu_0.5 PNWs (Pt/Cu atomic ratio of 1:1) reaches 0.80 A mg_Pt^?1, which is about 5 times higher than that of the commercial Pt/C catalyst. Notably, the improved activity of the porous nanowire catalyst is also confirmed in the single-cell test. In addition, the large contact area with the carrier and internal interconnection structure of Pt_0.5Cu_0.5 PNWs enables them to exhibit much better durability than the commercial Pt/C catalyst and Pt_0.5Cu_0.5 nanotubes in accelerated durability test.     

High performance catalysts based on Fe/N co-doped carbide-derived carbon and carbon nanotube composites for oxygen reduction reaction in acid media

The key issue of modern electrochemical technology is clean energy production and storage. Proton exchange membrane fuel cells (PEMFC) offer a way to produce electricity from hydrogen, but are hindered by the sluggish reduction of oxygen into water on the cathode, which requires Pt/C catalysts. Iron-nitrogen-carbon (Fe-N-C) catalysts have been shown in recent years to be viable alternatives. Here, we present highly performing Fe-N-C catalysts based on composite materials synthesised from carbide-derived carbon (CDC) and carbon nanotubes (CNT). B₄C, Mo₂C and TiC, which yield CDC materials with different porosity were chosen as the starting carbides, which are then doped with Fe, N and composited with CNTs using ball-milling and pyrolysis. 1,10-phenanthroline (Phen) and dicyandiamide (DCDA) serve as the nitrogen sources and Fe(II)acetate as the iron source. The catalyst derived from TiC shows a remarkable half-wave potential for oxygen reduction of 0.8 V vs RHE, which shifts negative 36 mV during 5000 potential cycles at 70 °C, while the composite material derived from it is more stable with a shift of only 15 mV during the same period.     

Flame synthesis of nitrogen,boron co-doped carbon as efficient electrocatalyst for oxygen reduction reaction

The flame synthesis provides a simple low-cost method to produce novel carbon materials. In this study, N, B co-doped carbon (NBC) materials have been prepared by flame synthesis. Among many as-prepared samples, the NBC catalyst which prepared under carbonization temperature of 1000 °C for 3 h with acetonitrile/acetone precursor of 1:1 exhibits the best catalytic activity and stability, as well as good resistance to methanol interference for oxygen reduction reaction (ORR), with half-wave potential being almost nearly to Pt/C, and a quasi-four-electron transfer process. This study would provide an economic, environmental feasible and scalable approach for fabricating novel heteroatom co-doped carbon materials for ORR applications.     

Facile preparation of Fe3C decorate three-dimensional N-doped porous carbon for efficient oxygen reduction reaction

Novel Fe₃C nanoparticles that decorate three-dimensional N-rich porous carbon (Fe₃C@3DNC) catalysts were designed and synthesized by double templates assisted high-energy ball milling and subsequent high-temperature pyrolysis for the oxygen reduction reaction (ORR). NaCl and Na₂SiO₃ are used as the mixed template while Fe(NO₃)₃·9H₂O and 2-Methylimidazole were used as the iron, nitrogen and carbon sources. The optimized Fe₃C@3DNC catalyst (Fe₃C@3DNC-1-900) had good ORR performance in alkaline medium, with an Eonest value of 0.968 V and E_1/2 value of 0.861. In addition, the catalytic process exhibited selectivity–nearly four-electron transfer kinetics and possesses a lower Tafel slope compared to commercial Pt/C catalyst as well as good methanol tolerance. In addition, the Fe₃C@3DNC-1-900 catalyst also had excellent ORR activity (E_1/2 = 0.72 V) and long-term stability (the half-wave potential only occurs at 10 mV after 5000 cycles) in acidic media. The good catalytic performance of the Fe₃C@3DNC-1-900 catalyst can be attributed to the 3D hierarchically porous structure and extremely high number of active sites around the porous carbon. The double template assisted high-energy ball milling strategy can be a promising and scalable method to prepare three-dimensional porous carbon-based composite materials for energy conversion and storage applications.     

Manganese coordinated with nitrogen in aligned hierarchical porous carbon for efficient electrocatalytic oxygen reduction reaction in alkaline and acidic medium

A Mn coordinated with N atoms aligned hierarchical porous carbon catalyst is prepared through an inorganic metal salt sublimation doping strategy. Gelatin is served as a carbon source and N source, Ca²⁺ is acted as templates to establish aligned porous structure during carbonization. MnCl₂ sublimates into gas to serve as Mn source after reaching the melting point. This method can effectively avoid the agglomeration of Mn atoms, which is beneficial to form Mn-N_x active sites. The prepared optimal catalyst exhibits a large specific surface area with an aligned hierarchical porous structure. XAFs result demonstrates that Mn coordinates with N atoms to form Mn-N_x configuration in the carbon structure. Notably, it exhibits outstanding catalytic ORR performance with a positive half-wave potential (0.86 V vs. RHE) and excellent durability, superior to Pt/C (20 wt%) catalyst under alkaline medium. Meanwhile, enhanced catalytic ORR performance and stability in an acidic medium are also achieved.     

Agaricus bisporus residue-derived Fe/N co-doped carbon materials as an efficient electrocatalyst for oxygen reduction reaction

Biomass-derived multielement-co-doped carbon materials with ultrahigh active-sites density and unique physicochemical properties hold great promise for oxygen reduction reaction (ORR) in fuel cells and metal-air batteries. Agaricus bisporus residue as a type of biomass waste is produced after microbial growth on biomass substrates, contributing to its natural multidimensional framework and nutrient elements residual. Based on this advantage, this paper further combined with (NH₄)₃PO₄ and FeCl₃·6H₂O to provide N, P, and Fe. Finally, the Fe/N co-doped carbon catalyst with hierarchical porous structure (SN-Fe-ZA) was fabricated by a facile hydrothermal-pyrolysis synthesis route. The characteristic of SN-Fe-ZA exhibited an obvious honeycomb porous structure, high nitrogen doping content of 2.36 at%, and its specific surface area was up to 1646.4 m²·g⁻¹ with abundant micro-/mesoporous. Electrochemical measurements further indicated that SN-Fe-ZA possessed a distinct ORR electrocatalytic activity in alkaline solution. Compared with the electrochemical parameters of commercial Pt/C electrocatalyst, SN-Fe-ZA had the equivalent onset potential (0.968 V) and half-wave potential (0.820 V). Besides, it showed a more excellent electrochemical stability and stronger methanol-tolerant. This research proposed a promising approach to prepare hierarchical porous and multielement-co-doped catalyst from renewable biomass waste as effective cathode electrocatalytic materials for alkaline fuel cells.     

Atomically dispersed Co atoms in nitrogen-doped carbon aerogel for efficient and durable oxygen reduction reaction

Developing non-noble-metal-based electrocatalysts as alternatives to replace Pt-based catalysts for oxygen reduction reaction (ORR) is crucial for large scale industrial application of fuel cells. Herein, we report a facile method to synthesize atomically dispersed Co atoms anchored on nitrogen-doped carbon aerogels with a 3D hierarchically porous network structure via F127-assisted pyrolysis of a phenolic resin/Co²⁺ composite and subsequent HCl etching treatment. HRTEM, AC-STEM, XRD, XPS, and Raman spectroscopy measurements demonstrate that Co atoms are homogeneously atomically dispersed on nitrogen-doped carbon aerogels within the porous structure by coordination with pyridinic-N. Among a series of samples, the Co-NCA@F127-1: 0.56 catalyst exhibits an enhanced ORR activity with onset potential (E_onset) of 0.935 V vs. RHE, the high diffusion limiting current density of 5.96 mA cm⁻² at 0.45 V, as well as an excellent resistance to methanol poisoning and good long-term stability in alkaline medium, comparable to the state-of-the-art Pt/C catalyst. This work may provide a novel and ingenious thought in the design and engineering of efficient and robust electrocatalysts based on single transition-metal atoms supported by nitrogen-doped carbon materials.     

Cobalt,sulfur, nitrogen co-doped carbon as highly active electrocatalysts towards oxygen reduction reaction

Rational design of efficient, cost-effective electrocatalyst towards oxygen reduction reaction (ORR) is of vital importance to the wide application of polymer electrolyte membrane fuel cells. In this work, a novel and simple Na₂SO₄-assisted pyrolysis strategy with ZIF-12 as the precursor is reported for the synthesis of cobalt, sulfur, nitrogen, co-doped carbon (termed as CoSNC-xNa₂SO₄-T) materials towards ORR. Different from CoNC-800 derived from pure ZIF-12, with the presence of Na₂SO₄, the derived CoSNC-0.5Na₂SO₄-800 material exhibits layered flake morphology with hierarchical meso-microporous structure. Besides, CoSNC-0.5Na₂SO₄-800 material shows higher content of pyridinic-N and graphitic-N, higher relative intensity of Co-N_x, higher content of carbon defect, as well as larger specific surface area in comparison with CoNC-800, which results in higher activity of CoSNC-0.5Na₂SO₄-800. The CoSNC-0.5Na₂SO₄-800 material displays a half-wave potential of 0.88 V, which is superior to that of commercial Pt/C (half-wave potential being 0.86 V). Moreover, CoSNC-0.5Na₂SO₄-800 demonstrates a better durability compared with Pt/C. The pyrolysis temperature and the amount of Na₂SO₄ are found to affect the physiochemical properties and electrochemical performance of the CoSNC-xNa₂SO₄-T materials. This work not only provides a facile and novel synthesis approach for the preparation of highly active Co, S, N co-doped carbon materials for ORR, but also disclosing the key structure properties for enhancing the performance of these catalysts.     

Phosphorus-doped hierarchical porous carbon as efficient metal-free electrocatalysts for oxygen reduction reaction

Recently, fuel cells and metal-air batteries have attracted extensive attentions. Researching and developing non-noble metal catalyst with high electrocatalytic activity and low cost is one of the important challenges for these energy storage and conversion devices. In this study, phosphorus doped hierarchical porous carbon (P-HPC) has been firstly synthesized via a hard template method. The prepared PHPC possesses a unique porous structure which consists of micropores, mesopores and macropores simultaneously. The electrocatalytic activity of the PHPC toward ORR in KOH solution has been studied and compared with the ordinary structured phosphorus doped carbon (PC) and the commercial Pt/C by means of rotating ring-disk electrode (RRDE) technique. The prepared PHPC exhibits an excellent electrocatalytic performance toward ORR in terms of the electrocatalytic activity, the reaction kinetics, the durability and the methanol tolerance. And the high electrocatalytic activity and durability of PHPC could be attributed to the special hierarchical porous structure. This research demonstrates that the rational design of the microstructures for catalyst plays significant roles in improving the catalytic activity for the ORR.     

Synthesis of porous nitrogen and sulfur co-doped carbon beehive in a high-melting-point molten salt medium for improved catalytic activity toward oxygen reduction reaction

The development of unique, reliable and scalable synthesis strategies for producing dual-heteroatom-doped nanostructured carbon materials with improved activity toward electrochemical oxygen reduction reaction (ORR) presents an intriguing technological challenge in the field of catalysis. Herein, we report a method to synthesize a three-dimensional (3D) N and S Co-doped carbon beehive (NS-CB) with open structure by direct pyrolysis of egg white in a high-melting-point molten salt medium, e.g. NaCl/KCl, under inert atmosphere. Physicochemical characterization shows that NS-CB possess hierarchical pores (including micro- and mesopore) with a high specific surface area of 1478 m² g^?1, which is obviously larger than as-prepared carbons synthesized in only NaCl (CNaCl) or KCl (CKCl) as molten salt medium. Importantly, 50% of the pore volume is contributed by micropores with average pore size of 1.4 nm, which is the ideal pore size for ORR. The remaining 50% of the pore volume is made of mesopores and open macropores, assembled in the form of interconnected carbon sheets. Due to its hierarchical structure and high specific surface area, NS-CB shows high ORR activity comparable to commercial Pt/C catalyst in KOH electrolyte in terms of the half wave potential and the onset potential of ORR. NS-CB also exhibits markedly high stability as an ORR catalyst.     

Co nanoparticles and ZnS decorated N,S co-doped carbon nanotubes as an efficient oxygen reduction catalyst in zinc-air batteries

The economical, efficient and durable oxygen reduction catalysts facilitate the enhancement of electrochemical energy devices competitiveness towards widespread applications. In view of this, we provide an innovative sulfuration inducing method for the synthesis of ZnS and cobalt nanoparticles decorated N, S co-doped CNTs (ZnS/Co-NSCNTs) catalyst. S introduced into the zinc-based zeolitic imidazolate frameworks (ZIF-8) and cobalt-based zeolitic imidazolate frameworks (ZIF-67) precursors via pyrolysis, and induced the generation of ZnS/Co-NSCNTs have been confirmed by XRD, SEM, TEM, and XPS techniques. The key features including activity sites, transfer channels and adsorption energy back up the excellent electrocatalytic activity of the as-prepared ZnS/Co-NSCNTs towards oxygen reduction reactions (ORR). ZnS/Co-NSCNTs additionally exhibited a positive half-wave potential of 0.871 V (vs. RHE) with improved current density towards ORR. In alkaline medium, ZnS/Co-NSCNTs catalyst displayed a high tolerance towards methanol and an excellent long-term cycling stability. The observed onset potential for our prepared ZnS/Co-NSCNTs catalyst is analogous with the commercially available noble metal catalysts. Also, ZnS/Co-NSCNTs catalyst as a cathode in zinc-air battery displayed an enhanced electrochemical performance with a highly specific capacity of 750.1 mAh g⁻¹, outstanding cycling stability, and high rate behavior. This work provides a new approach for the construction of stable low-cost alternative air-cathode catalysts for other energy conversion and storage applications.     

One-step carbonization of ZIF-8 in Mn-containing ambience to prepare Mn,N co-doped porous carbon as efficient oxygen reduction reaction electrocatalyst

Economical and efficient non-noble metal catalysts should be developed practically, instead of commercial Pt/C for fuel cells. In this paper, manganese, nitrogen co-doped porous carbon (Mn–N–C) was synthesized to catalyze oxygen reduction reaction (ORR) through the one-step carbonization of ZIF-8 in the Mn-containing (MnCl₂) atmosphere. During the carbonization process, MnCl₂ gas was captured with ZIF-8 and then transformed into uniform Mn–N active sites distributed in the porous carbon materials. The Mn–N–C catalyst exhibited plentiful porous structures, large specific surface areas, high graphitization and conductivity, which contributed to the transfer and transport of charge and exposed more active sites. The Mn–N–C catalyst exhibited superior catalytic ability in alkaline and acidic solutions. Half-wave potential of the Mn–N–C could reach 0.88 and 0.73 V in 0.1 M KOH and 0.5 M H₂SO₄, respectively. In addition, the Mn–N–C catalyst showed a prominent stability after the stability test of 18,000 s. Excellent electrochemical performance and endurance make the Mn–N–C expect to be an effective ORR catalyst to build high-performance fuel cells.     

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.     

Iron-based sulfur and nitrogen dual doped porous carbon as durable electrocatalysts for oxygen reduction reaction

The widespread use of fuel cell technology is hampered by the use of expensive and scarce platinum metal in electrodes which is required to facilitate the sluggish oxygen reduction reaction (ORR). In this work, a viable synthetic approach was developed to prepare iron-based sulfur and nitrogen dual doped porous carbon (Fe@SNDC) for use in ORR. Benzimidazole, a commercially available monomer, was used as a precursor for N doped carbon and calcined with potassium thiocyanate at different temperatures to tune the pore size, nitrogen content and different types of nitrogen functionality such as pyridinic, pyrrolic and graphitic. The Fe@SNDC–950 with high surface area, optimum N content of about 5 at% and high amount of pyridinic and graphitic N displayed an onset potential and half-wave potential of 0.98 and 0.83 V vs RHE, respectively, in 0.1 M KOH solution. The catalyst also exhibits similar oxygen reduction reaction performance compared to Pt/C (20 wt%) in acidic media. Furthermore, when compared to commercially available Pt/C (20 wt%), Fe@SNDC–950 showed enhanced durability over 6 h and poison tolerance in case of methanol crossover with the concentration up to 3.0 M in oxygen saturated alkaline electrolyte. Our study demonstrates that the presence of N and S along with Fe-N moieties synergistically served as ORR active sites while the high surface area with accessible pores allowed for efficient mass transfer and interaction of oxygen molecules to the active sites contributing to the ORR activity of the catalyst.     

Thermally-induced arrangement of cobalt and iron in the ZIF-derived Fe,Co,Zn-N/C catalysts for the oxygen reduction reaction

Heteroatom-doped carbon materials (HDCM) are perspective Pt-free alternatives for applications in fuel cells. The Fe,Co,Zn-N/C catalysts were obtained by pyrolysis (at 700 °C in Ar) of sacrificial bimetallic zeolitic imidazolate frameworks (Co,Zn-ZIF), prepared with different Co/Zn ratio by a microwave-assisted solvothermal synthesis (at 140 °C in DMF for 2 h). Co,Zn-ZIF hybrids were impregnated with a Fe^II-phenanthroline complex before the pyrolysis. The structural properties of prepared materials were assessed primarily by X-ray diffraction (XRD) and transmission electron microscopy (TEM), while X-ray fluorescence (XRF) and the scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (STEM-EDS) mapping and were used for the elemental content analysis. Because in the obtained HDCM both Fe and Co participate in formation of the bamboo-like structures, synchrotron-based X-ray absorption spectroscopy (XAS) studies were performed at their K-edges. The results of in situ XAS measurements during carbonization of Fe,Co,Zn-ZIF upon heating (up to 500 °C in Ar) as well as operando XAS measurements during the electrochemical cycling of HDCM are reported. The registered changes in the oxidative state of Fe and Co (XANES) and in their coordinative environment (EXAFS) were analyzed. The study is complemented by the electrochemical tests of the synthesized HDCM (in 0.1 M HClO₄ solution) towards the oxygen reduction reaction, demonstrating their high efficiency and stability in acidic medium.     

Nitrogen doped porous carbon with iron promotion for oxygen reduction reaction in alkaline and acidic media

Nitrogen doped water-hyacinth graphite with little iron (NFe-WHG) is synthesized by using water hyacinth as carbon source, dopamine hydrochloride as N source and Fe(NO₃)₃ as Fe source. The water hyacinth is carbonized to porous carbon; the addition of Fe increases pore diameter, graphitization degree, total N and pyridinic N content. The characterizations indicate that the doping N contributes great on ORR activity, yet the residual Fe species themselves show inconspicuous catalytic effect on ORR. The NFe-WHG with the above features displays superior ORR activity in alkaline media and comparable ORR activity to commercial Pt/C in acidic media. Due to the graphite matrix and that most of the Fe species have been removed, the NFe-WHG shows excellent stability in both alkaline and acidic media with excellent anti-methanol and anti-CO performances.