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.     

Natural aloe vera derived Pt supported N-doped porous carbon: A highly durable cathode catalyst of PEM fuel cell

Evolution of highly durable electrocatalyst for oxygen reduction reaction (ORR) is the most critical barrier in commercializing polymer electrolyte membrane fuel cell (PEMFC). In this work, Pt deposited N-doped mesoporous carbon derived from Aloe Vera is developed as an efficient and robust electro catalyst for ORR. Due to its high mesoporous nature, the aloe vera derived carbon (AVC) play a very vital role in supporting Pt nanoparticles (NPs) with N-doping. After doping N into AVC, more defects are created which facilitates uniform distribution of Pt NPs leading to more active sites towards ORR. Pt/N-AVC shows excellent ORR activity when compared with commercial Pt/C and showing a half wave potential (E_1/2–0.87 V Vs. RHE) and reduction potential (E_red ~ 0.72 V Vs. RHE) towards ORR. Even after 30,000 potential cycles, Pt/N-AVC shows in its E_1/2 only ~5 mV negative shift and lesser agglomeration of Pt NPs is seen in the catalyst. In membrane electrode assembly (MEA) fabrication, Pt/N-AVC as a cathode catalyst in a PEMFC fixture and performance were studied. The Pt/N-AVC shows good performance, which proves the potential application of this naturally available bio derived carbon, which serves as an excellent high durable support material in PEMFC. All these features show that the Pt/N-AVC is the most stable, efficient and suitable candidate for ORR catalyst.     

Polyoxomolybdate anchored graphite oxide: Noble metal-free electrocatalyst for oxygen reduction reaction

We present the synthesis of a noble metal-free electrocatalyst, polyoxomolybdate/reduced graphite oxide (PMA/rGO) composite, which showed enhancement in the kinetics for oxygen reduction reaction (ORR). The composite material was prepared by simple and cost effective method. Mere heating of the precursors at low temperature (200 °C) resulted in molecular assembly of PMA on GO in the form of clusters which behaved as active centers for efficient ORR. The electrochemical study of PMA/rGO-2 (PMA to GO weight ratio of 1:2) catalyst carried out by rotating disk electrode (RDE) method, showed considerable electrocatalytic activity with E_onset of 1.0 V vs. RHE and current density of 4.0 mA/cm² at 1600 rpm in alkaline condition. Additionally, as-prepared PMA/rGO-2 catalyst showed a single step ~ 4 electron transfer pathway similar to commercial Pt/C catalyst; confirmed through rotating ring disk electrode (RRDE) study. Interestingly, PMA/rGO-2 electrocatalyst exhibited substantially higher stability than Pt/C catalyst even after 20K potential cycles (though the current density of former catalyst is inferior to later). Further, in a methanol cross-over test, PMA/rGO-2 was found to be inactive towards methanol oxidation reactions, which could nullify the issues due to the fuel cross-over effect, if employed as cathode in direct methanol fuel cells. The enhanced ORR activity and significant stability is attributable to the anchoring and homogenous distribution of polyoxomolybdate clusters on graphite oxide.     

Rationale approach of nitrogen doping at defect sites of multiwalled carbon nanotubes: A strategy for oxygen reduction electrocatalysis

A development of electrocatalyst for oxygen reduction reaction (ORR) is one of the crucial reactions for low temperature fuel cell applications. The state-of-the-art catalyst (platinum based) have various limitations such as low abundance, extortionate price and sensitive towards impurities. Therefore, design of high performance non-platinum electrocatalyst is the most challenging issue for low temperature fuel cell. In this work, we discuss the nitrogen doping at defect sites of multiwalled carbon nanotubes (MWCNTs) using melamine foam as a template for efficient CNT assembly with subsequent role of different nitrogen containing agents such as melamine and hexamine. Templated assembly of functionalized CNT through melamine foam provides easy approach towards nitrogen doping that followed effective exposure of active sites (like pyridinic-N and oxidic-N) for electroreduction of oxygen. As-prepared N-CNT catalysts (prepared using both the precursors) show better ORR activity than Pt/C in alkaline medium. A sharp reduction peak in their cyclic voltammogram under O₂-saturated 0.1 M KOH solution proves their activity towards ORR electrocatalysis. More interestingly, the onset potentials of ~0.92 V and ~1.1 V versus RHE for N-CNT obtained by hexamine and melamine respectively indicate superior onsets than that of Pt/C (~1.04 V vs RHE). Furthermore, the best N-CNT catalyst (obtained by melamine) reveals better stability up to 15,000 cycles than Pt/C with zero response towards methanol, exhibiting an excellent methanol tolerance.     

Melamine-assisted synthesis of paper mill sludge-based carbon nanotube/nanoporous carbon nanocomposite for enhanced electrocatalytic oxygen reduction activity

Developing efficient and cheap electrocatalysts as substitutes for commercial Pt/C in the oxygen reduction reaction(ORR)is extremely necessary. Herein, paper mill sludge (PMS) was utilized to produce iron, nitrogen and sulfur co-doped carbon nanotube/nanoporous carbon nanocomposite (PMS-CNT/C) by pyrolysis. PMS-CNT/C-b, one of as-prepared PMS-CNT/C exhibited excellent oxygen reduction reaction activity with an onset potential of 0.99 V vs. RHE and half-wave potential of 0.77 V vs. RHE, which was similar to the commercial Pt/C catalyst (onset potential of 0.99 V vs. RHE and half-wave potential of 0.76 V vs. RHE). It had longer-term stability and higher methanol tolerance in alkaline medium than Pt/C. Moreover, the new catalyst also exhibited excellent catalytic performance in neutral solution. The energy output of microbial fuel cells loaded with PMS-CNT/C-b catalyst was also higher than that of commercial Pt/C under neutral condition. The excellent ORR performance of PMS-CNT/C-b was due to the carbon nanotube/nanoporous structure and the synergistic effect of abundant N groups, iron nitrides and thiophene-S. The formation of CNTs in the carbon nanotube/nanoporous carbon nanocomposite was mainly attributed to melamine, which was added into PMS and was at first just considered as a nitrogen source to develop N-doped PMS-based catalysis in this work. The synthesis of paper mill sludge-based carbon nanotube/nanoporous nanocomposite and its excellent ORR activity will make the new catalyst a promising cathodic electrocatalyst alternative for fuel cells.     

An improved Stӧber method towards iron and nitrogen co-doped porous carbon spheres for oxygen reduction reaction in alkaline media

The significant progress of non-precious metal cathodic electrocatalytic materials is impressive in electrochemical energy conversion application. Here, iron and nitrogen co-doped porous carbon spheres (Fe/N-PCS) have been designed via 3-aminophenol/formaldehyde (APF) resin spheres as carbon precursor, ferric nitrate as iron source, colloidal silica as template and tetramethylguanidine as catalyst by the improved Stöber method. Fe/N-PCS possesses uniform spherical morphology, abundant mesoporous shape and high surface area and exhibits higher oxygen reduction reaction (ORR) electrocatalytic activity (E_1/2, 0.838 V vs. RHE) compared with the Pt/C (E_1/2, 0.827 V vs. RHE) in alkaline media. In addition, the methanol tolerance and catalytic stability of Fe/N-PCS are greater than commercial Pt/C catalyst. The outstanding ORR behavior of Fe/N-PCS mainly benefits from the iron and nitrogen elements synergistic effect, pyridinic N and the spherical porous structure enabling plenty of active sites exposed. This method is prospective for preparation of highly efficient cathodic ORR electrocatalyst.     

ORR performance evaluation of Al-substituted MnFe2O4/ reduced graphene oxide nanocomposite

Active and durable oxygen reduction reaction (ORR) catalysts are of utmost importance to realize the commercialization of hydrogen fuel cells and metal-air batteries. Al-substituted MnFe₂O₄-based ternary oxide and reduced graphene oxide (MAF-RGO) nanocomposite is synthesized using an in-situ co-precipitation followed by a hydrothermal process and verified for ORR electrocatalysis in the alkaline electrolyte (0.1 M KOH). MAF-RGO is first analyzed using physicochemical characterization tools including X-ray diffraction, Raman spectroscopy, sorption studies, electron microscopy, X-ray photoelectron spectroscopy, etc. Further, the characteristic ORR peak centered at 0.56 V vs. reversible hydrogen electrode (RHE) in cyclic voltammetry (CV) studies confirms the electrocatalytic performance of MAF-RGO. The ORR onset potential of 0.92 V vs. RHE is obtained in linear sweep voltammetry (LSV) measurement at 1600 rpm in O₂-saturated electrolyte exhibiting an improved ORR performance as compared to the commercial electrocatalyst. The reduction kinetics is observed to follow the desirable near 4-e^- mechanism. In addition, the electrocatalyst exhibits improved relative current stability of 86% and methanol poisoning resistance of 82%, which is better in comparison to the standard Pt/C. The observed electrochemical performance results from the synergism between the oxygen vacancy-rich Al-substituted metallic oxide active species and the functional group enriched predominantly mesoporous RGO sheets with excellent electrical conductivity. The introduction of metallic species enhanced the inter-planar spacing between graphitic sheets easing the maneuver of reactant species through the electrocatalyst and accessing more ORR-active sites. This study establishes the potency of mixed transition metal oxide/nanocarbon composites as durable high-performance ORR-active systems.     

Cobalt-doped porous carbon nanofibers with three-dimensional network structures as electrocatalysts for enhancing oxygen reduction reaction

In this study, we design and prepare the cobalt-doped porous carbon nanofibers (Co@PCNFs) as efficient electrocatalysts based on the electro-blow spinning method and carbonization processes. The porous Co@PCNFs has the three-dimensional porous carbon network structures as the fast electron transport channels and endow the materials with high specific surface area. The central metal Co atoms will be converted into metal nanoparticles with high efficient catalysis in the PCNFs after the carbonization treatment. And the carbonized product still inherits the nanometer size of the ZIF-67 (40–50 nm) precursor, which is more beneficial to expose more active sites. These advantages enable the prepared electrocatalyst to exhibit excellent oxygen reduction reaction (ORR) performance (onset potential of 0.91 V vs. RHE, half-wave potential of 0.857 V vs. RHE), which is very close to commercial Pt/C. More importantly, the obtained Co@PCNFs catalyst exhibited superior electrochemical stability and methanol tolerance over commercial Pt/C under alkaline conditions. The work will open up novel options for various fields such as high performance Zn-air batteries and fuel cells in the future.     

Molecule-confined modification of graphitic C3N4 to design mesopore-dominated Fe-N-C hybrid electrocatalyst for oxygen reduction reaction

To design inexpensive carbon catalysts and enhance their oxygen reduction reaction (ORR) activity is critical for developing efficient energy-conversion systems. In this work, a novel Fe-N-C hybrid electrocatalyst with carbon nanolayers-encapsulated Fe₃O₄ nanoparticles is synthesized successfully by utilizing the molecular-level confinement of graphitic C₃N₄ structures via hemin biomaterial. Benefiting from the Fe-N structure prevalent on the carbon nanosheets and large mesopore-dominated specific surface area, the synthesized catalyst under optimized conditions shows excellent electrocatalytic performance for ORR with an E_ORR at 1.08 V versus reversible hydrogen electrode (RHE) and an E_1/2 at 0.87 V vs. RHE, and outstanding long-term stability, which is superior to commercial Pt/C catalysts (E_ORR at 1.04 V versus RHE and E_1/2 at 0.84 V versus RHE). Moreover, the low hydrogen peroxide yield (<11%) and average electron transfer number (~3.8) indicate a four-electron ORR pathway. Besides, the maximum power density of the home-made Zn-air battery using the obtained catalyst is 97.6 mW cm⁻². This work provides a practical route for the synthesis of cheap and efficient ORR electrocatalysts in metal-air battery systems.     

Stability of Pt-Ni/C (1:1) and Pt/C electrocatalysts as cathode materials for polymer electrolyte fuel cells: Effect of ageing tests

Carbon supported Pt and Pt-Ni (1:1) nanoparticles were prepared by reduction of metal precursors with NaBH₄. XRD analysis indicated that only a small amount of Ni alloyed with Pt (Ni atomic fraction in the alloy about 0.05). The as-prepared catalysts were submitted to chronoamperometry (CA) measurements to evaluate their activity for the oxygen reduction reaction (ORR). CA measurements showed that the ORR activity of the as-prepared Ni-containing catalyst was higher than that of pure Pt. Then, their stability was studied by submitting these catalysts to durability tests involving either 30 h of constant potential (CP, 0.8 V vs. RHE) operation or repetitive potential cycling (RPC, 1000 cycles) between 0.5 and 1.0 V vs. RHE at 20 mV s⁻¹. After 30 h of CP operation at 0.8 V vs. RHE, loss of all non-alloyed Ni, partial dissolution of the Pt-Ni alloy and an increase of the crystallite size was observed for the Pt-Ni/C catalyst. The ORR activity of the Pt-Ni/C catalyst was almost stable, whereas the ORR activity of Pt/C slightly decreased with respect to the as-prepared catalyst. Loss of all non-alloyed and part of alloyed Ni was observed for the Pt-Ni/C catalyst following repetitive potential cycling. Conversely to the results of 30 h of CP operation at 0.8 V vs. RHE, after RPC the ORR activity of Pt-Ni/C was lower than that of both as-prepared Pt-Ni/C and cycled Pt/C. This result was explained in terms of Pt surface enrichment and crystallite size increase for the Pt-Ni/C catalyst.     

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.     

An efficient Co-N/C electrocatalyst for oxygen reduction facilely prepared by tuning cobalt species content

Transition metal and nitrogen co-doped carbon catalysts for the oxygen reduction reaction (ORR) have emerged as promising candidates to replace the expensive platinum catalysts but still remain a great challenge. Herein, a novel and efficient nitrogen-doped carbon material with metal cobalt co-dopant (Co–N/C) has been prepared by pyrolyzing porphyrin-based covalent organic polymer where Co is anchored. The optimized 10%-Co-N/C catalyst through facilely and efficiently tuning the cobalt content is carefully characterized by XRD, Raman, XPS, SEM and TEM for composition and microstructure analysis. This catalyst with only 0.56% Co exhibits an excellent ORR catalytic activity with a positive half-wave potential of 0.816 V (vs. RHE) in 0.1 M KOH solution, which is comparable to that of commercial Pt/C (20 wt%). Notably, the 10%-Co-N/C catalyst displays better electrochemical stability with only a loss of 5.1% of its initial current density in chronoamperometric measurement and also gives rise to stronger methanol tolerance than Pt/C. The good ORR catalytic behaviour for this catalyst may be attributed to the dispersion of the Co-N_X active sites via adjusting the contents of cobalt species in porous organic framework.     

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.     

ZIF-8 derived bimetallic Fe–Ni-Nanoporous carbon for enhanced oxygen reduction reaction

The development of highly efficient nοn-nοble meta? catalysts for (ОRR) in PEMFCs is at the heart of the research, yet their performance is not satisfactory. The Fe–N active sites enclosed in carbon matrix are generally agreed to be the most promising active sites for ORR. In view of this, further effort is made to increase the Fe–N active sites. Here we present the fabrication of novel FeNi bimetallic electrоcatalyst obtained from ZIF, which consists of FeNi nanоallоys incorporated in N-doped carbon (FeNi-NC) featuring carbon nanotubes and porous carbon demonstrates outstanding results for ОRR. The Fe–N and Ni–N active sites synergistically enhance the ORR activity of FeNi-NC catalyst. The FeNi-NC showed remarkable performance in KОH with the half-wave and onset potential of 0.89 V and 0.99 V vs RHE, respectively. This catalyst shows exceptional stability in methanol equivalent to Pt/C commercial. The FeNi-NC retained 71%, while Pt/C commercial retained only 59% of its original current density. The exceptional stability and activity might be associated with the interplay among FeNi active sites and N-doped carbon, the distinct nanо-structure made up of porous carbon and carbon nanotubes with a high graphitization degree.     

A microstructure tuning strategy on hollow carbon nanoshells for high-efficient oxygen reduction reaction in direct formate fuel cells

The microstructure of carbon supports for electrocatalysts plays a crucial role in dispersing active sites, establishing oxygen/ion transport channels, and thus determining the oxygen reduction reaction (ORR) activity. A facile and simple microstructure tuning strategy is adopted to synthesize hollow carbon nanoshells (CNSs) with tuneable microstructure in this study. The CNSs with expected macroporous (300–966 nm) and mesoporous (2–5 nm) structures were achieved by adjusting heating ramp rates during pyrolysis. The CNS prepared at 1 °C min⁻¹ (CNS-1) possesses a well-developed mesoporous/macroporous structure, which is conducive to dispersing iron phthalocyanine during the synthesis and establishing triple-phase interfaces in the catalyst layer during the ORR. Therefore, the electrocatalyst (Fe–N/CNS-1), derived from the CNSs-1, exhibits a 44 mV higher half-wave potential (0.879 V vs. RHE) in a rotating disk electrode and a 14% higher maximum power density (16.1 mW cm⁻²) in a membrane-less direct formate fuel cell than that of Pt/C. This study delivers a promising microstructure tuning strategy for carbon supports to construct high-efficient ORR electrocatalysts.     

Spinel oxides wrapped on electrospun carbon nanofibers: Superior electrocatalysts boosted by enhanced conductivity and rich oxygen vacancies

Spinel oxides have been considered as promising precious metal-free catalysts for oxygen reduction reaction (ORR). However, the poor intrinsic conductivity and moderate electrocatalytic performance hinder their practical applications. Hence, various strategies have been explored and reported in addressing the issues. Herein, an elaborate approach for enhancing the ORR performance of spinel NiCo₂O₄ is proposed, by combining the decoration of NiCo₂O₄ nanoparticles on electrospun carbon nanofibers and defect engineering with rich oxygen vacancies on NiCo₂O₄ nanoparticles through a facilely controlling on calcination circumstance, which could not only increase more active sites and improve the intrinsic catalytic activity, but also render an excellent stability for long-term operation. Thus, the as-prepared hybrid exhibits significantly improved ORR electrocatalytic performance, including a high limited current density of −5.8 mA cm⁻², a positively shifting of the onset potential at 0.88 V and half-wave potential at 0.76 V (vs. RHE). The performance of rechargeable Zn-air battery based on the as-prepared catalyst surpasses the one based on Pt/C catalyst significantly. This work can be also applied to other metal oxides based electrocatalysts, and then provided an avenue for the realization of metal-air batteries and fuel cells with high efficient and cost-effective.     

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.     

Cu-assisted induced atomic-level bivalent Fe confined on N-doped carbon concave dodecahedrons for acid oxygen reduction electrocatalysis

Atomically dispersed transition metals anchored on N-doped carbon have been successfully developed as promising electrocatalysts for acidic oxygen reduction reaction (ORR). Nonetheless, how to introduce and construct single-atomic active sites is still a big challenge. Herein, a novel concave dodecahedron catalyst of N-doped carbon (FeCuNC) with well confined atomically dispersed bivalent Fe sites was facilely developed via a Cu-assisted induced strategy. The obtained catalyst delivered outstanding ORR performance in 0.5 M H₂SO₄ media with a half-wave potential (E_1/2) of 0.82 V (vs reversible hydrogen electrode, RHE), stemming from the highly active bivalent Fe-N_x sites with sufficient exposure and accessibility guaranteed by the high specific surface area and curved surface. This work provides a simple but efficient metal-assisted induced strategy to tune the configurations of atomically dispersed active sites as well as microscopy structures of carbon matrix to develop promising PGM-free catalysts for proton exchange membrane fuel cell (PEMFC) applications.     

Stable composite of flower-like NiFe-layered double hydroxide nucleated on graphene oxide as an effective catalyst for oxygen reduction reaction

Nowadays, it is an urgent need but challenging to develop an efficient and resource-rich electrocatalysts with electrocatalysts activity for the oxygen reduction reaction (ORR) electrocatalyst. Therefore, we rationally designed and synthesized a unique 3-dimensional (3D) structure of flower-like NiFe-layered double hydroxide (NiFe-LDH) growing on graphene oxide (GO) with large surface area, widely-exposed active sites and good electrical conductivity, of which the weight percentage of GO in NiFe-LDH/GO was about 27.37%. Consequently, compared with pure NiFe-LDH (0.71 V (vs RHE), 95 mV dec⁻¹) in alkaline electrolyte, the NiFe-LDH/GO possesses a relatively high onset potential of 0.88 V (vs RHE) and a smaller Tafel slope of 82 mV dec⁻¹. Impressively, the prepared optimized NiFe-LDH/GO presents a highly stability than commercial Pt/C after stability testing due to strong interaction between graphene oxide and LDHs. In view of the above properties, these composite materials have better research prospects and open up a new opportunity for rational design.     

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.