NiCo alloy nanoparticles encapsulated in N-doped 3D porous carbon as efficient electrocatalysts for oxygen reduction reaction

A series of N-doped three dimensional porous carbons loaded with NiCo alloy nanoparticles (NiCo@NpCs) have been successfully fabricated by a template-assisted in-situ pyrolysis strategy and the ORR activities of different-concentration alloy supported N-doped carbons are systematically investigated. The optimized sample exhibits a positive half-wave potential of 0.78 V (vs. RHE), a high diffusion-limited current density (5.120 mA cm⁻²), and a high durability over 92%, which is superior to the Pt/C. The excellent activity and stability are mainly due to synergistic effect between carbon matrix and NiCo alloy. The N-doped porous carbon support with high surface area and good conductivity not only provides more active sites but also promotes electron transport and mass transfer process. Furthermore, the unique core-shelled structure NiCo@NpCs can effectively avoid the dissolution and corrosion of alloy particles and the surface peeling of particles during the catalyze reaction, which is beneficial to improving the activity and stability.     

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.     

Direct synthesis of nitrogen and phosphorus co-doped hierarchical porous carbon networks with biological materials as efficient electrocatalysts for oxygen reduction reaction

We described a process of the preparation of N, P co-doped hierarchical porous carbon by one-step pyrolysis of the chitosan/phytic acid (CS/PA) precursor without extra activation processes, and the nitrogen and phosphorus were successfully incorporated into the carbon framework. Experimentally, the best performance was identified with NPC-1000 which possessed the highest BET specific surface area of 1117.2 m² g^?1. This NPC-1000 showed a half-wave potential of 50 mV difference with commercial Pt/C, better tolerance to methanol and a superior stability comparable to commercial Pt/C catalyst. The results suggest that it is a simple, feasible, and economical route to synthesis of hierarchical porous carbon which can be used as metal-free catalysts for oxygen reduction.     

Facile synthesis of 3D hierarchical mesoporous Fe-C-N catalysts as efficient electrocatalysts for oxygen reduction reaction

A salt crystal-templating synthesis route is proposed to synthesize a Fe-N-C catalyst with well-controlled mesoporous structure. In the presence of glucose, NaCl-template can efficiently tune the porous structure of catalyst and help to improve the oxygen reduction reaction (ORR) activity. The optimized catalyst possesses a hierarchical mesopore size distribution, a high Brunauer-Emmett-Teller surface area (up to 911.56 m² g^?1) and homogeneous distribution of abundant active sites. As a result, the obtained catalyst shows a desirable ORR activity in alkaline medium (half-wave potential of 0.84 V and kinetic mass activity at 0.8 V of 24.95 A g^?1), high selectivity (electron transfer number >3.92), excellent long term durability (only 16 mV negative shift of half-wave potential after 5000 potential cycles in O₂-saturated 0.1 M KOH) and good tolerance to methanol. The enhanced electrochemical performance enables the proposed catalyst to be the promising electrocatalyst candidate to commercial Pt/C towards ORR.     

Trimetallic PtNiCo nanoflowers as efficient electrocatalysts towards oxygen reduction reaction

Nanostructures of PtNiCo alloy have been prepared using a simple solvothermal process followed by annealing at higher temperature and studied for electrochemical oxygen reduction reaction (ORR) kinetics. PtNiCo/C catalyst has demonstrated an interesting trend of enhancement in the ORR activity along with long-term durability. The specific activity of 2.47 mA cm^?2 for PtNiCo-16h/C (PtNiCo/C prepared at reaction time of 16 h) is ～12 times higher than that of Pt/C (0.2 mA cm^?2). Further, X-ray diffraction, transmission electron microscopy and X-ray photo electron spectroscopy studies have been carried out systematically to understand the phase formation, morphology along with surface defects and elemental analysis respectively. The durability of the catalyst was evaluated over 10,000 potential cycles using standard triangular potential scan in the lifetime regime. Interestingly, after 10k durability cycles, PtNiCo-16h/C electrocatalyst showed enhanced ORR activity (32% higher activity; Im@10k cycles = 0.716 A mg_Pt^?1) and stability compared to commercial Pt/C signifying the retention of Ni and Co due to higher lattice contraction in PtNiCo alloy electrocatalyst.     

Shaddock peel derived nitrogen and phosphorus dual-doped hierarchical porous carbons as high-performance catalysts for oxygen reduction reaction

Oxygen reduction reaction (ORR) plays a key role in the application of fuel cells. Here, we used shaddock peel to fabricate a set of N, P dual-doped hierarchical porous carbons, abbreviated as NPSPs, where the carbons were carbonized, activated and dual-doped via a simple one-step pyrolyzation. Contrast results indicate the contents of pyridinic-N, graphitic-N and P–C species increase with the rising of temperatures, and the temperature also affects the degree of graphitization, surface area, morphology, thus influences the ORR performance. More importantly, the NPSP-900 demonstrates an outstanding ORR activity with a comparable half-wave potential (0.83 V vs. RHE) and higher current density with respect to commercial Pt/C, following 4e transfer pathway. Our work illustrates that NPSP-900 is a promising cathode for fuel cells because of its simple preparation, waste utilization, excellent ORR performance, good methanol tolerance and superior stability.     

Porous carbonized egg white as efficient electrocatalyst for oxygen reduction reaction

Hierarchical porous carbonized egg white (EW) is synthesized and used as oxygen reduction reaction (ORR) catalyst. The typical EW that is carbonized at 650 °C (EW-650) possesses ultrahigh specific surface area of 1904 m² g^?1, large average pore diameter of 9.8 nm, high contents of doped heteroatoms (N, O and S), fairly high graphitization degree and dense defects, corresponding to dense active sites and excellent transportation of both mass and electrons. Therefore, the EW-650 shows higher activity than commercial Pt/C for ORR in both alkaline and acidic media even at higher mass loadings, with excellent cyclic stability. The effects of reaction temperature and electrolyte concentration on ORR activity are also studied. It is found that appropriate temperature and electrolyte concentration speed up ORR kinetics, ensure higher oxygen solubility and favor mass transportation.     

MnO nanoparticles loaded on three-dimensional N-doped carbon as highly efficient electrocatalysts for the oxygen reduction reaction in alkaline media

It is very important to develop non-noble metal electrocatalysts for oxygen reduction reaction (ORR) to replace noble metal electrocatalysts to promote the large-scale application of fuel cells. Here, three-dimensional (3D) N-doped carbon supported MnO nanoparticles (MnO/NC) are prepared by two-step pyrolysis method. The MnO/NC performs excellent catalytic activity comparable to 20% Pt/C for ORR, for instance, a positive onset potential (0.92 V), half-wave potential (0.82 V) and peak potential (0.76 V). The MnO/NC shows a strong tolerance to methanol and long-term stability in an alkaline media. The high ORR activity of MnO/NC owes to its unique property of fast electron transport, high specific surface areas and the synergistic effect between MnO and 3D NC support. This study projects an innovative strategy to construct electrocatalysts of 3D structure composites, which is expected to offer efficient non-noble metal electrocatalysts for ORR.     

Duckweed derived nitrogen self-doped porous carbon materials as cost-effective electrocatalysts for oxygen reduction reaction in microbial fuel cells

Cost-effective metal-free electrocatalysts for oxygen reduction reaction were incredible significance of improvement about microbial fuel cells. In this research, a novel nitrogen self-doped porous carbon material is effectively inferred with KOH activation from a natural and renewable biomass, duckweed. Self-doped nitrogen in carbon matrix of nitrogen-doped porous carbon at 800 °C provides abundant active sites for oxygen reduction and improves the oxygen reduction kinetics significantly. Moreover, the porous structure of nitrogen-doped porous carbon at 800 °C encourages the transition of electrolyte and oxygen molecules throughout the oxygen reduction reaction. Oxygen on the three-phase boundary is reduced to water according to a four-electron pathway on nitrogen-doped porous carbon electrocatalyst. The single-chamber microbial fuel cell with nitrogen-doped porous carbon as electrocatalyst achieves comparable power density (625.9 mW m⁻²) and better stability compared to the commercial Pt/C electrocatalyst. This simple and low-cost approach provides a straightforward strategy to prepare excellent nitrogen-doped electrocatalyst derived from natural and renewable biomass directly as a promising alternate to precious platinum-based catalysts in microbial fuel cells.     

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.     

Astragali Radix-derived nitrogen-doped porous carbon: An efficient electrocatalyst for the oxygen reduction reaction

The development of biomass-derived nitrogen-doped porous carbons (NPCs) for the oxygen reduction reaction (ORR) is important for sustainable energy systems. Herein, NPCs derived from Astragali Radix (AR) via a cost-effective strategy are reported for the first time. The as-prepared AR-950-5 catalyst shows a stacked layer-like structure and porosity. Notably, the optimized AR-950-5 delivers catalytic activity comparable to that of commercial Pt/C (C-Pt/C), with high onset potential, positive half-wave potential and large limiting current density. It also displays superior long-term stability and methanol tolerance for ORR. This work will pave the way for a new approach in the development of highly active and low-cost NPCs for fuel cells.     

Pore-rich iron-nitrogen-doped carbon nanofoam as an efficient catalyst towards the oxygen reduction reaction

Developing cost-effective electrocatalysts is crucial for oxygen reduction reactions. In this work, a highly active iron-nitrogen co-doped carbon nanofoam is proposed and developed via a facile salt-assisted pyrolysis process of chitooligosaccharides. i) Chitooligosaccharides, a nitrogen-rich polymer with high water solubility and high thermostability, induce a coordination reaction between iron ions and amino/hydroxyl groups, forming large active sites. ii) FeCl₃/KCl salt, acting as a template, etching agent and catalyst for graphitization, facilitates the formation of pore-rich carbon, leading to enhanced mass transfer and electronic conduction. It has been found that this iron-nitrogen co-doped carbon nanofoam presents competitive activity over commercial Pt/C, as follows: i) a high onset potential approximately 0.965 V, ii) strong durability with a current retention rate of 88% after 30000 s, and iii) excellent fuel tolerance to methanol, ethanol and formate. This work provides a simple, low-cost and environmentally friendly method to prepare iron-nitrogen co-doped carbon materials that has great potential to be extended to other catalysts for energy-related 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.     

Pt nanodendrites anchored on bamboo-shaped carbon nanofiber arrays as highly efficient electrocatalyst for oxygen reduction reaction

In order to improve the Pt utilization and enhance their catalytic performance in fuel cells, a novel composite electrode composed of single-crystalline Pt nanodendrites and support constructed by bamboo-shaped carbon nanofiber arrays (CNFAs) on carbon paper, is reported. This electrode is designed by growing vertically CNFAs on carbon paper via plasma enhanced chemical vapor deposition, followed by the direct synthesis of Pt nanodendrites using a simple surfactant-free aqueous solution method. Electron microscopy studies reveal that the Pt nanodendrites are uniformly high dispersed and anchored on the surface of CNFAs. Electrochemical measurements demonstrate that the resultant electrode exhibits higher electrocatalytic activity and stability for oxygen reduction reaction than commercial Pt/C catalyst, suggesting its potential application in fuel cells.     

Fe2O3-encapsulated and Fe-Nx-containing hierarchical porous carbon spheres as efficient electrocatalyst for oxygen reduction reaction

It is highly desirable to develop high-efficiency non-precious electrocatalysts toward oxygen reduction reaction (ORR). In this work, Fe₂O₃-encapsulated and Fe-Nx-containing porous carbon spheres (Fe₂O₃/N-MCCS) with unique multi-cage structures and high specific surface area (1360 m² g^?1) are fabricated. The unique porous structure of Fe₂O₃/N-MCCS ensures fast transportation of oxygen during ORR. The combined effect of Fe₂O₃ nanoparticles and Fe-Nx configurations endows Fe₂O₃/N-MCCS (E_1/2 = 0.837 V vs. RHE) with superior ORR activity and methanol tolerance to Pt/C. And, Fe₂O₃/N-MCCS exhibits better stability than nitrogen-modified carbon. The characterization results of Fe₂O₃/N-MCCS after long-term test reveals its excellent structural stability. Impressively, zinc-air battery based on Fe₂O₃/N-MCCS showed a peak power density of 132.4 mW cm^?2 and a specific capacity of 797 mAh g^?1, respectively.     

Additional doping of phosphorus into polypyrrole functionalized nitrogenous carbon nanotubes as novel metal-free oxygen reduction electrocatalyst in alkaline solution

Novel phosphorus-doped polypyrrole functionalized nitrogenous carbon nanotubes (P/NCNTs) was developed for the first time as metal-free electrocatalyst for enhancing the oxygen reduction reaction (ORR) activity in alkaline medium. The P/NCNTs was successfully synthesized by pyrolyzing PPy and triphenylphosphane (TPP) under N₂, using pyrrole as carbon and nitrogen precursors, TPP as phosphorus precursor. Various characterizations such as transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectra, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) reveal that the P/NCNTs material has covalently bound P atoms with carbon framework, which can introduce defect sites and can induce uneven charge distribution. Moreover, the content of pyridine N increased after P-doping, which is of great significance in improving the ORR activity. The electrochemical behavior of the resultant material shows that the P/NCNTs has much enhanced electroactivity and better stability for ORR. Additionally, a direct four-electron pathway occurred efficiently on P/NCNTs modified electrode. These enhanced performances indicate that P/NCNTs catalyst may be an excellent cathode catalyst for ORR.     

Electrospun iron and nitrogen co-containing porous carbon nanofibers as high-efficiency electrocatalysts for oxygen reduction reaction

One-dimensional carbon nanofibers hold great promise to be potential candidates as high-efficiency electrocatalysts for oxygen reduction reaction (ORR). However, the catalysts in powder form always aggregate when preparing catalyst layer, which significantly hinders the extensive application. Herein, we report the facile synthesis of iron and nitrogen co-containing porous carbon nanofibers derived from PAN nanofibers existing as a flexible film via the electrospinning method, which could avoid aggregation when fabricating catalyst layer of fuel cells. The Fe–N/N–C NFs exhibit onset potential of 0.95 V and the half-wave potential of 0.78 V in 0.1 M KOH solution, suggesting superior electro-catalytic activity for ORR. Meantime, for Fe–N/N–C NFs catalyst, it shows a nearly four electron transferring process and the current density only decreases by 14.2% after 40,000 s. This easy and facile method provides a new idea for synthesis of oxygen reduction reaction with high-activity and good-stability.     

Electrochemical aspects of Co3O4 nanorods supported on the cerium doped porous graphitic carbon nitride nanosheets as an efficient supercapacitor electrode and oxygen reduction reaction electrocatalyst

Herein, the electrochemical performance of Ce-PGCN,NS/Co₃O₄ as a metal-free ORR electrocatalyst and supercapacitor electrode was investigated. FESEM, TEM, BET, FTIR, XRD, EDX, FTIR, and Raman tests were used to characterize the synthesized electrocatalysts. For ORR measurements, voltammetry (CV, LSV, Choronoamperometry) and EIS tests were used to investigate the electrocatalytic activity of the electrocatalysts. And for supercapacitor measurements, the CV and GCD tests were conducted to examine the electrode's capacitance. The results of the voltammetry tests show that Ce-PGCN,NS/Co₃O₄ with an onset potential of −0.027 V, selecting four-electron pathway (n = 3.86), Tafel slope of 137 mV/dec, charge transfer of 570 Ω, and high durability in alkaline media (0.1 M KOH) show an excellent electrochemical performance as an ORR electrocatalyst and can be introduced as a promising substitution for commercial Pt/C catalysts. On the other hand, the results of CV in supercapacitor mode and GCD reveal that Ce-PGCN,NS/Co₃O₄ electrode with the specific capacitance of 789 F g⁻¹ at the current density of 1 A g⁻¹ and high stability in alkaline media (2 M KOH), have superior performance as a supercapacitor electrode than other electrode based on the g-C₃N₄. Also, it is observed that converting bulk g-C₃N₄ to PGCN,NS, doping Cerium atoms on the structure of the PGCN,NS, and adding Co₃O₄ nanorods impact the electrocatalytic activity of g-C₃N₄ positively.     

Mn3O4 nanosheets coated on carbon nanotubes as efficient electrocatalysts for oxygen reduction reaction

MnO-MnC_x coated carbon nanotubes (MnO/MnC_x/CNTs) nanocomposites were prepared by a one-pot deposition method. The coating consisted of MnO, Mn₅C₂, Mn₁₅C₄ and Mn₂₃C₆ was formed on the surface of CNTs by heating a mixture of Mn particles and CNTs at 600 °C for 40 min under vacuum. Then after heated MnO/MnC_x/CNTs in air at 350 °C for 2 h, MnO nanoparticles were partially converted to Mn₃O₄ nanosheets. Then Mn₃O₄-MnC_x coated carbon nanotubes (Mn₃O₄/MnC_x/CNTs) composed of interconnected nanosheets structure were successfully synthesized by a two-step method of one-pot deposition and heat post-treatment. The Mn₃O₄/MnC_x/CNTs showed better oxygen reduction reaction performance in alkaline condition than MnO/MnC_x/CNTs and pristine CNTs. Besides, the formed MnC_x (Mn₅C₂ and Mn₂₃C₆) by one-pot deposition method provided a strong interface bonding between Mn₃O₄ and CNTs, leading to improved stability of Mn₃O₄/MnC_x/CNTs as an electrode material.     

Carbon supported Pt-Y electrocatalysts for the oxygen reduction reaction

Carbon supported Pt₃Y (Pt₃Y/C) and PtY (PtY/C) were investigated as oxygen reduction reaction (ORR) catalysts. After synthesis via reduction by NaBH₄, the alloy catalysts exhibited 10-20% higher mass activity (mA mg_Pt⁻¹) than comparably synthesized Pt/C catalyst. The specific activity (μA cm_Pt⁻²) was 23 and 65% higher for the Pt₃Y/C and PtY/C catalysts, respectively, compared to Pt/C. After annealing at 900 °C under a reducing atmosphere, Pt₃Y/C-900 and PtY/C-900 catalysts showed improved ORR activity; the Pt/C and Pt/C-900 (Pt/C catalyst annealed at 900 °C) catalysts exhibited specific activities of 334 and 393 μA cm_Pt⁻², respectively, while those of the Pt₃Y/C-900 and PtY/C-900 catalysts were 492 and 1050 μA cm_Pt⁻², respectively. X-ray diffraction results revealed that both the Pt₃Y/C and PtY/C catalysts have a fcc Pt structure with slight Y doping. After annealing, XRD showed that more Y was incorporated into the Pt structure in the Pt₃Y/C-900 catalyst, while the PtY/C-900 catalyst remained unchanged. Although these results suggested that the high ORR activity of the PtY/C-900 catalyst did not originate from Pt-Y alloy formation, it is clear that the Pt-Y system is a promising ORR catalyst which merits further investigation.