Novel multi walled carbon nanotube based nitrogen impregnated Co and Fe cathode catalysts for improved microbial fuel cell performance

For application in a microbial fuel cell (MFC), transition metal and nitrogen co-doped nanocarbon catalysts were synthesised by pyrolysis of multi-walled carbon nanotubes (MWCNTs) in the presence of iron- or cobalt chloride and nitrogen source. For the physicochemical characterisation of the catalysts, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) was used. The results obtained by rotating disk electrode (RDE) method showed an extraordinary electrocatalytic activity of these catalysts towards oxygen reduction reaction (ORR) in neutral media, which was also confirmed by the MFC results. The Co-N-CNT and Fe-N-CNT cathode catalysts exhibited maximum power density of 5.1 W m^?3 and 6 W m^?3, respectively. Higher ORR activity and improved electric output in the MFC could be attributed to the formation of the active nitrogen-metal centers. All findings suggest that these materials can be used as potential cathode catalysts for ORR in MFC to replace expensive noble-metal based materials.     

X-ray photoemission spectroscopy analysis of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells

We report on the electronic structure of three different types of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells observed by hard X-ray photoemission spectroscopy. Prepared samples are derived from: (1) melamine and poly(furfuryl alcohol), (2) nitrogen-doped carbon black and (3) cobalt phthalocyanine and phenolic resin. C 1s spectra show the importance of sp² carbon network formation for the oxygen reduction reaction (ORR) activity. N 1s spectra of the carbon-based cathode catalysts are decomposed into four components identified as pyridine-like, pyrrole- or cyanide-like, graphite-like, and oxide nitrogen. Samples having high oxygen reduction reaction activity in terms of oxygen reduction potential contain high concentration of graphite-like nitrogen. O 1s spectra are similar among carbon-based cathode catalysts of different oxygen reduction reaction activity. There is no correlation between the ORR activity and oxygen content. Based on a quantitative analysis of our results, the oxygen reduction reaction activity of the carbon-based cathode catalysts will be improved by increasing concentration of graphite-like nitrogen in a developed sp² carbon network.     

High-efficiency copper-based electrocatalysts for oxygen electroreduction by heating metal-phthalocyanine at superhigh temperature

The highly efficient Cu-based ORR catalysts (Cu–N–C) were obtained by the pyrolysis of mesoporous KIT-6 silica-supported phthalocyanines at superhigh temperature (1000 °C). The prepared Cu–N–C catalyst was demonstrated as one of the best Cu-based electrocatalysts for ORR, with 0.82 V half-wave potential in 0.1 M KOH and 0.72 V half-wave potential in 0.1 M HClO₄. It showed the competitive ORR activity to high-performance Fe- or Co-based carbon catalysts. Moreover, the ORR catalytic performance of Cu–N–C could be further enhanced by co-doping few Fe species (Fe–Cu–N–C) into the carbon framework. It revealed about 30 mV higher half-wave potential and better stability than Cu–N–C catalyst in both alkaline and acidic media. Cu–N–C and Fe–Cu–N–C electrocatalysts could be produced at a scale of over 15 g by facilely enlarging the amount of phthalocyanine precursors. The high-efficiency ORR performance and scalable synthesis of Cu–N–C and Fe–Cu–N–C catalysts enabled them to be the potential substitutes to Pt-based electrocatalyst for ORR.     

Electrocatalysis of oxygen reduction when varying the mass ratio of metal nanoparticles to carbon support for catalysts with a 10 to 10 to 80 mol% of Pt and Pd on Ag

The reduction of total Pt-loading in a cathode catalyst without sacrificing performance is one of the key objectives for the large-scale commercialization of proton exchange membrane fuel cell (PEMFC) technology. A core-shell type nanostructured catalyst with a Pt-loading 20 times lower than a commercial catalyst is demonstrated herein to be more active for the electrocatalysis of the oxygen reduction reaction (ORR) in acid electrolyte. The weight ratio of metal nanoparticles on carbon support is the key to achieving the highest ORR activity in a series of silver-based catalysts, all with 10 mol percent of Pt and 10 mol percent of Pd over 80 mol percent of silver (Ag) and supported on untreated Vulcan carbon to form an electrocatalyst (Ag@Pt₁₀Pd₁₀/C) with either 5, 10, 20 or 30 wt% of total metals on carbon; which correspond to a Pt concentration around 1, 2, 3 and 5 wt%, respectively. All metal nanostructures on carbon show a similar morphology, size and structure. Thin films of these four Ag@Pt₁₀Pd₁₀/C catalysts on rotating disk electrodes (TF-RDEs) all shown a 4-electrons pathway for the ORR and give higher exchange current densities (j_o > 3.8 mA/cm²) than a commercial Etek Pt₂₀/C catalyst (j_o = 2.4 mA/cm²). The Ag@Pt₁₀Pd₁₀/C catalyst with 5 wt% of total metals (1 wt% of Pt) on carbon gives the best electrocatalysis; reducing molecular oxygen to water two times faster and generating 25% higher current per milligram of platinum (mass activity) than the commercial catalyst (Pt₂₀/C). Therefore, the Ag@Pt₁₀Pd₁₀/C catalyst with 5 wt% of total metals is a new catalyst for ORR for a PEMFC with a lower Pt loading and cost.     

Metallic iron doped vitamin B12/C as efficient nonprecious metal catalysts for oxygen reduction reaction

The development of efficient nonprecious metal catalysts for oxygen reduction reaction (ORR) is crucial but challenging. Herein, one simple and effective strategy is developed to synthesize bimetallic nitrogen-doped carbon catalysts by pyrolyzing Fe-doped Vitamin B12 (VB12) supported carbon black (Fe-VB12/C). A typical Fe₂₀-VB12/C catalyst with a nominal iron content of 20 wt% pyrolyzed at 700 °C exhibits remarkably ORR activity in alkaline medium (half-wave potential of 0.88 V, 10 mV positive than that of commercial Pt/C), high selectivity (electron transfer number > 3.93), excellent stability (only 6 mV negative shift of half-wave potential after 5000 potential cycles) and good methanol-tolerance. The superior ORR activity of the composite is mainly attributed to the improved mesoporous structure and co-existence of abundant Fe-N_x and Co-N_x active sites. Meanwhile, the metallic Fe are necessary for the improved ORR activity by means of the interaction of metallic Fe with neighboring active sites.     

Iron and cobalt containing electrospun carbon nanofibre-based cathode catalysts for anion exchange membrane fuel cell

The use of Pt-based cathode catalyst materials hinders the widespread application of anion exchange membrane fuel cells (AEMFCs). Herein, we present a non-precious metal catalyst (NPMC) material based on pyrolysed Fe and Co co-doped electrospun carbon nanofibres (CNFs). The prepared materials are studied as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts in alkaline and acidic environments. High activity towards the ORR in alkaline solution indicated the suitability of the prepared NPMCs for the application at the AEMFC cathode. In the AEMFC test, the membrane-electrode assembly bearing a cathode with the nanofibre-based catalyst prepared with the ionic liquid (IL) (Fe/Co/IL–CNF–800b) showed the maximum power density (P_max) of 195 mW cm⁻², which is 78% of the P_max obtained with a commercial Pt/C cathode catalyst. Such high ORR electrocatalytic activity was attributed to the unique CNF structure, high micro-mesoporosity, different nature of nitrogen species and metal-N_x active centres.     

The supporting of Co2(OH)PO4 onto N,P Co-Doped graphene via an in-situ hydrothermal assembly synthesis for efficient oxygen reduction reaction

Developing efficient and durable non-noble catalysts toward oxygen reduction reaction (ORR) is an ongoing challenge. Herein, a highly efficient ORR catalyst (Co-NPG) is explored by assembling Co₂(OH)PO₄ on conductive nitrogen, phosphate co-doped graphene (NPG) via an in-situ hydrothermal process. The graphene oxide matrix ammoniated by ethylenediamine not only constructs stable building blocks for hosting active sites, but also induces strong interaction between assembled cobalt-based nanoparticles. Morphology characterizations demonstrate the formation of the bulk-like structure with rough surface for the hybrid. Electrochemical measurements confirm this designed catalyst displays more efficient ORR performance than the un-ammoniated graphene oxide based one, and even comparable to that of 20 wt% Pt/C under the identical experimental conditions. The high ORR activity of the hybrid originates from the joint effects of the four aspects: first, the ammoniated graphene oxide tends to induce stronger NPs interaction than graphene oxide due to polarization, causing higher electronic conductivity and resulting in orientated growth; second, the N and P co-doping effects modulate the electronic structure of graphene, exposing more defects; third, the hybrid employs a high specific BET surface area and mesoporous characteristics, which afford quick mass transport during the ORR process; last, the synergistic coupling between the formed Co₂(OH)PO₄ and NPG plays a critical role.     

A melamine formaldehyderesin route to in situ encapsulate Co2O3 into carbon black for enhanced oxygen reduction in alkaline media

Enhancing the activity and stability of the non-precious metal catalyst (NPMC) for oxygen reduction reaction (ORR) is vital for the commercialization of fuel cells. Herein, we put forward a method in which the melamine formaldehyderesin was used as a precursor to encapsulate in situ Co₂O₃ into carbon black to form Co₂O₃@MF-C catalysts. The prepared catalysts were characterized by TEM, XRD, XPS, BET, and Raman spectroscopy. The electrocatalytic activity was measured by using rotating disk electrode (RDE) voltammetry. The Co₂O₃@MF-Cs shows outstanding electrocatalytic activity in alkaline solution compared with the commercial Pt/C catalyst. The 20%Co₂O₃@MF-C-650 shows the highest activity for ORR and its initial reduction potential and half-wave potential reach 1.01 V and 0.94 V, respectively, in 0.1 M KOH solution. The prepared catalysts also follow the 4-electron pathway ORR process both in alkaline and in acid conditions.     

Highly efficient and ORR active platinum-scandium alloy-partially exfoliated carbon nanotubes electrocatalyst for Proton Exchange Membrane Fuel Cell

Oxygen reduction reaction (ORR) in Proton Exchange Membrane Fuel Cell (PEMFC) is the most sluggish reaction, which impedes the performance and commercialization of PEMFC. Platinum-based alloys show higher ORR activity than Pt and it is suggested by density functional theory calculations that Pt₃Sc alloy has high stability and higher ORR activity due to filling the metal d-bands and lowers binding energy of the oxygen species respectively. Herein, we report Pt₃Sc alloy nanoparticles (NPs) dispersed over partially exfoliated carbon nanotubes (PECNTs) as a cathode catalyst for single-cell measurements of PEMFC where Pt₃Sc alloy shows a lower binding energy towards oxygen and facilitates ORR with much faster kinetics. The ORR activity of Pt₃Sc/PECNTs electrocatalyst, investigated by cyclic voltammetry, Rotating Disk electrode (RDE) and Rotating Ring Disk electrode (RRDE), shows the higher mass activity and lower H₂O₂ formation than the commercial catalyst Pt/C-TKK. Accelerated Durability Tests (ADT) was performed to evaluate the stability of catalysts in acidic medium. In single-cell measurements, Pt₃Sc/PECNTs cathode catalyst exhibits a power density of 760 mW cm⁻² at 60 °C. Our study gives an important insight into the design of a novel ORR electrocatalyst with an excellent stability and high power density of PEMFC.     

Nitrogen doped mesoporous carbon supported Pt electrocatalyst for oxygen reduction reaction in proton exchange membrane fuel cells

Nitrogen doped mesoporous carbons are employed as supports for efficient electrocatalysts for oxygen reduction reaction. Heteroatom doped carbons favour the adsorption and reduction of molecular oxygen on Pt sites. In the present work, nitrogen doped mesoporous carbons (NMCs) with variable nitrogen content were synthesized via colloidal silica assisted sol-gel process with Ludox-AS40 (40 wt% SiO₂) as hard template using melamine and phenol as nitrogen and carbon precursors, respectively. The NMC were used as supports to prepare Pt/NMC electrocatalysts. The physicochemical properties of these materials were studied by SEM, TEM, XRD, BET, TGA, Raman, XPS and FTIR. The surface areas of 11 wt% (NMC-1) and 6 wt% (NMC-2) nitrogen doped mesoporous carbons are 609 m² g^?1 and 736 m² g^?1, respectively. The estimated electrochemical surface areas for Pt/NMC-1 and Pt/NMC-2 are 73 m² g^?1 and 59 m² g^?1, respectively. It is found that Pt/NMC-1 has higher ORR activity with higher limiting current and 44 mV positive onset potential shift compared to Pt/NMC-2. Further, the fuel cell assembled with Pt/NMC-1 as cathode catalyst delivered 1.8 times higher power density than Pt/NMC-2. It is proposed that higher nitrogen content and large pyridinic nitrogen sites present in NMC-1 support are responsible for higher ORR activity of Pt/NMC-1 and high power density of the fuel cell using Pt/NMC-1 cathode electrocatalyst. The carbon support material with high pyridinic content promotes the Pt dispersion with particle size less than 2 nm.     

High-performance direct ethanol fuel cell using nitrate reduction reaction

In this study, we propose a high-performance direct ethanol fuel cell (DEFC) using nitrate reduction reaction with a carbon felt electrode (DEFC-HNO₃) instead of oxygen reduction reaction (ORR) on a Pt catalyst (DEFC-O₂). The activation energy for the nitrate reduction reaction on the carbon electrode is found to be relatively low at ～14.2 kJ mol^?1, compared to the ORR. By using the nitrate reduction reaction at the cathode and oxidation of ethanol as a fuel at the anode, the DEFC shows a significantly high open circuit voltage of 0.85 V and two-fold maximal power density of 68 mW cm^?2 at 80 °C, compared to the DEFC-O₂, due to the significantly fast reaction rate of the nitrate reduction reaction.     

Enhancement of oxygen reduction activity with addition of carbon support for non-precious metal nitrogen doped carbon catalyst

An improved synthesis scheme of non-precious metal N-doped carbon catalysts for oxygen reduction reaction is reported. The non-precious metal N-doped carbon catalysts were prepared by pyrolysis of the mixture (phenol resin, Ketjen black carbon support and cobalt phenanthroline complex). The drastic improvement of distribution state of Ketjen black supported non-precious metal N-doped carbon catalysts was observed by means of transmission electron microscopy (TEM). In addition, the non-precious metal N-doped carbon catalyst synthesized with Ketjen black carbon support showed much higher oxygen reduction reaction (ORR) activity relative to unsupported non-precious metal N-doped carbon catalyst in O₂-saturated 0.5 mol l⁻¹ H₂SO₄ at 35 °C. Moreover, the highest ORR activity was obtained with addition of optimum amount of Ketjen black carbon support was thirtyfold compared to unsupported non-precious metal N-doped carbon catalyst at 0.7 V. Similarly, the performance of a polymer electrolyte fuel cell (PEFC) using the non-precious metal N-doped carbon catalyst as the cathode electrode catalyst was obviously better than that of the non-precious metal N-doped carbon catalyst before optimization. Microstructure, specific surface area and surface composition of the non-precious metal N-doped carbon catalysts were analyzed by XRD, XPS and BET measurement with nitrogen physisorption, respectively.     

FeCo alloys in-situ formed in Co/Co2P/N-doped carbon as a durable catalyst for boosting bio-electrons-driven oxygen reduction in microbial fuel cells

Non-noble metal catalyst with high catalytic activity and stability towards oxygen reduction reaction (ORR) is critical for durable bioelectricity generation in air-cathode microbial fuel cells (MFCs). Herein, nitrogen-doped (iron-cobalt alloy)/cobalt/cobalt phosphide/partly-graphitized carbon ((FeCo)/Co/Co₂P/NPGC) catalysts are prepared by using cornstalks via a facile method. Carbonization temperature exerts a great effect on catalyst structure and ORR activity. FeCo alloys are in-situ formed in the catalysts above 900 °C, which are considered as the highly-active component in catalyzing ORR. AC-MFC with FeCo/Co/Co₂P/NPGC (950 °C) cathode shows the highest power density of 997.74 ± 5 mW m^?2, which only declines 8.65% after 90 d operation. The highest Coulombic efficiency (23.3%) and the lowest charge transfer resistance (22.89 Ω) are obtained by FeCo/Co/Co₂P/NPGC (950 °C) cathode, indicating that it has a high bio-electrons recycling rate. Highly porous structure (539.50 m² g^?1) can provide the interconnected channels to facilitate the transport of O₂. FeCo alloys promote charge transfer and catalytic decomposition of H₂O₂ to ?OH and ?O₂^?, which inhibits cathodic biofilm growth to improve ORR durability. Synergies between metallic components (FeCo/Co/Co₂P) and N-doped carbon energetically improve the ORR catalytic activity of (FeCo)/Co/Co₂P/NPGC catalysts, which have the potential to be widely used as catalysts in MFCs.     

Composition effect of oxygen reduction reaction on PtSn nanorods: An experimental and computational study

In the development of emerging energy, proton exchange membrane fuel cells (PEMFCs) have been widely researched. Nevertheless, because of the high price and scarcity of Pt and its sluggish kinetics for oxygen reduction reaction (ORR), the preparation of highly effective cathode catalysts becomes one of the main challenges for PEMFCs in the practical application. In this study, carbon supported PtSn nanorods (NRs) with metal loading of 50 wt % and different Pt/Sn ratios of 80/20, 65/35 and 50/50 have been prepared by formic acid reduction method. The ORR performance of the catalysts can be promoted synergistically by one-dimensional (1-D) NRs and is varied with the Pt/Sn ratios. The experimental and computational efforts reveal that the Sn addition can lower the unoccupied d-band of neighboring Pt and the oxygen-containing species (OCS) on Sn can suppress their oxidation through the repulsion effect. Consequently, PtSn electrodes show the improved ORR activity; Pt₅₀Sn₅₀ with the highest Sn content results in the highest mass activity. On the other hand, the negatively charged OCS on Sn attracts the positively charged Pt and destructs the structures of PtSn NRs. Accordingly, Pt₈₀Sn₂₀ with the lowest Sn contain has the highest concentration of 1-D PtSn NRs and shows the best stability in the accelerated durability test (ADT). Our results clarify the mechanism of ORR on PtSn electrodes and suggest the importance of the precise control of atomic ratios on PtSn catalysts for the practical purpose. The findings open new perspectives about the origins of the activity and stability of the PtSn catalysts, especially for 1-D catalysts.     

Poison tolerance of non-precious catalyst towards oxygen reduction reaction

Oxygen reduction reaction (ORR) plays an important role in microbial fuel cell (MFC) performance. But the poison ions in wastewater may have a considerable effect on the activity of ORR catalysts. In this paper, we herein investigated the effect of typical NH₄⁺ and S^2? ions on the activity of different ORR catalysts, such as biomass derived carbon (bamboo charcoal (BC)), nitrogen doped graphene (N-G), iron/nitrogen co-doped graphene (Fe/N-G) and Pt/C catalysts. The results showed that the ORR catalytic activity was decreased in the presence of both NH₄⁺ and S^2? ions. In detail, the NH₄⁺ ion only had a slight and similar effect on the catalysts. However, the effect of S^2? on catalyst activity was much more negative, compared to that of NH₄⁺. Notably, the BC, N-G and Fe/N-G catalysts exhibited a higher poison tolerance than Pt/C, indicating that BC, N-G and Fe/N-G catalysts could serve as poison tolerance ORR catalysts in both of NH₄⁺ and S^2? condition.     

Taming transition metals on N-doped CNTs by a one-pot method for efficient oxygen reduction reaction

Various transition metals have been incorporated into nitrogen-doped carbon nanotubes (M-N-C/CNT, M = Fe, Co, Mn, and Ni) via a one-pot method using dopamine as nitrogen source and metal salts as precursors for oxygen reduction reaction (ORR). Raman spectra and XRD patterns of the catalysts were collected to characterize the graphitization degree and metal state. XPS was employed to determine atom state and element fraction. The electrochemical performance of the catalysts for ORR were evaluated in alkaline media at ?0.8 V to 0.2 V. The E_onset and E_1/2 with the values of ?100 mV and ?170 mV (vs Ag/AgCl) are achieved on Mn-N-C/CNT-800. The superior selectivity toward the 4e^? pathway are obtained on Mn-N-C/CNT-800 and Co-N-C/CNT-800 with the transferred electron numbers per O₂ molecule of 4.12 and 3.94, respectively. Results show that the states of doped transition metal play a key role on determining ORR performance. The electron transfer number of Ni-N-C/CNT at ?0.5 V is increased from 3.22 (Ni-N-C/CNT-800) to 3.99 (Ni-N-C/CNT-600) when the metallic Ni has been eliminated at lower pyrolysis temperature.     

Encapsulated iron-based oxygen reduction electrocatalysts by high pressure pyrolysis

Non-precious metal catalysts (NPMCs) are candidate materials to replace platinum for proton exchange membrane fuel cells (PEMFCs). Herein we reported a type of iron-based NPMCs prepared by high pressure pyrolysis for the oxygen reduction reaction (ORR) in acidic media. The catalysts are in form of carbon microspheres in a sub-microscale consisting of iron-containing nanoparticles encapsulated by graphitic layers. By tailoring temperatures and duration of pyrolysis, the best ORR catalyst was achieved at 700 °C and 75 min, which exhibits an onset potential of 0.85 V at 0.1 mA cm^?2 and a half-wave potential of 0.72 V in acid media. After 10,000 potential cycles, only 25 mV shift of half-wave potential is observed showing excellent stability. An analogue material prepared from nitrogen-free precursors shows significant electrochemical activity though it is much lower than that from the nitrogen containing precursors and can be improved by post treatment in ammonia. These results indicate the contribution to the catalysis from surface nitrogen functionalities and encapsulated metal-containing nanoparticles.     

CoFe2O4 nanoparticles anchored on N/S co-doped mesoporous carbon spheres as efficient bifunctional electrocatalysts for oxygen catalytic reactions

The development of a promising bifunctional electrocatalyst for oxygen catalytic reactions such as the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly desirable owing to the sluggish kinetics that limit these reactions. In this study, CoFe₂O₄ nanoparticles anchored on nitrogen and sulfur co-doped mesoporous carbon spheres (CFO/NS-MCS) were prepared as nonprecious metal catalysts, using a facile pyrolysis and hydrothermal treatment process. The co-doping of N and S into the carbon spheres was achieved using thiourea, which played a key role in the bimetallic covalent coupling in the NS-MCS. The as-prepared CFO/NS-MCS exhibited a more promising ORR catalytic performance compared with that of commercial Pt/C, which was attributed to the presence of highly active sites. Remarkably, the CFO/NS-MCS catalysts also showed a high OER catalytic performance comparable with that of commercial RuO₂/C in the aspects of onset potential and Tafel slope, and showed a better durability for oxygen catalytic reactions in an alkaline solution. The approach indicated in this research can be applied to develop high-performance electrocatalysts for practical implementation in energy storage and conversion devices.     

Facile synthesis of efficient core-shell structured iron-based carbon catalyst for oxygen reduction reaction

Controlled synthesis of efficient core-shell non-precious metal catalysts for oxygen reduction reaction (ORR) is undoubtedly crucial but challenging for the extensive application of fuel cells and metal-air batteries. Herein, we prepared a core-shell structured Fe/FeC_x nanoparticles and porous carbon composited catalyst (Fe/FeC_x@NC) via a facile two-step heat treatment strategy. The Fe/FeC_x@NC-800_?0.5 prepared with secondary anneal at 800 °C for 0.5 h exhibits superior ORR performance to the commercial Pt/C in terms of comparable onset potential, higher half-wave potential, and outstanding long-term durability in alkaline media. Through combining the physical and electrochemical characterizations of Fe/FeC_x@NC-T_?t with different anneal temperature and precursors, the outstanding ORR performance of Fe/FeC_x@NC-800_?0.5 is caused by the synergistic effect between Fe/FeC_x core and enriched pyridinic N- and graphitic N-doped carbon shell as well as porous carbon with large specific surface area. The structure-activity relationship of core-shell structured Fe–N–C catalysts for ORR provides directions for the development of advanced nonprecious metals catalysts.     

Controllable synthesis of three-dimensional nitrogen-doped graphene as a high performance electrocatalyst for oxygen reduction reaction

Three-dimensional nitrogen-doped graphene (3D-NG@SiO₂) is prepared by pyrolyzing poly (o-phenylenediamine) (POPD) with high nitrogen content. POPD is prepared via an in situ chemical oxidation polymerization of o-phenylenediamine (OPD) in acetic acid with silica colloid as templates. The optimum parameter is OPD:SiO₂ = 1:2, pyrolysis @ 900 °C. SEM and TEM images show the wrinkled and porous graphene structures. Raman spectra indicate that 3D-NG@SiO₂ consists of 4–6 layers graphene. N₂ adsorption–desorption isotherms reveal that the pore size distributions mainly centralize at 5–10 nm. XRD illustrates the amorphous structure. XPS analysis shows that the nitrogen content is 3.6% and nitrogen mainly exists in the form of pyridinic nitrogen and pyrrolic nitrogen. The oxygen reduction reaction (ORR) performance investigated using a rotating disk electrode shows that the initial potential of 3D-NG@SiO₂ is 0.08 V (vs. Hg/HgO). The electron transfer number is 3.92 @ ?0.3 V (vs. Hg/HgO), indicating that 3D-NG@SiO₂ mainly occurs via a four-electron process. The oxygen reduction current density decreases by 21% after 60 h in the chronoamperometry test. The CVs manifests a current density loss of 0.16 mA cm^?2 after scanning for 5000 cycles. The high activity and durability indicate the promising potential of 3D-NG@SiO₂ as ORR catalysts.