Materials For Oxygen Reduction Reaction Research Articles

Biomass‐derived Graphene‐like Catalyst Material for Oxygen Reduction Reaction

AbstractA novel and sustainable method was established to prepare a nitrogen doped graphene‐like material from a renewable, secondary raw material with potential application in the catalysis of oxygen reduction reaction (ORR). Alder wood char was used as a precursor material for producing a sustainable graphene‐like carbon catalyst for the ORR. Alder wood char was first activated (AWC) and then doped with nitrogen (N−AWC). The graphene‐like structure was confirmed using transmission electron microscopy (TEM) and Raman spectroscopy. Electrochemical characterization was carried out in 0.1 M KOH, showing that in alkaline media the ORR activity of the N‐doped wood char‐based graphene‐like material is superior compared to non‐sustainable commercial N‐doped graphene. The onset potential of the ORR on N‐AWC was shifted to positive direction by 75 mV in comparison to the commercially available nitrogen‐doped graphene and the half‐wave potential was shifted even by 239 mV. This renewable biomass‐derived graphene‐like carbon catalyst shows a great potential alternative to current synthetic graphite, graphene nanoplatelets and graphene materials in areas such as fuel cells and batteries.

Applicability of gas-phase isotope exchange method for investigation of porous materials

Oxygen transport in ceramic oxide materials has been actively explored over the past decades. This is due to the desire to design high-temperature electrochemical devices for energy conversion. The research of oxygen transport is connected with necessity in understanding of processes proceeding between oxide materials and oxygen of gas phase. It is known that some functional parts of electrochemical devices have porous structure. Known methods for analyzing the kinetic interaction of oxygen in the gas phase and oxygen oxide, such as the use of 18O-labeled oxygen, are not always applicable for the study of porous materials. The paper shows the applicability of the isotope exchange method with the gas phase analysis to investigate porous ceramic materials using the La0.6Sr0.4MnO3–δ catalytic materials for oxygen reduction reaction. These measurements were taken in situ on materials with different porosity at temperature 800 °C and oxygen pressure 0.67 kPa. This paper shows the relationship between the intrinsic heterogeneous exchange rate (rH) and oxygen diffusion coefficient (D), and the effective apparent values obtained on the porous sample.

Novel Way to Turn Spent Li-Ion Battery Graphite into Valuable and Active Catalyst for Electrochemical Oxygen Reduction

Employing Li-ion batteries (LIBs) in portable electronics has become a necessity in the modern world but, due to the short application time for any given battery (1-3 years) [1], the quantity of spent LIBs (SLIBs) waste is becoming substantial. As LIBs contain different valuable materials (the cathode layer holds Li, Co, Ni, Mn, Al and the anode layer graphite and Cu), the recycling of SLIBs is economically and environmentally beneficial. Additionally, the potential resource strain, as well of the geographical limitations found in the mining/production of the raw materials, will make recycling crucial for sustainable production of LIBs. However, current SLIBs recycling strategies has been focused on cathode materials alone while largely overlooking the anode of the battery [1–3]. In turn, anode recycling has so far concentrated mostly on the metal in the electrode and only very recently has the focus shifted towards the recycling of graphite powders.In this work, a novel strategy for recycling SLIB graphite and reforming it as a valuable catalyst material for electrochemical oxygen reduction reaction (ORR) is proposed. A modified Hummers method was used to fabricate graphene oxide (GO) from SLIB graphite powder. The GO doping was done by pyrolyzing at 800 °C in the presence of dicyandiamide (DCDA). The mass ratio of GO-to-DCDA was 1:20. The prepared nitrogen-doped graphene, from SLIB graphite powder, (NG-Bat) was characterised by various physical (XRD, Raman, XPS, SEM, TEM) and electrochemical characterization methods. Electrochemical properties of the catalyst material was investigated by using the rotation disc electrode voltammetry and electrochemical impedance methods. For electrochemical characterisation the glassy carbon (CG) electrodes were modified with synthesized catalyst and the experiments were carried out in 0.1 M KOH solution. The GC disc electrodes were modified with NG ethanol suspensions (4 mgcatalyst ml-1) containing 6 µl aQAPS-S14 (2%) ionomer from Hephas Energy per 1ml ethanol. The physical and electrochemical characteristics of NG-Bat were compared with commercially available nitrogen doped graphene (NG-Com).Based on XRD and Raman data, it was shown that SLIB-derived graphite maintains its high quality, even after intense exploitation in the batteries and is therefore a valuable material that is worth recycling. The homogeneous distribution of carbon, nitrogen, and oxygen in NG-Bat was demonstrated by elemental mapping. The overall nitrogen content in NG-Bat was found to be 18.4 at%, from which pyridinic N constitutes 55.5 at%, graphitic N 21.7 at%, pyrrolic N 17.8 at% and oxidized N 5.0 at%. The onset potential of the ORR for the NG-Bat catalyst material is −0.11 V, and for the NG-Com catalyst −0.18V (Figure 1). The NG-Bat shows a larger oxygen reduction current and higher electrocatalytic activity than the catalyst based on NG-Com. Based on EIS fitting results very different charge transfer resistance and double-layer capacitance values are achived, probably caused by different conductivities of the catalyst materials. Catalyst material NG-Bat showed much high electrocatalytic activity towards the ORR than did a NG-Com, caused probably by a higher content of active nitrogen species and the presence of carbon vacancies on the surface of graphene, as confirmed by XRD, Raman and XPS experiments.These findings demonstrate that SLIB graphite is still a valuable material and a very suitable precursor for GO fabrication and SLIB anode layer needs to be recycled and returned to usage in a new form. Based on the result of this work, one of the potential applications of the SLIB-derived graphene could be the production of catalyst material for the oxygen reduction reaction (ORR), thereby open new avenues to the fuel cell, metal-air battery, and sensor industries.

Biomass-Derived Graphene-like Catalyst Material for Oxygen Reduction Reaction

Fuel cell (FC) is considered to be one of the most promising energy conversion devices that could possibly be a good alternative replacing the fossil-fuel based technologies in the future. One of the greatest shortcomings of the low-temperature FCs is the poor kinetics of the oxygen reduction reaction (ORR) happening at the cathode side. As it is widely known, the most extensively used cathode catalyst for FCs is Pt or its alloys. But many research groups all over the world study nitrogen-doped metal-free catalyst materials that could possibly be used in FCs as well [1].In recent years, the conversion of biomass into more valuable carbon nanomaterials has been a topic of great interest [2]. The conversion of biomass to carbon nanostructures paves the way for a new avenue of nanomaterial synthesis and could potentially solve scale-up issues with traditional methods of graphene production. Biomass is abundant, the global production of agricultural lignocellulosic wastes is around ~200 billion per year [3].In this research we demonstrate a two-step synthesis method of producing nitrogen-doped graphene-like material from biomass that shows better electrochemical activity towards the ORR than commercially produced nitrogen-doped graphene oxide. A novel and sustainable method was established to prepare nitrogen doped graphene from the renewable, secondary raw material with potential application in the catalysis of ORR. Current research is also proposing a good alternative solution to the increasing need of synthetic graphite, graphene nanoplatelets and graphene by the various industries, including fuel cells and batteries.In this work, alder wood char was used as a precursor material for producing a graphene-like carbon catalyst for the ORR. In the first step, activated carbon (AC) was prepared using chemical activation with NaOH, the ratio of activator vs wood char was 3:1 and the process was carried out in the flowing argon atmosphere. The activation process is important to achieve higher specific surface area. The second step was the doping of AC with nitrogen using dicyandiamide (DCDA) as a nitrogen source, the mass ratio of carbon material/DCDA was 1:20. The graphene-like structure was determined using transmission electron microscopy and Raman spectroscopy. The successful doping of nitrogen was confirmed with using X-ray photoelectron spectroscopy. The most abundant nitrogen component was pyridinic-N (42%), followed by amine (37%) and pyrrolic-N (21%). Electrochemical characterisation was carried out in 0.1 M KOH using rotating disc electrode (RDE) method. Glassy carbon (GC) electrodes were modified with the catalyst ink (4 mg ml−1). The initial loading of the catalyst material on the GC electrode was 400 μg cm−2. Electrochemical measurements showed that the ORR activity of the N-doped wood-based graphene-like catalyst (N-AWC) is superior compared to commercial N-doped graphene (N-GO) in the alkaline media (Figure 1a). Onset potential of the ORR was shifted to positive direction by 75 mV in comparison to the commercially available nitrogen-doped graphene and half-wave potential was shifted even by the magnitude of 1.5. For comparison the graphene oxide (GO) polarisation curve can also be seen (Figure 1). In the studied range, the number of electrons transferred per O2 molecule was 4, indicating that the process proceeds via 4-electron pathway.Usually the conversion of biomass may include many steps, including an additional pre-treatment step, but our two-step approach has a potential to also be integrated in the larger scale synthesis processes.[1] Q. Wei, X. Tong, G. Zhang, J. Qiao, Q. Gong, S. Sun, Catalysts 2015, 5, 1574.[2] M. Borghei, J. Lehtonen, L. Liu, O. J. Rojas, Adv. Mater. 2017, 1703691.[3] J. K. Saini, R. Saini, L. Tewari, 3 Biotech 2015, 5, 337. Figure 1

Metal–Support Interactions in a Molybdenum Oxide Anchored PtNi Alloy for Improving Oxygen Reduction Activity

The PtNi alloy exhibits excellent catalytic activity for oxygen reduction. However, particle agglomeration and support corrosion during the electrochemical reaction inevitably decrease its catalytic stability. Herein, we synthesize PtNi anchored on MoOx (PtNi-MoOx/NC) catalysts by pyrolysis treatment and the ethylene glycol method. It exhibits better catalytic stability than the commercial Pt/C and the prepared PtNiMo ternary catalysts. After the 30k cycle accelerated degradation test, the catalytic activity attenuations for PtNi–MoO3/NC and PtNi–MoO2/NC are 17 and 24%, respectively, which are lower than that of the commercial Pt/C (59%) and the prepared PtNiMo/NC (70%). The stability enhancement can be attributed to the strong metal–support interactions that effectively restrain the aggregation and shedding of PtNi nanoparticles. This work provides a promising strategy to improve the catalytic stability by introducing insoluble metal oxides as support materials for oxygen reduction reaction.

Metal (Mn, Fe, Co, Ni, Cu, and Zn) Phthalocyanine-Immobilized Mesoporous Carbon Nitride Materials as Durable Electrode Modifiers for the Oxygen Reduction Reaction.

In the search for alternative sources to replace fossil fuels, carbon nitride materials can be used in a variety of ways. In the present work, porosity is introduced to the carbon nitride material using mesoporous silica material, MCM-41, as a hard template, and a mesoporous carbon nitride (MCN) material is synthesized. Further, the MCN is modified by immobilizing metal phthalocyanine (MPc, where M = Mn, Fe, Co, Ni, Cu, and Zn). The resulting MPc-incorporated MCN materials (MPc@MCN) were tested for the electrocatalytic oxygen reduction reaction (ORR) in acidic and basic media. Detailed studies reveal that the FePc@MCN and CoPc@MCN materials exhibit higher ORR activity than the other composites in 0.1 M KOH. FePc@MCN follows a direct four-electron oxygen reduction mechanism and shows ORR onset potential (vs RHE) at 0.93 V (in 0.1 M KOH), which is very close to the onset potential exhibited by the state-of-the-art material, Pt-C (1.0 V), and higher than several similar composites of MPc with carbon supports tested in similar environments. Besides, due to the inherent property of coordination through nitrogen present on the MCN, FePc@MCN shows excellent stability even after 3000 cyclic voltammetry (CV) cycles. FePc@MCN was found to have a better methanol tolerance in comparison to Pt-C in basic medium. CoPc@MCN shows a highly selective two-electron reduction reaction in both acidic and basic media at lower overpotential than many of the reported catalysts for the two-electron oxygen reduction. Therefore, these materials (FePc@MCN and CoPc@MCN) can be used as suitable alternatives to replace Pt and other expensive materials in ORR and related applications.

Using a Fe-doping MOFs strategy to effectively improve the electrochemical activity of N-doped C materials for oxygen reduction reaction in alkaline medium

For the rational design of heteroatom-doping carbon catalysts toward the oxygen reduction reaction (ORR), various structure-wise and porous metal-organic-frameworks (MOFs) were preferred especially the transition metal imidazoles frameworks (ZIFs) with abundant N and C elements. Herein, taking advantage of the volatile nature of Zn in ZIF-Zn at high temperatures, we synthesized the bimetallic ZIFs with Zn/Fe molar ratio of 10:1 firstly, and then obtained a structure-define and porous Fe- and N-doped C electrocatalyst by calcining at 900 °C in Ar flow. With the well-defined polyhedrons morphology, high surface area, and evenly distributed C-Nx and Fe-Nx active sites, the as-synthesized Fe-N-C catalysts including the acid-leached Fe-N-C gave superior ORR capability, selectivity, and stability in 0.1 M KOH, and can be also applied in acidic electrolyte. Inspiringly, Fe-N-C exhibited excellent ORR activity exceeding Pt/C benchmark in 0.1 M KOH with a half-wave potential (E1/2) of 0.878 V and the kinetic current density (jk at 0.85 V) of 13.2 mA cm−2, and the single N-C material. And after acid leaching, the obtained Fe-N-C(L) catalyst still maintained the excellent ORR activity (E1/2 = 0.855 V, jk = 6.8 mA cm−2). Additionally, though their ORR performance in acid was inferior to that of Pt/C, the gap was also significantly narrowed by Fe-introduction into N-C structures. Experiments demonstrated that Fe-Nx structure in N-doped C matrix and cooperated with C-Nx centers were very essential to deliver the significantly enhanced ORR activity, in addition to good structural characteristics, i.e., the high pore volume, abundant defects, and good conductivity. This synthesis method based on M-doped MOFs was expected to be transplanted to obtain other energy-relative non-precious metal catalysts.

Fabrication of MEA from Biomass-Based Carbon Nanofibers Composited with Nickel-Cobalt Oxides as a New Electrocatalyst for Oxygen Reduction Reaction in Passive Direct Methanol Fuel Cells

Biomass has some advantages including renewability, abundant resources, being eco-friendly, easy processing, and low cost; and it is an important step in designing electrocatalysts in fuel cells as clean energy sources. In this study, a biomass-based carbon nanofiber of Typha domingensis, as available biomass source, and nickel-cobalt oxides is synthesized. The physicochemical techniques including X-ray powder diffraction, Fourier-transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, Barrett-Joyner-Halenda, and Brunauer-Emmett-Teller as well as electrochemical techniques are used to evaluate the surface morphology, crystal structure, and electrochemical performance of composites. The biomass-derived composite is used as a new electrocatalyst for the oxygen reduction reaction and oxygen evaluation reaction. A membrane electrode assembly is prepared by employing of the produced composite for alkaline passive direct methanol fuel cell, which characterized by polarization, power density curves, methanol crossover test, and stability test for 8 h. Electrochemical results show that the composite is an appropriate electrode material for oxygen reduction reaction in passive direct methanol fuel cells.

Identification of Active Sites of Pure and Nitrogen-Doped Carbon Materials for Oxygen Reduction Reaction Using Constant-Potential Calculations

Nitrogen-doped carbon materials are promising metal-free catalysts for the electrochemical oxygen reduction reaction (ORR). A better theoretical understanding on the nature of the active site(s) wo...

N-doped carbon nanosheet supported Fe2O3/Fe3C nanoparticles as efficient electrode materials for oxygen reduction reaction and supercapacitor application

N-doped carbon encased iron catalyst is a potential alternative of Pt/C for oxygen reduction reaction (ORR). The adjacent Fe-Nx and FexC within the Fe@N/C structure is normally identified as the main active sites toward ORR. Here, we prepared Fe2O3/Fe3C nanoparticles wrapped in nitrogen doped porous carbon nanosheets (Fe-N@C) via pyrolyzing the composites of L-leucine and FeCl3. The optimized sample Fe-N@C-800 showed high ORR catalytic activities with the half-wave potential of 0.82 V (vs. RHE), the onset potential of 0.90 V and electronic transfer number of 3.82. It also exhibited stronger methanol tolerance and better electrochemical stability than commercial Pt/C under 0.1 M alkaline condition. The good ORR performance of the catalyst could be associated with the synergy among Fe3C, Fe2O3 nanoparticles and nitrogen doped carbon. Besides, Fe-N@C-800 also possessed the high specific capacitance (240 F g−1) and good rate capability in KOH aqueous electrolyte. The assembled symmetric capacitor based on Fe-N@C-800 shown a high energy density of 15.4 Wh kg−1 at the power density of 225 W kg−1 in 1 M Na2SO4 aqueous electrolyte. In particular, the capacitance of Fe-N@C-800 was not attenuated after 130,000 cycles in alkaline electrolyte, indicating excellent long-term stability.

Solid-Solutions as Supports and Robust Photocatalysts and Electrocatalysts: A Review

AbstractSome solid solutions have been strongly utilized over the years as good materials for the synthesis of electrocatalysts and photoctalysts. Sometimes, they are used as supports in order to improve electrocatalytic and photocatalytic properties. We show various achievements of solid solutions as good electrocatalysts, and also, good electrocatalysts support materials in oxygen reduction reaction (ORR), hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Also, we demonstrate various works utilizing solid solutions as good photocatalysts, and good photocatalysts support materials in overall water splitting and carbon dioxide reduction. In all these reports, solid solutions proved to posses the necessary properties needed of any material as electrocatalysts and photocatalysts. In many cases, their use as catalysts supports recorded great improvements. X-ray photoelectron spectroscopy (XPS) was largely used to confirm the chemical environment of the results obtained, together with X-ray diffraction (XRD). In the electrochemical methods, cyclic voltammograms (CVA), chronoamperometry and rotating disk electrode (RDE), were also carried out. Linear sweep voltametry (LSV) curve was carried out in some cases to measure the current at a working electrode, and tables were shown for clear explanation. In addition, a photoluminescence spectrum (PL) was used to probe the electronic structure of the various solid solutions.

Seaweed-derived KOH activated biocarbon for electrocatalytic oxygen reduction and supercapacitor applications

Seaweed blooms have become a serious worldwide environmental, economic and social problem. Reducing the cost of electrodes for electrochemical generation/storage systems is crucial for its commercialization. Ascophyllum nodosum grows abundantly in northern oceans, in this study, we evaluate A. nodosum derived chemically activated biocarbon (AKPH) with potassium hydroxide (KOH) as electrode material for oxygen reduction reaction and supercapacitors. Physical–chemical, morphological and electrochemical characterizations were performed. SEM micrographs revealed the morphology changes in AKPH due to KOH activation. AKPH nitrogen and sulfur contents were 0.80 and 5.62 (wt.%), respectively and it exhibited 1493 m2 g−1 surface area with an ID/IG intensity ratio of 1.34 ± 0.01. The electrochemical performance indicates a good performance when compared to commercial platinum, with an onset and half-wave potential of 0.878 and 0.75 V vs. RHE, respectively; and a current density of 5.2 mA cm−2. AKPH exhibited a capacitance of 207.3 F g−1 at 0.5 A g−1 and good stability after 2500 cycles at 5 A g−1 with a retention capability of 92.3%. This performance turns seaweed in a promising way to synthesize materials for applications in energy conversion and storage field.

A green method for Nitrogen-doped graphene and its application for oxygen reduction reaction in alkaline media

ABSTRACT Due to the unique chemical and physical properties of graphene, as a promising material for energy conversion and storage applications, functional groups introduction on graphene surface or edges is a useful strategy for modification of its properties. For the first time, we suggest a simple, eco-friendly, and scalable for synthesising of N-rGO as a cathode material for oxygen reduction reaction (ORR) in fuel cells. An electrochemical method has been employed to investigate the mechanism of N-doping. The N-rGO electrocatalyst prepares by a one-pot electrochemical way using the raw materials of graphite rod and urea solution with DC power supply. The N-rGO had a high N content (6.8 at. %) in comparison to literature. The mechanism of N-doped reduced graphene oxide been carefully studied.

Pyrolyzed Co-Nx/C Electrocatalysts Supported on Different Carbon Materials for Oxygen Reduction Reaction in Neutral Solution

In this work, a non-noble metal material, i.e., 5, 10, 15, 20-Tetrakis(4-methoxyphenyl)−21H, 23H-porphine cobalt(II) (CoTMPP), is chosen as the metal complex which adsorbs on three different carbon support materials, namely, black pearls 2000 (BP), ordered mesoporous carbon (MPC) and single layer graphene oxide (GO), to form CoTMPP/BP, CoTMPP/MPC, and CoTMPP/GO catalyst precursors, respectively. These precursors are heat-treated at high temperatures to form Co-Nx/BP, Co-Nx/MPC, and Co-Nx/GO catalysts for ORR in neutral electrolyte solution, respectively. Several characterization methods including XRD, SEM/TEM and XPS are employed. Electrochemical methods such as cyclic voltammetry (CV), rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques are used to quantitatively measure the catalyzed ORR kinetic parameters. Effects of both carbon supports and heat-treatment temperature on the catalyst physical properties and catalytic ORR activities were also studied. Regarding the catalytic ORR activity, the activity order was measured as: Co-Nx/BP > Co-Nx/MPC > Co-Nx/GO. The overall electron transfer number catalyzed by Co-Nx/BP is measured to be 4, while those by Co-Nx/MPC and Co-Nx/GO catalysts are 2-electron transfer pathways. Based on these measurements and our analysis, an ORR mechanism is also proposed for facilitating further investigation and understanding.

A computational evaluation of MoS2-based materials for the electrocatalytic oxygen reduction reaction

The potential of modified MoS2-based materials in oxygen reduction reaction (ORR) was evaluated by DFT calculations.

First principles investigation on the applicability of ruthenium as a potential ORR catalyst

Exploration of new materials for oxygen reduction reaction has long been a major area of research in heterogeneous catalysis. As the currently available oxygen reduction catalysts have not achieved the optimal efficiency, search for alternative resources is a continuing effort. Realizing the wide acceptance of ruthenium as a promising catalyst for various catalytic reactions, we have investigated the plausibility of Ru to perform in the bulk as well as nanoparticle forms as an efficient oxygen reduction reaction catalyst. Two nanoclusters with face-centred and hexagonal symmetry were scrutinized for ORR activity along with Ru(111) and Ru(0001) surfaces as periodic counterparts and compared the activity with Pt(111) surface. We report here that Ru cannot be an alternative to the Pt-based catalysts owing to a high overpotential. The catalytic activity of ruthenium catalysts for ORR was investigated with reference to the recent advancements in the development of ruthenium catalysts for various electrochemical reactions. The results reveal that both the surface as well as nanocluster based ruthenium systems do not outperform the Pt(111) catalyst.

Identification of Catalytic Sites for Oxygen Reduction in Metal/Nitrogen‐Doped Carbons with Encapsulated Metal Nanoparticles

AbstractThe development of metal‐N‐C materials as efficient non‐precious metal (NPM) catalysts for catalysing the oxygen reduction reaction (ORR) as alternatives to platinum is important for the practical use of proton exchange membrane fuel cells (PEMFCs). However, metal‐N‐C materials have high structural heterogeneity. As a result of their high‐temperature synthesis they often consist of metal‐Nx sites and graphene‐encapsulated metal nanoparticles. Thus it is hard to identify the active structure of metal‐N‐C catalysts. Herein, we report a low‐temperature NH4Cl‐treatment to etch out graphene‐encapsulated nanoparticles from metal‐N‐C catalysts without destruction of co‐existing atomically dispersed metal‐Nx sites. Catalytic activity is much enhanced by this selective removal of metallic nanoparticles. Accordingly, we can confirm the spectator role of graphene‐encapsulated nanoparticles and the pivotal role of metal‐Nx sites in the metal‐N‐C materials for ORR in the acidic medium.

Identification of Catalytic Sites for Oxygen Reduction in Metal/Nitrogen-Doped Carbons with Encapsulated Metal Nanoparticles.

The development of metal-N-C materials as efficient non-precious metal (NPM) catalysts for catalysing the oxygen reduction reaction (ORR) as alternatives to platinum is important for the practical use of proton exchange membrane fuel cells (PEMFCs). However, metal-N-C materials have high structural heterogeneity. As a result of their high-temperature synthesis they often consist of metal-Nx sites and graphene-encapsulated metal nanoparticles. Thus it is hard to identify the active structure of metal-N-C catalysts. Herein, we report a low-temperature NH4 Cl-treatment to etch out graphene-encapsulated nanoparticles from metal-N-C catalysts without destruction of co-existing atomically dispersed metal-Nx sites. Catalytic activity is much enhanced by this selective removal of metallic nanoparticles. Accordingly, we can confirm the spectator role of graphene-encapsulated nanoparticles and the pivotal role of metal-Nx sites in the metal-N-C materials for ORR in the acidic medium.

Changes in Active Sites on Nitrogen‐Doped Carbon Catalysts Under Oxygen Reduction Reaction: A Combined Post‐Reaction Characterization and DFT Study

AbstractNitrogen‐doped carbon nanostructures (CNx) have been shown to be promising catalysts to replace Pt‐based materials for oxygen reduction reaction (ORR) in PEM fuel cell cathodes. This work reports the use of a combination of post‐reaction X‐ray photoelectron spectroscopy (XPS) and density functional theory (DFT) aimed at examining changes to the nitrogen species in CNx after potential application in an oxygen saturated acidic electrolyte. The results hence obtained reveal interesting changes to the pyridinic, quaternary and pyridinic N+O− binding energy envelopes as a result of protonation of sites and formation of ORR intermediates after the CNx electrodes were subjected to electrochemical potential holds in the kinetic and mass transfer limited regimes of the ORR cyclic voltammogram of the catalyst.

Superior durability and stability of Pt electrocatalyst on N-doped graphene-TiO2 hybrid material for oxygen reduction reaction and polymer electrolyte membrane fuel cells

To accelerate the commercialization of polymer electrolyte membrane fuel cells (PEMFCs), studies on durable support materials that can replace conventional carbon-based supports are being conducted. In this study, we prepared N-doped TiO2 on the N-doped graphene hybrid material (NG-TiON) using a facile hydrothermal method to develop a support for a platinum catalyst with both high stability and electrical conductivity. As-prepared NG-TiON supports were characterized using transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The stability of the Pt/NG-TiON catalyst was considerably improved compared to that of Pt/C, and their high oxygen reduction reaction (ORR) activities were similar. The durabilities of the Pt catalysts were investigated using the accelerated durability test. Single cell measurements revealed that Pt/NG-TiON has high stability and corrosion resistance with a performance degradation rate of only 9 % after 5000 accelerated durability test cycles while the performance of Pt/C decreased 83 %.