High Electrocatalytic Activity For Oxygen Reduction Reaction Research Articles

Electrochemical Performance of Metal-Free Carbon-Based Catalysts from Different Hydrothermal Carbonization Treatments for Oxygen Reduction Reaction.

This research investigates the difference between products obtained through two hydrothermal carbonization treatments. Our aim is to synthesize metal-free, carbon-based catalysts for the oxygen reduction reaction (ORR) to serve as efficient and cost-effective alternatives to platinum-based catalysts. Catalysts synthesized using the traditional hydrothermal approach exhibit a higher electrocatalytic activity for ORR in alkaline media, despite their more energy-intensive production process. The superior performance is attributed to differences in the particle morphology and the chemical composition of the particle surfaces. The presence of functional groups on the surfaces of catalysts obtained via a traditional approach significantly enhances ORR activity by facilitating deprotonation reactions in an alkaline environment. Our research aims to provide a reference for future investigations, shifting the focus to the fine-tuning of surface chemical compositions and morphologies of metal-free catalysts to enhance ORR activity.

Enhanced oxygen reduction of porous N-doped carbon nanosheets with graphitic N and defects obtained from coal-based graphene quantum dots

Metal-free carbon-based electrocatalysts for oxygen reduction reaction (ORR) have received considerable attention owing to their abundance and low cost. However, designing carbon-based electrocatalysts with excellent performance in a facile manner remains a challenge. In this work, porous nitrogen-doped carbon nanosheet (PNCNs) catalysts with high contents of graphitic N and defects were readily prepared via a simple self-doping method, in which coal-based graphene quantum dots (GQDs) were used as the carbon and nitrogen resource. Based on the results, PNCNs-900 (obtained at 900 °C) displayed good ORR performance, with a half-wave potential (E1/2) of 0.80 V. It also exhibited high stability and methanol tolerance compared with commercial Pt/C. Experimental investigations and theoretical calculations prove that the increased ORR electrocatalytic activity of PNCNs-900 is due to the synergistic effect of a large number of defects and graphitic N. Furthermore, its higher electrocatalytic activity for ORR also benefits from the porous lamellar structure, which facilitates the mass transfer process. This study offers a novel approach for developing effective ORR catalysts and for the high value-added utilization of coal resources.

High-Performance Perovskite Bifunctional Electrocatalysts for Oxygen Reduction Reaction and Oxygen Evolution Reaction

Perovskite structured earth-abundant metal oxides are attractive candidates as bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolytes. Herein, we present a series of perovskite electrocatalysts (La0.65Sr0.3)zFeO3−δ with different A-site cation deficiencies through a simple and scalable solid-state synthesis method. Their electrocatalytic activities toward ORR and OER are studied by rotating disk electrode and rotating-ring disk electrode techniques in an alkaline electrolyte. Two obvious oxygen reduction potential regions are first reported in this work for these perovskites; the electron transfer number during ORR in the first oxygen reduction potential region is ∼2 and that in the second region is ∼4, indicating two different ORR mechanisms in these two potential regions. Among these perovskites, (La0.65Sr0.3)1.00FeO2.95 exhibits the highest electrocatalytic activity for ORR in the first ORR potential region with an onset potential of 0.72 V, a potential of 0.6 V at −1 mA cm–2, and a Tafel slope of 60.4 mV dec–1 in 0.1 M KOH. For OER in the alkaline electrolyte, (La0.65Sr0.3)0.89FeO2.9 with the highest A-site cation deficiency is proved to be the most active catalyst among these perovskites, which is mainly caused by its highest surface oxygen vacancy content. As a result, our work could provide guidance in the further development of easily prepared, scalable, and earth-abundant perovskite metal oxides.

Modulating the electrocatalytic activity of N-doped carbon frameworks via coupling with dual metals for Zn\u2013air batteries

N-Doped carbon electrocatalysts are a promising alternative to precious metal catalysts to promote oxygen reduction reaction (ORR). However, it remains a challenge to design the desired active sites on carbon skeletons in a controllable manner for ORR. Herein, we developed a facile approach based on oxygen-mediated solvothermal radical reaction (OSRR) for preparation of N-doped carbon electrocatalysts with a pre-designed active site and modulated catalytic activity for ORR. In the OSRR, 2-methylimidazole reacted with Co and Mn salts to form an active site precursor (MnCo-MIm) in N-methyl-2-pyrrolidone (NMP) at room temperature. Then, the reaction temperature increased to 140 °C under an oxygen atmosphere to generate NMP radicals, followed by their polymerization with the pre-formed MnCo-MIm to produce Mn-coupled Co nanoparticle-embedded N-doped carbon framework (MnCo-NCF). The MnCo-NCF showed uniform dispersion of nitrogen atoms and Mn-doped Co nanoparticles on the carbon skeleton with micropores and mesopores. The MnCo-NCF exhibited higher electrocatalytic activity for ORR than did a Co nanoparticle only-incorporated carbon framework due to the improved charge transfer from the Mn-doped Co nanoparticles to the carbon skeleton. In addition, the Zn–air battery assembled with MnCo-NCF had superior performance and durability to the battery using commercial Pt/C. This facile approach can be extended for designing carbon electrocatalysts with desired active sites to promote specific reactions.Graphical

Improved oxygen reduction performance of a N, S co-doped graphene-like carbon prepared by a simple carbon bath method

Rationally designing and optimizing metal-free electrocatalysts for the oxygen reduction reaction (ORR) isof great importance for fuel cells and metal-air batteries, but remains a great challenge. A N,S-codoped graphene-like carbon (GLC) was synthesized by a simple carbon-bath pyrolysis method, in which urea and thiourea (1:1 w/w) were used as both the sacrificial template and source of nitrogen and sulfur, and glucose as the carbon precursor. A mixture of these materials was placed in a crucible that was contained in a larger crucible full of carbon powder. Compared with N-doped or S-doped GLCs synthesized using only urea or thiourea, respectively, the N,S-codoped GLC had a pore volume of 0.63 cm3/g and a larger specific surface area of 583.68 m2/g, the highest micropore to total surface area of 29.39% and micropore to total pore volume of 12.70%, and the highest pyridinic-N and graphitic-N content of up to 92.2%.The N,S-codoped GLC showeda high electrocatalytic activity for ORR with a mid-wave potential (E1/2) of 0.82 VRHE, which was more positive than that of Pt/C (E1/2=0.80 VRHE) in an alkaline electrolyte. The N,S-codoped GLC catalyst had better stability and superior methanol tolerance compared with commercial Pt/C (20 wt%), abenchmark catalyst.

B‒site-ordered Co-based double perovskites Sr2Co1−xNbxFeO5+δ as active and stable cathodes for intermediate-temperature solid oxide fuel cells

Highly active and stable cathodes for oxygen reduction reaction (ORR) are vital to develop intermediate-temperature solid oxide fuel cells (IT-SOFCs). Here we report a novel class of cathodes with B-site-ordered Co-based double perovskites Sr2Co1−xNbxFeO5+δ (SCNxF, x = 0.0–0.2). The SCNxF oxides have a single-phase cubic structure and good structural stability and chemical compatibility with La0.9Sr0.1Ga0.8Mg0.2O3–δ (LSGM) and Ce0.8Sm0.2O1.9 electrolytes. The Nb doping improves the thermodynamical stability and the thermal expansion compatibility of the SCNxF materials as compared to the undoped Sr2CoFeO5+δ. The area specific resistances of SCNxF cathodes with x = 0.0, 0.1, and 0.2 on the LSGM electrolyte are 0.048, 0.081, and 0.174 Ω cm2 at 700 °C, respectively. Also the SCN0.1F cathode shows better cell performance and electrochemical stability in the practical SOFC. The findings indicate that the SCN0.1F is a promising cathode material of IT-SOFCs with high electrocatalytic activity for ORR, functional stability, and high electrical conductivity.

Structures of Pt Ultra-Thin Films on Ni Substrate Prepared By Galvanic Replacement

Introduction Polymer electrolyte fuel cell (PEFC) has been expected as a high-power and clean electric source to solve the social problems such as environmental pollution and energy crisis [1]. In order to operate the PEFC at room temperature, it is necessary to promote the reaction rate of the oxygen reduction reaction (ORR), which is the rate determining step of the cathode reaction, by Pt as a cathode electro-catalyst. However, there are some problems with Pt catalyst for actual operation and wide general spread of PEFC; Pt is the expensive and precious metal and electro-catalytic activity of Pt for ORR is insufficient. In order to widely spread PEFC, therefore, it is indispensable to reduce the amount of Pt catalyst and to increase its ORR activity. It is well known, on the other hand, that ultra-thin noble metal layers formed on foreign metal surface often have higher electro-catalytic activity, because they have different surface energy from their bulk crystal [2]. Pt ultra-thin film covered with a low cost metal surface is one of the candidate as a cheaper electro-catalyst with higher electro-catalytic activity for ORR in PEFC. We have succeeded to electrochemically prepare Ni core Pt shell (Ni@Pt) nanoparticles using Ni as a cheaper metal core and demonstrated that its electro-catalytic activity for ORR is higher than Pt itself [3,4]. In these studies, such Pt thin layer coated Ni nanoparticles were prepared by a galvanic replacement technique. There are several methods to form the Pt ultra-thin film on the foreign metal surface. Among them, the galvanic replacement technique, in which such Pt ultra-thin film can be prepared by a simple operation, just dipping a substrate into a solution containing Pt ion, is one of the best candidates. However, there are few reports to structurally investigate the galvanic replacement process with an atomic dimension. In this report, the galvanic replacement process of Ni substrate surface with Pt was structurally investigated by the electrochemical and angle-resolved X-ray photoelectron spectroscopy (ARXPS) measurements. Experiments After several pre-treatments of Ni substrate, several droplets of the solution containing Pt2+ ion were added to the 0.05 M Na2SO4 solutions with pHs of 3.0, 4.0, and 5.0 as the Ni substrate was immersed into each solution during monitoring the open circuit potential (OCP). After the OCP was stabilized to a constant value, the substrate was taken out from the solution and rinsed with ultrapure water by a sonication for ca. 5 min. After drying the substrate, cyclic voltammogram (CV) and ARXPS were measured to obtain the Pt surface area and Pt film thickness, respectively. Results and Discussion In all the solutions, OCP was positively shifted and Pt existed onto the Ni substrate, although Ni oxide also existed of all the substrates. Thickness value of Pt thin film was dependent on pH value of solution. Pt thin film prepared from the solution with pH 3.0 was thinnest but its surface was quite rough. In addition, Pt black was also formed on this substrate surface and it was easy to wash it off with ultrapure water from the surface. Details of the Galvanic replacement are now under investigation.

Cobalt and Iron Oxides Co‐supported on Carbon Nanotubes as an Efficient Bifunctional Catalyst for Enhanced Electrocatalytic Activity in Oxygen Reduction and Oxygen Evolution Reactions

AbstractDeveloping efficient non‐precious metal electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in energy conversion and storage devices is highly desirable but challenging. This report describes a general approach for preparing cobalt and iron oxide nanoparticles co‐supported on nitrogen‐doped carbon materials as an efficient oxygen electrode catalyst with an improved catalytic activity toward OER and ORR; these nanoparticles were obtained through pyrolysis of Co‐ and Fe‐based metal–organic frameworks grown directly on the surface of polyvinylimidazole‐functionalized carbon nanotubes (CNTs). The Fe/Co–CNTs‐800 catalyst pyrolyzed at 800 °C exhibited high electrocatalytic activity for ORR, with only ∼50 mV lesser activity than that of Pt/C at the half‐wave potential, and for OER, with only ∼70 mV lesser activity than that of RuO2 at a current density of 10 mA⋅cm−2 in a 0.1 M KOH solution. The potential difference between OER and ORR for Fe/Co–CNTs‐800 (ΔEOER–ORR) was 0.905 V, which was significantly lower than that for noble‐metal catalysts (20 wt% Pt/C (1.137 V) and RuO2 (1.341 V)). The preparation temperature and value of Fe/Co in the catalyst composite are crucial for achieving high electrocatalytic activity for both ORR and OER.

Hierarchically structured iron-doped silver (Ag-Fe) lotus flowers for an efficient oxygen reduction reaction.

The development of cheap and efficient electrocatalysts for the oxygen reduction reaction (ORR) is vital for the immediate commercialization of fuel cells which are still limited by the high cost and low performance of the utilized commercial Pt-based electrodes. As a promising alternative, this study reports on the synthesis of hierarchical iron-doped silver lotus flowers (AgFelotus) by a facile chemical procedure as robust and efficient ORR electrocatalysts. Succinic acid was used as a structure directing agent to tune the morphology of undoped and iron-doped silver particles. In the absence of succinic acid, ball-like silver particles were obtained, while using 2 mM succinic acid led to peony-like flower structures. The doping of silver peony-flowers with iron resulted in lotus-like flower structures with high electrocatalytic activity for ORR together with outstanding tolerance against poisoning with various hydrocarbon (HC) impurities, in situ generated during fuel cell operation, as well as different fuels from anodic crossover. AgFelotus exhibited a superior ORR activity with more than 40 times higher stability than the commercial Pt/C catalyst in alkaline media. This substantial performance enhancement is attributed to the unique lotus-like flower structures providing more electroactive surface sites, in addition to the iron dopants which facilitate ORR charge transfer.

Highly efficient iron–nitrogen electrocatalyst derived from covalent organic polymer for oxygen reduction

Developing non-precious metal catalyst with high activity, good stability and low cost for electrocatalytic oxygen reduction reaction (ORR) is critical for the wide application of energy conversion system. Here, we developed a cost–effective synthetic strategy via silica assistance to obtain a novel Fe3C/Fe–Nx–C (named as COPBP-PB-Fe-900-SiO2) catalyst with effective active sites of Fe–Nx and Fe3C from the rational design two-dimensional covalent organic polymer (COPBP-PB). The nitrogen-rich COP effectively promotes the formation of active Fe–Nx sites. Additionally, the silica not only can effectively suppress the formation of large Fe-based particles in the catalysts, but also increases the degree of carbonization of the catalyst. The as-prepared COPBP-PB-Fe-900-SiO2 catalyst exhibits high electrocatalytic activity for ORR with a half-wave potential of 0.85 V vs. reversible hydrogen electrode (RHE), showing comparable activity as compared with the commercial Pt/C catalysts in alkaline media. Moreover, this catalyst also shows a high stability with a nearly constant onset potential and half-wave potential after 10,000 cycles. The present work is highly meaningful for developing ORR electrocatalysts toward wide applications.

Biomass-Derived Porous Carbon As Noble-Metal Free Catalysts for Oxygen Reduction Reaction

Efficient electrocatalysts for the oxygen reduction reaction (ORR) play a critical role in the performance of fuel cells. In this work, biomass-derived porous carbon was prepared by a facile procedure based on simple pyrolysis of spinach at controlled temperatures (700 – 900 °C) and different activation agents. The obtained porous carbon exhibited high specific surface area and porosity. Electrochemical measurements showed that the porous carbons possessed a high electrocatalytic activity for ORR in alkaline media. The ORR onset potential for the catalyst is +0.96 V vs. RHE. Moreover, it showed excellent long-term stability, and methanol tolerance, as compared to the commercial Pt/C. The catalytic performance of porous carbon obtained by various activation agent will be compared. The results suggest a very promising route towards the development of value-added carbon materials for effective cathode catalysts for alkaline fuel cells.

TCNQ-induced in-situ electrochemical deposition for the synthesis of silver nanodendrites as efficient bifunctional electrocatalysts

Sliver (Ag) nanodendrites (AgNDs) directly growing on the glassy carbon electrode (GCE) were obtained by an in-situ electrodepositing route under the induction of organic semiconductor 7,7,8,8-tetracyanoquinodimethane (TCNQ). The morphology of the Ag nanostructures can be controlled by the electrodepositing time, applied potentials, and the concentrations of Ag ions. The AgNDs/TCNQ/GCE obtained at the optimized conditions displays the oxygen reduction reaction (ORR) onset potential of 0.98V, which is the same as that over Pt/C-JM catalyst (0.98V). It demonstrated that AgNDs possessed the highest electrocatalytic activity for ORR among the various Ag-based electrocatalysts reported in literature in alkaline electrolyte. At the same time, the performance of AgNDs/TCNQ/GCE toward hydrogen peroxide detection was investigated in a range of the concentration from 10μM to 17mM. It also showed the higher catalytic activity for hydrogen peroxide reduction reaction with the hydrogen peroxide detection limit reaching 0.47μM level. The Tafel polarization curve, electrochemically active surface area, and the electrochemical impedance were measured to understand and explore the catalytic behavior of the prepared AgNDs/TCNQ/GCE. The enhanced performance of AgNDs for ORR and hydrogen peroxide detection can be ascribed to the special tree-like morphology with highly-exposed surface and the improved electron transportation capacity of interface between AgNDs and GCE.

Electrocatalytic Activity for Oxygen Reduction Reaction of Electrochemically Prepared Ni Core - Pt Shell Nanoparticles

In order to widely spread of the PEFC, it is essential to decrease the loading amount of the current Pt catalyst and increase the electrocatalytic activity for oxygen reduction reaction (ORR). From a viewpoint of finding a clue for the design of high performance and low cost cathode catalysts, in this study, the Ni core – Pt shell (Ni@Pt) nanoparticles were electrochemically prepared and their electrocatalytic activities for ORR were investigated. We can prepare the Ni@Pt nanoparticle, which shows higher electrocatalytic activity for ORR than that of the polycrystalline Pt.

Intrinsically Conductive Perovskite Oxides with Enhanced Stability and Electrocatalytic Activity for Oxygen Reduction Reactions

The oxygen reduction reaction (ORR) is traditionally catalyzed by carbon-supported precious metals, heteroatom-doped carbons, and transition-metal–carbon hybrids. Despite their good electric conductivity and high catalytic activities, these carbon-containing catalysts suffer from electrochemical carbon corrosion which limits their utility in metal–air batteries and fuel cells. Here, we report a class of perovskite La0.5Sr0.5Mn1–xNixO3−δ nanocrystals that are intrinsically conductive with good electrocatalytic activity for the ORR. Among these perovskites, La0.5Sr0.5Mn0.9Ni0.1O3−δ (δ = 0.06, LSMN) exhibited the highest electrocatalytic activity for ORR with an onset potential of 1.02 V, a half-wave potential of 0.80 V, and a Tafel slope of −68 mV decade–1 in 0.1 M potassium hydroxide aqueous solution. Negligible degradation of oxygen reduction currents was observed after 300 cyclic voltammetry scans from 1.08 to 0.15 V. We demonstrated that the electrically conductive perovskites with transition-metal redo...

Electrocatalytic Activity for Oxygen Reduction Reaction of Electrochemically Prepared Ni Core - Pt Shell Nanoparticles

Introduction. Because of modern social problems such as an environmental pollution and energy crisis, polymer electrolyte fuel cell (PEFC) has been expected as one of the clean and high power sources. PEFC has been intensively developed for applications to fuel cell vehicle (FCV) and residential cogeneration systems [1]. In order to operate PEFC at room temperature, it requires platinum (Pt) as a cathode catalyst for oxygen reduction reaction (ORR) due to its slow kinetics. However, electrocatalytic activity of polycrystalline Pt for ORR is not enough for actual operation of PEFC, and moreover, Pt is the expensive and precious metal, and then the commercially available PEFC is too expensive, unfortunately. For a goal of the widely spread of the PEFC, it is essential to decrease the loading amount of the Pt catalyst and to increase its ORR activity. We previously reported that Pt ultra-thin layers deposited on the foreign metal surface, which have different surface energy from the polycrystalline Pt, have higher electrocatalytic activity [2]. Moreover, using Ni as a low cost core material can lead to the cost reduction. Thus, Ni@Pt is expected as a key cathode material for the PEFC. From a viewpoint of finding a clue for the design of high performance and low cost cathode catalysts, in this report, the Ni core – Pt shell (Ni@Pt) nanoparticles were electrochemically prepared and their electrocatalytic activities for ORR were investigated. Experimentals. In the preparation of the Ni@Pt nanoparticles, the simple potential step chronoamperometry and galvanic replacement were employed [3,4]. From the cathodic peak potential values in the cyclic voltammogram measured in the electrolyte solutions containing Ni2+, the deposition potentials were determined. The Ni nanoparticles were electrodeposited on the glassy carbon electrode (GCE) by applying the determined deposition potentials for several periods. Just after the GCE was disconnected, for the galvanic replacement of Pt with Ni on the Ni nanoparticle surface, a few drops of concentrated Pt2+ solution were added or the GCE was immersed in the solution containing Pt2+, for the certain periods. After ultrasonic cleaning, electrocatalytic activity of the prepared Ni@Pt nanoparticles for ORR was qualified with the rotating ring-disk electrode (RRDE) system. The size and structure of the prepared Ni@Pt nanoparticles were evaluated by scanning electron microscopy (SEM). Results and Discussion. From the linear sweep voltammograms of the GCE modified with the Ni@Pt nanoparticles, which were measured in the oxygen saturated 0.1 M HClO4, all Ni@Pt nanoparticles, which were prepared in the several Ni2+ solutions for several Ni deposition periods, indicated that cathodic current due to ORR was observed at the potentials more negative than ca. 1.00 V. Moreover, the typical results of them had higher electrocatalytic activity for ORR than that of polycrystalline Pt. SEM image of the Ni nanoparticles showed that the shapes were spherical and uniformly distributed. In addition, the size was strongly dependent on the deposition time in preparation. But, the size and also the shape of nanoparticles were much dependent both on the period in Galvanic replacement and pH of the Pt2+ solution. More optimum conditions and the details of the relationship between the ORR activity and the characteristics of the Ni@Pt nanoparticle, such as the size, the shape, and the composition, are now under investigation. References. [1] R. R. Adzic, et al., Top. Catal., 45 (2007) 249. [2] T. Kondo, et al., Chem. Lett., 40 (2011) 1235. [3] H. Nagai, et al., ECS Trans., 58 (2014) 27. [4] M. Ueda et al., Pacifichem 2015, Honolulu (2015) #333.

Low Pt-Loaded Mesoporous Sodium Germanate as a High-Performance Electrocatalyst for the Oxygen Reduction Reaction.

Although Pt/C catalysts show relatively high activities for the oxygen reduction reaction (ORR) and great potential for use in polymer electrolyte membrane fuel cells, the large amount of Pt required and the poor stability of Pt/C-based catalysts remain big challenges. Herein, mesoporous Na4 Ge9 O20 micro-crystals have been successfully synthesized to serve as a new kind of electrocatalyst support owing to its special structural characteristics and high structural stability. After loading a low amount of Pt (5 wt %) nanoparticles of 2-5 nm in diameter, the obtained mesoporous Pt/Na4 Ge9 O20 composite shows not only high electrocatalytic activity for ORR in both acidic and alkaline electrolyte media, which are comparable to those of conventional 20 wt % Pt/C, but also remarkably enhanced Pt mass-specified ORR current density and durability. Synergetic catalytic effects between loaded Pt and the support for the ORR activity has been proposed.

Inexpensive Ipomoea aquatica Biomass-Modified Carbon Black as an Active Pt-Free Electrocatalyst for Oxygen Reduction Reaction in an Alkaline Medium.

The development of inexpensive and active Pt-free catalysts as an alternative to Pt-based catalysts for oxygen reduction reaction (ORR) is an essential prerequisite for fuel cell commercialization. In this paper, we report a strategy for the design of a new Fe–N/C electrocatalyst derived from the co-pyrolysis of Ipomoea aquatica biomass, carbon black (Vulcan XC-72R) and FeCl3·6H2O at 900 °C under nitrogen atmosphere. Electrochemical results show that the Fe–N/C catalyst exhibits higher electrocatalytic activity for ORR, longer durability and higher tolerance to methanol compared to a commercial Pt/C catalyst (40 wt %) in an alkaline medium. In particular, Fe–N/C presents an onset potential of 0.05 V (vs. Hg/HgO) for ORR in an alkaline medium, with an electron transfer number (n) of ~3.90, which is close to that of Pt/C. Our results confirm that the catalyst derived from I. aquatica and carbon black is a promising non-noble metal catalyst as an alternative to commercial Pt/C catalysts.

Electrocatalysis of oxygen reduction on multi-walled carbon nanotube supported copper and manganese phthalocyanines in alkaline media

Manganese phthalocyanine (MnPc) and copper phthalocyanine (CuPc)-modified electrodes were prepared using multi-walled carbon nanotubes (MWCNTs) as a support material. The catalyst materials were heat treated at four different temperatures to investigate the effect of pyrolysis on the oxygen reduction reaction (ORR) activity of these electrocatalysts. The MWCNT to metal phthalocyanine ratio was varied. Scanning electron microscopy (SEM) was employed to visualise the surface morphology of the electrodes and the x-ray photoelectron spectroscopic (XPS) study was carried out to analyse the surface composition of the most active catalyst materials. The ORR was studied in 0.1 M KOH solution employing the rotating disk electrode (RDE) method. Glassy carbon (GC) electrodes were modified with carbon nanotube-supported metal phthalocyanine catalysts using Tokuyama AS-4 ionomer. The RDE results revealed that the highest electrocatalytic activity for ORR was achieved upon heat treatment at 800 °C. CuPc-derived catalyst demonstrated lower catalytic activity as compared to the MnPc-derived counterpart, which is in good agreement with previous literature, whereas the activity of MnPc-based catalyst was higher than that reported earlier.

One-step nanocasting synthesis of sulfur and nitrogen co-doped ordered mesoporous carbons as efficient electrocatalysts for oxygen reduction

Ordered mesoporous carbon co-doped with sulfur and nitrogen (SN–OMC) is synthesized via one-step nanocasting route. Diphenylthiocarbazone is used as a single precursor for carbon, sulfur and nitrogen in the preparation of SN–OMCs. These catalysts are subjected to the physicochemical characterization and electrochemical evaluation toward the oxygen reduction reaction (ORR) in an alkaline electrolyte. SN–OMC obtained at 900°C exhibits a high electrocatalytic activity for ORR and the impressive durability and methanol-tolerance. The synergistic effect of nitrogen and sulfur in mesoporous carbon walls may contribute to high oxygen electroreduction performance of SN–OMC.

Surprisingly High Activity for Oxygen Reduction Reaction of Selected Oxides Lacking Long Oxygen-Ion Diffusion Paths at Intermediate Temperatures: A Case Study of Cobalt-Free BaFeO3-δ

The widespread application of solid oxide fuel cell technology requires the development of innovative electrodes with high activity for oxygen reduction reaction (ORR) at intermediate temperatures. Here, we demonstrate that a cobalt-free parent oxide BaFeO(3-δ) (BF), which lacks long-range oxygen-ion diffusion paths, has surprisingly high electrocatalytic activity for ORR. Both in situ high-temperature X-ray diffraction analysis on room-temperature powder and transmission electron microscopy on quenched powder are applied to investigate the crystal structure of BF. Despite the lack of long oxygen-ion diffusion paths, the easy redox of iron cations as demonstrated by thermal gravimetric analysis (TGA) and oxygen temperature-programmed desorption and the high oxygen vacancy concentration as supported by iodometric titration and TGA benefit the reduction of oxygen to oxygen ions. Moreover, the electrical conductivity relaxation technique in conjunction with a transient thermogravimetric study reveals very high surface exchange kinetics of BF oxide. At 700 °C, the area specific resistance of BF cathode, as expressed by a symmetrical cell configuration, is only ∼0.021 Ω cm(2), and the derived single fuel cell achieves high power output with a peak power density of 870 mW cm(-2). It suggests that an undoped BF parent oxide can be used as a high-efficiency catalyst for ORR.