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Search for a Platinum metal-free catalyst for Proton Exchange Membrane Fuel Cells (PEMFCs) is a concern to scientists as the Pt-catalyzed electrode comprises about 45% of the entire fuel cell stack cost. Due to layered structure, Two-dimensional (2D) MoS2 nanostructured materials have recently drawn attention as effective catalysts for oxygen reduction reaction (ORR). The 1T-phase of MoS2 (1T-MoS2) has higher electronic conductivity than the 2H-phase (2H-MoS2); high surface area 1T-MoS2 can have high electrocatalytic activity towards PEFFCs. Here, we report hydrothermally synthesized 2H-MoS2 and solvothermally synthesized mixed 1T/2H-MoS2 phases as a catalyst for ORR in PEM Fuel Cells. Owing to the high BET-specific surface area, hybrid 1T/2H-MoS2 showed better ORR activity than 2H-MoS2. The limiting current density of the 1T/2H-MoS2 hybrid structure is ‒7.1 mA cm−2 compared to Pt/C (‒8.2 mA cm−2) at 1600 rpm. The Tafel slope values of 2H-MoS2, 1T/2H-MoS2, and Pt/C are 92.7 mV dec−1, 57.5 mV dec−1, and 39.3 mV dec−1, respectively. The electron transferred during ORR are 3.8 and 1.8, respectively, for 1T/2H-MoS2 and 2H-MoS2 (in 0.1 M KOH) ; suggesting less formation of undesirable peroxide formation than 2H-MoS2. The 1T/2H-MoS2 displays better electrochemical durability compared to 2H-MoS2 (after 2000 CV cycles). [ABSTRACT FROM AUTHOR]

In this work, carbon-supported Pt-Fe catalysts (Pt-Fe/C) have been synthesized to determine the electrochemical activity toward oxygen reduction reaction (ORR). Compared to the Pt/C catalyst, the Pt-Fe/C catalyst showed around 23% less area-specific activity but 8.6% more mass activity. These findings suggest the possibility to develop a catalyst that is both more active and cost-efficient than platinum. Furthermore, Pt-Fe/C catalyst was successfully compared as a cost-effective catalyst alternative to the Pt/C catalyst. [ABSTRACT FROM AUTHOR]

We report the development of a novel electrocatalyst composed of nanoarchitectured spinel cobalt manganese oxide and graphene for the oxygen reduction reaction (ORR). A combination of co-precipitation and hydrothermal methods achieved the unique nanoarchitecture of the electrocatalyst. The formation of CoMn2O4 electrocatalyst was confirmed by X-ray diffraction, transmission electron microscopy, and other spectroscopic and microscopic techniques. In addition to synthesizing CoxOy and MnxOy as control electrocatalysts, we created a physical mixture of CoMn2O4 and graphene to investigate the impact of their interface on electrocatalytic activity. Our findings indicate that CoMn2O4/graphene exhibits improved ORR activity, stability, and methanol tolerance in an alkaline medium. This enhancement can be attributed to the synergistic effect and strong interface interaction between CoMn2O4 and graphene. This study demonstrates the potential of the proposed electrocatalyst as a cost-effective and eco-friendly alternative for oxygen reduction in fuel cells applications. [ABSTRACT FROM AUTHOR]

The rational construction and preparation of efficient, stable, and economic electrocatalysts for the oxygen reduction reaction (ORR) are necessary for fuel cells. In this work, we fabricated a porous carbon skeleton structure consisting of bimetallic organic framework (BMMOF)-derived N-doped microspheres linked with graphene oxide (GO) conducting network (denoted as UA-Co/RSC@NGF, where "UA" stands for ultrasound-assisted, "RSC" stands for resin microspheres, and "NGF" stands for N-doped graphene framework) as an efficient ORR catalyst by an ultrasound-assisted and one-step pyrolysis method. In this configuration, benefiting from the support of carbon microspheres and the strong synergistic coupling with GO, the structure of UA-Co/RSC@NGF is stabilized, and the large specific surface area enhances the density of active sites. With UA-Co/RSC@NGF as the catalyst, significant ORR properties were achieved with a high half-wave potential (E1/2, 0.90 V), an onset potential (Eonset, 1.03 V), and a large limited current density (5.37 mA cm−2). The durability and methanol resistance of UA-Co/RSC@NGF in alkaline media outperform commercially available Pt/C. This study may open a pathway for rationally designing multidimensional composite-structured carbon-based ORR catalysts for energy-related applications. [ABSTRACT FROM AUTHOR]

The weak interaction between common carbon support and Pt nanoparticles results in low efficiency for the oxygen reduction reaction (ORR) with high overpotentials, which greatly limits the practical application of proton exchange membrane fuel cells. Employing strong metal–support interaction (SMSI) is a promising method for tuning the electronic structure of Pt to boost the ORR, accompanied by rapid improvement in durability. Herein, titanium carbide (TiC) was grown on the surface of carbon black by the sol–gel method coupled with high-temperature treatment (denoted as TiC-C). Based on the SMSI that occurred between TiC and Pt, the obtained Pt/TiC-C catalyst exhibits higher mass ORR activity, which is twice that of the commercial Pt/C-JM under the same conditions. In addition, the Pt/TiC-C exhibits superior durability relative to the Pt/C-JM by preventing the aggregation and dissolution of Pt nanoparticles during the ORR process. [ABSTRACT FROM AUTHOR]

Highlights: A comprehensive discussion of monitoring the structure evolutions of catalysts during ORR via multiple in-situ techniques to identify the active sites is presented. The extensive applications of in-situ techniques in elucidating the oxygen reduction reaction (ORR) mechanisms/pathways are reviewed. The challenges and recommendations of current in-situ techniques for monitoring the various dynamic evolutions in ORR are pointed out. Electrocatalytic oxygen reduction reaction (ORR) is one of the most important reactions in electrochemical energy technologies such as fuel cells and metal–O2/air batteries, etc. However, the essential catalysts to overcome its slow reaction kinetic always undergo a complex dynamic evolution in the actual catalytic process, and the concomitant intermediates and catalytic products also occur continuous conversion and reconstruction. This makes them difficult to be accurately captured, making the identification of ORR active sites and the elucidation of ORR mechanisms difficult. Thus, it is necessary to use extensive in-situ characterization techniques to proceed the real-time monitoring of the catalyst structure and the evolution state of intermediates and products during ORR. This work reviews the major advances in the use of various in-situ techniques to characterize the catalytic processes of various catalysts. Specifically, the catalyst structure evolutions revealed directly by in-situ techniques are systematically summarized, such as phase, valence, electronic transfer, coordination, and spin states varies. In-situ revelation of intermediate adsorption/desorption behavior, and the real-time monitoring of the product nucleation, growth, and reconstruction evolution are equally emphasized in the discussion. Other interference factors, as well as in-situ signal assignment with the aid of theoretical calculations, are also covered. Finally, some major challenges and prospects of in-situ techniques for future catalysts research in the ORR process are proposed. [ABSTRACT FROM AUTHOR]

Fabrication of an advanced electrocatalyst for oxygen reduction reaction (ORR) is important for the commercialization of fuel cells. Herein, we report an ORR electrocatalyst with Fe atoms evenly distributed on crumple-rich nitrogen-doped carbon (N–C) nanospheres via a simple melamine-assisted pyrolysis strategy, where crumple-rich N–C nanospheres are prepared by a dual soft template approach. The as-obtained Fe–N-C-M electrocatalyst shows a better onset potential (1.02 V vs. RHE) and half-wave potential (0.883 V vs. RHE) in alkaline solution, superior to the commercial Pt/C (0.97 and 0.860 V vs. RHE, respectively). Moreover, the Fe–N-C-M also displays outstanding stability with 80.4% of relative current remained after a 10-h stability test at 0.8 V vs. RHE and remarkable methanol tolerance with 79.2% of relative current sustained after adding 3 M methanol, outperforming the commercial Pt/C (49.4% and 48.5%, respectively). All of these excellent properties are contributed to the unique crumple-rich structure, large specific surface area, and high content of Fe-Nx and pyridinic-N active centers. [ABSTRACT FROM AUTHOR]

The development of active and durable proton exchange membrane fuel cell catalysts with high loading (ca. 40%) is critical for the commercialization of hydrogen fuel cells. Herein we report on the synthesis of a novel Pt/C catalyst using a novel bowl-like broken hollow carbon sphere (and N-doped sphere) support (carbon shell thickness ~ 4.6 nm). Highly dispersed Pt nanoparticles (dPt ~ 4 nm) were deposited on both supports and within the carbon shell. The Pt particles in the pores were exposed on both sides of the shell, while the shell porosity ensured pore confinement of the Pt. Both catalysts exhibited high electrochemical surface areas (60–65 m2 g−1) and cycling durability (6000 cycles) that was superior to a commercial benchmark Pt/C catalyst. These studies indicate that high loadings of confined small Pt particles on both sides of thin interconnected carbons can lead to high oxygen reduction reaction activities and durability. [ABSTRACT FROM AUTHOR]

The development of metal-free carbon-based catalysts for alkaline fuel cells has been the subject of current interest, because of the low cost and improving fuel cell efficiency. Particularly, nitrogen-doped carbon shows prominent results. Here, we show an oxygen reduction reaction (ORR) activity of nitrogen-doped graphene-like carbon materials (N-GLC) prepared by heating bagasse-derived carbon and melamine in a 1:15 ratio. The N-GLC catalyst displays excellent electro-catalytic activity towards the ORR with an onset potential of 0.92 V vs. reversible hydrogen electrode (RHE) in alkaline media (0.1 M KOH). Moreover, the half-wave (E1/2) potential 0.83 V is almost the same compared to Pt-C (40 wt%) catalyst and the diffusion limiting current of 4 mA cm–2. The rotating ring disc experiment showed a four-electron pathway (n = 3.65) with the moderate peroxide ( HO 2 - ) yield. Due to its promising ORR activity and long-term electrochemical stability, N-GLC catalyst is used in alkaline anion exchange membrane fuel cell (AEMFC) as a single cell, about 6 mW cm–2 peak power density was achieved at the load current density of ~20 mA cm–2. So the N-GLC can be a cheap alternative ORR catalyst for AEMFC applications. [ABSTRACT FROM AUTHOR]

ZIF-67/CNT materials are prepared by using in situ growth method with cobalt nitrate and 2-methylimidazole (2-MI) as raw materials, polyvinyl pyrrolidone (PVP) as complexing agents. A series of N-Co@C/CNT catalysts are prepared through heating ZIF-67/CNT in N2 atmosphere. The effects of additional proportion of CNT on the catalytic performance of N-Co@C/CNT catalysts for oxygen reduction reaction (ORR) are studied. The chemical states of the materials, micro-morphology, elemental composition, and crystalline structure are analyzed by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results show that polyhedral ZIF-67 has grown on the surfaces of CNTs. After heat treatment, ZIF-67/CNT transforms to N-Co@C/CNT. The particle size of Co is 10–20 nm. N-Co@C/CNT-2.6 shows the best catalytic performance for ORR in alkaline solution with the onset potential of 0.94 V, half-wave-potential of 0.83 V, and limiting diffusion current density of 5.6 mA cm−2. The ORR on N-Co@C/CNT proceeds through a four-electron path and the yield of H2O2 is 12%, which is close to Pt/C. N-Co@C/CNT shows higher methanol-tolerant ability than Pt/C. The addition of CNT makes N-Co@C expose more active sites. CNT plays an important role in connecting different N-Co@C particles and enhancing the electron conductivity. The contents of graphitic nitrogen and pyridine nitrogen in N-Co@C/CNT-2.6 catalysts are 15.8% and 38.6%, respectively, which are higher than those in N-Co@C (7% and 34%). [ABSTRACT FROM AUTHOR]

Layered perovskite (La1−xSrx)2CoO4±δ (x = 0.3, 0.4, 0.5) oxides were prepared using sol–gel route and evaluated as the cathode materials for intermediate-temperature solid-oxide fuel cells. (La1−xSrx)2CoO4±δ has a tetragonal structure with space group of I4/mmm in all cases of x levels. The average thermal expansion coefficient of (La1−xSrx)2CoO4±δ is relatively low and slightly increases with x, which can be ascribed to the sway of Sr doping on the spin-state transition of Co ions. X-ray photoelectron spectroscopy and thermogravimetric analysis show that Co ions exist in mixed oxidation states, but the lattice oxygen content considerably varies with x. Regarding transport property, (La1−xSrx)2CoO4±δ behaves like a semiconductor in the temperature range of 200–800 °C, and the electrical conductivity significantly increases with x. As one of the most important results, electrochemical performance of (La1−xSrx)2CoO4±δ cathode is affected by x in a complex manner, and x = 0.4 cathode, i.e., La1.2Sr0.8CoO4±δ, has the most favored area-specific resistance of 0.062 Ω cm2 and the highest power density of 630 mW cm−2 in an electrolyte-supported single cell at 800 °C, showing a rapid kinetics toward oxygen reduction reaction. This study demonstrates that the structural, transport, thermal, and electrochemical properties of (La1−xSrx)2CoO4±δ cathodes significantly depend on the La/Sr ratio at the A-site of lattice. Rietveld refinement profile and temperature-dependent electrochemical performance for La1.2Sr0.8CoO4±δ cathode material [ABSTRACT FROM AUTHOR]

The design of bifunctional non-precious metal catalyst with good ORR and OER activity is of great significance for the development and commercialization of fuel cells. However, the sluggish and strong irreversible nature of the oxygen electrochemical kinetics makes it difficult to manufacture single bifunctional material. Therefore, we prepared a bifunctional catalyst (Co3O4/N-rGO) with different particle diameters through a one-pot synthesis method, and studied the dependence of the electrocatalytic performance of the catalyst on the particle size of Co3O4. The results showed that Co3O4/N-rGO with 27–31 nm particle size prepared by using N-rGO as the carrier, cobalt acetate concentration of 0.075 M, hydrothermal temperature of 190 °C, and hydrothermal time of 3 h takes a 4e-reaction pathway, which exhibited better ORR and OER activity, excellent current stability and methanol tolerance than JM 20% Pt/C and JM 5% RuO2/C. [ABSTRACT FROM AUTHOR]

The key to sustainable energy application is the rational utilization of abundant materials on the earth. Fe, Co, and Cu theoretically exhibit high oxygen reduction capability close to Pt. However, their high diffusion behaviors make it difficult to homogeneously incorporate with carbon at elevated fabrication temperature. Here, polyaniline is developed an incorporated frame to realize the homodisperse of Fe, Co, or Cu. Three efficient oxygen reduction catalysts, including Fe-polyaniline/carbon (Fe-N/C), Co-N/C, and Cu-N/C are synthesized by a three-step method combining polymerization, complexation, and pyrolysis. All catalysts with metal doping reveal high catalytic activity, good cyclic stability, and the activity varies with different doping metal. The Fe-doped catalyst exhibits the best oxygen reduction ability with onset and half-wave potentials of − 104 mV and − 199.5 mV. Furthermore, the influence of complexation time and the pyrolysis temperature on the oxygen reduction activity are also studied systematically. These interesting discoveries may contribute to provide important ideas to oxygen reduction catalysts. [ABSTRACT FROM AUTHOR]

Electrocatalysts for oxygen reduction reaction have been the study of interest because of their importance in various energy storage and conversion reactions. Though platinum-based catalysts are found to be the most active catalysts for oxygen reduction reactions, their high cost and scarcity have led researchers to discover alternative active and cost-effective catalysts. In this regard, heteroatom- and metalloid-doped catalysts were explored as possible alternatives to traditional platinum-based catalysts. Consequently, a large number of heteroatom- and metalloid-doped catalysts have been synthesized and evaluated for oxygen reduction activity. Synergistic catalysts, with dual-doped, tri-doped, and multi-heteroatom-doped catalysts, were also synthesized by doping more than one heteroatom. In this review, we discuss the fundamental principles and reasons behind the origin of ORR catalysis of heteroatom- and metalloid-doped catalysts discussed with the support of literatures. [ABSTRACT FROM AUTHOR]

Fuel cells and metal-air batteries have been comprehensively investigated in recent years because of their high energy capacity, good efficiency and environmental friendly nature. Slow kinetics of oxygen reduction reaction (ORR), one of the main processes in fuel cells and metal-air batteries, is improved with platinum catalysts that confine the prevalent utilization of such electrochemical devices with increasing worth for them. However, platinum catalysts after long time usage exhibit weak operations due to the crossover effect and agglomeration. Metal–organic frameworks (MOFs), the porous crystalline materials, consisting of metal centers coordinated to organic ligands, are appropriate catalysts due to their superior properties such as high surface area and carbon content, tunable pore size and diverse metal nodes. In this review, we summarize the recent progress in synthesis and design of MOF-derived ORR electrocatalysts in acidic and alkaline fuel cells. Our focus is on the different methods developed for improving the activity and stability of MOF based ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

Cyclic voltammetry as a simple electrochemical deposition method was developed in order to prepare a platinum nano-electrocatalyst for oxygen reduction reaction (ORR) in low-temperature fuel cell systems. The morphology of the prepared platinum was evaluated by scanning electron microscopy and energy dispersive x-ray analysis. The effects of platinum concentration in electrodeposition solution and scan numbers of cyclic voltammetry (scan rate: 50 m V s−1, between 1.489 and − 0.311 versus reversible hydrogen electrode) on the performance of prepared electrocatalysts for ORR were studied. The fabricated electrodes were evaluated by cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The results revealed that the optimum conditions for the preparation of electrocatalysts were 2E−3 M H2PtCl6 and 30 scan numbers. The optimized electrode showed high stability after 1200 cycles. [ABSTRACT FROM AUTHOR]

Abstract: Atomic layer deposition (ALD) was used to modify two different types of carbon black-based Pt oxygen reduction catalysts with protective TiO2 nanostructures to increase catalyst durability. Rates of ALD growth and the structure of deposited TiO2 were observed to be highly dependent on oxygen content of the catalyst substrate. Electrochemical durability was enhanced with the addition of TiO2 ALD nanostructures, with up to 70% retention in mass activity measured over accelerated durability testing. High-temperature treatment of the top-performing ALD catalyst, which was found to promote structural rearrangement of the TiO2 and Pt phases into hybrid nanoparticles, yielded a twofold increase in activity but was detrimental to durability.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Abstract: C-MnO2 is an alternative catalyst support in polymer electrolyte membrane fuel cells. In this study, C-MnO2 was prepared by hydrothermal method using KMnO4 as the Mn source. Meanwhile, Pt/C-MnO2 electrocatalyst was prepared by impregnation chemical reduction using ethylene glycol as reducing agent and H2PtCl6 as Pt precursor. The structure and morphology of C-MnO2 and Pt/C-MnO2 were characterized by X-ray diffraction energy-dispersive spectroscopy and transmission electronic microscopy analyses. Electrochemical performance was investigated by cyclic voltammetry analyses. A rotating disk electrode (RDE) was used to examine catalytic oxygen reduction reactions (ORRs) to explore the oxygen reduction of Pt/C-MnO2. The Pt/C-MnO2 exhibited better activity and stability than those of Pt/C. In contrast to Pt/C, MnO2 possessed unique characteristics; the oxide functions as an effective Pt support and hence enhances ORR activity and durability. The RDE results for the ORR indicated that the main reaction of the Pt/C-MnO2 catalyst was the direct reduction of O2-H2O. This reaction is similar to the mechanism of the Pt/C catalyst and both with a four-electron charge transfer. The results of the single cell polarization experiment and the ON-OFF cycling test revealed that MnO2 improves proton exchange membrane fuel cells performance and durability. This paper also investigated the mechanism through which MnO2 promotes oxygen reduction.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Abstract: We evaluated the performance and durability of platinum-iron-copper with an L10 ordered face-centered tetragonal structure (fct-PtFeCu) as cathode catalysts of membrane-electrode assemblies (MEAs) in polymer electrolyte fuel cells. The exchange current density per unit active surface area of Pt in fct-PtFeCu/C, measured in the MEA, was sufficiently higher than that of commercial Pt/C. The durability of the MEAs was evaluated by three accelerated degradation tests: (1) a load cycle durability test, which mainly accelerates the degradation of catalysts; (2) an open-circuit voltage (OCV) hold test, which mainly degrades membranes; and (3) a hybrid of the load cycle test and OCV hold test. Despite the possible negative effects of dissolved transition metals on the durability of MEAs, fct-PtFeCu/C showed higher durability than commercial Pt/C and at least comparable durability with in-house Pt/C in the OCV hold test, and showed high durability in the hybrid test up to 200 h. These results suggest that the presence of Fe and Cu did not negatively affect the durability of the MEA with fct-PtFeCu/C, and rather the other factor, carbon support, affected more in retaining the durability.Graphical Abstract: [ABSTRACT FROM AUTHOR]

The present work reports novel soft X-ray Fresnel CDI ptychography results, demonstrating the potential of this method for dynamic in situ studies. Specifically, in situ ptychography experiments explored the electrochemical fabrication of Co-doped Mn-oxide/polypyrrole nanocomposites for sustainable and cost-effective fuel-cell air-electrodes. Oxygen-reduction catalysts based on Mn-oxides exhibit relatively high activity, but poor durability: doping with Co has been shown to improve both reduction rate and stability. In this study, we examine the chemical state distribution of the catalytically crucial Co dopant to elucidate details of the Co dopant incorporation into the Mn/polymer matrix. The measurements were performed using a custom-made three-electrode thin-layer microcell, developed at the TwinMic beamline of Elettra Synchrotron during a series of experiments that were continued at the SXRI beamline of the Australian Synchrotron. Our time-resolved ptychography-based investigation was carried out in situ after two representative growth steps, controlled by electrochemical bias. In addition to the observation of morphological changes, we retrieved the spectroscopic information, provided by multiple ptychographic energy scans across Co L3-edge, shedding light on the doping mechanism and demonstrating a general approach for the molecular-level investigation complex multimaterial electrodeposition processes. [ABSTRACT FROM AUTHOR]

Large-scale production of active and stable porous carbon catalysts for oxygen reduction reaction (ORR) from protein-rich biomass became a hot topic in fuel cell technology. Here, we report a facile strategy for synthesis of nitrogen-doped porous nanocarbons by means of a simple two-step pyrolysis process combined with the activation of zinc chloride and acid-treatment process, in which kidney bean via low-temperature carbonization was preferentially adopted as the only carbon-nitrogen sources. The results show that this carbon material exhibits excellent ORR electrocatalytic activity, and higher durability and methanol-tolerant property compared to the state-of-the-art Pt/C catalyst for the ORR, which can be mainly attributed to high graphitic-nitrogen content, high specific surface area, and porous characteristics. Our results can encourage the synthesis of high-performance carbon-based ORR electrocatalysts derived from widely-existed natural biomass. [ABSTRACT FROM AUTHOR]

Nitrogen (N)-doped carbons reportedly exhibit good electrocatalytic activity for the oxygen reduction reaction (ORR) of fuel cells. This work provides theoretical insights into the ORR mechanism of N-doped graphene by using density functional theory calculations. All possible reaction pathways were investigated, and the transition state of each elementary step was identified. The results showed that OOH reduction was easier than O–OH breaking. OOH reduction followed a direct Eley–Rideal mechanism (the OOH species was in gas phase, but H was chemisorbed on the surface) with a significantly low reaction barrier of 0.09 eV. Pathways for both four-electron and two-electron reductions were possible. The rate-determining step of the two-electron pathway was the reduction of O 2 (formation of OOH), whereas that of the four-electron pathway was the reduction of OH into H 2O. After comparing the barriers of the rate-determining steps of the two pathways, we found that the two-electron pathway was more energetically favored than the four-electron pathway. [ABSTRACT FROM AUTHOR]

There is a growing interest in designing more effective fuel cell cathode catalyst precursors. Here the partial pyrolysis of animal bloods has been used to produce the blood pyropolymers, which are an intermediate substance between a polymer and carbonaceous material. These pyropolymers were yielded by carbonization process below 600°C. The structural changes in the pyropolymers were characterized by X-ray diffraction, and their formation was checked by micro-IR spectra, thermogravimetric and differential thermal analysis. Their potential electrocatalytic properties were evaluated using the linear sweep voltammetry in the O-saturated KOH solution. It is found that the process of pyropolymer formation began about 200°C and completed around 500°C. The change of particle phase depends on the formation of the pyropolymers, but has no effect to their internal carbon structures which are controlled by pyrolysis process only. Meanwhile, it is confirmed that the crystalline phases in the pyropolymers can exist at the surface of heat-treated materials. It can be also found that the carbon materials are active toward oxygen reduction and their activity is associated with the carbonization level. Our study will stimulate the designers to design the highly active catalysts by using native blood pyropolymers as the precursors. [ABSTRACT FROM AUTHOR]

The electrocatalytic activity for oxygen reduction reaction (ORR) at neutral pH of citrate-capped silver nanoparticles (diameter = 18 nm) supported on glassy carbon (GC) is investigated voltammetrically. Novelly, the modification of the substrate by nanoparticles sticking to form a random nanoparticle array and the voltammetric experiments are carried out simultaneously by immersion of the GC electrode in an air-saturated 0.1 M NaClO solution (pH = 5.8) containing chemically-synthesized nanoparticles. The experimental voltammograms of the resulting nanoparticle array are simulated with homemade programs according to the two-proton, two-electron reduction of oxygen to hydrogen peroxide where the first electron transfer is rate determining. In the case of silver electrodes, the hydrogen peroxide generated is partially further reduced to water via heterogeneous decomposition. Comparison of the results obtained on a silver macroelectrode and silver nanoparticles indicates that, for the silver nanoparticles and particle coverages (0.035%-0.457%) employed in this study, the ORR electrode kinetics is slower and the production of hydrogen peroxide larger on the glassy carbon-supported nanoparticles than on bulk silver. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon (CN x) nanotubes were synthesized by thermal decomposition of ferrocene/ethylenediamine mixture at 600-900 °C. The effect of the temperature on the growth and structure of CN x nanotubes was studied by transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. With increasing growth temperature, the total nitrogen content of CN x nanotubes was decreased from 8.93 to 6.01 at.%. The N configurations were changed from pyrrolic-N to quaternary-N when increasing the temperature. Examination of the catalytic activities of the nanotubes for oxygen reduction reaction by rotating disk electrode measurements and single-cell tests shows that the onset potential for oxygen reduction in 0.5 M HSO of the most effective catalyst (CN x nanotubes synthesized at 900 °C) was 0.83 V versus the normal hydrogen electrode. A current density of 0.07 A cm at 0.6 V was obtained in an H/O proton-exchange membrane fuel cell at a cathode catalyst loading of 2 mg cm. [ABSTRACT FROM AUTHOR]

Cobalt phthalocyanine (CoPc)-impregnated functionalized multi-walled carbon nanotubes (CNTs) were used as nonprecious electrocatalysts for oxygen reduction reaction (ORR). The electrocatalysts were thermally treated at temperatures ranging from 450 to 850 °C, and the effect of pyrolysis temperature and their relationship to the electrocatalytic activity for ORR were investigated. Thermo gravimetric analysis, X-ray diffraction, and electron microscopy were used to study the thermal stability, crystal structure, and morphology of these catalysts. Cyclic voltammetry and rotating disk electrode results showed that CoPc/CNTs pyrolyzed at a temperature of 550 °C had the highest electrocatalytic activity for ORR, and the catalytic activity decreased with further increase in pyrolysis temperature. X-ray photoelectron spectroscopy showed decrease in functional groups at a temperature higher than 550 °C, correlating with the decreased catalytic activity. The result suggests that oxygen functional groups introduced by acid oxidation for anchoring the CoPc on CNT plays a major role in determining the electrocatalytic activity. [ABSTRACT FROM AUTHOR]

It is of great significance in exploring alternative catalysts to platinum (Pt)-based materials for oxygen reduction reaction (ORR), because this reaction is invariably involved in various fuel cells and metal-air batteries. We herein reported the nitrogen doped graphene nanosheets (NGNSs) with pore volume of as high as 3.42 m/g and investigated their potential application as ORR catalysts, it was demonstrated the NGNSs featured high activity, improved kinetics and excellent long-term stability for ORR. The NGNSs were successfully used as cathode catalysts of microbial fuel cells (MFCs) and performed even better than the commercial Pt/C (Pt 10%) catalysts at the maximum power output. [ABSTRACT FROM AUTHOR]

Pd nanoparticles have been synthesised using different reducing agents, including ethylene glycol (EG), formaldehyde and sodium borohydride and their activity for the oxygen reduction reaction (ORR) evaluated. The use of EG led to the best morphology for the ORR and this synthetic method was optimised by adjusting the system pH. Carbon-supported Pd nanoparticles of approximately 7 nm diameter were obtained when reduction took place in the alkaline region. Pd synthesised by EG reduction at pH 11 presented the highest mass activity 20 A g and active surface area 15 m g. These synthetic conditions were used in further synthesis. The effect of heat treatment in H atmosphere was also studied; and increased size of the palladium nanoparticles was observed in every case. The Pd/C catalyst synthesised by reduction with EG at pH 11 was tested in a low temperature H/O (air) PEMFC with a Nafion 112 membrane, at 20 and 40 °C. Current densities at 0.5 V, with O fed to the cathode, at 40 °C were 1.40 A cm and peak power densities 0.79 W cm, approximately; which compared with 1.74 A cm and 0.91 W cm, respectively for a commercial Pt/C. [ABSTRACT FROM AUTHOR]

Macrocyclic compounds such as metallophthalocyanines demonstrated good catalytic activities toward electrochemical reactions. The characteristics of the central cations in metallophthalocyanines significantly influenced their electrocatalytic activities. Addition of conjugated polymers in electrodes improved the electrocatalytic activity by enhancing the electric conductivity. The electrocatalytic activities of macrocyclic compounds could be further improved by heat treatment. The formation of metallic clusters or metal containing organic fragments after pyrolyzing played an important role in improving electrocatalytic activities of macrocyclic compounds. It was considered that macrocyclic compounds might be functioned as a precursor to obtain well-distributed metallic clusters or metal containing organic fragments. [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFCs) are a potential method for enhanced water and waste treatment, which offer the additional benefit of energy generation. Manganese oxide was prepared by a simple chemical oxidation using potassium permanganate. Carbon-supported manganese oxide nanoparticles were successfully characterised as cathode materials for MFCs. The manganese oxide particles when used in a two-chamber MFC, using inoculum from an anaerobically digested sewage sludge, were found to exhibit similar oxygen reduction performance to that in separate electrochemical tests. MFC tests were conducted in a simple two chamber cell using aqueous air-saturated catholytes separated from the anode chamber by a Nafion membrane. MFC peak power densities were ca. 161 mW m−2 for MnO x/C compared to 193 mW m−2 for a benchmark Pt/C, in neutral solution at room temperature. The catalyst materials demonstrated good stability in the 7.0–10.0 pH range. Theoretical (IR free) peak power densities were 937 mW m−2 for MnO x/C compared with 1037 mW m−2 for Pt/C in the same experimental conditions: showing the MFCs performances can easily be improved by using more favourable conditions (more conductive electrolyte, improved cathode catalyst etc.). Our studies indicated that the use of our low cost MnO x/C catalysts is of potential interest for the future application of MFC systems. [ABSTRACT FROM AUTHOR]

A three-dimensional numerical model is developed to simulate the transport phenomena on the cathodic side of a polymer electrolyte membrane fuel cell (PEMFC) that is in contact with parallel and interdigitated gas distributors. The computational domain consists of a flow channel together with a gas diffusion layer on the cathode of a PEMFC. The effective diffusivities according to the Bruggman correlation and Darcy's law for porous media are used for the gas diffusion layer. In addition, the Tafel equation is used to describe the oxygen reduction reaction (ORR) on the catalyst layer surface. Three-dimensional transport equations for the channel flow and the gas diffusion layer are solved numerically using a finite-volume-based numerical technique. The nature of the multi-dimensional transport in the cathode side of a PEMFC is illustrated by the fluid flow, mass fraction and current density distribution. The interdigitated gas distributor gives a higher average current density on the catalyst layer surface than that with the parallel gas distributor under the same mass flow rate and cathode overpotential. Moreover, the limiting current density increased by 40% by using the interdigitated flow field design instead of the parallel one. [ABSTRACT FROM AUTHOR]

Great efforts have been dedicated to finding economic and efficient oxygen reduction reaction (ORR) for fuel cell technology. Among various catalysts, N-doped carbon-based nanomaterials have attracted much attention due to low-cost, noble metal free, and good durability. Herein, we developed a facile and economic strategy to prepare nitrogen-doped carbon networks for efficient ORR application. The g-C3N4 is used as the template and N source, and dopamine is used as the carbon source. By simple hydrothermal treatment and sintering, N-doped carbon network structures with high specific surface area, effective ORR activity, and superior durability could be acquired. The present strategy is free of involving generally multistep, poisonous reagents, and complication of removing template for fabrication of 3D carbon structures. [ABSTRACT FROM AUTHOR]

Developments of high efficient materials for electrocatalyst are significant topics of numerous researches since a few decades. Recent global interests related with energy conversion and storage lead to the expansion of efforts to find cost-effective catalysts that can substitute conventional catalytic materials. Especially, in the field of fuel cell, novel materials for oxygen reduction reaction (ORR) have been noticed to overcome disadvantages of conventional platinum-based catalysts. Various approaching methods have been attempted to achieve low cost and high electrochemical activity comparable with Pt-based catalysts, including reducing Pt consumption by the formation of hybrid materials, Pt-based alloys, and not-Pt metal or carbon based materials. To enhance catalytic performance and stability, numerous methods such as structural modifications and complex formations with other functional materials are proposed, and they are basically based on well-defined and well-ordered catalytic active sites by exquisite control at nanoscale. In this review, we highlight the development of nano-structured catalytic materials for ORR based on recent findings, and discuss about an outlook for the direction of future researches. [ABSTRACT FROM AUTHOR]