Low Peroxide Yield Research Articles

One-pot gamma radiolysis synthesis of a graphene oxide-supported cobalt oxyhydroxide electrocatalyst for oxygen reduction reaction

In this work, high-performance non-platinum group metal (non-PGM) electrocatalysts for oxygen reduction reaction (ORR) are synthesized from graphene oxide-supported cobalt oxyhydroxide nanoparticles via a one-pot gamma radiolysis method. Investigations are conducted into how cobalt precursor concentration and the amount of gamma radiation affect the electrocatalysts' ability to perform oxygen reduction reactions as well as their physicochemical characteristics. Results show that the electrocatalyst prepared with the 0.1 M cobalt precursor and gamma radiation dose of 25 kGy has an advantage over the other samples in displaying good oxygen reduction activity. The characterization results of the synthesized electrocatalyst obtained through field-emission scanning electron microscopy–energy dispersive spectroscopy and X-ray diffraction combined with Rietveld refinement confirm the presence of nanosized cobalt oxyhydroxide particles that are evenly distributed on the surface of graphene oxide. ORR results show that the electrocatalyst has an onset potential of 0.90 V (vs. the reversible hydrogen electrode or RHE), a half-wave potential of 0.75 V (vs. RHE), a low peroxide yield of 7.08%, and an electron transfer number of 3.86, indicating a four-electron transfer path-way in the ORR process. This work provides an alternative facile means to mass-produce competitive non-PGM ORR electrocatalysts for fuel cell applications.

Cobalt-Containing Nitrogen-Doped Carbon Materials Derived from Saccharides as Efficient Electrocatalysts for Oxygen Reduction Reaction

The development of non-precious metal electrocatalysts towards oxygen reduction reaction (ORR) is crucial for the commercialisation of polymer electrolyte fuel cells. In this work, cobalt-containing nitrogen-doped porous carbon materials were prepared by a pyrolysis of mixtures of saccharides, cobalt nitrate and dicyandiamide, which acts as a precursor for reactive carbon nitride template and a nitrogen source. The rotating disk electrode (RDE) experiments in 0.1 M KOH solution showed that the glucose-derived material with optimised cobalt content had excellent ORR activity, which was comparable to that of 20 wt% Pt/C catalyst. In addition, the catalyst exhibited high tolerance to methanol, good stability in short-time potential cycling test and low peroxide yield. The materials derived from xylan, xylose and cyclodextrin displayed similar activities, indicating that various saccharides can be used as inexpensive and sustainable precursors to synthesise active catalyst materials for anion exchange membrane fuel cells.

Utilizing waste duckweed from phytoremediation to synthesize highly efficient Fe[sbnd]Nx[sbnd]C catalysts for oxygen reduction reaction electrocatalysis

Duckweed is a universal aquatic plant to remove nitrogen source pollutants in the field of phytoremediation. Due to the naturally abundant nitrogen, synthesis of carbon materials from duckweed would be a high-value approach. In oxygen reduction reaction (ORR) of metal-air batteries and fuel cells, non-noble metals and heteroatoms co-doped electrocatalysts with excellent catalytic activity and remarkable stability are promising substitutes for Pt-based catalysts. The first-class ORR performance is determined by appropriate pore structure and active sites, which are strongly associated with the feasible synthesis methods. Herein, a facile one-step synthesis strategy for the transition metals- and nitrogen-codoped carbon (MNxC) based catalysts with hierarchically porous structure was developed. The MNxC (M = Fe, Co, Ni, and Mn) active sites were constructed and FeNxC (D-ZB-Fe) was the best electrocatalyst with excellent ORR performance. Results showed that D-ZB-Fe exhibited an obvious honeycomb porous structure with specific surface area of 1342.91 m2·g−1 and total pore volume of 1.085 cm3·g−1. It also possessed considerable active atoms and sites, where the proportion of pyridine N and graphite N was up to 72.9%. The above feature made for a superior ORR electrocatalytic activity. In specific, the onset and half-wave potential were 0.974 V and 0.857 V vs. RHE (Reversible Hydrogen Electrode), respectively. When compared with performances of commercial Pt/C, the four-electron pathway and relatively low peroxide yield, ca. 5%, were almost equivalent. Furthermore, D-ZB-Fe showed an excellent stability and remarkably methanol tolerance by the durability test. In conclusion, this research provides a new synthesis strategy of electrocatalysts with porous structures and active sites.

Heteroatom-Doped Graphites Oxygen Reduction Catalysts for Anion Exchange Membrane Fuel Cells

Catalysts for the oxygen reduction reaction (ORR) are crucial for electrochemical energy conversion and storage devices. The development of active, ultra-low-cost, critical raw materials-free catalysts is vital for the success of the anion exchange membrane fuel cell (AEMFC) technology [1]. In this work, we present metal-free oxygen reduction catalysts based on heteroatoms (I, N, S or B)-doped graphites by a scalable and reproducible one-step planetary ball milling protocol [2]. The distribution and the morphology of these ultra-low cost catalysts are characterized by advanced electron microscopy showing uniform distribution of heteroatoms in the graphite matrix. We have tested the catalysts for ORR in 0.1 M KOH solution in a rotating ring disk electrode (RRDE) and doped-graphites showed enhanced ORR performance relative to the pristine graphite. Among these, the N-graphite exhibiting the highest ORR onset potential of 0.87 V with a low peroxide yield of 15%@0.1 V. Good ORR kinetic (jk,s ) and mass (ik,m ) activities were also obtained. The catalysts also show remarkable stability in both RDE stress and corrosion tests. Finally, we showed good performance in operando H2-O2 AEMFC, reaching ~350 mW cm‒ 2 at 60 oC with a high voltage efficiency. These results encourage further development of metal-free ultra-low-cost and stable catalysts, easily scalable for AEMFC cathode production.

Regulating Electrocatalytic Oxygen Reduction Activity of a Metal Coordination Polymer via d-π Conjugation.

Non-noble transition metal complexes have attracted growing interest as efficient electrocatalysts for oxygen reduction reaction (ORR) while their activities still lack rational and effective regulation. Herein, we propose a d-π conjugation strategy for rough and fine tuning of ORR activity of TM-BTA (TM=Mn/Fe/Co/Ni/Cu, BTA=1,2,4,5-benzenetetramine) coordination polymers. By first-principle calculations, we elucidate that the strong d-π conjugation elevates the dxz /dyz orbitals of TM centers to enhance intermediate adsorption and strengthens the electronic modulation effect from substitute groups on ligands. Based on this strategy, Co-TABQ (tetramino benzoquinone) is found to approach the top of ORR activity volcano. The synthesized Co-TABQ with atomically distributed Co on carbon nanotubes exhibits a half-wave potential of 0.85 V and a specific current of 127 mA mgmetal -1 at 0.8 V, outperforming the benchmark Pt/C. The high activity, low peroxide yield, and considerable durability of Co-BTA and Co-TABQ promise their application in oxygen electrocatalysis. This study provides mechanistic insight into the rational design of transition metal complex catalysts.

Regulating Electrocatalytic Oxygen Reduction Activity of a Metal Coordination Polymer via d–π Conjugation

AbstractNon‐noble transition metal complexes have attracted growing interest as efficient electrocatalysts for oxygen reduction reaction (ORR) while their activities still lack rational and effective regulation. Herein, we propose a d–π conjugation strategy for rough and fine tuning of ORR activity of TM‐BTA (TM=Mn/Fe/Co/Ni/Cu, BTA=1,2,4,5‐benzenetetramine) coordination polymers. By first‐principle calculations, we elucidate that the strong d–π conjugation elevates the dxz/dyz orbitals of TM centers to enhance intermediate adsorption and strengthens the electronic modulation effect from substitute groups on ligands. Based on this strategy, Co‐TABQ (tetramino benzoquinone) is found to approach the top of ORR activity volcano. The synthesized Co‐TABQ with atomically distributed Co on carbon nanotubes exhibits a half‐wave potential of 0.85 V and a specific current of 127 mA mgmetal−1 at 0.8 V, outperforming the benchmark Pt/C. The high activity, low peroxide yield, and considerable durability of Co‐BTA and Co‐TABQ promise their application in oxygen electrocatalysis. This study provides mechanistic insight into the rational design of transition metal complex catalysts.

Two-step pyrolytic engineering to form porous nitrogen-rich carbons with a 3D network structure for Zn-air battery oxygen reduction electrocatalysis

It is of great urgency to design inexpensive and high-performance oxygen reduction reaction (ORR) electrocatalysts derived from biowastes as substitutes for Pt-based materials in electrochemical energy-conversion devices. Here we propose a strategy to synthesize three-dimensional (3D) porous nitrogen-doped network carbons to catalyze the ORR from two-step pyrolysis engineering of biowaste scale combined with the use of a ZnCl2 activator and a FeCl2 promotor. Electrochemical tests show that the synthesized network carbons have exhibited comparable ORR catalytic activity with a half-wave potential (~0.85 V vs. RHE) and outstanding cyclical stability in comparison to the Pt/C catalyst. Beyond that, a high electron transfer number (~3.8) and a low peroxide yield (<7.6%) can be obtained, indicating a four-electron reaction pathway. The maximum power density is ~68 mW cm−2, but continuous discharge curves (at a constant potential of ~1.30 V) for 12 h are not obviously declined in Zn-air battery tests using synthesized network carbons as the cathodic catalyst. The formation of 3D porous structures with high BET surface area can effectively expose the surface catalytic sites and promote mass transportation to boost the ORR activity. This work may open a new idea to prepare porous carbon-based catalysts for some important reactions in new energy devices.

Dual-nitrogen-source strategy for N-doped graphitic layer-wrapped metal carbide toward efficient oxygen reduction reaction

Rational design of low-cost and high-efficient non-precious-metal catalysts for oxygen reduction reaction (ORR) has drawn tremendous attention. Herein, we report a facile template-sacrificing strategy to synthesize N-doped hierarchically porous graphitic layers wrapped iron carbide (Fe3C@NPGL). Cost-effective graphitic carbon nitride (g-C3N4) combined with dopamine were used as dual-nitrogen-source which provide more active sites for ORR. By virtue of abundant Fe-N coordination sites and unique porous structure of NPGL, the as-fabricated Fe3C@NPGL exhibits excellent ORR performances with a half-wave potential of 0.87 V, a limited current density of 6.3 mA cm−2, and a low peroxide yield (<2.5%), which outperform commercial Pt/C and most of the reported non-precious-metal catalysts. This work provides a feasible strategy to design novel ORR electrocatalysts.

Designed self-assembly of iron encapsulated doped porous carbon as durable electrocatalyst for oxygen reduction reaction in alkaline medium

A probable pore-formation mechanism of self-assembled doped porous carbon has been proposed. Hydrogen-bonding interaction between different precursors plays a crucial role in determining the porous morphology. The high specific surface area of porous carbon network consists of an abundant number of mesopores as well as micropores which promote the enhanced diffusion of ions and further reduce the mass transfer losses by increasing the number of triple phase boundaries (TPBs). Encapsulation of iron particles within the porous framework not only preserves the intrinsic catalytic properties of the metal also enhances the durability of the catalyst. Iron incorporation in nitrogen (N), boron (B) and co-doped porous carbon predominantly improves the reaction kinetics compared to metal-free catalysts in terms of onset potential and current density. Iron incorporated N and B co-doped porous carbon (Fe/NBPC) has exhibited an onset potential of −0.12 V vs SCE with low peroxide yield of 12%. Comprehensive theoretical analysis based on net charge transfer and total density of states reveal the superiority of co-doping. Present work validates multi-element doped carbon network can be considered as a promising replacement of Pt-based catalysts for fuel cells in alkaline medium.

Harnessing inherently hierarchical microstructures of plant biomass to construct three-dimensional nanoporous nitrogen-doped carbons as efficient and durable oxygen reduction electrocatalysts.

Exploiting the natural structures of plants to prepare high-performance carbon-based electrocatalysts is highly desirable. Herein, the inherently hierarchical microstructures of Euphorbia tirucalli (E. tirucalli) are employed to construct three-dimensional nanoporous nitrogen-doped carbons that act as efficient and durable electrocatalysts towards the oxygen reduction reaction (ORR). During the preparation process, agar is used in order to reduce the dissipation of nitrogen and to protect the fine structures of E. tirucalli. The as-prepared ORR catalyst, with a high density of pyridinic and graphitic nitrogens, presents a high catalytic activity (onset potential of 0.97 V vs. RHE, half-wave potential of 0.82 V vs. RHE, limiting current density of 5.64 mA cm−2 and Tafel slope of 59 mV dec−1), four-electron pathway, low peroxide yield, long-term stability (current retention of 95.3% after 50 000 s) and strong methanol tolerance in 0.1 M KOH, all superior to the benchmark 20% Pt/C commercial catalyst. This work demonstrates an effective method for the utilization of inherently hierarchical microstructures of plant biomass to make efficient and durable carbon-based metal-free ORR electrocatalysts.

Structure-Activity-Durability Relationships of (CM+PANI)-Me-C PGM-Free Catalysts

The development of durable and highly active platinum group metal-free (PGM-free) electrocatalysts is key to overcoming the greatest barrier in the commercialization of fuel cell electric vehicles: the high cost and limited availability of PGM catalysts utilized in polymer electrolyte fuel cells. While the majority of research on PGM-free catalysts has focused on developing active and selective materials for the sluggish oxygen reduction reaction (ORR), minimal work has been devoted to the understanding of the physical and chemical structure of active PGM-free catalysts and its relationship with the long-term stability of these novel materials. This understanding is imperative for the further development of next-generation PGM-free catalysts with improved activity and durability that could ultimately replace PGM-based ORR catalysts in fuel cells. PGM-free catalysts with high volumetric activity, four-electron selectivity (i.e., low hydrogen peroxide yield), and long-term stability in highly acidic and strongly oxidizing environment of the fuel cell cathode are desired as replacements for PGM-based ORR catalysts. For this presentation, state-of-the-art PGM-free ORR catalysts, developed by our group [1, 2], which are obtained via high-temperature treatment of dual nitrogen precursors, cyanamide (CM) and polyaniline (PANI), different transition metal precursors (Fe, Co, Mn), and with or without carbon support are used as model PGM-free catalyst systems. Depending on the transition metal used, catalysts with different physical and electrochemical characteristic properties are obtained. Specifically, Fe-based catalysts are generally known for their high activity and low peroxide yield generation. However, Co- and Mn-based catalysts generate highly graphitic structures which could improve catalyst long-term stability. In this work, structure-activity-durability relationships are developed based on comprehensive physical, chemical, and electrochemical characterization of highly active (CM+PANI)-Me-C catalysts (Me = Fe, Co, Mn), correlating properties such as carbon structure, elemental speciation, and CO2 generation. Acknowledgement Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged. [1] Chung, H.T., Holby, E.F., Purdy, G.M., Babu, S.K., Litster, S., Cullen, D.A. More, K.L., Zelenay, P. (2015). “Combining Nitrogen Precursors in Synthesis of Non-Precious Metal ORR Catalysts with Improved Fuel Cell Performance.” ECS Meeting s, MA2015-02 (37), 1278. [2] Martinez, U., Holby, E.F., Dumont, J.H., Chung, H.T., Zelenay, P. (2016) “Non-PGM ORR Catalysts Based on Transition Metals Alternative to Iron.” ECS Meeting s, MA2016-01, 1719.

Transformation from FeS/Fe3C nanoparticles encased S, N dual doped carbon nanotubes to nanosheets for enhanced oxygen reduction performance

Carbon nanotubes-supported non-precious metal nanoparticles emerge as promising catalyst candidate for fuel cell. Although it is well known that carbon nanotubes can influence the catalytic activity of transition metal nanoparticles, insights into whether the unrolling of carbon nanotubes can be exploited to enhance the oxygen reduction performance are lacking. Herein we demonstrate the transformation from FeS/Fe3C nanoparticles coupled S, N dual doped carbon nanotubes (FeS/Fe3C@S, N-C) to nanosheets can yield the improved oxygen reduction performance. Under a glucose protective strategy, the walls of FeS/Fe3C@S, N-C nanotubes were unrolled and extended, creating FeS/Fe3C nanoparticles coupled S, N dual doped carbon nanosheets (FeS/Fe3C@S, N-C g(50)) with larger surface area and higher doping level, which allowed for the exposure of sufficient accessible active sites. Consequently, FeS/Fe3C@S,N-C g(50) exhibited an onset potential of 0.938 V, together with low peroxide yield, good selectivity and durability. Our investigations showed that the carbon matrix with an opened structure and abundant accessible active sites is critical to the electrocatalysts. Furthermore, the synergetic effect of the S, N dual doped carbon nanosheets and FeS/Fe3C nanoparticles contributed to the enhanced oxygen reduction activity. We expect the presented structure–activity relationship can provide guidance for future design of advanced electrocatalysts.

Novel highly active and selective Fe-N-C oxygen reduction electrocatalysts derived from in-situ polymerization pyrolysis

Among several candidates considered to replace expensive platinum based catalysts for oxidation reduction reaction (ORR) in fuel cells, iron-nitrogen-carbon (Fe-N-C) composites attract the most interest. In this work, we design a novel method to prepare Fe-N-C catalysts for ORR in both acid and alkaline media. It involves initial polymerization of different amino-pyridines to form a C-N-C backbone, followed by their high-temperature pyrolysis on silica template, HF etching and second heat treatment in ammonia. Polymerization of 2-amino-6-methylpyridine and 2,6-diaminopyridine was done by in-situ and ex-situ templating methods. The catalysts synthesized by this method possess half-wave potentials of ~ 0.88V versus RHE in O2 saturated 1M KOH electrolyte, and the best catalyst based on 2-amino-6-methylpyridine was seen to achieve an E1/2 greater than 0.7V in the O2 saturated 0.5M sulfuric acid electrolyte. Importantly, the catalysts prepared by this novel method exhibit remarkably low peroxide yield in both acid and base media (< 4% and < 1.3%, respectively) as revealed by rotating ring disk electrode (RRDE) studies.

High‐Performance Oxygen Reduction Electrocatalyst Derived from Polydopamine and Cobalt Supported on Carbon Nanotubes for Metal–Air Batteries

The development of nonprecious metal‐based electrocatalysts for the oxygen reduction reaction holds the decisive key to many energy conversion devices. Among several potential candidates, transition metal and nitrogen co‐doped carbonaceous materials are the most promising, yet their activity and stability are still insufficient to meet the needs of practical applications. In this study, a core–shell hybrid electrocatalyst is developed via the self‐polymerization of dopamine and cobalt on carbon nanotubes (CNTs), followed by high‐temperature pyrolysis. The polymer‐derived carbonaceous shell contains abundant structural defects and facilitates the formation of CoN/C active sites, whereas the graphitic carbon nanotube core provides high electrical conductivity and corrosion resistance. These two components separately fulfill different functionalities, and jointly afford the catalyst with excellent electrochemical performance. In 1 m KOH, CoN/CNT exhibits a positive half‐wave potential of ≈0.91 V, low peroxide yield of &lt;7%, as well as great stability. When used as the air catalyst of primary Zn–air and Al–air batteries, this hybrid electrocatalyst enables large discharge current density, high peak power density, and prolonged operation stability.

A Three-Dimensionally Structured Electrocatalyst: Cobalt-Embedded Nitrogen-Doped Carbon Nanotubes/Nitrogen-Doped Reduced Graphene Oxide Hybrid for Efficient Oxygen Reduction.

To develop low-cost and efficient oxygen reduction reaction (ORR) catalysts, a novel hybrid comprising cobalt-embedded nitrogen-doped carbon nanotubes and nitrogen-doped reduced graphene oxide (Co-NCNT/NrGO-800) was simply prepared by pyrolysis. The combination of nanotubes and graphene, and the efficient doping with cobalt and nitrogen, greatly contribute to the excellent ORR performance. This optimized Co-NCNT/NrGO catalyst exhibits a positive onset potential of 0.91 V and a half-wave potential of 0.82 V, combined with a relatively low peroxide yield, better durability, and better methanol tolerance than commercially available Pt/C, which makes it a promising candidate as a low-cost and effective non-precious-metal ORR catalyst.

Iron polyphthalocyanine sheathed multiwalled carbon nanotubes: A high-performance electrocatalyst for oxygen reduction reaction

The past decade has witnessed a rapid surge of interest in the research and development of non-precious metal-based electrocatalysts for the oxygen reduction reaction (ORR). Until now, the best catalysts in acidic electrolytes have exclusively been Fe-N-C-type materials from high-temperature pyrolysis. Despite the ORR activities of metal phthalocyanine or porphyrin macrocycles having long been known, their durability remains poor. In this work, we use these macrocycles as a basis to develop a novel organic-carbon hybrid material from in-situ polymerization of iron phthalocyanine on conductive multiwalled carbon nanotube scaffolds using a low-temperature microwave heating method. At an optimal polymerto- carbon ratio, the hybrid electrocatalyst exhibits excellent ORR activity with a positive half-wave potential (0.80 V), large mass activity (up to 18.0 A/g at 0.80 V), and a low peroxide yield (<3%). In addition, strong electronic coupling between the polymer and carbon nanotubes is believed to suppress demetallization of the macrocycles, significantly improving cycling stability in acids. Our study represents a rare example of non-precious metal-based electrocatalysts prepared without high-temperature pyrolysis, while having ORR activity in acidic media with potential for practical applications.

Small-sized tungsten nitride anchoring into a 3D CNT-rGO framework as a superior bifunctional catalyst for the methanol oxidation and oxygen reduction reactions

The application of direct methanol fuel cells (DMFC) is hampered by high cost, low activity, and poor CO tolerance by the Pt catalyst. Herein, we designed a fancy 3D hybrid by anchoring tungsten nitride (WN) nanoparticles (NPs), of about 3 nm in size, into a 3D carbon nanotube-reduced graphene oxide framework (CNT-rGO) using an assembly route. After depositing Pt, the contacted and strongly coupled Pt–WN NPs were formed, resulting in electron transfer from Pt to WN. The 3D Pt–WN/CNT-rGO hybrid can be used as a bifunctional electrocatalyst for both methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). In MOR, the catalysts showed excellent CO tolerance and a high mass activity of 702.4 mA·mgPt –1, 2.44 and 3.81 times higher than those of Pt/CNT-rGO and Pt/C(JM) catalysts, respectively. The catalyst also exhibited a more positive onset potential (1.03 V), higher mass activity (151.3 mA·mgPt –1), and better cyclic stability and tolerance in MOR than ORR. The catalyst mainly exhibited a 4e-transfer mechanism with a low peroxide yield. The high activity was closely related to hybrid structure. That is, the 3D framework provided a favorable path for mass-transfer, the CNT-rGO support was favorable for charge transfer, and strongly coupled Pt–WN can enhance the catalytic activity and CO-tolerance of Pt. Pt–WN/CNT-rGO represents a new 3D catalytic platform that is promising as an electrocatalyst for DMFC because it can catalyze both ORR and MOR in an acidic medium with good stability and highly efficient Pt utilization.

Carbon Supported Noble Metal (Pd and Au) Catalysts Synthesized by an Oxide Route with High Performance for Oxygen Reduction in Acidic Media

Carbon supported palladium (C/Pd) and gold (C/Au) catalysts were synthesized through a synthesis route involving oxide precipitation and partial reduction, and their performance for the oxygen reduction reaction (ORR) in acidic media was studied. Scanning electrochemical microscopy (SECM) ORR screening and tip-generation/substrate collection performed on glassy carbon supported metal spots showed a strong effect of the reactant ratio (precursor salt/precipitant/reducing agent) on the performance of the resulting catalysts for oxygen reduction and hydrogen peroxide production. These SECM results were further confirmed using a rotating ring-disk electrode with Nafion-embedded Vulcan carbon supported dispersed metal nanoparticles, and characterization with XRD and TGA. A significant enhancement in the overall activity for the ORR was observed on both C/Pd and C/Au catalysts under conditions involving metal oxide reduction, compared to those catalysts that were synthesized by direct metal salt reduction. For C/Pd, this enhanced overall activity with concomitant low peroxide yield is due to the different ways in which the metal and unreduced metal oxide in the catalysts interact with the hydrogen peroxide pathway. For C/Au, a highly dispersed metal with high electroactive area is obtained that shifts the potentials for the reduction of oxygen to hydrogen peroxide to near-reversible conditions.

Graphene Oxide Based Non Precious Metal Catalysts for Oxygen Reduction Reaction in Alkaline Media

The commercialization and widespread of polymer electrolyte fuel cells (PEFCs) has been limited by the high cost of Pt-based catalysts used in both PEFC anode and cathode. Recently, non-precious metal catalysts (NPMCs) have demonstrated high volumetric activity, low peroxide yield, and stability[1-2] and appear as potential candidates for the replacement of Pt-based oxygen reduction reaction (ORR) catalysts in the PEFC cathode. State-of-the-art NPMCs are typically synthesized from highly heterogeneous precursors[1,3,4], making understanding of the ORR active site in such catalysts particularly arduous. Catalysts based on graphene and graphene-oxide (GO) are more homogeneous and possess properties such as good chemical stability, excellent conductivity, and more importantly, can potentially be functionalized in a controlled manner[5]. GO inherently has a high defect density and can be modified with various functional moieties, e.g. carboxyl, hydroxyl, and epoxy groups using various synthesis techniques such as Hummers or Hoffmans methods. The desire to have a high defect density arises from the possibility that defect sites may serve as niches for the chemical doping of heteroatoms, such as nitrogen (N) that have been proven to play a critical role in the overall performance of NPMCs. Further, the N-doped sites might serve as anchors for the coordination of transition metal atoms such as Fe, leading to the formation of the ORR active sites. In this work, we have synthesized GO using different chemical routes and, subsequently, treated it with different drying strategies and finally doped it with ammonia at various temperatures (500°C-900°C). The electrochemical performance of the synthesized catalysts in oxygen reduction reaction was measured using RDE. In a 0.5 M H2SO4 electrolyte, a half-wave potential of 0.70 V and low peroxide formation were obtained. Conversely, in a 0.1 M NaOH electrolyte, a half-wave potential of 0.85 V was observed. Lower peroxide yields were observed when a drying treatment was part of the synthesis process. A detailed ICP-MS study identified ppm levels of Mn and Fe in the sample, possibly due to the intrinsic GO synthesis method used. Results obtained using other characterization techniques, such as Raman and XPS, will be presented to further understand the role of the metal and nitrogen doping in the performance of GO-based catalysts. These first results indicate high performance of treated GO-based NPMCs in both acidic and alkaline media. Although, we have demonstrated effective oxygen reduction activity and have a better understanding of GO-based catalysts, we are now focusing our efforts on the progressive addition of different metal precursors such as Co and Ni. Acknowledgement Financial support from the Los Alamos National Laboratory, Laboratory-Directed Research and Development (LDRD) is gratefully acknowledged.

A mechanistic study of 4-aminoantipyrine and iron derived non-platinum group metal catalyst on the oxygen reduction reaction

A highly active non-platinum group metal (non-PGM) catalyst derived from iron and 4-aminoantipyrine precursors was synthesized using a sacrificial support method (SSM) to obtain a highly porous, open framed structure. The ratio of iron to 4-aminoantipyrine had been previously optimized to catalyze the reduction of oxygen in both acid and alkaline media. In this study, the mechanism of the reduction of oxygen in both media was investigated, and it was found to follow the 2×2 pathway. On its face, electrochemical analysis seems to suggest that the direct 4 electron transfer pathway is favored due to the low peroxide yield, but a closer examination reveals that the 2×2 pathway is followed, where the fast step is the partial reduction to peroxide, and the ensuing reduction step to water is also fairly rapid.