Oxygen Reduction Reaction In Alkaline Media Research Articles

N-, P-, and S-doped graphene-like carbon catalysts derived from onium salts with enhanced oxygen chemisorption for Zn-air battery cathodes

Compared to currently studied metal-based catalysts, metal-free heteroatom-doped carbon catalysts have many advantages including no issues of degradation and contamination from metal dissolution. Relying on single type of doping usually cannot yield optimal electronic and geometric structures favorable for the oxygen reduction reaction (ORR). Herein, heteroatom N, P, and S simultaneously doped graphene-like carbon (NPS-G) was successfully synthesized from onium salts by a facile one-step pyrolysis method. The resulting metal-free NPS-G catalyst with optimized N, P, and S contents exhibits enhanced catalytic activity towards the ORR in alkaline media, relative to any single doping. In particular, this metal-free catalyst shows an encouraging half-wave potential (E1/2 = 0.857 V) comparable to that of metal-based catalysts. It also demonstrates excellent electrochemical stability and methanol tolerance. This catalyst was further studied as a cathode in a primary Zn-air battery, showing exceptional open-circuit voltage (1.372 V) and power density (0.151 W cm−2). The NPS-G cathode delivers a specific capacity of 686 mA h gZn-1 at a current density of 10 mA cm−2 while utilizing 82.2% of the theoretical capacity (835 mA h gZn-1). The origin of high activity associated with various heteroatom dopings is elucidated through X-ray photoelectron spectroscopy analysis and density functional theory studies. The enhanced chemisorption of oxygen species (*OOH, *O and *OH) onto the dopants of the NPS-G catalysts reduces charge transfer resistance and facilitate the ORR. The porous 2D structure also contributes to the increase of active site density and facile mass transport.

Hierarchical Flowerlike Highly Synergistic Three-Dimensional Iron Tungsten Oxide Nanostructure-Anchored Nitrogen-Doped Graphene as an Efficient and Durable Electrocatalyst for Oxygen Reduction Reaction.

A unique and novel structural morphology with high specific surface area, highly synergistic, remarkable porous conductive networks with outstanding catalytic performance, and durability of oxygen reduction electrocatalyst are typical promising properties in fuel cell application; however, exploring and interpreting this fundamental topic is still a challenging task in the whole world. Herein, we have demonstrated a simple and inexpensive synthesis strategy to design three-dimensional (3D) iron tungsten oxide nanoflower-anchored nitrogen-doped graphene (3D Fe-WO3 NF/NG) hybrid for a highly efficient synergistic catalyst for oxygen reduction reaction (ORR). The construction of flowerlike Fe-WO3 nanostructures, based on synthesis parameters, and their ORR performances are systematically investigated. Although pristine 3D Fe-WO3 NF or reduced graphene oxides show poor catalytic performance and even their hybrid shows unsatisfactory results, impressively, the excellent ORR activity and its outstanding durability are further improved by N doping, especially due to pyridinic and graphitic nitrogen moieties into a graphene sheet. Remarkably, 3D Fe-WO3 NF/NG hybrid nanoarchitecture reveals an outstanding electrocatalytic performance with a remarkable onset potential value (∼0.98 V), a half-wave potential (∼0.85 V) versus relative hydrogen electrode, significant methanol tolerance, and extraordinary durability of ∼95% current retention, even after 15 000 potential cycles, which is superior to a commercial Pt/C. The exclusive porous architecture, excellent electrical conductivity, and the high synergistic interaction between 3D Fe-WO3 NF and NG sheets are the beneficial phenomena for such admirable catalytic performance. Therefore, this finding endows design of a highly efficient and durable nonprecious metal-based electrocatalyst for high-performance ORR in alkaline media.

Selenium Decorated Reduced Graphene Oxide Supported CoSe2 Nanoparticles as Efficient Electrochemical Catalyst for the Oxygen Reduction Reaction

AbstractDeveloping efficient electrocatalysts for the oxygen reduction reaction (ORR) based on non‐precious catalytic centers is critical to improve the efficiency of low temperature fuel cells. Herein, we report on a catalyst containing CoSe2 supported on selenium decorated reduced graphene oxide (CoSe2/Se‐rGO), which was synthesized via a one‐pot solvothermal method using Se‐rGO as support. Importantly, the CoSe2/Se‐rGO showed an enhanced catalytic activity for ORR in alkaline medium with an onset potential of 0.903 V vs. RHE and a half‐wave potential of 0.803 V vs. RHE. Its stability and methanol tolerance ability were significantly improved as compared to 20 wt% Pt/C, respectively. The strategy developed here provided a novel and efficient approach to prepare non‐precious electrocatalysts for ORR.

Nitrogen and Sulfur Co-Doped MWCNT/Rgo Composite As Highly Active Electrocatalyst for Oxygen Reduction Reaction in Alkaline Fuel Cell

Recently a major effort in fuel cell research and development have been undertaken to displace platinum with platinum-free or even better, totally metal free catalyst materials. With the possibility of using heteroatom doped carbon-based materials as electrocatalysts for oxygen reduction reaction (ORR) instead of Pt, anion exchange membrane fuel cells (AEMFCs) have big advantage over other low-temperature fuel cells. Beside other carbon nanomaterials, carbon nanotubes and graphene have shown good electrocatalytic and catalyst supporting properties for different fuel cell cathode catalysts. Graphene and/or carbon nanotubtube doping with heteroatoms is a common strategy to increase the electrocatalytic activity of these materials towards the ORR [1]. Different heteroatoms, such as nitrogen, phosphorous, sulfur and boron have been studied as promising dopants to prepare electrocatalysts for ORR in alkaline media [2]. In this work the electrocatalytic activity of nitrogen and sulfur co-doped MWCNT/rGO was studied towards the ORR in alkaline media (0.1 M KOH) using the rotating disc electrode (RDE) method. The catalyst materials were prepared by doping of MWCNT/rGO with N and S via simple one-pot synthesis method using high-temperature pyrolysis in inert gas atmosphere. The resulting catalyst material exhibited excellent electrocatalytic activity towards the ORR in alkaline media. Catalyst samples were characterized also by transmission electron microscopy, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy methods. Fuel cell experiments were carried out using Fumatech Fumapem® FAA anion-exchange membrane and FAA ionomer. Methanol tolerance and long-term stability tests were performed. The results revealed remarkable catalytic activity of nitrogen and sulfur co-doped carbon towards the ORR in alkaline media, as well good methanol tolerance. Composition analysis with different physical characterization methods confirmed that nitrogen and sulfur have been grafted onto the carbon support. RDE tests demonstrated highly improved catalytic activity in comparison with undoped MWCNT/rGO and fuel cell tests showed a great potential of N and S doped carbon as alternative cathode catalyst and catalyst carrier for anion exchange membrane fuel cells.

Vulcan Xc-72R Supported Silver-Based Bimetallic Nanoparticles As Novel Electrocatalytic Platforms for Improve Performance in Oxygen Reduction Reactions

The Oxygen Reduction Reaction (ORR) is an essential process for energy transformation required by technological devices such as batteries and fuel cells.1,2 This reaction is responsible for controlling the activity and the activity of such devices suffers from a slow kinetic drawback at the cathode which hinders its overall performance.3 Thus, to accelerate ORR kinetics in a fuel cell, an active catalyst is required with qualities such as low cost and high catalytic stability.3 Platinum has proven to be the optimal catalyst for ORR but, due to its high cost and low abundance, adequate efforts have been made to be able to replace it.4 As of now, researchers have focused on silver metal because it is inexpensive and has proven to be a good catalyst for ORR in alkaline media.5 Hence, to improve the ORR in a fuel cell, we are depositing silver nanoparticles (NPs) onto electrochemically reduced vulcan XC-72R to achieve greater conductivity and surface area to the nanocomposite. Silver bimetallics have proven to be five times better in performance than pure silver in alkaline media. Thus, we will compare our Ag/GOx NPs with bimetallic NPs (Ag/Au) and (Ag/ Pd) at a 4:1 ratio to examine the catalytic activity for ORR. These nanocatalysts will be obtained directly using a robust electrodeposition method consisting of the rotating disk slurry electrode (RoDSE) technique in powder form, to obtain Ag nanoparticles highly dispersed on Vulcan XC-72R for ORR in alkaline media minimizing the time spent in catalyst preparation(fig 1). Afterwards, the sample’s electrochemical activity will be assessed for the ORR using both: cyclic voltammetry and spectroscopic analysis. The RoDSE method used to obtain highly dispersed Ag nanoparticles does not require the use of a reducing agent or stabilizing agent, and the noble-metal loading was controlled by the addition and tuning of the metal precursor concentration. This technique consists of dissolving a salt of the precursor metal in a carbon support to form the slurry solution in which a constant reducing potential is applied at a constant speed to achieve the electrodeposition of metal in the carbon support instead of the electrode.Particle size and characteristic of the bimetallic fcc crystal facets were determined by X-ray diffraction with an approximate size of 21.6, 18.8 and 19.8 nm for Ag, Ag/Au and Ag/Pd respectively. Cyclic voltammetry of electrodeposited 12 % Ag/Pd/Vulcan XC-72R showed a higher catalytic current density for oxygen reduction reaction when compared with the others bimetallic under study.

Leveraging Commercial Silver Inks as Oxidation Reduction Reaction Catalysts in Alkaline Medium

Alkaline exchange membrane fuel cells (AEMFCs) development is impeded by the lack of low-cost processes for fabricating catalyst layers. One bottleneck lies in using large amounts of precious group metals during the layer deposition process by spray-painting. One possible solution would be to leverage inkjet printing technologies known for their full recovery of the printed material. Recent advances in printed electronics has led to the commercialization of silver (Ag) inks. We demonstrate the electrocatalytic properties (oxygen reduction reaction (ORR)) of Ag ink. Moreover, we show that a simple galvanic replacement reaction (GRR) on the Ag ink yields Ag0.9M0.1 (M = Pt or Pd) hollow nanoparticles. The resultant electrocatalyst demonstrated high activity for the ORR in alkaline medium. The Ag colloidal dispersion (the ink) reacted with a minute amount of platinum group metals precursors (PGMs). X-ray diffraction (XRD) and electron microscopy confirmed the hollow morphology and the formation of Pt or Pd-ri...

N,S Co-Doped Carbon Nanofibers Derived from Bacterial Cellulose/Poly(Methylene blue) Hybrids: Efficient Electrocatalyst for Oxygen Reduction Reaction

Exploring inexpensive and highly efficient electrocatalyst to decrease the overpotential of oxygen reduction reaction (ORR) is one of the key issues for the commercialization of energy conversion and storage devices. Heteroatom-doped carbon materials have attracted increasing attention as promising electrocatalysts. Herein, we prepared a highly active electrocatalyst, nitrogen, sulfur co-doped carbon nanofibers (N/S-CNF), via in situ chemical oxidative polymerization of methylene blue on the bacterial cellulose nanofibers, followed by carbonization process. It was found that the type of nitrogen/sulfur source, methylene blue and poly(methylene blue), has significantly influence on the catalytic activity of the resultant carbon nanofibers. Benefiting from the porous structure and high surface area (729 m2/g) which favors mass transfer and exposing of active N and S atoms, the N/S-CNF displays high catalytic activity for the ORR in alkaline media with a half-wave potential of about 0.80 V, and better stability and stronger methanol tolerance than that of 20 wt % Pt/C, indicating great potential application in the field of alkaline fuel cell.

Core-shell Co/CoNx@C nanoparticles enfolded by Co-N doped carbon nanosheets as a highly efficient electrocatalyst for oxygen reduction reaction

The enhancement of oxygen reduction reaction (ORR) catalytic activity of non-precious metal catalysts is extremely desirable but still full of challenges. Here, a novel hybrid, core-shell Co/CoNx@C nanoparticles enfolded by Co-N doped carbon nanosheets was successfully prepared by a facile two-step method, including the formation of well-curved porous carbon nanosheets by a facile sintering of trisodium citrate dehydrate and subsequent introduction of cobalt and nitrogen doping. Owing to the distinctive architecture and the synergistic effects between crystalline Co/CoNx@C nanoparticles and non-crystalline CoNxCy active sites, the resultant Co-N-PC catalyst exhibits an outstanding electrocatalytic activity towards ORR in alkaline media with a half-wave potential of 0.833 V (vs. RHE) and a higher limiting current density of 5.70 mA cm−2, which is superior to commercial 20 wt% Pt/C. In addition, it also displays better electrochemical durability and stronger methanol tolerance than Pt/C.

Double Perovskites as Model Bifunctional Catalysts toward Rational Design: The Correlation between Electrocatalytic Activity and Complex Spin Configuration.

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) properties of double perovskite catalysts La2CoMnO6-δ and La2NiMnO6-δ have been investigated. The experimental results demonstrate that these samples are efficient OER and ORR catalysts. For the La2CoMnO6 compound annealed at 600 °C, its half-wave potential of ORR in alkaline media is as low as 0.75 V versus reversible hydrogen electrode. As for the correlation between electrocatalytic activities and the eg orbital occupation numbers, it is found that the eg-filling rule proposed by Shao-Horn and co-workers is valid in La2CoMnO6-δ when the eg electrons of two kinds of transition-metal ions are all considered. In the case of La2NiMnO6-δ, because the samples which prepared in different conditions all have unity average eg occupation, the eg-filling rule should be amended. We suggest that the average deviation from unity eg occupation is a suitable activity descriptor, which can be used to design perovskite catalysts with unity average eg occupation.

General Synthesis of Three-Dimensionally Ordered Macro-/Mesoporous Materials and Their Electrocatalytic Applications

Three-dimensionally (3D) ordered macro-/mesoporous (3DOM/m) materials, which combine the advantages of high surface area of the mesopores, efficient mass transport within the macropores, and strong structural stability of the 3D interconnected porous frameworks, have shown remarkable performances in a wide range of applications. Herein, we demonstrate a novel dual-hard-templating technique as a general synthetic strategy for constructing the 3DOM/m materials by nanocasting mesoporous silica confined within the regular voids of a silica colloidal crystal (opal). Through this method, various materials, such as 3DOM/m Pt, Pd, Ni2P, carbon and N/P co-doped carbon (NPC), have been successfully synthesized. The as-prepared 3DOM/m Ni2P and NPC are demonstrated to exhibit outstanding electrocatalytic performance for the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), respectively. The 3DOM/m Ni2P exhibits a low overpotential of 92 mV at 10 mA cm−2 and a small Tafel slope of 41 mV per decade, as well as a long-term durability for the HER in acidic medium. The 3DOM/m NPC exhibits comparable catalytic activity but higher durability in comparison with the commercial 20 wt% Pt/C catalyst for the ORR in alkaline medium. Details on the fabrication and characterization of these materials are presented including scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, nitrogen adsorption, X-ray photoelectron spectroscopy, and electrocatalytic activity studies.

Morphology Control of Carbon-Free Spinel NiCo2O4 Catalysts for Enhanced Bifunctional Oxygen Reduction and Evolution in Alkaline Media

Spinel NiCo2O4 is considered a promising precious metal-free catalyst that is also carbon-free for oxygen electrocatalysis applications. Current efforts mainly focus on optimal chemical doping and substituent to tune its electronic structures for enhanced activity. Here, we study its morphology control and elucidate the morphology-dependent catalyst performance for bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Three types of NiCo2O4 catalysts with significantly different morphologies were prepared using temple-free, Pluronic-123 (P-123) soft, and SiO2 hard templates, respectively, via hydrothermal methods following by a calcination. While the hard-template yields sphere-like dense structures, soft-template assists the formation of a unique nano-needle cluster and flower-like assembly containing abundant meso- and macro pores. Then, the effect of morphology of NiCo2O4 on their corresponding bifunctional catalytic performance was systematically investigated. The flower-like nano-needle assembly NiCo2O4 catalyst via the soft template method exhibited the highest catalytic activity and stability for both ORR and OER. In particular, it exhibited an onset and half-wave potentials of 0.94 and 0.82 V vs. RHE, respectively, for the ORR in alkaline media. Although it is still inferior to Pt, the NiCo2O4 represents one of the best ORR catalyst compared to other reported carbon-free oxides. Meanwhile, remarkable OER activity and stability were achieved with an onset potential of 1.48 V and a current density of 15 mA/cm2 at 1.6 V, showing no activity loss after 20,000 potential cycles (0 to 1.9 V). The demonstrated stability is even superior to Ir for the OER. The morphology-controlled approach provides an effective solution to create a robust 3D architecture with increased surface areas and enhanced mass transfer. Importantly, the soft template can yield high degree of spinel crystallinity with ideal stoichiometric ratios between Ni and Co, thus promoting structural integrity with enhanced electrical conductivity and catalytic properties. The high performance bifunctional oxide catalyst is carbon free and can eventually overcome the stability issue resulting from carbon corrosion in reversible fuel cells and metal-air batteries.

Cobalt-Based Coordination Polymer for Oxygen Reduction Reaction.

Lack of control over the structure and electrically nonconductive properties of coordination polymers (CPs) creates a major hindrance to designing an active electrocatalyst for oxygen reduction reaction (ORR). Here, we report a new semiconductive and low-optical band gap CP structure [{Co3(μ3-OH)(BTB)2(BPE)2}{Co0.5N(C5H5)}], 1, that exhibits high-performance ORR in alkaline medium. The electrical conductivity of compound 1 was measured using impedance spectroscopy and found to be 5 × 10–4 S cm–1. The Ketjenblack EC-600JD carbon used as a support for all the electrochemical methods such as cyclic voltammetry, rotating disk electrode, rotating ring-disk electrode and Koutecký–Levich analysis. The as-synthesized Co-based catalyst has the ability to reduce O2 to H2O by a nearly four-electron process. The crystal structure of 1 shows that the trimeric unit {Co3(μ3-OH)(COO)5N3} and monomeric unit {Co(COO)2(NC5H4)2}2+ are linked with BTB and BPE linkers to form a three-dimensional structure. Theoretical calculations predict that the monomeric center acts as an active catalytic site for ORR. This could be due to the efficient overlap of highest occupied molecular orbital–lowest unoccupied molecular orbital between monomer and O2 molecule. This CP, 1, shows facile 3.6-electron ORR, and it is inexpensive compared with widely used Pt catalysts. Therefore, this CP can be used as a promising cathode material for fuel cells in terms of efficiency and cost effectiveness.

N-doped carbon nanocages: Bifunctional electrocatalysts for the oxygen reduction and evolution reactions

Highly efficient metal-free, carbon-based, bi-functional electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) have attracted increased attention for use in electrochemical energy conversion systems, owing to their low cost and high activity. In this work, N-doped carbon nanocages (N-CCs) with a porous self-supported architecture and high specific surface area are synthesized by a facile interfacial assembly synthetic route. The materials are comprehensively characterized by scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption experiments, X-ray diffraction, and X-ray photoelectron spectroscopy. Cyclic voltammetry, chronoamperometry, and linear sweep voltammetry demonstrate that the as-prepared N-CC could serve as an effective metal-free electrocatalyst with excellent catalytic activity, long-term operation durability, and excellent methanol tolerance for the ORR in alkaline media. In the presence of 3 mM methanol, the half wave potential of the N-CCs for the ORR is 190 mV; this is more positive than that of the commercial Pt/C electrocatalyst. Meanwhile, the N-CCs also show an OER activity comparable to that of the commercial Ru/C electrocatalyst, revealing their bifunctional property.

Evolution of silver to a better electrocatalyst: Water-assisted oxygen reduction reaction at silver chloride nanowires in alkaline solution

Oxygen reduction reaction (ORR) is of great interest in various areas, including energy conversion. This paper presents the simple synthesis and characterization of one-dimensional silver halides nanowires (AgClNW and AgBrNW) as an electrocatalyst for ORR in alkaline media, as well as an investigation of the ORR pathway at AgCl. AgClNW and AgBrNW were prepared via a galvanic replacement reaction (GRR) between silver nanowires (AgNW) and a halide precursor. AgClNW exhibited excellent ORR catalytic activity that was comparable to or better than that for commercial Pt (20 wt% Pt loading on Vulcan carbon), demonstrating potential to replace Pt-based catalysts. A scanning electrochemical microscopy (SECM) analysis supports the existence of an associative ORR pathway at AgCl, and first-principles density functional theory (DFT) calculations suggest that the high ORR activity of AgCl is possibly attributed to the up-shifted Ag d-band center energy in AgCl as well as the assistance of adsorbed water molecules.

A bio-inspired N-doped porous carbon electrocatalyst with hierarchical superstructure for efficient oxygen reduction reaction

The bio-inspired hierarchical “grape cluster” superstructure provides an effective integration of one-dimensional carbon nanofibers (CNF) with isolated carbonaceous nanoparticles into three-dimensional (3D) conductive frameworks for efficient electron and mass transfer. Herein, a 3D N-doped porous carbon electrocatalyst consisting of carbon nanofibers with grape-like N-doped hollow carbon particles (CNF@NC) has been prepared through a simple electrospinning strategy combined with in-situ growth and carbonization processes. Such a bio-inspired hierarchically organized conductive network largely facilitates both the mass diffusion and electron transfer during the oxygen reduction reactions (ORR). Therefore, the metal-free CNF@NC catalyst demonstrates superior catalytic activity with an absolute four-electron transfer mechanism, strong methanol tolerance and good long-term stability towards ORR in alkaline media.

Nanosheets/Mesopore Structured Co3O4@CMK‐3 Composite as an Electrocatalyst for the Oxygen Reduction Reaction

AbstractThe exploration of highly effective and low‐cost non‐noble‐metal electrocatalysts for the oxygen reduction reaction (ORR) will have a significant impact on the area of fuel cells and metal–air batteries. Here, we report a facile, efficient, and environmentally friendly method to deposit transition metal oxide nanosheets (NSs) on the backbone of ordered mesoporous carbon (CMK‐3) by the pyrolysis of the metal‐precursor@CMK‐3. The optimized CMK‐3 catalyst with a coating of Co3O4 NSs possesses a high surface area of 2396 m2 g−1 and demonstrates an excellent electrocatalytic activity towards the ORR in alkaline media, which is much better than that of other transition metal oxide@CMK‐3 catalysts and other carbon‐based catalysts (such as carbon nanotubes). In addition, the as‐prepared catalyst possesses a comparable electrochemical performance and a superior durability and higher tolerance to methanol compared with commercially available Pt/C, which can be ascribed to the distinctive structure of the nanosheets and mesopores, indicative of potential applications in metal–air batteries.

Synergistic effect of heat treatments and KOH activation enhances the electrochemistry performance of polypyrrole nanochains (PPy-NCs)

A highly intriguing class of advanced materials, nanochains have gained attention due to their advantages in stability, enlarged surface area and enhanced electrocatalytic activity toward oxygen reduction reaction (ORR). Here in, we describe the synthesis of polypyrrole nanochains (PPy-NCs) by a facile emulsion polymerization process using cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) as surfactants. The PPy-NCs are further activated using potassium hydroxide (KOH) as the activation agent for producing a porous nitrogen-containing carbon structure. Subsequently, low-temperature carbonization (500–800 °C) and KOH activation leads to abundant ultrasmall pores and strong oxygen molecule binding sites, which are essential in enhancing the capacitance as well as ORR activity. The morphologies and structures of the PPy-NCs samples have been characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and Brunauer–Emmett–Teller (BET). The electrochemical studies were analyzed by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy, which demonstrate superior electrochemical performance as supercapacitors electrode application. The maximum specific capacitance of 1502 F g−1 at scan rate 2 mV s−1, as well as capacitance retention (93%) after completing 1500 cycles are obtained for the PPy-NCs-800 electrode in 1.0 M KOH aqueous solution. Moreover, PPy-NCs-800 exhibits a considerably good electrocatalytical activity through desirable 4–electron transfer process for ORR in alkaline medium. This work suggested that PPy-NCs had potential application in supercapacitors, and oxygen reduction reaction (ORR).

CuAg@Ag Core-Shell Nanostructure Encapsulated by N-Doped Graphene as a High-Performance Catalyst for Oxygen Reduction Reaction.

Development of a robust, cost-effective, and efficient catalyst is extremely necessary for oxygen reduction reaction (ORR) in fuel cell applications. Herein, we reported a well-defined nanostructured catalyst of highly dispersed CuAg@Ag core-shell nanoparticle (NP)-encapsulated nitrogen-doped graphene nanosheets (CuAg@Ag/N-GNS) exhibiting a superior catalytic activity toward ORR in alkaline medium. The synergistic effects produced from the unique properties of CuAg@Ag core-shell NPs and N-GNS made such a novel nanohybrid display a catalytic behavior comparable to that of the commercial Pt/C product. In particular, it demonstrated a much better stability and methanol tolerance than Pt/C under the same conditions. Because of its outstanding electrochemical performance and ease of synthesis, CuAg@Ag/N-GNS material was expected to be a promising low-cost catalyst for ORR in alkaline fuel cell applications.

PdCo Alloy Nanonetworks−Polyallylamine Inorganic–Organic Nanohybrids toward the Oxygen Reduction Reaction

AbstractRationally controlling the morphology, chemical composition, and interfacial property of metal nanostructures can remarkably enhance their electrocatalytic performance, such as activity, selectivity, and durability. In this work, a facile functional molecule‐assisted cyanogel‐reduction method is developed to successfully synthesize the polyallylamine (PAA)‐functionalized PdCo alloy nanonetworks (PdCo‐NNW@PAA) inorganic–organic nanohybrids. The solid, double‐metal, and 3D backbone properties of jelly‐like K2PdCl4/K3Co(CN)6 cyanogel intermediate contribute to the high alloying degree and network structure of PdCo‐NNW@PAA nanohybrids. During the reduction, PAA molecules not only serve as surfactant to decrease the particle size but also act as functional molecule to modify the metal surface. The oxygen reduction reaction (ORR) polarization and chronoamperometry tests demonstrate that PdCo‐NNW@PAA nanohybrids have outstanding electrocatalytic activity, excellent resistance to alcohol crossover effect, and good durability toward the ORR in alkaline media. This work provides a new strategy for synthesizing the chemical functionalized multimetallic alloy nanonetworks at room temperature and reveals that the interfacial property of metal nanocrystals strongly affects their electrocatalytic activity and selectivity.

Carbon Paper-Supported NiCo/C–N Catalysts Synthesized by Directly Pyrolyzing NiCo-Doped Polyaniline for Oxygen Reduction Reaction

In this study, we report the findings that the C–N composites containing Ni and Co (Ni1Co1/C–N, Ni3Co1/C–N, Ni6Co1/C–N, Ni9Co1/C–N, Ni[Formula: see text]Co0/C–N and Ni0Co[Formula: see text]/C–N) can be produced by direct pyrolysis of the NiCo-doped polyaniline (PANI) precursors in N2 atmosphere at 800[Formula: see text]C and show efficient electroactivity for oxygen reduction reaction (ORR) in alkaline media. Distribution and compositions of the catalysts were characterized by SEM, TEM, EDS and XRD techniques. The catalysts were loaded on carbon paper to prepare gas diffusion electrodes, in which electrocatalytic activity for ORR in alkaline media was investigated by voltammetric techniques. The ORR current density on these carbon paper-supported NiCo/C–N catalysts exhibits a linear increase with the negative shift of ORR potential. The ORR onset potential is around [Formula: see text]0.2[Formula: see text]V (versus Ag/AgCl) in alkaline media. Among the prepared catalysts, the catalyst Ni6Co1/C–N presents the largest ORR current density, which is 68.5[Formula: see text]mA[Formula: see text]cm[Formula: see text]@[Formula: see text]0.8[Formula: see text]V (versus Ag/AgCl) in alkaline media. Moreover, Ni6Co1/C–N catalyst also presents good electrocatalytic activity stability for ORR.