Electrocatalytic Performance For Oxygen Reduction Research Articles

Long-range order, short-range disorder: Engineering one-dimensional flow channel arrays with hierarchically porous reaction interfaces for electrocatalytic reduction of oxygen

Fuel cell performance depends heavily on electrochemical reaction kinetics and mass transport. Rapid kinetics requires high-activity catalysts while good mass transport demands efficient transport domains. Recent fundamental studies in these areas focus more on the improvement in catalyst activity, whereas the importance of mass transport should not be underestimated, which is the focal point of this work. Hierarchical pores are generally considered to be conducive to enhancing reaction kinetics and mass transport, but the degree of order of pore structures has a significant influence over the fuel cell performance. Herein, we introduce the concept of ‘long-range order, short-range disorder’ to design transport domains and reaction interfaces: dispensing with conventional microfabrication techniques, well-ordered, one-dimensional channel arrays are constructed using vascular bundles of natural material, capable of decreasing tortuosity, increasing porosity, optimizing reactant distribution and thus minimizing concentration losses; further, intrinsic biominerals and tissues of organisms existing on the inner and outer walls of channel arrays are harnessed to form hierarchically porous domains, that is, raising the roughness of reaction interfaces by increasing the degree of short-range disorder. The combination of one-dimensional flow channels (long-range order) and hierarchically porous reaction interfaces (short-range disorder), analogous to blood vessels composed of arteries/veins and capillaries, ensures the optimization of mass transport and catalytic kinetics, leading to an electrocatalytic oxygen reduction performance enhancement over a wide array of biomass-derived carbonaceous materials. Accordingly, this work provides inspiration for finding the right balance between mass transport and reaction kinetics from an order perspective.

Solution combustion synthesis of ternary Ni/WC/C composites with efficient electrocatalytic oxygen reduction performance.

In this paper, a fast processing route involving a wet-chemical method (solution combustion synthesis, SCS) and carbonization in a CH4 environment was demonstrated, through which nanosized Ni/WC/C powder with an average size of 80 nm was obtained. In the catalyst powder, Ni was evenly distributed and it could form NiOOH to promote catalysis, and an amorphous carbon (C) layer with a thickness of <10 nm was formed on the surface of the composite particles, improving the stability of the Ni/WC powder and promoting electron transport. Due to the characteristics of uniformity and a large specific surface area and the synergistic effect of Ni, WC, and C, this powder showed significantly improved ORR catalytic activity in alkaline solution. When the amount of Ni doping was 15 wt%, the composite powder showed the smallest particle size and the best ORR catalytic performance. Its cathode peak potential was −0.31 V and the half wave potential was −0.34 V. The number of electrons transferred in the ORR reaction was 3.6. This work provided a fast and cheap method for the preparation of multicomponent composite catalyst materials.

Metalloporphyrin-immobilization MOFs derived metal-nitrogen-carbon catalysts for effective electrochemical oxygen reduction

The development of noble metal-free and activity-stable catalysts for oxygen reduction reaction (ORR) is critical to renewable energy technologies. ZIF-67, a kind of metal-organic frameworks (MOFs), are used to immobilize two different metalloporphyrins (Co/Mn [5,10,15,20-tetrakis (4-carboxyphenyl)porphyrin], Co-TCPP and Mn-TCPP) as precursors and to synthesize a series of metal-nitrogen-carbon catalysis materials (M@NC) via pyrolysis at different temperatures. The pyrolysis products Co@NC-800 and Mn/Co@NC-800 under an inert atmosphere at 800 ​°C displayed excellent electrocatalytic oxygen reduction performance in alkaline medium. Among them, Co@NC-800 has the best electrocatalytic oxygen reduction performance and its onset potential (Eonset)，half-wave-potential and limiting current density are very similar to the corresponding values of commercial 20% Pt/C. Furthermore, the resulting Co@NC-800 shows the best long-term durability and methanol tolerance than commercial Pt/C, indicative of its potential applications in fuel cells. The introduction of metalloporphyrin on ZIF-67 not only increases the metal content and N content in the pyrolysis products but also makes it easier to start decomposition at a lower temperature, and also easy to generate more Co-NX species, which makes them have a high electrocatalytic activity.

Preparation of bimetal-based FeNi-N/C catalyst and its electrocatalytic oxygen reduction performance

A kind of bimetal-based FeNi-N/C catalysts were prepared by combining ultrasonic reaction and high temperature heat treatment using dicyandiamide (DCD) as nitrogen source, FeCl3·6H2O and Ni(OAc)2·4H2O as bimetal source, BP2000 as carbon carrier. The composition and structure of the catalysts as-prepared were characterized by XRD, FT-IR and XPS. The catalytic activity of the catalysts on the oxygen reduction reaction(ORR) under alkaline conditions were tested by using linear sweep voltammetry (LSV) with a rotating disk electrode, and the prepared conditions, active site composition, the stability and methanol resistance of the as-prepared catalysts and the kinetic ORR mechanism were studied successively. The results show that the best FeNi-N/C-800 catalytic activity for ORR with the onset potential of 0.965 V (vs. RHE). The number of transferred electrons in catalytic ORR process is between 3.59 and 3.98, indicating the 4e− dominated ORR mechanism and a direct conversion process from O2 into H2O. The nature of the metal and the heat treatment temperature are important key factors in the preparation of the catalyst. From this work, Ni can be regarded as a catalyst for N and metal Fe atoms into the carbon support, and Fe-Nx-C (Fe bonds with pyridine-N) is the main active sites of the catalyst FeNi-N/C and a synergistic effect of the two sites of Fe-Nx-C and Ni-Nx-C enhances their catalytic activity for ORR further.

Single iron atoms coordinated to g-C3N4 on hierarchical porous N-doped carbon polyhedra as a high-performance electrocatalyst for the oxygen reduction reaction.

Catalysts composed of isolated single Fe atoms coordinated to graphitic carbon nitride (g-C3N4) dispersed on hierarchical porous N-doped carbon polyhedra (Fe-g-C3N4/HPNCPs) were successfully prepared. The optimized catalyst, Fe-g-C3N4/HPNCP-0.8, showed excellent electrocatalytic activity for the oxygen reduction reaction under alkaline conditions with a half-wave potential of 0.902 V, significantly outperforming commercial Pt/C, as well as high durability. The high performance stems from the synergistic effect of the atomically dispersed Fe-N2 sites and the advantages of the hierarchical porous structure for promoting mass transport and improving the accessibility of the active sites.

Fe, N, S-codoped carbon frameworks derived from nanocrystal superlattices towards enhanced oxygen reduction activity

Recently, iron, nitrogen and sulfur codoped carbon-based materials have gained increasing attention for their synergistic effect towards superior electrocatalytic oxygen reduction performance. To gain insight into the contributions of the heteroatoms, we developed a facile and reproducible method for constructing Fe, N, S-codoped carbon frameworks derived from self-assembled Fe3O4 nanocrystal superlattices. The material constructed by the suggested method exhibited excellent ORR activity with more positive half-wave potential (∼ 0.869 V, vs RHE), higher diffusion-limiting current density (∼ 5.88 mA/cm2) and smaller Tafel slope (45 mV/dec) compared with Fe, N-codoped carbon frameworks and Pt/C. Notably, Fe3O4 nanocrystals served as both the building blocks for constructing carbon frameworks and the source of Fe residues leaving in the frameworks at the same time. By artificially tailoring the doping type and level as well as the homogeneousness of heteroatoms, the results discussed herein prove the importance of each kind of heteroatom in boosting ORR activity.

A Bimetallic Zn/Fe Polyphthalocyanine‐Derived Single‐Atom Fe‐N4 Catalytic Site:A Superior Trifunctional Catalyst for Overall Water Splitting and Zn–Air Batteries

AbstractDeveloping an efficient single‐atom material (SAM) synthesis and exploring the energy‐related catalytic reaction are important but still challenging. A polymerization–pyrolysis–evaporation (PPE) strategy was developed to synthesize N‐doped porous carbon (NPC) with anchored atomically dispersed Fe‐N4 catalytic sites. This material was derived from predesigned bimetallic Zn/Fe polyphthalocyanine. Experiments and calculations demonstrate the formed Fe‐N4 site exhibits superior trifunctional electrocatalytic performance for oxygen reduction, oxygen evolution, and hydrogen evolution reactions. In overall water splitting and rechargeable Zn–air battery devices containing the Fe‐N4 SAs/NPC catalyst, it exhibits high efficiency and extraordinary stability. This current PPE method is a general strategy for preparing M SAs/NPC (M=Co, Ni, Mn), bringing new perspectives for designing various SAMs for catalytic application.

A Bimetallic Zn/Fe Polyphthalocyanine-Derived Single-Atom Fe-N4 Catalytic Site:A Superior Trifunctional Catalyst for Overall Water Splitting and Zn-Air Batteries.

Developing an efficient single-atom material (SAM) synthesis and exploring the energy-related catalytic reaction are important but still challenging. A polymerization-pyrolysis-evaporation (PPE) strategy was developed to synthesize N-doped porous carbon (NPC) with anchored atomically dispersed Fe-N4 catalytic sites. This material was derived from predesigned bimetallic Zn/Fe polyphthalocyanine. Experiments and calculations demonstrate the formed Fe-N4 site exhibits superior trifunctional electrocatalytic performance for oxygen reduction, oxygen evolution, and hydrogen evolution reactions. In overall water splitting and rechargeable Zn-air battery devices containing the Fe-N4 SAs/NPC catalyst, it exhibits high efficiency and extraordinary stability. This current PPE method is a general strategy for preparing M SAs/NPC (M=Co, Ni, Mn), bringing new perspectives for designing various SAMs for catalytic application.

Formation of Single-Holed Cobalt/N-Doped Carbon Hollow Particles with Enhanced Electrocatalytic Activity toward Oxygen Reduction Reaction in Alkaline Media.

Design and construction of metal‐organic framework (MOF) composite precursors have recently been considered as a promising strategy for the preparation of different structured metal/carbon‐based functional materials. Here, an MOF composite‐assisted strategy to synthesize single‐holed cobalt/N‐doped carbon hollow particles is reported. The yolk–shell polystyrene@zeolitic imidazolate framework‐67 (PS@ZIF‐67) composite precursors are first synthesized, followed by a controlled pyrolysis to obtain cobalt/N‐doped carbon hollow particles with a large single hole on each shell. Moreover, the MOF‐coating approach reported in this work can be extended to prepare various core‐shell ZIF‐67 composites with different structures and compositions. Benefiting from the structural and compositional advantages, the as‐derived single‐holed cobalt/N‐doped carbon hollow particles manifest superior electrocatalytic oxygen reduction performance with high activity and excellent durability.

Template-directed synthesis of nitrogen- and sulfur-codoped carbon nanowire aerogels with enhanced electrocatalytic performance for oxygen reduction

Heteroatom doping, precise composition control, and rational morphology design are efficient strategies for producing novel nanocatalysts for the oxygen reduction reaction (ORR) in fuel cells. Herein, a cost-effective approach to synthesize nitrogen- and sulfur-codoped carbon nanowire aerogels using a hard templating method is proposed. The aerogels prepared using a combination of hydrothermal treatment and carbonization exhibit good catalytic activity for the ORR in alkaline solution. At the optimal annealing temperature and mass ratio between the nitrogen and sulfur precursors, the resultant aerogels show comparable electrocatalytic activity to that of a commercial Pt/C catalyst for the ORR. Importantly, the optimized catalyst shows much better long-term stability and satisfactory tolerance for the methanol crossover effect. These codoped aerogels are expected to have potential applications in fuel cells.

Reaction‐Kinetics‐Tuned Synthesis of Platinum Nanorods and Nanodendrites with Enhanced Electrocatalytic Performance for Oxygen Reduction

AbstractWe report a facile strategy to tune the growth behavior and surface structures of Pt nanocrystallites by varying the concentration of oleylamine (OAm) in mixed solutions of OAm and octadecene (ODE); the resulting Pt nanorods (NRs) and nanodendrites (NDs) show superior electrocatalytic performance for the oxygen reduction reaction (ORR). Long wormlike NRs with uniformly small diameters and NDs branched with NRs were obtained at low and medium concentrations of OAm, respectively. Time‐dependent morphology measurements showed that small Pt nanoparticles (NPs) were initially formed, which evolved into NRs or NDs depending on the reaction kinetics for Pt atom formation. Benefiting from the selective exposure of the ORR‐active (111) facet, the wormlike Pt NRs exhibited significantly higher ORR activity and electrochemical stability than state‐of‐the‐art Pt NP catalysts, which are enclosed with both the (111) and (100) facets. The ORR activity and stability of these catalysts were further enhanced by forming Pt NDs, probably as a result of the fact that the NR‐interconnected architectures produce more‐active high‐index facets in the junction areas.

A Highly Efficient Metal-Free Oxygen Reduction Electrocatalyst Assembled from Carbon Nanotubes and Graphene.

A novel carbon-nanotube-graphene hybrid nanostructure is developed using an aerosol-assisted assembly approach. After doping with nitrogen and phosphorus, the prepared hybrid nanomaterials exhibit excellent electrocatalytic performance for oxygen reduction in both alkaline and acidic media. This research presents a continuous and low-cost route to prepare high-performance metal-free electrocatalysts while replacing Pt-based materials.

N-Doped graphene frameworks with superhigh surface area: excellent electrocatalytic performance for oxygen reduction.

N-Doped carbon materials are promising candidates as alternative catalysts to noble metals in promoting the oxygen reduction reaction (ORR) in fuel cells. However, methods to further reduce the ORR overpotential and improve related kinetics remain to be developed. This study reports that N-doped graphene frameworks (NGFs) synthesized from the rapid pyrolysis of solid glycine particles in the presence of sodium carbonate, display an extremely large specific surface area (1760 m(2) g(-1)) and a graphitic-N-dominant C-N configuration. The NGFs can efficiently catalyze the electrochemical reduction of molecular oxygen into water following a 4e pathway, with a low overpotential (0.98 V of onset potential vs. RHE), very high kinetic limiting current density (16.06 mA cm(-2)), and turnover frequency (121 s(-1)), much better than the commercial Pt/C catalyst.

In-situ Preparation and Electrocatalytic Oxygen Reduction Performance of N-doped Graphene@CNF

In-situ Preparation and Electrocatalytic Oxygen Reduction Performance of N-doped Graphene@CNF

Electrocatalytic Oxygen Reduction Performance of Silver Nanoparticle Decorated Electrochemically Exfoliated Graphene.

We have developed a potentiostatic double-pulse technique for silver nanoparticle (Ag NP) deposition on graphene (GRn) with superior electronic and ionic conductivity. This approach yielded a two-dimensional electrocatalyst with a homogeneous Ag NP spatial distribution having remarkable performance in the oxygen reduction reaction (ORR). GRn sheets were reproducibly prepared by the electrochemical exfoliation of graphite (GRp) at high yield and purity with a low degree of oxidation. Polystyrenesulfonate added during exfoliation enhanced the stability of the GRn solution by preventing the restacking of the graphene sheets and increased its ionic conductivity. The potentiostatic double-pulse technique is generally used to electrodeposit Pt nanoparticles and remains challenging for silver metal that exhibits nucleation and growth potentials relatively close to each other. We judiciously exploited this narrow margin of potential, and for the first time we report Ag NP electrodeposited onto graphene with the subsequent ability to control both the density and the size of metallic nanoparticles. Considering the high activity along with the lower cost of Ag compared to Pt, these findings are highly relevant to the successful commercialization of fuel cells and other electrochemical energy devices.

Graphene Quantum Dots Supported by Graphene Nanoribbons with Ultrahigh Electrocatalytic Performance for Oxygen Reduction.

A new class of oxygen reduction reaction (ORR) catalysts based on graphene quantum dots (GQDs) supported by graphene nanoribbons (GNRs) has been developed through a one-step simultaneous reduction reaction, leading to ultrahigh performance for O reduction with an excellent electrocatalytic activity (higher limiting current density and lower overpotential than those of platinum) and high selectivity and stability in alkaline media comparable to the best C-based ORR catalysts reported so far. Electron microscopy revealed numerous surface/edge defects on the GQD/GNR surfaces and at their interface to act as the active sites. This, coupled with efficient charge transfer between the intimately contacted GQDs and GNRs, rationalized the observed ultrahigh electrocatalytic performance for the resultant GQD-GNR hybrids. Thus, this study opens a new direction for developing low-cost, highly efficient, C-based ORR electrocatalysts.

Facile one-pot synthesis of platinum nanoparticles decorated nitrogen-graphene with high electrocatalytic performance for oxygen reduction and anodic fuels oxidation

Due to exceptional electronic properties of graphene (Gr) and nitrogen doped graphene (N-Gr), they are considered as superior supporting platforms for novel metal nanoparticle decorations. Here, we report, a novel one-step electrochemical method for synthesis of Nitrogen-doped graphene sheets uniformly decorated with platinum nanoparticles (Pt/N-Gr). A graphite rod and platinum wire are respectively used for graphene and platinum nanoparticles production. The potential is cycled from −3V to +3V in acetonitrile solution as a nitrogen dopant source. By increasing the number of cycles the nitrogen-doped graphene/platinum nanoparticles composite is generated. After heat-treating the composite is characterized with various techniques such as FTIR, Raman, XPS, SEM and TEM. The electrocatalytic activity of the prepared composite toward the reduction of O2 and the oxidation of usual anodic fuels such as methanol, ethanol, hydrazine and formic acid is investigated using cyclic voltammetry technique. In comparison to commercial platinum/carbon, the onset potentials and the current densities for both O2 reduction and fuels oxidation are remarkably improved. Furthermore, the modified electrode by this composite shows good long-term stability and poisoning tolerance.

Facile synthesis of platinum–gold alloyed string-bead nanochain networks with the assistance of allantoin and their enhanced electrocatalytic performance for oxygen reduction and methanol oxidation reactions

In this work, a facile one-pot wet-chemical method is developed for preparation of bimetallic platinum–gold (Pt–Au) alloyed string-bead nanochain networks, using allantoin as a structure-directing agent, without any template, surfactant, or seed. The characterization experiments are mainly performed by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) spectroscopy. The as-prepared Pt–Au nanocrystals show enhanced electrocatalytic performance toward oxygen reduction reaction (ORR) mainly predominated by a four-electron pathway, and display improved catalytic activity and high stability for methanol oxidation reaction (MOR) over commercial Pt black and Pt–Ru black.

Β-cyclodextrin polymer as a linker to fabricate ternary nanocomposites AuNPs/pATP-β-CDP/rGO and their electrochemical application.

Based on the self-assembly strategy, β-cyclodextrin polymer (β-CDP) was used as a linker to connect reduced graphene oxide (rGO) and p-aminothiophenol (pATP). Then, pre-prepared gold nanoparticles (AuNPs) can self-assemble onto the surface of pATP-β-CDP/rGO to obtain new ternary nanocomposites AuNPs/pATP-β-CDP/rGO. The amount or the density of AuNPs can be adjusted by changing the concentration of pATP. UV-vis and (1)H NMR spectra confirmed the formation of inclusion complex between pATP and β-CDP. β-CDP might improve the dispersity of rGO in aqueous and the surface property of rGO. AuNPs/pATP-β-CDP/rGO modified electrode displayed high electrochemical response toward a pesticide-imidacloprid (IDP). The enrichment capability and molecular recognition of β-CDP and the catalytic property of AuNPs for IDP molecules synergistically promoted the electrochemical response of rGO modified electrode. Additionally, ternary nanocomposites exhibited the good electrocatalytic performance for oxygen reduction in O2-saturated 0.1M H2SO4 solution. The proposed synthesis strategy provided a facile, feasible and effective method for development of electrochemical sensors and Au-based catalysts for fuel cells.

Synthesis and Electrocatalytic Oxygen Reduction Performance of the Sulfur-Doped Carbon Nanocages

The sluggish oxygen reduction reaction (ORR) is the bottleneck in the development of fuel cells, and replacing precious and nondurable Pt catalysts by the material with low cost, high activity and good stability is a main challenge. Car- bon-based metal-free ORR electrocatalysts have become a promising alternative of commercial Pt/C catalyst due to their superior catalytic activity, high stability and low cost. Recent studies revealed that the doping of N, B, P or S atoms could boost the ORR electrocatalytic performance of carbon nanomaterials, and the catalytic activities were highly dependent on the doping elements, amounts and microstructures. In this study, sulfur-doped carbon nanocages (SCNCs) were synthesized by chemical vapor deposition method using in situ generated MgO as template and thiophene/benzene as precursors. The resultant SCNCs possessed high specific surface area of ca. 1000 m 2 •g -1 , abundant pore structure and superior graphitization degree. The X-ray photoelectron spectroscopy result showed sulfur atoms were doped into the carbon framework as the C― S―C moieties. The content of sulfur in the SCNCs was adjusted in the range of 0~3.45 at% by changing the amount of thiophene in the precursor. All the SCNCs samples had comparable specific surface area and similar pore structure. As an electrocatalyst for oxygen reduction reaction (ORR) in alkaline medium, the SCNCs exhibited a sulfur-content-dependent performance. The SCNCs with sulfur content of 0.84 at% demonstrated the optimal ORR performance. With further increas- ing the sulfur content, the ORR performance of the SCNCs gradually degraded and even inferior to that of the pure CNCs when the sulfur content was higher than 1.61 at%. In addition, the SCNCs showed better stability and immunity to methanol crossover than the Pt/C catalyst. This result is suggestive for designing advanced metal-free ORR electrocatalysts by regulat- ing the species and content of dopants and doping microstructures. Keywords carbon nanocages; sulfur doping; oxygen reduction; metal-free; fuel cells