Oxygen Reduction Reaction Catalytic Performance Research Articles

Ordered Mesoporous Carbon Confined Highly Dispersed PtCo Alloy for the Oxygen Reduction Reaction: The Effect of Structure and Composition on Performance

Pt-based catalysts are the most promising catalysts for proton exchange membrane fuel cells (PEMFCs) but still suffer from sluggish kinetics for the oxygen reduction reaction (ORR). Alloying Pt with transition-metal (M) elements is an efficient approach to modulate the electronic structure of Pt-based catalysts and improve the catalytic performance for the ORR. However, owing to the distinguishing surface state caused by different synthetic approaches, there still exist contradictory views about the relationship between the structure of Pt-based alloys and the catalytic performance for the ORR. In this work, PtCo alloys with a similar surface state but diverse structures and compositions are obtained by regulating the annealing temperatures and the precursor ratios. Accompanied by the structure and composition evolution, the electronic structure of Pt has also changed. PtCo@sOMC-900-1/3 with the intermetallic compound structure achieves the best kinetic activity as well as durability, indicating its potential for practical application. This work provides a more accurate understanding of the relationship between the alloy structure and the catalytic ORR performance and highlights a feasible strategy to mass-produce cathode catalysts for PEMFC applications.

High-Performance Heteroatoms (B, S) Single- and Dual-Doped Co/C Catalysts for Oxygen Reduction Reaction

Developing effective non-precious metal catalysts for oxygen reduction reaction (ORR) is of great importance in a wide range of clean electrochemical energy conversion technologies. In this work, N-free heteroatoms (B, S) single- and dual-doped Co/C catalysts for ORR are synthesized, characterized and compared with respect to their ORR catalytic performances. Electrochemical results show that BS-Co/C has a high ORR catalytic performance with an ORR peak potential (865 mV) and a half-wave potential (850 mV), better than both B-Co/C (842 mV and 818 mV) and S-Co/C (859 mV and 842 mV). Moreover, BS-Co/C has a main 4-electron ORR pathway, a good stability and strong methanol-tolerance. Compared to B-Co/C and S-Co/C, a synergistic ORR catalysis of BS-Co/C is observed in this work. The results of several structural characterizations indicate that this BS-Co/C possesses a structure of B and S dual-doped carbon with amorphous Co to improve the ORR catalytic performance.

Mechanochemical Synthesis as a Greener Way to Produce Iron‐based Oxygen Reduction Catalysts

AbstractIron‐based catalysts have been reported manifold and studied as platinum group metal (PGM) free alternatives for the catalysis of the oxygen reduction reaction (ORR). However, their sustainable preparation by greener synthesis approaches is usually not discussed. In this work, we propose a new method for the sustainable preparation of such catalysts by using a mechanochemical approach, with no solvents and non‐toxic chemicals. The materials obtained from low temperature carbonization (700 °C) exhibit considerable and stable catalytic performance for ORR in alkaline medium. A catalyst obtained from iron hydroxide, tryptophan, dicyandiamide, and ammonium nitrate shows the best electrocatalytic performance with an overpotential of 921 mV vs. RHE at 0.1 mA/cm2 and an electron transfer number of 3.4.

Hydrothermal Synthesis of γ‐Fe2O3/rGO Hybrid Nanocomposite as an Efficient Electrocatalyst for the Oxygen Reduction Reaction

AbstractThe preparation of a low‐cost, recycled and efficient electrocatalyst for oxygen reduction reaction (ORR) is highly desirable in fuel cells and metal‐air batteries. Herein, γ‐Fe2O3/reduced Graphene oxide (rGO) nanocomposite is fabricated through a simple and environmentally friendly approach and applied as a high‐performance ORR electrocatalyst. Multiple characterizations confirm the formation of γ‐Fe2O3/rGO nanocomposite and exhibit well crystal structure, microstructure, and magnetic properties. Furthermore, the cyclic voltammetry and linear sweep voltammetry measurements confirm that the γ‐Fe2O3/rGO exhibits high ORR catalytic performance for the synergistic effect. Consequently, the obtained γ‐Fe2O3/rGO might be a promising non‐precious, cheap and recycled catalyst for fuel cells and metal‐air batteries.

Co2N Nanoparticles Anchored on N‐Doped Active Carbon as Catalyst for Oxygen Reduction Reaction in Zinc–Air Battery

The development of efficient catalytic electrode toward oxygen reduction reaction (ORR) is still a great challenge for the wide use of zinc–air batteries. Herein, Co2N nanoparticles (NPs) anchored on N‐doped carbon from cattail were verified with excellent catalytic performances for ORR. The onset and half‐wave potentials over the optimal catalyst reach to 0.96 V and 0.84 V, respectively. Current retention rates of 96.8% after 22‐h test and 98.8% after running 1600 s were obtained in 1 M methanol solution. Density functional theory simulation proposes an apparently increased electronic states of Co2N in N‐doped carbon layer close to the Fermi level. Higher charge density, favorable adsorption, and charge transfer of intermediates originate from the coexistence of Co2N NPs and N atoms in carbon skeleton. The superior catalytic activity of composites also was confirmed in zinc–air batteries. This novel catalytic property and controllable preparation approach of Co2N‐carbon composites provide a promising avenue to fabricate metal‐containing catalytically active carbon from biomass.

Bimetal-organic framework-derived carbon nanocubes with 3D hierarchical pores as highly efficient oxygen reduction reaction electrocatalysts for microbial fuel cells

Noble metal-free and highly efficient electro-catalytic materials with hierarchically porous structures continue to be studied for the oxygen reduction reaction (ORR) in microbial fuel cells (MFCs). We report bimetal-organic framework (bi-MOF)-derived nanocubic Swiss cheese-like carbons with a novel three-dimensional hierarchically porous structure (3D Co-N-C) prepared by utilizing cetyltrimethylammonium bromide (CTAB) as a structure-directing agent to control the formation of a nanocubic skeleton, and silica spheres as a template to form a mesoporous structure. The elemental composition and chemical morphology of this material can be tuned through the Zn/Co ratio to optimize its ORR catalytic activity. The optimized 3D Co-N-C displays excellent ORR catalytic performance (half-wave potential as high as 0.754 V vs. reversible hydrogen electrode and diffusion-limiting current density of 5.576 mA cm−2) in 0.01 mol L−1 phosphate-buffered saline (PBS electrolyte), showing it can compete with the commercial 20 wt% Pt/C catalysts. The catalytic capability and long-term durability of 3D Co-N-C as an air-filled cathode electrocatalyst in an MFC device are tested, showing that the 3D CoNC-MFC can reach a high power density of 1257 mW m−2 and provide a competitive voltage during a periodic feeding operation for 192 h; these values are much higher than those of the Pt/C-MFC.

Green synthesis of nitrogen and fluorine co-doped porous carbons from sustainable coconut shells as an advanced synergistic electrocatalyst for oxygen reduction

Abstract Exploring a convenient and sustainable strategy to fabricate inexpensive and efficient electrocatalysts for oxygen reduction reaction (ORR) is one of the main challenges to achieve the goal of large-scale commercial application of fuel cells. Herein, an environmental and convenient strategy is presented to ingeniously fabricate nitrogen and fluorine co-doped porous carbon (NF-PC) catalyst using coconut shells as a green carbon source. In particular, the integration of N and F atoms into the coconut shells-derived carbon framework plays a significant role in boosting the ORR catalytic performance, since the synergistic catalysis introduced by the co-doping of N and F. Benefiting from the favorable characteristics of microporous conductive carbon framework, moderate N and F co-doping, as well as synergistic effect between N and F dopants, the developed NF-PC catalyst possesses remarkable catalytic activity, methanol resistance and cycle stability, even surpassing than that of commercial Pt/C. In addition to providing a promising metal-free ORR catalysts, most importantly, the sustainable and convenient strategy explored in this research offers great potential for commercial applications in fuel cells and other clean energy technologies.

First-principle-data-integrated machine-learning approach for high-throughput searching of ternary electrocatalyst toward oxygen reduction reaction

Platinum (Pt) alloys are expected to overcome long-standing issues of Pt/C electrocatalysts for oxygen reduction reaction (ORR). Entangled with serious uncertainty in configurational and compositional information, the design of a promising multi-component electrocatalyst, however, has been delayed. Here, we demonstrate that a first-principle database-driven machine-learning approach is extremely useful for the purpose via exploring materials beyond the regime of pure quantum mechanical calculations. Guided by a computational ternary phase diagram we indeed experimentally synthesized a PtFeCu nanocatalyst with 2 g per batch capacity and measured its catalytic performance for ORR. Both our computation and experiment consistently demonstrate that PtFeCu is highly active due to the atomic distribution of Cu leading to beneficial modulation of surface strain and segregation. Strikingly, PtFe high Cu low (776 μA cm −2 Pt and 0.67 A mg −1 Pt ) exhibits not only 3-fold better specific and mass activities than Pt/C but also little performance degradation over the accelerated stress test. • First-principle establishment of catalytic property data for ternary nanoparticles • Parametrization of atomistic interaction into neural network potentials • A striking consistency between computational prediction and experimental validation • Exceptional catalytic mass activity of PtFeCu 3-fold higher than that of Pt/C One of the challenging issues in nanocatalyst design for catalysis applications is to introduce the atomic-level functionalities of nanoparticles, determining the activity and stability. Multi-component systems can be promising, but the enormous configurational degrees of freedom and optimization routes for a target reaction remained unsolved. We demonstrate the combination of a machine-learning approach and experimental tests of PtFeCu nanoparticles for oxygen reduction reaction. Promising candidates were efficiently screened theoretically and successfully validated by the experiments. Both our computational and experimental outcomes indicate that the highly active electrocatalytic performance of PtFeCu originates from Cu atomic distribution. Our study suggests that first-principle calculations combined with machine-learning technology can be a promising approach in design of nanocatalysts to reduce the gap between the simulations and experiments. To efficiently design the Pt-based alloy nanocatalysts for oxygen reduction reaction, we utilized first-principle data integrated with machine learning to search for PtFeCu configurational spaces. We identified the promising candidates and revealed the atomic-level understanding via first-principle calculations. Cu atomic distribution remarkably modulated surface strain energies and segregation of the alloying components toward better oxygen reduction reaction performance. Tuning of Cu contents led to the high electrochemical performance of PtFeCu nanocatalysts, which was successfully validated by experiments.

Electrochemical catalytic mechanism of single transition metal atom embedded BC3 monolayer for oxygen reduction and evolution reactions

The graphene embedded with single transition metal (TM) atom shows great potential to replace precious metals as the electrochemical catalyst of fuel cells and metal-air batteries. However, the electrochemical catalytic mechanism of single TM atom supported on other substrates is less well understood. Herein, a density functional theory calculation of single 3d TM atom embedded on two-dimensional BC3 as an active site for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is performed. The electronic structure analysis reveals that the hybridized antibonding orbitals formed by TM-3d and O-2p orbitals possess lower energy level and higher occupancy, weakening the interaction between OH and TM, further determines the catalytic activity of TM-N4 active site. Among all considered active sites, the Fe-N4 and Mn-N4 sites show the best ORR catalytic performance while Co-N4 site shows the best OER catalytic performance. Finally, an adsorption factor is put forward via the coordination environment around TM atom to provide a guidance on the exploration of new high-performance single atom catalysts family.

Trace Bimetallic Iron/Manganese Co-Doped N-Ketjenblack Carbon Electrocatalyst for Robust Oxygen Reduction Reaction

Massive commercial Al-air batteries heavily depend on highly efficient, low-cost, and scalable oxygen reduction reaction (ORR) electrocatalysts. Herein, trace bimetallic iron, manganese co-doped N-ketjenblack carbon (Fe-Mn/KB) electrocatalyst was fabricated for efficient ORR via a facile and scalable route with cheap and abundant raw materials. The synthesis route of Fe-Mn/KB only includes one-pot hydrothermal reaction, mild calcination, and acid treatment procedures. The co-doping of trace Fe and Mn elements was confirmed by X-ray photoelectron spectroscopy (XPS) and EDS elemental mapping technique. In addition, nitrogen element was also successfully doped into the ketjenblack carbon. The trace amount of Fe, Mn and the doped nitrogen element synergistically improved the ORR catalytic activity. The Fe-Mn/KB electrocatalyst outperformed Fe/KB electrocatalyst, in terms of a more positive half-wave potential (0.78 V) and a higher limiting current density (6.0 m A·cm−2). Moreover, the ORR catalytic performance of the Fe-Mn/KB electrocatalyst is comparable to the commercial 20 wt.% Pt/C (0.82 V, 5.3 mA·cm−2, respectively). The galvanostatic discharge of the full Al-air battery demonstrated that Fe-Mn/KB maintained a stable discharge voltage of 1.50 V (extremely close to the Pt/C 1.53 V) up to 20 h. Owing to its simple, economical, scalable, and high efficiency, the proposed Fe-Mn/KB will become a competitive candidate to replace platinum group electrocatalysts.

Rich Surface Oxygen Vacancies of MnO2 for Enhancing Electrocatalytic Oxygen Reduction and Oxygen Evolution Reactions

Development of catalysts for the electrochemical oxygen reactions, namely, oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), is critical for the application of various renewable energy technologies. The aim of this work is to prepare low‐cost MnO2 electrocatalyst with high activity for the ORR and OER via introduction of surface oxygen vacancies (OVs). Herein, the procedure of thermal heating treatment under air or H2 has been demonstrated as an efficient way to create OVs on the surface of α‐MnO2 and β‐MnO2 nanorods, which are found to be highly active for both ORR and OER. The existence of surface OVs can modulate the intrinsic activity of α‐MnO2 and β‐MnO2 and improve their ORR and OER kinetics. More importantly, the H2‐treated MnO2 possesses much more surface OVs and thus exhibits much better catalytic performances for ORR and OER in comparison with MnO2 obtained by common annealing treatments under air. Especially, the H2‐treated α‐MnO2 nanorods show the best activity for the ORR and OER. The results confirm that the heating treatment under H2 reducing atmosphere can be a facile and efficient process to develop bifunctional Mn‐based electrocatalysts for electrochemical oxygen reactions.

Hollow Co3O4-x nanoparticles decorated N-doped porous carbon prepared by one-step pyrolysis as an efficient ORR electrocatalyst for rechargeable Zn-air batteries

Composites of cobalt oxides and nitrogen-doped porous carbon, as electrocatalysts for oxygen reduction reaction (ORR), offer considerable potential in new-style energy conversion and storage devices. Herein, a straightforward method for production of N-doped porous carbon (Co3O4-‍x@N–C) decorated by hollow Co3O4-x nanoparticles with oxygen vacancies has been studied by one-step pyrolysis of Co-doped quinone-amine polymer in gas mixture of NH3 and Ar. The nanosized CoO/Co3O4 heterostructure can boost the electron transport, while the hollow structure can ensure the structural and chemical stability of the catalyst, and the oxygen vacancy can change the surface electron structure and lower the activation energy barrier for oxygen reduction. Consequently, the as-prepared catalyst Co3O4-x@N–C exhibits excellent ORR catalytic performance (E1/2 = 0.845 V vs. RHE), exceeding that of Pt/C and most recently reported ORR catalysts. The Zn-air batteries assembled with Co3O4-x@N–C present a high open circuit potential (1.524 V), a large peak power density (105.2 mW cm−‍2) and great discharge-charge cycling performance, superior to the Zn-air batteries assembled with Pt/C. The excellent electrocatalytic performances of Co3O4-x@N–C make it an ideal alternative for precious metal catalyst (Pt/C) in rechargeable Zn-air batteries.

Tuning the Electrocatalytic Properties of Black and Gray Arsenene by Introducing Heteroatoms.

On the basis of density functional theory calculations, we explored the catalytic properties of various heteroatom-doped black and gray arsenene toward the oxygen reduction reaction (ORR), the oxygen evolution reaction (OER), and the hydrogen evolution reaction (HER). The calculation results show that pristine black (b-As) and gray arsenene (g-As) exhibit poor catalytic performance because of too weak intermediate adsorption. Heteroatom doping plays a key role in optimizing catalytic performance. Among the candidate dopants O, C, P, S, and Sb, O is the most promising one used in arsenene to improve the ORR and OER catalytic performance. Embedding O atoms could widely tune the binding strength of reactive intermediates and improve the catalytic activity. Single O-doped g-AsO1 can achieve efficient bifunctional activity for both the OER and the ORR with optimal potential gap. b-AsO1 and b-AsO2 exhibit the optimal OER and ORR catalytic performance, respectively. For the HER, double C-doped g-AsC2 could tune the adsorption of hydrogen to an optimal value and significantly enhance the catalytic performance. These findings indicate that arsenene could provide a new platform to explore high-efficiency electrocatalysts.

Porous N, B co-doped carbon nanotubes as efficient metal-free electrocatalysts for ORR and Zn-air batteries

The flexible design and construction of oxygen reduction reaction (ORR) catalysts with high activity, great stability, and superior cost efficiency are essential for metal-air batteries and fuel cells. Hollow carbon nanotubes (CNTs) are considered promising electrocatalysts owing to their outstanding thermal stability, robust chemical properties, and high specific surface area. Herein, a convenient and controllable solid-phase route is proposed for the preparation of porous nitrogen (N) and boron (B) co-doped carbon nanotubes (NBCNT) by using tubular polypyrrole (PPy) and sodium tetraphenylboron ((C6H5)4BNa), in which (C6H5)4BNa serves not only as a B source but also as a pore-forming agent that can help to regulate N configuration and expose more active sites. Due to the synergistic effects of porous one-dimensional hollow structure and the binary heteroatom doping, the optimized NBCNT catalyst demonstrates superior catalytic performance for ORR in both acidic and alkaline electrolytes. Moreover, Zn-air batteries are constructed based on the as-prepared catalysts, which reveal a high operating voltage (1.43 V) and peak power density (173.93 mW cm−2), further demonstrating a comparable electrocatalytic performance of the catalysts to commercial Pt/C catalyst. This work reveals a novel construction of high-efficiency and cost-effective metal-free catalysts for various energy conversion and storage technologies.

Synthesis of N-doped Co@C/CNT materials based on ZIF-67 and their electrocatalytic performance for oxygen reduction

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%).

Study on Oxygen Reduction Method of Phosphorus-doped Hydrogenated Nano-silicon

In recent years, hydrogenated nano-silicon has attracted much attention due to its high specific energy density. However, the slow kinetic oxygen reduction reaction (ORR) and oxygen evolution reaction (ORE) reduce the efficiency of hydrogenation of nano-silicon and hinder its practical application. The development of non-precious catalysts with excellent performance and low price is of great significance to the development of hydrogenated nano-silicon. Among many hydrogenation nano-silicon catalysts, cobalt-based compounds have good ORR and ORE catalytic performance, and are rich in Co reserves and low in price. Especially doped compounds have excellent stability. In the thesis, three series of hydrogenated nano-silicon composite materials of Co-SrCO3/NC, Co-Nd/NC and Co-Ce/NC were successfully synthesized through heating reflow method and subsequent high-temperature calcination. XRD, Raman, XPS, TEM, nitrogen isothermal adsorption and desorption and other analytical methods were used to characterize the structure of the above composite materials. Through chemical tests, the composite materials were evaluated for the catalytic performance of ORR and ERR, and their structure-activity relationship was analyzed. The Co_SrC03/NC series composite materials were calcined at different temperatures. The results showed that the generated SrCO3 nanorods were embedded in the graphite shell and contacted with hydrogenated nano-silicon. In an oxygen-saturated 0.1MKOH solution, Co-SrCO3/NC series composites have excellent ORR/ORE catalytic activity, especially Co-SrCO3/NC-600 has more stable activity than precious metal catalysts of 20wt% Pt/C and Ir02. Sex. The air prepared with Co-SrCO3/NC-600 has better performance. During the in-depth study of 10mA_cnT2, Co-SrC03/NC-600 was used as the air to maintain a stable platform of 1.10V, and the platform of 20wt%Pt/C under the same conditions was 1.17V.

Electronically Modified Atomic Sites Within a Multicomponent Co/Cu Composite for Efficient Oxygen Electroreduction

AbstractRational design of cost‐effective and active electrocatalysts is an essential step toward the large‐scale realization of hydrogen fuel cells and metal–air batteries. Its success requires a drastic improvement in the kinetics of the cathodic oxygen reduction reaction (ORR). Herein, a novel ORR catalyst formed by encapsulating thin Cu layer decorated Co nanoparticles inside graphitic carbon layers that are embedded with abundant CoNx and CuNx atomic sites (denoted as SA‐CoCu@Cu/CoNP), is reported. The multicomponent SA‐CoCu@Cu/CoNP composite exhibits a remarkable ORR catalytic activity, exceptional stability, and excellent methanol tolerance in alkaline media, outperforming the commercial platinum carbon under identical testing conditions and also being active in acidic media. The excellent ORR catalytic performance is ascribed to the modified electronic structure of the CoNx active sites due to an electron donating effect from the embedded nanoparticles and the nearby CuNx species, as revealed by X‐ray spectroscopic results and density functional theory computations. Moreover, the effective role of CuNx sites in suppressing the peroxide formation during ORR is also identified, endowing the resultant catalyst a prolonged stability and enhanced efficiency that are beneficial for practical applications.

Strained Ultralong Silver Nanowires for Enhanced Electrocatalytic Oxygen Reduction Reaction in Alkaline Medium.

Many noble metals are efficient catalysts for oxygen reduction reaction (ORR), including silver (Ag). Among all these noble metals, Ag is the most affordable because of its relative abundance. Surface energy has been proven to play a crucial role in the catalytic process, and straining is an effective operation to raise the surface energy over electrocatalysts. In this work, sonication was utilized to induce strain in Ag nanowires (NWs) through lattice deformation. A 0.18 J/m2 improvement of the surface energy around the stacking faults area has been calculated via density functional theory. The diffusion-limiting current density was evaluated and increases by >20% (from -4.98 to -6.00 mA/cm2) after sonication straining. Meanwhile, the onset potential remains almost constant (i.e., 0.95 V vs RHE). The results show that induction of strain has a strong impact on the diffusion-limiting current density and significantly improves the ORR catalytic performance of Ag NWs.

Engineering single MnN4 atomic active sites on polydopamine-modified helical carbon tubes towards efficient oxygen reduction

Among various earth-abundant and noble metal-free catalysts for oxygen reduction reaction (ORR), Mn and N co-doped carbon (Mn-N-C) is highly desirable and promising, which, however, suffer from the limited amount of active sites largely abating its ORR catalytic performance. Herein we demonstrate an effective strategy to elevate the ORR active site density by designing a helical graphitized carbon tubes to highly disperse the single Mn atomic sites coordinated with nitrogen. The obtained polydopamine-modified helical MnNC-PDA-700 catalyst shows excellent ORR electrocatalytic performance with a half-wave potential of 0.87 V and extra-high Zn-air battery power density of 122.7 mW cm−2, which are comparable to and even higher than those of Pt/C. Such an excellent electrocatalytic performance is attributed to the much enhanced amount of MnN4 active sites created on the helical graphitized carbon tubes owing to high surface area helical structure of the carbon tubes and the strong bonding of polydopamine molecules onto the tubes. The density functional theory (DFT) calculations further confirm that the MnN4 sites are the origin of the superior ORR activity via a 4e− pathway in alkaline media.

Efficient ORR activity of N-doped porous carbon encapsulated cobalt electrocatalyst derived from a novel bimetal-organic framework

Transition metal nitrogen-doped carbon catalysts have been feasible substitutes for Pt-based electrocatalysts for oxygen reduction reaction (ORR). Herein, porous cobalt N-doped carbon materials with core-shell nanostructure were synthesized by direct carbonization of bimetal-organic framework CoxZn100-x(adeninate)4(biphenyldicarboxylate)6 (x = 0, 3, 5, 8) precursors at various temperatures (800, 900, 1000 °C) in Ar atmosphere. The as-prepared catalysts present core-shell nanostructure and highly graphitic hollow carbon-ring structure. Meanwhile, Co nanoparticles are evenly distributed in the nitrogen-doped carbon matrix. The effects of different molar ratios of Co/Zn and pyrolysis temperatures on ORR catalytic performance were evaluated. After replacement of 5 % Zn in the precursor by Co, the Co5-N-C-900 exhibited superior oxygen reduction activity to that of 20 wt% commercial Pt/C catalyst in 0.1 M KOH, as evidenced by higher half-wave potential (0.86 V vs. 0.85 V) and diffusion-limited current density (−5.79 mA cm−2 vs.−5.26 mA cm−2) vs. RHE. Additionally, the catalyst has long-time stability than that of Pt/C catalyst. Co core-shell nanostructure, large surface area, porous structure and Co-Nx active sites of Co5-N-C-900 were beneficial to the oxygen reduction property, which enlarged the contact area between catalyst and oxygen molecules, exposed sufficient active sites, and elevated mass diffusion and electron transfer rates. Overall, this study provides an appropriate strategy for the synthesis and application of bimetal-organic framework-derived transition metal nitrogen-doped carbon materials as oxygen reduction electrocatalysts.