Catalytic Activity For Oxygen Reduction Reaction Research Articles

Highly Durable PtNi Alloy on Sb-Doped SnO2 for Oxygen Reduction Reaction with Strong Metal-Support Interaction.

Carbon-supported Pt is currently used as catalyst for oxygen reduction reaction (ORR) in fuel cells but is handicapped by carbon corrosion at high potential. Herein, a stable PtNi/SnO2 interface structure has been designed and achieved by a two-step solvothermal method. The robust and conductive Sb-doped SnO2 supports provide sufficient surfaces to confine PtNi alloy. Moreover, PtNi/Sb0.11 SnO2 presents a more strongly coupled Pt-SnO2 interface with lattice overlap of Pt (111) and SnO2 (110), together with enhanced electron transfer from SnO2 to Pt. Therefore, PtNi/Sb0.11 SnO2 exhibits a high catalytic activity for ORR with a half-wave potential of 0.860 V versus reversible hydrogen electrode (RHE) and a mass activity of 166.2 mA mgPt -1 @0.9 V in 0.1 M HClO4 electrolyte. Importantly, accelerated degradation testing (ADT) further identify the inhibition of support corrosion and agglomeration of Pt-based active nanoparticles in PtNi/Sb0.11 SnO2 . This work highlights the significant importance of modulating metal-support interactions for improving the catalytic activity and durability of electrocatalysts.

Mesoporous and dual-shelled hollow CeO2@CoNC nanospheres as efficient and stable oxygen reduction reaction electrocatalysts

The electrocatalytic oxygen reduction reaction (ORR) is the key bottleneck of fuel cells and rechargeable metal-air batteries, and recently, metalnitrogen complex carbon (MNC) demonstrates great potential in these fields. However, the complex and easily degraded MNC structure often results in inferior activity and poor durability in electrolysis. Herein, we fabricate a catalyst of h-CeO2@CoNC through the extended Stöber method and subsequent pyrolysis, involving the hollow CeO2 as the core and CoNC as the shell. The h-CeO2@CoNC catalyst exhibits notable ORR catalytic performances in 0.1 M KOH with a half-wave potential of 0.82 V and excellent durability, attributed to the synergistic interaction between CeO2 and CoNC matrix. Specifically, the inner layer of CeO2 is principally responsible for enhancing the chemical stability and the outer one of CoNC matrix is beneficial to boosting the ORR catalytic activity. This work provides an efficient preparation approach and further insight of rational design of the unique MNC catalysts for energy storage.

Nanostructured Mg-doped Mn–Cr spinel oxide cathodes for solid oxide fuel cells with optimized performance

The cathode properties are critical for solid oxide fuel cells (SOFCs) performance and a major challenge for commercialization. This study employs the impregnation method to produce uniformly distributed Mg-doped manganese-chromium spinel oxide nanoparticles infiltrated into a network on the Gd0.1Ce0.9O1.95 (GDC) skeleton as SOFC cathodes. The effects of Mg doping on the performance of these nanostructured spinel oxides are investigated. Both experimental results and density functional theory (DFT) calculations demonstrate that Mg doping can optimize the electronic structure of the manganese-chromium spinel oxide, increase the oxygen vacancy concentration, and significantly enhance the electrical conductivity and oxygen reduction reaction (ORR) catalytic activity. The Mg-doped manganese-chromium spinel oxide cathode exhibits superior performance, with an area-specific polarization resistance of 0.33 Ω cm2 and a maximum power density of 976 mW cm−2 at 800 °C. Moreover, the nanostructures of the cathode barely change after 100 h of cell operation. These findings provide a new strategy for optimizing the performance of SOFC spinel oxide cathodes.

(Digital Presentation) Structure-Activity Relationship of M-N-C Electrocatalysts Synthesized Using a General Solution-Phase Coordination Approach

Metal- and nitrogen-doped carbon (M-N-C) catalysts have great potential in heterogeneous catalysis. They are used to catalyze various crucial electrochemical reactions, such as the oxygen reduction reaction (ORR), the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), and the CO2 reduction reaction (CO2RR).1-4 The nitrogen-coordinated metal sites (MNx) have been considered the main active sites in these M-N-C catalysts. However, the synthesis of MNx moieties often undergoes a high-temperature heat-treatment step, resulting in low site density. On the other side, the coordination environment in the MNx sites is also affected by the metal species which induced the site formation. Therefore, it is challenging to single out the role of central metal in the structure-activity relationships for these MNx sites.In this presentation, we will discuss our recent progress in the development of a solution-phase coordination synthesis approach targeting M-N-C catalysts with high active-site density and well-defined coordination environments.5, 6 A series of M-N-C catalysts are synthesized via this approach by coordinating electroactive target metal ions with the nitrogen-coordinated metal-vacancy (MVNx) sites in N-C templated by sacrificial metals. With a combined experimental and computational approach, we explore the role of sacrificial metals, including s-, p-, 3d-, 4d-, and f-block metals, in forming various MVNx sites with unique coordination configurations. The structure-activity relationship between the coordination environment and the catalytic activity for ORR, HER, OER, and CO2RR is established by comparing the MNx site structures induced by various sacrificial metals. Furthermore, we will present the activity series of metal centers in M-N-C catalysts with the same and well-defined coordination environment for ORR, HER, OER, and CO2RR. These results will guide the future development of M-N-C catalysts. Acknowledgments Financial support from the State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences is greatly appreciated. This study is financially supported by the Shanxi Province grant (Grant No. 20210302123011, 202203021212007, and 202103021224442), and Key Research and Development (R&D) Projects of Shanxi Province (202102070301018). References J. Cui, Q. Chen, X. Li and S. Zhang. Recent advances in non-precious metal electrocatalysts for oxygen reduction in acidic media and PEMFCs: an activity, stability and mechanism study. Green Chemistry, 23, 6898 (2021).H. He, H. H. Wang, J. Liu, X. Liu, W. Li and Y. Wang. Research Progress and Application of Single-Atom Catalysts: A Review. Molecules, 26, 6501 (2021).U. Martinez, S. Komini Babu, E. F. Holby, H. T. Chung, X. Yin and P. Zelenay. Progress in the Development of Fe-Based PGM-Free Electrocatalysts for the Oxygen Reduction Reaction. Advanced Materials, 31, 1806545 (2019).Y. Wang, X. Cui, L. Peng, L. Li, J. Qiao, H. Huang and J. Shi. Metal–Nitrogen–Carbon Catalysts of Specifically Coordinated Configurations toward Typical Electrochemical Redox Reactions. Advanced Materials, 33, e2100997 (2021).M. Huang, R. Ding, J. Yang, W. Shi, S. Shi, L. Chen, S. Liu and X. Yin. Formation of Nitrogen-Coordinated Metal Sites (M = Fe, Co) via Solution-Phase Coordination on Nickel- And Nitrogen-Co-Doped Carbon Templates with Metal Vacancy-Nx Sites. Journal of The Electrochemical Society, 169, 106507 (2022).M. Huang, L. Chen, R. Ding, W. Shi, Q. Qin, J. Yang, S. Liu and X. Yin. Solution-Phase Synthesis of Co-N-C Catalysts Using Alkali Metals-Induced N-C Templates with Metal Vacancy-Nx sites. ChemRxiv, doi: 10.26434/chemrxiv-2022-xnh88 (2022).

Atomically Dispersed Transition Metal-Nitrogen-Carbon Electrocatalysts: Design, Synthesis, Characterization, Reactivity and Durability

Platinum group metal-free (PGM-free) catalysts have been targeted as possible Earth Abundant Elements solution to many electrochemical energy conversion technologies. Special attention has been given to PGM-free electrocatalysis with atomically dispersed (AD) transition metal moieties decorated over nitrogen-doped carbonaceous materials (a.k.a. M-N-C catalysts). Major applications for M-N-Cs are in cathode catalysts for oxygen reduction reaction (ORR). 1 These materials are employed across the pH-range: in proton exchange membrane fuel cells (PEMFC), biological (microbial) fuel cells (MFC) and alkaline, including anion/hydroxyl exchange membrane fuel cells (AFC, AEMFC/HEMFC). We have successfully introduced M-N-C catalysts synthesized by sacrificial support method (SSM) as a hard template approach based on high temperature pyrolysis.2 In most cases a secondary pyrolysis is being performed to promote AD display of the transition metal.3 This talk will address structure-to-property correlations for M-N-C catalysts in ORR based on electrochemical activity obtained in rotating ring-disk electrodes (RRDE) with those spectroscopic and microscopic observations and density functional theory (DFT) calculations of oxygen binding on AD transition metal. We will discuss the role of the AD transition metal, participation of the surface N-groups as co-catalysts/alternative active sites and the possible role of surface oxides as co-catalysts or hydrophilic/hydrophobic properties descriptor. M-N-C catalysts performance in single membrane electrode assembly (MEA) fuel cells will also be discussed in the context of its surface chemistry and materials structure/morphology. We will focus on local hydrophobicity of SSM-based M-N-C electrocatalystsand its impact on the MEA performance.A broad spectrum of AD transition metal decorated MNCs have been synthesized and evaluated for catalytic activity in ORR (and other processes). The use of such materials as “active supports” for highly dispersed platinum or platinum alloy nanoparticles will be discussed. New developments in synthesis protocols enabling “green chemistry” scalable solutions will be discussed.

Hybridization of Carbon Nanotube Tissue, MnO2 Catalyst and CFx as an Advanced Air Cathode in Metal–Air Batteries

We first present the utilization of hybrid carbon nano-tube (CNT) – manganese dioxide (MnO2) tissues as air electrodes in nonaqueous aluminum- and lithium-based battery systems. The CNT tissues are impregnated with α-manganese dioxide nanoparticles via a straightforward binder-free ultrasonic treatment, thereby enabling an improved oxygen reduction reaction (ORR) catalytic activity. Half-cell potentiodynamic measurements along with full-cell discharge evaluations of Li- and Al-based battery systems are reported. Higher discharge potentials and capacities were obtained from generic and advanced hybrid CNT–MnO2 air cathodes. The discharge products obtained on the air cathode surface were studied using high-resolution scanning electron microscopy. Their chemical compositions were evaluated using elemental mapping energy-dispersive X-ray spectroscopy. The stability of the α-MnO2 catalyst was studied using X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy, thereby indicating the ongoing formation of an outer MnF2 shell layer, which affected the α-MnO2 functionality, as an efficient ORR catalyst. We conclude this part of the talk by showing that the function of the metal–air battery is enabled by using porous carbon nanotube (CNT)-based tissue substrates loaded with MnO2 catalyst.In contrast, fluorinated graphite (CFx) coating on the CNT substrate provides an additional discharge process, enhancing discharge capacity. Two CFx loadings are investigated, and their performances are compared with that of a pristine CNT tissue. Electrochemical evaluations, including half- and full-cell measurements, are performed to examine the effect of the coating layer thickness on the ability of the cell to function at high discharge rates.

Nitrogen-doped carbon shell armored ‘Janus’ Co/Co9S8 heterojunction as robust bi-functional oxygen reduction reaction/oxygen evolution reaction catalysts in seawater-based rechargeable Zn-air batteries

It is of paramount importance to develop highly efficient and Cl−corrosion-resistant bi-functional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for application in seawater-based Zn-air batteries (S-ZABs), but the process remains full of challenges. Herein, a facile and effective strategy was adopted to fabricate the N-doped carbon shell armored ‘Janus’ Co/Co9S8 heterojunction catalyst (denoted as Co/Co9S8-NMC). The well-defined ‘Janus’ structure endows the catalyst with a ‘synergistic effect’ between Co and Co9S8 species, which can also accelerate the electron transfer via ‘Janus’ interfaces, thus boosting ORR/OER performance. Besides, N-doped carbon shells can be considered armor for protecting the catalyst from Cl− corrosion. By virtue of these merits, the resulting Co/Co9S8-NMC catalyst exhibits excellent catalytic activity for ORR and OER in seawater electrolyte, accompanied by a half-wave potential of 0.83 V and a low overpotential of 298 mV to achieve a current density of 10 mA/cm2. Besides, the S-ZABs based on the Co/Co9S8-NMC catalyst deliver a high maximum power density of 162.29 mW/cm2 and robust stability over 600 h. This work advances the development of highly efficient bi-functional catalysts for S-ZABs.

Effect of pre-annealing on chemical configuration and heteroatom doping of highly active carbon catalysts for the oxygen reduction reaction

Heteroatom-doped carbon catalysts are promising alternatives to platinum group metal-free catalysts for oxygen reduction reaction (ORR). To enhance the ORR activity of carbon-based catalysts, the break of electroneutrality and number of active sites must be maximized. In this study, an annealing process at a mild temperature was introduced before heteroatom doping to control the content and configuration of the oxygen functional groups on the graphene oxide (GO). Pre-annealing affects the chemical configuration and the porosity of GO such that the epoxy groups are converted into carbonyl groups accompanying the defect formation. Interestingly, The carbonyl-enriched environment allowed ammonia borane, as a dopant with nitrogen and boron atoms, the enhanced doping performance, inducing the formation of higher number of heteroatom doping sites and additional defects in the graphene lattice. The aBNG-150 catalyst demonstrated outstanding ORR activity in both half- and single-cell evaluations because it had the highest heteroatom content and meso/macropores derived from the elimination of oxygen functional groups, which can facilitate ORR catalytic activity and O2 diffusion pathway. Therefore, we believe that this approach provides an effective route for synthesizing carbon-based catalysts with remarkable ORR performances.

Metal‐free nanostructured‐carbon inks for a sustainable fabrication of zinc/air batteries: From ORR activity to a simple prototype

AbstractZinc/air batteries are convenient energy storage devices for both small and massive applications. While future perspectives indicate the need for low‐cost components and sustainable fabrication processes, the battery performance is in part controlled by the kinetics of the oxygen reduction reaction (ORR), which typically involves transition metals as catalysts. In this context, we prepare a series of metal‐free water‐based carbon inks, which are tested for their catalytic performance, once deposited on a gas‐diffusion substrate, in the air cathode of a simple battery prototype. The inks contain a variety of well‐defined carbon nanomaterials and additives, exhibiting different physicochemical properties that critically influence the interaction with the gas diffusion hydrophobic substrate. The intrinsic ORR catalytic activity of the ink material is also analyzed on a glassy carbon electrode by the rotating ring‐disc electrode (RRDE) method and specific capacitance measurements. The discharge capacity on our zinc/air battery prototype correlates well with the intrinsic catalytic activity in the RRDE. However, only the activity in the RRDE does not actually assure the performance on the commercial cathode of the prototype, since other chemical compatibility issues play a role. Thus, we highlight the importance of catalyst testing, not only on the RRDE but also under realistic device conditions.

Manipulating Pt-skin of porous network Pt-Cu alloy nanospheres toward efficient oxygen reduction

Designing Pt-skin on the catalyst surface is critical to developing efficient and stable electrocatalysts toward oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. In this paper, an acidic reductant is proposed to synchronously manipulate in-situ growth of Pt-skin on the surface of alloyed Pt-Cu nanospheres (PtCuNSs) by a facile one-pot synthesis in an aqueous solution. Ascorbic acid can create a Pt-skin of three atomic layers to make the typical PtCu-alloy@Pt-skin core/shell nanostructure rather than the uniform alloys generated by using alkaline reductants. Surfactant as soft-template can make the alloyed PtCuNSs with a three-dimensional porous network structure. Multiple characterizations of XRD, XPS and XAFS are used to confirm Pt-alloying with Cu and formation of core/shell structure of such a catalyst. This PtCuNSs/C exhibits a half-wave potential of 0.913 V (vs. RHE), with mass activity and specific activity about 3.5 and 6.4 times higher than those of Pt/C, respectively. Fuel cell tests verify the excellent activity of PtCuNSs/C catalyst with a maximum power density of about 1.2 W cm−2. Moreover, this catalyst shows excellent stability, achieving a long-term operation of 40,000 cycles. Furthermore, theoretical calculations reveal the enhancement effect of characteristic PtCu-alloy@Pt-skin nanostructure on both catalytic ORR activity and stability.

Regulation of oxygen vacancies and electronic structures by substituting Ba2+ at A-sites of LaNi0.5Mn0.5O3 double perovskites enabling high-performance catalysts for Mg-air batteries

The air cathodes impact the electrochemical performance of primary Mg-air batteries greatly, in which the activity of catalysts plays a decisive role. Perovskites attract significant attention for their high oxygen reduction reaction (ORR) catalytic activity, unique structure, simple synthesis, and low cost. Herein, a series of La1-xBaxNi0.5Mn0.5O3 (x = 0.1, 0.2, 0.3, 0.4, 0.5) catalysts fabricated by substituting Ba2+ for La3+ at the A-sites of LaNi0.5Mn0.5O3 are reported. As a result, the catalytic performance toward ORR exhibits a volcano curve with the increase of doping amount and the highest catalytic activity was achieved at 30 % of Ba2+ content. Importantly, the experimental and computational results explain the enhancement by the large O2 adsorption capacity, the formation of oxygen vacancies, the increase in the content of Mn3+ as an adsorption active site, and the upshift of the Mn-3d band center toward the Fermi level, thereby facilitating the O2 adsorption and reducing the energy barrier of the rate determining step of ORR. The Mg-air battery with the La0.7Ba0.3Ni0.5Mn0.5O3 catalyst displays a high discharge voltage of 1.37 V and a maximum power density of 65.224 mW·cm-2. Therefore, this new ORR catalyst presents great potential in practical Mg-air batteries.

High-efficient OER/ORR bifunctional electrocatalysts based on hexagonal boron nitride enabled by co-doping of transition metal and carbon

The construction of highly active earth-abundant electrocatalysts, which hold bifunctional oxygen reduction and evolution reactions simultaneously, is of great importance for inexpensive and high-performance electrochemical energy devices, yet still challenging. Here, we demonstrate that the inert hexagonal boron nitride (h-BN) can accommodate single atomic 3d transition metal (TM) sites by co-doping of carbon atoms as high-performance bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The TM atoms including Fe, Co, and Ni have been anchored with either four or two substituting carbon atoms forming TM–C4–BN and TM–C2N2–BN structures, in which the latter exhibits higher structural stability and stronger adsorption in response to the oxygen-containing intermediates such as OH*, O*, and OOH* in the reaction pathways. The optimal OER/ORR bifunctional catalyst is determined to be Co–C2N2–BN, showing ηOER of 0.42 V and ηORR of 0.26 V. Especially, its excellent ORR catalytic activity can be compared to that of well-known Pt(111) surface. It exhibits high thermodynamic stability and most favorable binding strength toward OER/ORR intermediates. The density functional theory calculations of the charge transfer and redistribution reveal the origin of the excellent catalytic activity in Co–C2N2–BN. This work provides a promising and feasible solution in searching for high-performance non-precious bifunctional oxygen electrocatalysts.

Enhancing oxygen reduction on a bimetallic Ag-Fe-N-C electrocatalyst for a zinc-air battery

Bi-metallic organic frameworks (MOFs) have been rarely reported to be functioned as non-platinum (Pt) electrocatalysts for oxygen reduction reaction (ORR). In this work, here we synthesize a carbon-based bimetallic Ag-Fe-N-C electrocatalyst for the ORR by jointly introducing Ag and Fe ions into the internal structure of MOFs derived from zinc acetate and 2-methylimidazole (2-MIM). The Ag-Fe-N-C catalyst possesses a porous carbon network structure with an specific surface area of 961.3 m2g−1, which is woven by carbon nanotubes/layers-encapsulated Fe3C or Ag nanoparticles. This catalyst has demonstrated a distinguished ORR catalytic activity with a half-wave potential of 0.883 V (vs. RHE) and an outstanding stability in an alkaline electrolyte. In addition, it gained a higher peak power density of 211 mWcm−2 and specific energy density of 875 Whkg−1Zn, a narrower charge-discharge potential gap of 77 mV and a better catalytic durability compared to the corresponding Pt/C-based zinc-air batteries. Our results may provide a facile strategy for activity enhancement of carbon-based ORR electrocatalysts via the controllable doping of bi-metallic ions.

Mitigating Co Metal Particle Agglomeration and Enhancing ORR Catalytic Activity through Nitrogen-Enriched Porous Carbon Derived from Biomass

Biomass-derived porous carbon has gained significant attention as a cost-effective and sustainable material in non-noble metal carbon-based electrocatalysts for the oxygen reduction reaction (ORR). However, during the preparation of transition metal catalysts based on biomass-derived porous carbon, the agglomeration of transition metal atoms often occurs, leading to a notable decline in catalytic activity. In this study, we present a straightforward synthetic approach for the preparation of nitrogen-enriched soybean-derived porous carbon (Co@SP-C-a) as an electrocatalyst for the ORR. To achieve this, we employed a two-step method. In the first step, a chemical activator (KCl) was utilized to enhance the porosity of the self-doped nitrogen biomass carbon material. In the second step, a constant pressure drop funnel technique was employed to uniformly disperse bimetal cobalt/zinc-based zeolitic imidazolium frameworks (ZIF-L and ZIF-67) containing different metal ions (Zn2+ and Co2+) into the activated biomass carbon material. Subsequent high-temperature calcination of the ZIF-L and ZIF-67@SP-C-a composite precursor yielded the Co@SP-C-a catalyst. The obtained catalyst exhibited remarkable ORR activity in an alkaline solution (Eonset = 0.89 V, E1/2 = 0.83 V, JL = −6.13 mA·cm−2) and exceptional long-term stability. This study presents an effective strategy to prevent the agglomeration of metal nanoparticles when integrating them with biomass-based carbon materials, thus leading to enhanced catalytic performance.

Influence of Fe–N–C morphologies on the oxygen reduction reaction in acidic and alkaline media

AbstractThe development of nonnoble metal oxygen reduction reaction (ORR) catalysts for fuel cells has been motivated by the high cost and limited supply of noble metals, as well as the desire to improve the performance and durability of this type of energy conversion device. In this study, nonnoble Fe–N–C catalyst was synthesized using a zeolitic imidazole framework (ZIF‐8), poly (aniline), and 10,10′‐dibromo‐9,9′‐bianthry as precursors to produce Fe–N–C with hollow sphere (HS), amorphous bulky structure (B), and sheet‐like thin sheet (N) structure. The Fe–N–C catalyst was analysed in terms of their shape, crystal structure, pore characteristics, and elemental composition. Among all the Fe–N–C catalysts, Fe–N–C_HS had the highest total surface area, followed by Fe–N–C_B and Fe–N–C_N. To evaluate their ORR catalytic activity, a half‐cell electrochemical experiment with .1 M KOH and .1 M HClO4 as the alkaline and acidic electrolytes was conducted. This study revealed that Fe–N–C_HS exhibited the highest onset potential but the Fe–N–C_B has the highest limiting current density in alkaline medium; meanwhile, in acidic media, Fe–N–C_HS shows the best ORR performance with the highest onset potential and limiting current. This highly porous Fe–N–C_HS catalyst also demonstrated active site activation and excellent stability compared with the other samples as well as commercial Pt/C in acidic electrolyte, which suggests its potential for application in proton exchange membrane fuel cells (PEMFCs).

Multifunctional catalytic activity of Cu3N (001) surface: A first-principles study

Multifunctional catalysts that exhibit high catalytic performance for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) in a single material hold great promise for broad-spectrum applications, including overall water splitting, fuel cells, and metal–air batteries. In this first-principles study, Cu 3 N is computationally demonstrated as a multifunctional electrocatalyst for the HER, OER, and ORR owing to the unique coordination of N and Cu atoms on the (001) surface. Cu 3 N exhibits better HER catalytic activity than noble Pt-based catalysts. Furthermore, its OER and ORR catalytic activity is comparable to that of commercialized unifunctional catalysts, and its 4e – pathway selectivity is high during the ORR. The catalytic performance of the ORR is significantly improved by the introduction of vacancy defects. The integration of highly efficient HER, OER, and ORR catalytic performance in earth-abundant Cu 3 N not only opens an avenue for developing cost-efficient omnipotent catalysts but also facilitates advances in clean and renewable energy.

Covalent organic framework-derived fluorine, nitrogen dual-doped carbon as metal-free bifunctional oxygen electrocatalysts

The construction of heteroatom-doped metal-free carbon catalysts with bifunctional catalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is highly desired for Zn-air batteries, but remains a great challenge owing to the sluggish kinetics of OER and ORR. Herein, a self-sacrificing template engineering strategy was employed to fabricate fluorine (F), nitrogen (N) co-doped porous carbon (F-NPC) catalyst by direct pyrolysis of F, N containing covalent organic framework (F-COF). The predesigned F and N elements were integrated into the skeletons of COF precursor, thus achieving uniformly distributed heteroatom active sites. The introduction of F is beneficial for the formation of edge-defects, contributing to the enhancement of the electrocatalytic activity. Attributing to the porous feature, abundant defect sites induced by F doping, as well as the strong synergistic effect between N and F atoms to afford a high intrinsic catalytic activity, the resulting F-NPC catalyst exhibits excellent bifunctional catalytic activities for both ORR and OER in alkaline mediums. Furthermore, the assembled Zn-air battery with F-NPC catalyst shows a high peak power density of 206.3 mW cm−2 and great stability, surpassing the commercial Pt/C + RuO2 catalysts.

Quasi-Three-Dimensional Cyclotriphosphazene-Based Covalent Organic Framework Nanosheet for Efficient Oxygen Reduction

HighlightsJUC-610-nanosheet exhibits highly efficient oxygen reduction reaction (ORR) catalytic activity in alkaline electrolyte with half-wave potential of 0.72 V versus reversible hydrogen electrode, which is one of the best covalent organic frameworks (COF)-based ORR electrocatalysts reported so far.It has been confirmed by experiments and density functional theory calculations that the abundant electrophilic structure in Q3CTP-COFs induces a highly density of carbon active sites, and the unique bilayer stacking facilitates the exposure of active carbon sites and accelerates the mass diffusion during ORR.JUC-610-nanosheet can also serve as a promising cathode for Zn-air batteries (power density of 156 mW cm–2 at 300 mA cm–2), which promotes the development of metal-free carbon-based electrocatalysts.

Probing the origin of transition metal carbide VC for oxygen reduction reaction: A DFT study

The development of oxygen reduction reaction (ORR) electrocatalysts with high activity, high stability and low-cost is still a grand challenge. Transition metal carbides (TMCs)-based catalysts have been reported as one species of oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) trifunctional catalyst with high efficient and favorable stability. Particularly, TMCs exhibit excellent ORR activity in electrochemical catalysis, even be profitable comparable with Pt in some situations, but the clarification of the intrinsic catalytic mechanism of VC remains a challenge. Herein, the potential performance of VC system on the ORR by using the first-principles calculation method based on density functional theory and quantum mechanics. The results showed that both end-on and side-on adsorptions on the surface of VC system all possess have satisfactory ORR catalytic activity. In this study, our work proposed a reasonable design scheme for the development of multifunctional electrocatalysts with the conversion and storage of renewable energy, and provided a new possibility for the application of TMCs.

Promotion mechanism of PtCo intermetallic ordered alloys in oxygen reduction reaction and its application in fuel cells

Ordered intermetallic Pt-M alloys are promising as next-generation low-Pt catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) due to the high ORR activity and excellent long-term stability. However, the mechanism behind the enhancement of ORR activity by ordering mostly comes from theoretical calculations, and experimental evidence is very lacking. Herein, we prepared a surface Pt-rich PtCo ordered alloy of about 3 nm in size, which exhibited high ORR catalytic activity, achieving impressive performance of 1.4 W cm−2 @ 0.6 V in H2-air fuel cell and mass activity of 0.62 A mgPt-1 @ 0.9 ViR-free in H2-O2 fuel cell. The key ORR intermediate, adsorbed *O2, was successfully detected by electrochemical in situ infrared spectroscopy. Compared with Pt and disordered PtCo, the ordered PtCo alloy has optimal adsorption interaction with *O2, accelerating the ORR kinetics.