Oxygen Reduction Reaction Reaction Research Articles

Regulating Fe-spin state by doping P heteroatom in Fe-N-C catalyst derived from colloidal nanoparticles encapsulated ZIF-8 to boost oxygen reduction activity

Over the past decades, Fe-N-C carbon materials have been considered as one of the most ideal alternatives to the noble metal catalysts (e.g. Pt/C) for the sluggish oxygen reduction reaction (ORR) in zinc-air batteries and fuel cells. In this research, ZIF-8 cage encapsulation confinement strategy coupled with post P-doping has been employed to design porous P, N and Fe co-doped carbon (FeNC-P) for efficient oxygen reduction reaction (ORR). The zero-field cooling (ZFC) temperature-dependent magnetic susceptibility measurement revealed that incorporation of P in the Fe-N-C catalysts can induce the transition of spin polarization configuration, which promotes the desorption of *OH in the crucial step of the ORR reaction process. The best-performing FeNC-P catalyst displays a 1.00 V (vs RHE) of Eonset (onset potential) and a 0.90 V (vs RHE) of E1/2 (half-wave potential) in an alkaline solution, which exceeds the benchmark Pt/C catalyst. Moreover, it also delivers a high power density of 130 mW·cm−2 in the self-made zinc-air battery, surpassing the benchmark Pt/C catalyst (90 mW·cm−2).

Unlocking the catalytic potential of tungsten carbide coordinated with 3d transition metals in oxygen electrochemistry

As one of the keystones of electrochemistry, the oxygen reduction reaction (ORR) offers an enthralling approach to oxygen monitoring, and energy conversion/storage. At present, only 3d transition metals (TMs)-based catalysts have proven to be reliable options for electrochemical O2 activation, while non-3d TM catalysts such as 5d tungsten (W) typically exhibit much lower electrochemical ORR activities. Herein, we propose a simple and controllable approach for accelerating the ORR and oxygen evolution reaction (OER) on the surface of tungsten carbides coordinated with 3d metal, i.e., TM3W3-xC (TM=Mn, Fe, Co, Ni, and Cu). Among them, Mn3W3-xC is found to display exceptional ORR activity (Eonset = 0.83, and E1/2 = 0.73 V), which is on par with that of the commercial Pt/C catalyst (Eonset = 0.84, and E1/2 = 0.75 V) in alkaline media. Furthermore, Mn3W3-xC has outperformed Pt/C in terms of durability and methanol resistance due to the carbon shell protecting the metal nanoparticles from agglomeration or dissolution in alkaline media. The coordination of Mn centers to the W3-xC surface not only allows the precise regulation of the electronic structure of W ions but also creates dual-metal sites (MnW) to facilitate interfacial charge transfer. Such electron transfer enables the MnW surface more electrophilic, in turn increasing its affinity for hydroxide ions. As a result, the MnW coordinated with the carbide surface has OER-favorable MnW-oxo and MnW-hydroxo configurations within their oxidized surfaces. Overall, this research discovered that the catalytic potential of inactive W elements in oxygen electrochemistry can be unlocked by coordinating with 3d TMs.

Prussian Blue Analogues Derived Bimetallic CoNi@NC as Efficient Oxygen Reduction Reaction Catalyst for Mg‐Air Batteries

The magnesium‐air (Mg‐air) batteries are regarded as a highly promising system for electrochemical energy conversion and storage, owing to exceptional energy density, notable safety and eco‐friendliness. The development of high‐performance and durable non‐noble metal catalysts for the cathodic oxygen reduction reaction (ORR) is crucial for advancing the practical use of Mg‐air batteries. The synergistic interaction between different metals in bimetallic catalysts is an effective strategy for enhancing the activity and stability of the catalysts. Herein, various prussian blue analogues (PBA) were selected as precursors to synthesis the bimetallic CoNi@NC, monometallic Co@NC and Ni@NC catalysts due to tunable chemical compositions. Compared with Co@NC and Ni@NC, the bimetallic CoNi@NC pyrolyzed at 600°C (CoNi@NC‐600) exhibits outstanding ORR performances and stability in alkaline (0.1 M KOH) and neutral (3.5 wt% NaCl) electrolytes. Following 5000 CV cycles, the half‐wave potentials for CoNi@NC‐600 show only minor negative shifts of 8 and 7 mV, respectively. Meanwhile, the CoNi@NC‐600 possesses the similar ORR reaction mechanism and activity with Pt/C. The primary Mg‐air battery assembled with CoNi@NC‐600 displays better discharge performances than that of Co@NC and Ni@NC. This study lays the foundation for future investigations into the advancement of non‐precious bimetallic catalysts for ORR in Mg‐air batteries.

Role of Vacancy Defects and Nitrogen Dopants for the Reduction of Oxygen on Graphene.

Disentangling the roles of nitrogen dopants and vacancy defects (VG) in metal-free carbon catalysts for the oxygen reduction reaction (ORR) ideally requires studying both the dopants and defects separately. Here, we systematically introduced nitrogen dopants and VGs via plasma treatment into the basal plane of monolayer graphene as a model carbon catalyst to investigate their specific roles in ORR catalysis. An increased defect density including dopants is positively associated with boosted ORR activity. Nitrogen dopants are responsible for an improved current via a 2e- pathway generating hydroperoxide, while VGs result in enhanced kinetics and water production. We therefore infer that VGs in graphene are responsible for the improved ORR kinetics, while nitrogen dopants majorly influence the selectivity of ORR reaction products. The nitrogen dopants without VGs lead to a higher overpotential compared with the pristine graphene. Instead of the attribution of the ORR active site to only nitrogen species in carbon materials, the improved ORR activity in nitrogen-doped carbon materials should be attributed to the active sites constituted of VGs, oxygen dopants, and nitrogen dopants. Through this work, we provide important insights into the intertwined roles of nitrogen and VGs as well as oxygen dopants in nitrogen-doped metal-free catalysts for a more efficient ORR.

Hydrogen Peroxide-Induced Overoxidation of Fe-N-C Catalysts: Implications for ORR Activity.

Fe-N-C (iron-nitrogen-carbon) electrocatalysts have emerged as promising alternatives to precious metals for the oxygen reduction reaction (ORR), but they remain insufficiently stable for widespread adoption in fuel cell technologies. One plausible mechanism to explain this lack of stability, and the associated catalyst degradation, is oxidative attack on the catalyst surface by hydrogen peroxide, a non-selective byproduct of the ORR. In this work, we perform a detailed analysis of this degradation mechanism, using a combination of periodic Density Functional Theory (DFT) calculations and ab-initio molecular dynamics (AIMD) simulations to probe the thermodynamics and kinetics of hydrogen peroxide activation on a series of candidate active sites for the Fe-N-C catalyst. The results demonstrate that carbon atoms neighbouring FeN4 active sites can be strongly over-oxidized via formation of hydroxyl or epoxy groups when hydrogen peroxide is present in the electrolyte. In most cases, the interaction between the over-oxidizing groups and the ORR reaction intermediates reduces the ORR activity, and we further propose that the over-oxidized sites are likely precursors to irreversible carbon corrosion and further catalyst deactivation.

Impact of the Potential Dependent Surface Adlayer Composition on the ORR Activity and H2O2 Formation on Ru(0001) in Acid Electrolytes

AbstractStimulated by the increasing interest in ion adsorption effects on electrocatalytic reactions and by recent more detailed reports on the potential dependent adlayer structures formed on Ru(0001) in pure HClO4 and H2SO4 electrolytes, we revisited the oxygen reduction reaction (ORR) on structurally well‐defined Ru(0001) single crystal surfaces prepared under ultrahigh vacuum conditions. We demonstrate that the complex, potential‐dependent activity both for the ORR and for H2O2 formation is closely related to potential‐dependent changes in the composition and structure of the adlayer. Our results demonstrate the enormous effects adsorbed species can have on the ORR reaction characteristics, either by surface blocking, e. g., by (co‐)adsorbed bisulfate species, or by participation in the reaction, e. g., by *H transfer from adsorbed H or OH to O2. The comparison with results obtained on polycrystalline Ru, which differ significantly from Ru(0001) data, furthermore underlines the importance of using structurally well‐defined surfaces as a reference system for future theoretical studies.

Distribution of relaxation times used for analyzing the electrochemical impedance spectroscopy of polymer electrolyte membrane fuel cell

In this paper, a 25 cm2 polymer electrolyte membrane single cell is prepared by ultrasonic spraying coating method. The polarization curves and Electrochemical Impedance Spectroscopies (EIS) data of this cell are collected under different conditions, such as cell temperature, humidity, back pressure and pure O2. EIS data are analyzed by Distribution of Relaxation Time (DRT), and some results are concluded: (i) with the increase of current density, the Oxygen Reduction Reaction (ORR) time constant became lower, and the ORR reaction resistance and oxygen diffusion resistance both increases. (ii) With the increase of back pressure, the DRT peak assigned to oxygen diffusion process in cathode moves to low frequencies, the peak area decreases simultaneously. (iii) the proportion of the ORR polarization resistance gradually increases from 77 % to 84 % with the cell temperature increase from 65 °C to 80 °C. (iv) With the increase of humidity, the performance of the cell is decreased. (v) The oxygen diffusion resistance is negligible in pure oxygen working condition analyzed by DRT method.

Synergistic Effect of Electrocatalyst for Enhanced Oxygen Reduction Reaction: Low Pt-Loaded CuPt Alloy Nanoparticles Supported on N-Doped Hierarchical Porous Carbon.

It is challenging to synthesize oxygen reduction reaction (ORR) electrocatalysts that are highly efficient, affordable, and stable for use in proton exchange membrane fuel cells. To address this challenge, we developed a low platinum-loading (only 6.68% wt) ORR catalyst (PtCu1-NC), comprising CuPt nanoparticles (average size: 1.51 nm) supported on the N-doped carbon substrates. PtCu1-NC possesses a high specific surface area of 662 m2 g-1 and a hierarchical porous structure, facilitating efficient mass transfer. The synergistic effect from introduced copper and the electron effect from nitrogen modify the electronic structure of platinum, effectively accelerating the ORR reaction and enhancing stability. Density functional theory calculations demonstrate the catalytic mechanism and further verify the synergistic effect. Electrochemical assessments indicate that PtCu1-NC exhibits specific activity and mass activity 5.3 and 5.6 times higher, respectively, than commercial Pt/C. The half-wave potential is 27 mV more positive than that of commercial Pt/C. The electrochemical active surface area value is 104.3 m2 g-1, surpassing that of Pt/C. Approximately 78% of current is retained after 10,000 s chronoamperometry measurement. These results highlight the effectiveness of alloying in improving the catalyst performance.

Designing a MnF2/MnO2 heterostructure for enhanced electrocatalysis in the oxygen reduction reaction

Studying noble-metal-free oxygen reduction reaction (ORR) catalysts is crucial for advancing fuel cells. Manganese dioxide (MnO2) has garnered widespread attention due to its convenient synthesis, low cost, high electrochemical activity, and diverse structures. However, it still faces challenges, such as poor conductivity and relatively lower inherent catalytic activity. In this study, a novel ORR electrocatalyst is introduced by constructing a heterostructure of manganese fluoride (MnF2) and MnO2, referred to as MnF2/MnO2. In a 0.1 M KOH solution, the ORR half-wave potential (E1/2) of MnF2/MnO2 is measured at 0.804 V, surpassing that of the original MnO2 catalyst (0.69 V). Compared to the MnO2 electrocatalyst, the MnF2/MnO2 heterostructure exhibits faster ORR reaction kinetics and a larger electrochemically active surface area. Density functional theory (DFT) calculations confirm that the MnF2/MnO2 heterostructure possesses enhanced intrinsic conductivity, facilitating the rapid transfer of ions of and electrons. Therefore, this study provides a promising pathway for enhancing the ORR catalytic activity of noble-metal-free electrocatalysts through rational heterostructure design.

Site-specific reactivity of stepped Pt surfaces driven by stress release.

Heterogeneous catalysts are widely used to promote chemical reactions. Although it is known that chemical reactions usually happen on catalyst surfaces, only specific surface sites have high catalytic activity. Thus, identifying active sites and maximizing their presence lies at the heart of catalysis research1-4, in which the classic model is to categorize active sites in terms of distinct surface motifs, such as terraces and steps1,5-10. However, such a simple categorization often leads to orders of magnitude errors in catalyst activity predictions and qualitative uncertainties of active sites7,8,11,12, thus limiting opportunities for catalyst design. Here, using stepped Pt(111) surfaces and the electrochemical oxygen reduction reaction (ORR) as examples, we demonstrate that the root cause of larger errors and uncertainties is a simplified categorization thatoverlooks atomic site-specific reactivity driven by surface stress release. Specifically, surface stress release at steps introduces inhomogeneous strain fields, with up to 5.5% compression, leading to distinct electronic structures and reactivity for terrace atoms with identical local coordination, and resulting in atomic site-specific enhancement of ORR activity. For the terrace atoms flanking both sides of the step edge, the enhancement is up to 50 times higher than that of the atoms in the middle of the terrace, which permits control of ORR reactivity by either varying terrace widths or controlling external stress. Thus, the discovery of the above synergy provides a new perspective for both fundamental understanding of catalytically active atomic sites and design principles of heterogeneous catalysts.

Co(O)4(N)‐type single‐atom‐based catalysts and ligand‐driven modulation of electrocatalytic properties for reducing oxygen molecules

AbstractSingle‐atom‐based catalysts are intriguing electrocatalytic platforms that combine the advantages of molecular catalysts and conductive carbon‐based materials. In this work, hybrids (Co‐NrGO‐1 and Co‐NrGO‐2) were generated by wet‐reactions between organometallic complexes (Co(CH3COO)2 and Co[CH3(CH2)3CH(C2H5)COO]2, respectively) and N‐doped reduced graphene oxide at 25°C. Various characterizations revealed the formation of atomically dispersed Co(O)4(N) species in Co‐NrGO‐2. Density functional theory (DFT) calculations explained the effect of the aliphatic C7 group in Co2 on the formation processes. The Co‐NrGO‐2 hybrid showed excellent catalytic performance, such as onset (0.94 V) and half‐wave (0.83 V) potentials, for electrochemical oxygen reduction reaction (ORR). Co‐NrGO‐2 outperformed Co‐NrGO‐1, which was explained by more back donation to the antibonding orbitals of O2 from electron‐rich aliphatic groups. DFT calculations support this feature, with mechanistic investigations showing favored ORR reactions and facile breakage of double bonds in O2.

New insights into the performance and durability degradation mechanisms of PEMFCs caused by Cr3+ contaminant

It is known that contamination ions stemming from the corrosive deterioration of vital subassemblies, such as bipolar plates (BPs) and sealing gaskets, exert a profound influence on the performance and durability degradation of PEM fuel cells. The impacts of Cr3+ on the catalyst layers (CLs) and single-cell performance were investigated by immersing the cathode catalyst layer (CCL) and anode catalyst layer (ACL) in a Cr3+ solution with different concentrations for contamination treatment. During the fuel cell test, polarization curves (PCs), electrochemical impedance spectroscopy (EIS), H+ transfer impedance, and cyclic voltammetry (CV) curve results were recorded. The effects of Cr3+ contamination on the kinetic for oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) were analyzed in a three-electrode system. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to explore the degradation mechanisms of Cr3+ contamination on fuel cell activity. The results indicate that the presence of Cr3+ increased the ohmic impedance from 0.200 Ω cm2 to 0.449 Ω cm2, resulting in a voltage attenuation rate as high as 55.21 %. Moreover, the presence of Cr3+ slowed the ORR reaction rate and changed the ORR reaction pathway. Cr3+ contamination caused irreversible damage to PEMFC performance and durability.

In situ Activation of Molecular Oxygen at Intermetallic Spacing-Optimized Iron Network-Like Sites for Boosting Electrocatalytic Oxygen Reduction.

The oxygen reduction reaction (ORR) catalyzed by transition-metal single-atom catalysts (SACs) is promising for practical applications in energy-conversion devices, but great challenges still remain due to the sluggish kinetics of O═O cleavage. Herein, a kind of high-density iron network-like sites catalysts are constructed with optimized intermetallic distances on an amino-functionalized carbon matrix (Fe-HDNSs). Quasi-in situ soft X-ray absorption spectroscopy and in situ synchrotron infrared characterizations demonstrate that the optimized intermetallic distances in Fe-HDNSs can in situ activate the molecular oxygen by fast electron compensation through the hybridized Fe 3d‒O 2p, which efficiently facilitates the cleavage of the O═O bond to *O species and highly suppresses the side reactions for an accelerated kinetics of the 4e- ORR. As a result, the well-designed Fe-HDNSs catalysts exhibit superior performances with a half-wave potential of 0.89V versus reversible hydrogen electrode (RHE)and a kinetic current density of 72mAcm-2@0.80V versus RHE, exceeding most of the noble-metal-free ORR catalysts. This work offers some new insights into the understanding of 4e- ORR kinetics and reaction pathways to boost electrochemical performances of SACs.

Dual-atom Fe(II,III)N2(µ2-N)2Cu(I,II)N moieties anchored on porous N-doped carbon driving high-efficiency oxygen reduction reaction

Atomically distributed iron electrocatalyst is valid for oxygen reduction reaction (ORR). However, accurate regulation of the structure improving its intrinsic activity is a challenge. Herein, a dual-atom catalyst FeCu-NC with atomically distributed Fe and Cu co-anchored on porous N-doped carbon is obtained. The FeN4 and CuN3 couple sites bridged by two nitrogen atoms, exist as Fe(II,III)N2(µ2-N)2Cu(I,II)N moieties with the metal distance of ∼2.5 Å in the structure of FeCu-NC. The synergistic effect of Fe and Cu dual-atom reducing the dissociation energy of *OOH intermediate, allows an optimized 4e- ORR reaction pathway. The FeCu-NC exhibits high-efficiency ORR activity with the half-wave potential (E1/2) of 0.889 V (vs RHE) and outstanding stability without obvious decay for the E1/2 after 10,000 cycles. The FeCu-NC based Zn-air battery presents large specific capacity of 795 mAh g−1 and energy density of 998 Wh kg−1 as well as high charge-discharge cycling stability superior to the Pt/C.

Hydrophobic-aerophilic composite catalysts enable the fast-charging Zn-air battery to operate 1200 h at 50 mA cm−2

High-efficient bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are central to Zn-air batteries (ZABs). However, the bifunctional activity of catalysts is still unsatisfactory, which restricts the fast-charge performance of ZABs. In this work, we constructed a hydrophobic-aerophilic bifunctional catalyst, where CoFe nanoparticles (NPs) and single atoms (SAs) are separately loaded on zeolite imidazolate fame (ZIF)-derived carbon and hollow carbon tubes respectively (CoFe NP@SA). Thereinto, CoFe SAs are known to be highly active to ORR reaction. Moreover, the in-situ Raman illustrates that CoFe NPs are transformed to CoOOH and FeOOH by electrochemical reconstruction, which can boost the OER activity. Furthermore, the hydrophobic-aerophilic surface can repel water molecules to create abundant solid–liquid-gas three-phase reaction interfaces and expose active sites, which consequently promote the diffusion of reactive molecules/ions across the interface and the oxygen adsorption. Thus, the CoFe NP@SA catalyst exhibit an ultralow ORR/OER potential gap of 0.6 V. After assembled as zinc-air battery (ZAB), it demonstrates a low charge potential (2.09 V) under a high current density of 50 mA cm−2 with the 1200-hour durability. This strategy paves the way to realize the high-power-density and fast-charging ZABs.

Strontium doped Fe-based porous carbon for highly efficient electrocatalytic ORR and MOR reactions

The catalytic activity improvement of Fe-based active sites derived from metal organic frameworks toward oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) remains a major challenge. In this study, the growth of strontium decorated 2-methylimidazole zinc salt (Sr/ZIF-8) is prepared as a carrier to vapor deposited iron formation Sr doped Fe-based nitrogen-doped carbon framework (named as Sr/FeNC). After high-temperature pyrolysis and vapor deposition, strontium carbonate nanocrystals are evenly dispersed on the shrunk dodecahedron carbon frame and multitudinous Fe-based active catalytic sites are embedded in carbon skeleton. The optimal Sr/FeNC-2 catalyst demonstrates the outstanding ORR performance in terms of a half-wave potential of 0.851 V and an onset potential of 0.90 V, while Sr/FeNC-2 exhibits a high current density of 18.2 mA cm−2 and a lower Tafel slope of 21 mV dec-1 in MOR. The exceptional catalytic activity could be ascribed to the synergistic coupling effect of strontium compounds with Fe-based catalytic sites (Fe-Nx, Fe, and iron oxide). In particular, the formation of SrCO3 affects the bonding configuration of the iron species sites, leading to an optimization of the electronic structure within the multihole carbon matrix. The synthetic approach presents a prospective strategy for future endeavors in developing innovative and advanced bifunctional catalysts for ORR and MOR.

Synthesis of novel hollow carbon nanotubes @ Co-Fe alloy/iron phthalocyanine electrocatalyst by self-assembly method for OER and ORR study

The exploration of an inexpensive catalyst with effective oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activities to replace precious metal electrocatalysts has been of great interest in recent years. In this paper, CNT@Co-Fe/FePc composites were synthesized with high efficiency using a self-assembly strategy. In the synthesis process, carbon nanotubes (CNTs) were synthesized as the base material using crab shells as templates and honey as the carbon and nitrogen source. CoFe alloy nanoparticles derived from CoFe-based prussian blue analogs were self-assembled and anchored on CNTs, and then iron phthalocyanine with Fe-N4 portion was coupled with CNTs by π-π stacking. Finally formed a homogeneous and stable composite material. The self-assembly method is simple and efficient to achieve good metal loading. The prepared CNT@Co2-Fe1/FePc exhibits excellent catalytic performance and stability for OER and ORR in alkaline electrolyte. The overpotential at 10 mA cm−2 of CNT@Co2-Fe1/FePc for OER is 343 mV with a very small Tafel slope of 43.59 mV dec−1. CNT@Co2-Fe1/FePc has high methanol tolerance and persistence for ORR. This work provides a strategy for the construction of transition metal-carbon composite electrocatalytic materials with excellent catalytic performance and stability for OER and ORR reactions.

The Durability of the Platinum/Polypyrrole Nanotubes' Catalysts in Oxygen Reduction Reaction

Platinum (Pt) catalysts supported on carbon-based materials are effective catalysts for fuel cells. However, the durability of the carbon supports in acidic media needs to be improved. Platinum/polypyrrole (PPy) nanotubes have emerged as promising catalysts for the oxygen reduction reaction (ORR) due to their high surface area and good electrocatalytic activity. Furthermore, the nitrogen atoms within the chemical structure of PPy nanotubes are expected to improve their durability.In this study, we investigated the performance and durability of Pt catalysts during ORR by decorating different carbon-based materials with Pt nanoparticles. The catalytic activity and durability were analyzed using the rotation ring-disk electrode (RRDE) technique. We also examined the influence of the different supports on the electrochemical degradation of the catalysts.Our results showed that Pt/PPy nanotubes exhibited high activity and durability in ORR reactions. We paid particular attention to the chemical changes of the catalysts' surfaces, including both the metal and support components, during the ex-situ electrochemical measurements. The surface of the catalysts was characterized using photoelectron X-ray spectroscopy (XPS), synchrotron radiation photoelectron spectroscopy (SRPES), and near-edge X-ray absorption fine structure (NEXAFS) analysis before and after electrochemical degradation. Based on our findings, we proposed degradation mechanisms of the Pt/PPy nanotubes catalysts.In addition, we tested the Pt/PPy nanotubes catalysts in fuel cells and observed their high performance. These findings suggest that Pt/PPy nanotubes catalysts can serve as durable and effective catalysts for ORR reactions, even under harsh conditions. Further research is needed to optimize the synthesis conditions and operating parameters of these catalysts to improve their performance and durability.

(Keynote) Experimental and Computational Insights into Electronic Structure and Redox Properties of Bare and Doped Co3O4 Nanocrystals of Euhedral Morphology and Their Heterojunctions with Alien Oxides and Carbon Materials

One of the most attractive oxide materials with remarkable record of widespread applications are cobalt spinels and their derivatives obtained by doping with alien redox (3dn) and nonredox (Li) cations or via hybridization with other oxides (CeO2, TiO2, a-Al2O3) or carbon support. They have recently received a great deal of theoretical and practical attention because of an outstanding activity in many redox processes important for photo/electro/catalysis. Among many potential applications, their relevance as promising substitutes for platinum in oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) can be mentioned, in particular. The properties of nanostructured cobalt spinel materials depend on their size, shape, doping and interfacing features. In this context, euhedral spinel nanocrystals that expose well defined crystallographic planes, allow for sensible investigations into establishment of the surface/bulk structure-redox reactivity relationships in real conditions.In this presentation application of S/TEM and inverse Wulff hull matching techniques supported by image simulation was discussed for elucidation the mechanism of hydrothermal synthesis of euhedral cobalt spinel nanocrystals the their shape retrieving. Periodic spin unrestricted DFT-PW91+U and hybrid DFT/HSE06 calculations were applied for modeling the morphology, structure and electronic properties (DOS structure) relevant for redox behavior of bare and doped cobalt spinel nanocrystals. The results allowed for thorough characterization of the structure and reconstruction of the exposed low index (100), (110), and (111) planes, and explain the influence of dopants. The effect of the valence state of lithium (Li+ or Li0), and its locus on the valence pining of the cobalt cations was determined. DFT calculations together with the ab initio thermodynamic modeling were used to study the electronic structure of the created defects, and stability of different terminations of cobalt spinel and Li-doped Co3O4 under various redox conditions. The associated electronic and spin relaxation processes were discussed as well. For the most stable stoichiometric (100) and (111) facets, the surface redox state diagrams in a wide stoichiometry range were constructed, and analyzed in detail. Intrinsic charge transfer processes involving electron (n-conductivity) and hole (p-conductivity) transfer between the octahedral and tetrahedral cobalt cations were modeled using a small polaron approximation (Marcus-Dupuis model). Formation of n-p junctions (Co3O4|CeO2, Li-Co3O4|CeO2) and MxCo3-xO4/carbon hybrids were analyzed by S/TEM, XPS spectroscopy (band alignment), contactless electronic conductivity and work function measurements, corroborated by DFT modeling. The redox properties of the interface and spinel faceting, and the role of electric conductivity and the nature of the carbon support functional groups were discussed in the context of the ORR, OER performance, and catalytic redox reactivity (activation of O2).AcknowledgmentsS.W. thanks for the financial support of the project “High-performance electrocatalyst for oxygen reduction reaction with low platinum content” carried on within the Program “Pearls of Science” of the Ministry of Education and Science of Poland.

N-Doped Norbornane sp2 Carbon Framework: An Efficient Electrocatalyst for Oxygen Reduction and Hydrogen Evolution Reaction

At present, development of Pt free bifunctional electrocatalyst for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is necessary for the advancement of sustainable and cost-effective solutions for energy conversion and storage technology. In this direction, herein we report N doped sp2 hybridized carbon framework (N-CF) as a metal-free electrocatalyst for ORR and HER. This work inspects the effect of N doping that converts a hybrid structure of CF {Norbornane or bicyclo [2, 2, 1] heptane structure} into planar N-CF. A series of N-doped CF with different doping concentrations has been prepared using a facile and cost-effective technique. This robust electrocatalysts exhibits a promotional effect in the activity, porosity, thermal and electrochemical stability for the ORR and HER reactions. A rich delocalized electronic density of the sp2 bounded N species helps in modulating antibonding state of molecular oxygen and facilitates the breakage of O=O bond in ORR. It also promotes proton adsorption via bonding between proton and valence electron rich catalyst surface to aid HER. The research sought to investigate the employability of N-CF for fabricating sustainable energy devices with electrocatalyst possessing multiple electrocatalytic activities for ORR and HER. Figure 1