Intrinsic Oxygen Reduction Reaction Research Articles

Deep Eutectic Solvent and Molten Salt-Assisted Construction of Wheat Straw-Derived N/O Co-Doped Porous Carbon for Flexible Zinc-Air Batteries.

As a common biomass resource, wheat straw is gradually being derived as carbon materials for oxygen reduction reaction (ORR) in zinc-air batteries (ZABs). Herein, the wheat straw-derived carbon was prepared by ball milling and pyrolysis using deep eutectic solvent (DES) as the medium, which avoided the cumbersome procedures. The hydrogen bond of DES was utilized to reconstructed into a hydrogen bond network structure between DES and lignin/cellulose/hemicellulose of wheat straw. The hydrogen bond network structure was converted into N/O co-doped porous carbon (N/O-WSPC) with abundant N/O co-doped sites after high-temperature pyrolysis. Meanwhile, KHCO3 was employed to further generate hierarchical pore structures and increase the specific surface area of the N/O-WSPC. The N/O co-doped sites provided intrinsic ORR activity, while the porous structure facilitates the mass transfer effect. Therefore, the N/O-WSPC exhibited a half-wave potential of 0.87 V (vs. RHE) and a limiting current density of 5.98 mA cm-2 for ORR. The N/O-WSPC-based flexible ZAB displayed an energy density of 652.23 Wh kg-1 and a charging-discharging cycle duration for over 19 h. The DES-assisted strategy facilitates the sustainable and efficient application of wheat straw-derived carbon materials in energy storage and conversion devices.

Unique electron-feeding mechanism in CoN3O for enhanced acidic oxygen reduction

Co-centered single-atom catalysts (SACs) have emerged as an increasingly promising non-platinum group candidate for acidic oxygen reduction reaction (ORR) due to their balanced activity and stability. However, the intrinsic ORR activity of present Co-centered SACs remains far below the commercial Pt/C. Herein, a CoN3O-structured SAC is successfully fabricated by a gas-phase strategy and achieves a peak power density of 492.6 mW cm−2 under the 1.0 bar H2/air condition, demonstrating its excellent application potential in practical fuel cells. Unique electron-feeding mechanism is revealed to account for the remarkably enhanced ORR activity inner CoN3O SAC. It is indicated that the electron interaction inner active site governed by both electronegativity in σ bond and d-p back-feeding in π bond reaches balance at CoN3O, thus optimized adsorption of oxygen-containing intermediates. Our work provides multiple insights into the orbital scale laws for higher-performance PGM-free ORR catalysts.

High Oxygen Reduction Efficiency and Durability of Nano-Honeycomb Pt3(NiFeCo) Replenished by High-Entropy Metallic Glass Support.

Developing low-Pt oxygen reduction reaction (ORR) catalysts with high efficiency and robustness is critical for practical fuel cells. The most advanced ORR catalysts either feature high percentages of Pt (>70 at.%) or exhibit poor durability when reducing Pt loading. Herein, a multicomponent solid-solution Pt3(FeCoNi) honeycomb nano-framework supported by the specially designed high-entropy metallic glass (MG) is reported for efficient ORR. This hybrid catalyst with a low surface Pt loading of 5.79µgcm-2 displays exceptional mass and specific activities of 7.02Amgpt -1 and 8.15mAcmPt -2 at 0.9V, respectively, which are ≈15 and 22 times higher compared with commercial Pt/C. The analyses reveal the weakened chemisorption of oxygenated species, which is induced by the strong strain and ligand effects originating from the synergistic multicomponent alloying. This in turn enhances the intrinsic ORR activity. Moreover, benefiting from a unique replenishment behavior, the hybrid catalyst delivers ultra-high durability with negligible activity decay even after 50 000 potential cycles. This mechanism is achieved by sacrificing the interior MG supplementary support to dynamically compensate for the loss of catalytically active surface. The work provides an alternative way to design more efficient and durable low-Pt electrocatalysts for electrochemical devices.

Built-in Electric Field in 1D/2D Heterostructure Boosts Zinc Air Battery Performance.

The realization of a rechargeable zinc-air battery (ZAB) is hindered by the low intrinsic oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activities. In this work, an abundant built-in electric field is noticed in a 1D/2D CoO/CoS2 heterostructure, triggering electron transfer from CoO to CoS2 associated with a downshifted d band center of the Co atom mitigating the strong electrochemical adsorption of *OH species on active sites; thereby, boosted OER and ORR performance are achieved. Namely, the OER specific activity of CoO/CoS2 is enhanced by 3.8- and 2.2-fold compared to the counterpart of CoO and CoS2, respectively. Furthermore, the kinetic current density of CoO/CoS2, a fingerprint of intrinsic ORR activity, is promoted by 46 and 6.6 times relative to CoO and CoS2. The rechargeable ZAB performance attains 215.6 mW cm-2, 1.6-times better than Pt/C-IrO2. Moreover, the superior performance remained for 600 h. Besides, the battery performance of the all-solid-state ZAB reaches 83.8 mW cm-2, revealing its promising application in wearable device.

S-Block Metal Mg-Mediated Co─N─C as Efficient Oxygen Electrocatalyst for Durable and Temperature-Adapted Zn-Air Batteries.

In the quest to enhance Zn-air batteries (ZABs) for operating across a wide spectrum of temperatures, synthesizing robust oxygen electrocatalysts is paramount. Conventional strategies focusing on orbital hybridization of d-d and p-d aim to moderate the excessive interaction between the d-band of the transition metal active site and oxygen intermediate, yet often yield suboptimal performance. Herein, an innovative s-block metal modulation is reported to refine the electronic structure and catalytic behavior of Co─NC catalysts. Employing density functional theory (DFT) calculations, it is revealed that incorporating Mg markedly depresses the d-band center of Co sites, thereby fine-tuning the adsorption energy of the oxygen reduction reaction (ORR) intermediate. Consequently, the Mg-modified Co─NC catalyst (MgCo─NC) unveils remarkable intrinsic ORR activity with a significantly reduced activation energy (Ea) of 10.0kJmol-1, outstripping the performance of both Co─NC (17.6kJmol-1), benchmark Pt/C (15.9kJmol-1), and many recent reports. Moreover, ZABs outfitted with the finely tuned Mg0.1Co0.9─NC realize a formidable power density of 157.0mWcm-2, paired with an extremely long cycle life of 1700h, and an exceptionally minimal voltage gap decay rate of 0.006mVh-1. Further, the Mg0.1Co0.9─NC-based flexible ZAB presents a mere 2% specific capacity degradation when the temperature fluctuates from 25 to -20°C, underscoring its robustness and suitability for practical deployment in diverse environmental conditions.

Insightful Understanding of Synergistic Oxygen Reduction on PtCo3(111) Toward Zinc-Air Batteries.

Theory-guided materials design is an effective strategy for designing catalysts with high intrinsic activity whilst minimizing the usage of expensive metals like platinum. As proof-of-concept, herein it demonstrates that using density functional theory (DFT) calculations and experimental validation that intermetallic PtCo3 alloy nanoparticles offer enhanced electrocatatalytic performance for the oxygen reduction reaction (ORR) compared to Pt nanoparticles. DFT calculations established that PtCo3(111) surfaces possess better intrinsic ORR activity compared to Pt(111) surfaces, owing to the synergistic action of adjacent Pt and Co active sites which optimizes the binding strength of ORR intermediates to boost overall ORR kinetics. With this understanding, a PtCo3/NC catalyst, comprising PtCo3 nanoparticles exposing predominantly (111) facets dispersed on an N-doped carbon support, is successfully fabricated. PtCo3/NC demonstrates a high specific activity (3.4mAcm-2mgPt -1), mass activity (0.67AmgPt -1), and cycling stability for the ORR in 0.1M KOH, significantly outperforming a commercial 20wt.% Pt/C catalyst. Moreover, a zinc-air battery (ZAB) assembled with PtCo3/NC as the air-electrode catalyst delivered an open-circuit voltage of 1.47V, a specific capacity of 775.1mAhgZn -1 and excellent operation durability after 200 discharge/charge cycles, vastly superior performance to a ZAB built using commercial Pt/C+IrO2 as the air-electrode catalyst.

Single-atom Fe catalysts with pyrrolic-type FeN4 sites for efficient oxygen reduction reaction: Identifying the roles of different N species

Developing electrocatalysts with efficient cathode oxygen reduction reaction (ORR), for example, iron-based single-atom catalysts (Fe-SACs), has been deemed necessary to accelerate the commercialisation process of zinc (Zn)–air batteries. Nevertheless, determining how various nitrogen species and active metal centres coordinate on an atomic scale remains unclear and inadequately explained. Herein, we demonstrate a soft-template-aided technique using Fe-containing molecules (e.g. iron phthalocyanine [FePc], Fe-1,10-phenanthroline [Fe-Phen] and Fe-glucose) to enhance the performance of Fe-SACs in terms of ORR. In this technique, FePc molecules can be converted into atomically dispersed pyrrolic-type iron–nitrogen (FeN4) sites during a pyrolytic process. The resultant catalyst exhibits excellent ORR activity (half-wave potential = 0.90 V) in alkaline medium and standing battery performance when used in Zn–air batteries (peak power density = 197.3 mW cm−2 and specific capacity = 796.2 mAh g−1). As per the findings from control experiments and characterisation studies, electron transfer between the support and the active Fe centre amplifies the ORR performance. Theoretical calculations substantiate that Fe sites coordinated with pyrrolic N atoms govern the electronic configuration of the catalysis, reducing the free energy absorption of reaction intermediates and thus increasing its intrinsic ORR capability. Herein, we aim to offer a fresh perspective on the relation between coordination environments and catalytic activity in ORR catalysts.

Efficient Proton-exchange Membrane Fuel Cell Performance of Atomic Fe Sites via p-d Hybridization with Al Dopants.

Orbital hybridization to regulate the electronic structures and surface chemisorption properties of transition metals is of great importance for boosting the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs). Herein, we developed a core-shell rambutan-like nanocarbon catalyst (FeAl-RNC) with atomically dispersed Fe-Al atom pairs from metal-organic framework (MOF) material. Experimental and theoretical results demonstrate that the strong p-d orbital hybridization between Al and Fe results in an asymmetric electron distribution with moderate adsorption strength of oxygen intermediates, rendering enhanced intrinsic ORR activity. Additionally, the core-shell rambutan-like structure of FeAl-RNC with abundant micropores and macropores can enhance the density of active sites, stability, and transport pathways in PEMFC. The FeAl-RNC-based PEMFC achieves excellent activity (68.4 mA cm-2 at 0.9 V), high peak power (1.05 W cm-2), and good stability with only 7% current loss after 100 h at 0.7 V under H2-O2 condition.

Regulation Strategies for Fe-N-C and Co-N-C Catalysts for the Oxygen Reduction Reaction.

Proton exchange membrane fuel cells (PEMFCs) and alkaline membrane fuel cells (AEMFCs) have received great attention as energy devices of the next generation. Accelerating oxygen reduction reaction (ORR) kinetics is the key to improve PEMFC and AEMFC performance. Platinum-based catalysts are the most widely used catalysts for the ORR, but their high price and low abundance limit the commercialization of fuel cells. Non-noble metal-nitrogen-carbon (M-N-C) is considered to be the most likely material class to replace Pt-based catalysts, among which Fe-N-C and Co-N-C have been widely studied due to their excellent intrinsic ORR performance and have made great progress in the past decades. With the improvement of synthesis technology and a deeper understanding of the ORR mechanism, some reported Fe-N-C and Co-N-C catalysts have shown excellent ORR activity close to that of commercial Pt/C catalysts. Inspired by the progress, regulation strategies for Fe-N-C and Co-N-C catalysts are summarized in this Review from 5 perspectives: (1) coordinated atoms, (2) environmental heteroatoms and defects, (3) dual-metal active sites, (4) metal-based particle promoters, and (5) curved carbon layers. We also make suggestions on some challenges facing Fe-N-C and Co-N-C research.

Intrinsic Defect‐Rich Carbon‐Supported Iron Phthalocyanine as Beyond‐Pt Oxygen Reduction Catalysts for Zinc–Air Batteries

Molecular iron phthalocyanine (FePc) bearing a single‐atom Fe–N4 moiety is a high‐profile non‐platinum catalyst toward the oxygen reduction reaction (ORR), but its unsatisfactory activity and inadequate stability hinder the practical application. Herein, a novel strategy by hybridizing FePc with fullerene‐derived intrinsic defect‐rich carbon to improve its ORR activity and stability is reported. Via alkali‐assisted thermal pyrolysis, C60 molecules are disintegrated into tiny fragments that then restructure into pentagon‐ and edge‐rich carbon (FC). Utilizing FC as a support of FePc leads to a significantly improved ORR activity compared to other supports including reduced graphene oxide and carbon nanotube that hold distinct structural features. The optimized FePc/FC with a Fe loading of 3 wt% presents a half‐wave potential of 0.917 V, far beyond that of Pt/C (0.846 V), via selective four‐electron ORR pathway and excellent stability under accelerated stress test. The practical applicability of FePc/FC is also demonstrated as a high‐performing cathode catalyst of aqueous zinc–air batteries. It is, for the first time, explicitly disclosed that strong interactions between FePc molecules and intrinsic carbon defects (e.g., pentagons and edges) not only strengthen the anchoring effect of supported FePc but also enhance the intrinsic ORR activity of single‐atom Fe–N4 sites.

Trifunctional robust electrocatalysts based on 3D Fe/N‐doped carbon nanocubes encapsulating Co4N nanoparticles for efficient battery‐powered water electrolyzers

AbstractHerein, we have designed a highly active and robust trifunctional electrocatalyst derived from Prussian blue analogs, where Co4N nanoparticles are encapsulated by Fe embedded in N‐doped carbon nanocubes to synthesize hierarchically structured Co4N@Fe/N–C for rechargeable zinc–air batteries and overall water‐splitting electrolyzers. As confirmed by theoretical and experimental results, the high intrinsic oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction activities of Co4N@Fe/N–C were attributed to the formation of the heterointerface and the modulated local electronic structure. Moreover, Co4N@Fe/N–C induced improvement in these trifunctional electrocatalytic activities owing to the hierarchical hollow nanocube structure, uniform distribution of Co4N, and conductive encapsulation by Fe/N–C. Thus, the rechargeable zinc–air battery with Co4N@Fe/N–C delivers a high specific capacity of 789.9 mAh g−1 and stable voltage profiles over 500 cycles. Furthermore, the overall water electrolyzer with Co4N@Fe/N–C achieved better durability and rate performance than that with the Pt/C and IrO2 catalysts, delivering a high Faradaic efficiency of 96.4%. Along with the great potential of the integrated water electrolyzer powered by a zinc–air battery for practical applications, therefore, the mechanistic understanding and active site identification provide valuable insights into the rational design of advanced multifunctional electrocatalysts for energy storage and conversion.

Boosting Oxygen Reduction at Pt(111)|Proton Exchange Ionomer Interfaces through Tuning the Microenvironment Water Activity.

A proton exchange ionomer is one of the most important components in membrane electrode assemblies (MEAs) of polymer electrolyte membrane fuel cells (PEMFCs). It acts as both a proton conductor and a binder for nanocatalysts and carbon supports. The structure and the wetting conditions of the MEAs have a great impact on the microenvironment at the three-phase interphases in the MEAs, which can significantly influence the electrode kinetics such as the oxygen reduction reaction (ORR) at the cathode. Herein, by using the Pt(111)|X ionomer interface as a model system (X = Nafion, Aciplex, D72), we find that higher drying temperature lowers the onset potential for sulfonate adsorption and reduces apparent ORR current, while the current wave for OHad formation drops and shifts positively. Surprisingly, the intrinsic ORR activity is higher after properly correcting the blocking effect of Pt active sites by sulfonate adsorption and the poly(tetrafluoroethylene) (PTFE) skeleton. These results are well explained by the reduced water activity at the interfaces induced by the ionomer/PTFE, according to the mixed potential effect. Implications for how to prepare MEAs with improved ORR activity are provided.

Enhanced Oxygen Reduction Activity of Platinum Micropore

AbstractThe high overpotential of oxygen reduction reaction (ORR) prevents the wide commercialization of fuel cells and metal‐air batteries. To accelerate the reaction rate, porous electrocatalysts draw attention to obtain a higher specific surface area. However, the effect of micropores on ORR kinetics has not been understood because of the non‐uniform pore sizes, length, and tortuosity of practical electrocatalysts. In this study, we evaluate ORR activity in a micropore using platinum model electrodes with arrays of cylindrical pores with a uniform pore diameter of 1.8 nm. The model electrodes having pore lengths of 45, 100, and 380 nm are fabricated, and their ORR performances are examined by electrochemical measurements and numerical simulations in 0.1 mol dm−3 KOH aqueous solution. The intrinsic ORR activity of the micropore is successfully obtained with the electrode having a pore length of 45 nm, where oxygen transport resistance in the micropore has little effect on ORR. It is found that the intrinsic ORR activity of the micropore is higher than that of a planar Pt surface. X‐ray photoelectron spectroscopy and CO stripping voltammetry indicate a downshift of the d‐band center, which can be the origin of the high intrinsic ORR activity.

Lamellar structured Ce-S-NC heterogeneous electrocatalyst as the highly durable cathode for passive direct liquid fuel cells

Passive direct liquid fuel cells are promising power generation devices with the advantages of convenient transportation, storage for liquid fuel and high power density. This paper focuses on improving the intrinsic electrocatalytic performance and durability of nitrogen-doped carbon (N-C) cathodic electrocatalysts. Then, lamellar structured Ce-S-NC heterogeneous electrocatalyst was synthesized and used as a highly durable cathode for two types of passive direct liquid fuel cells, i.e., direct methanol fuel cells (DMFCs) and direct borohydride fuel cells (DBFCs). In this work, the effect of the S/C molar ratio on the microstructure and electrocatalytic performance of the Ce-S-NC electrocatalysts was investigated, and excellent intrinsic oxygen reduction reaction activity was obtained at an S/C molar ratio of 0.15. The peak power densities of Ce-S-NC based DMFCs reached up to 12.5, 23.6 and 41.9 mW·cm−2 at 20, 40 and 60 °C, respectively. The peak power densities of 59.3, 84.6 and 132.6 mW·cm−2 were obtained in Ce-S-NC based DBFCs at 20, 40 and 60 °C, respectively. In the durability tests, both the Ce-S-NC based air-breathing DBFCs and passive DBFCs showed the stable operation than that of N-C and Ce-NC. When the current density increased from 50 to 150 mA·cm−2, the Ce-S-NC based DBFC can be operated for 882 h, and only 34 and 91 h for that of N-C and Ce-NC. The electrochemical impedance spectroscopy tests proved Ce-S-NC based DBFC showed the faster mass transfer efficiency. The outstanding durability of Ce-S-NC is mainly attributed to the improved defect density and mass transfer.

Influence of the Pt/ionomer/water interface on the oxygen reduction reaction: insights into the micro-three-phase interface.

Understanding the Pt/ionomer/water interface structure and its impact on the oxygen reduction reaction (ORR) activity is essential for enhancing catalyst utilization and performance of fuel cells. This study aimed to investigate the influence of sulfonic acid groups on the Pt/ionomer/water interface and the ORR mechanism. By using a combination of DFT, AIMD, and microkinetic simulations, the results showed that when the sulfonic acid group is located at the edge of the Helmholtz plane, it creates an optimal three-phase interface, providing more available active sites, a stronger interfacial electric field, and a more continuous H-bond network. This configuration results in the *OOH dissociation becoming the rate-determining step, demonstrating significantly higher intrinsic ORR activity with a much lower theoretical overpotential of 0.11 V. Conversely, when the sulfonic acid group is in contact with the Pt surface, it causes the Pt surface's d-band center to shift down, weakens the interfacial electric field, and disrupts the H-bond network, resulting in a blocking effect on the ORR with an overpotential of 0.23 V. These insights shed light on the role of solid-solid-liquid interfaces in the ORR performance and provide valuable information for the rational design of catalyst interfaces.

Non-PGM Cathode Electrocatalysts for PEM Fuel Cells

Polymer electrolyte membrane fuel cells, PEMFCs, are considered the most ideal next generation energy conversion device, able to provide power to a broad range of applications; automotive, combined heat and power, portable electronic devices. Pt-based electrocatalysts are regarded as ideal for promoting the desired redox reactions of a fuel cell, especially the sluggish oxygen reduction at the cathode, ORR. High expense and scarcity of Pt are the greatest impediments to successful commercialization of this technology. The replacement of unsustainable noble-metal catalysts with platinum group metal (PGM)-free catalysts for oxygen reduction reaction (ORR) is essential for material wise and market value viable PEMFCs.Among the different attempts towards non-PGM catalysts, incorporating atomically dispersed transition metal atoms (Fe, Mn, etc.) and heteroatoms (N, S, etc.) into carbon frameworks is the most promising [1,2]. Large specific surface area, high intrinsic ORR electrocatalytic activity, efficient porosity and sufficient stability in acid media and/or in the actual working environment are the least requirements to consider when designing the catalysts. So far, despite the tremendous efforts, many drawbacks still persist that include poor understanding of the nature of active centres and their control over the synthesis, as well as fast decay of the structure under operation.In this work, we will present a rationally designed strategy to prepare hybrid composite catalysts by developing Fe–N–C materials onto different 2D and 3D templates [3,4] with differentiated surface chemistry (silicon and heteroatom-doped carbon structures). Despite structural and physicochemical characterization, the study includes extensive electrochemical characterization in terms of activity and durability in relative to the application conditions. An example is depicted in Figure 1 for a single atom Fe-N-C catalyst synthesized using porous silica nanotubes as the sacrificial template resulting in a hierarchically porous structure with a surface area of 370 m2/g. Electrochemical study revealed a half-wave potential of 0.72 V and an onset potential of 0.88 V with high stability in acidic environment.Very importantly, the different findings are correlated to one another, thereby establishing a composition to function relationship to provide a pathway for the integrated engineering of novel structures with improved performance. Acknowledgments Funding from the Operational Program “Competitiveness, Entrepreneurship & Innovation” (EPAnEK), NSRF 2014-2020 through the project Solar2HyP Τ2ΕΔΚ-01877 References [1] L. Osmieri, et al., Current Opinion in Electrochemistry 25 (2020) 100627.[2] T. Asset, et al., Joule 4 (2019) 33-44.[3] Jin-Cheng Li et al., Asia Materials 10 (2018) e461[4] Nan Zhang et al., Energy Environ. Sci. 13 (2020) 111-118 Figure 1

Local Single Co Sites at the Second Shell of Fe‐N4 Active Sites to Boost Oxygen Reduction Reaction

AbstractFe single‐atom catalysts (SACs) are a promising catalyst for oxygen reduction reaction (ORR) in both Zn–air batteries (ZABs) but have a certain distance to compete with Pt‐based catalysts. Rational modulation of the coordination environment in the second coordination shell of SACs offers an opportunity to improve the intrinsic ORR activity, yet a challenge. Here, a novel strategy is reported to construct a dual‐metal catalyst by introducing a single Co atom in the second coordination shell of the Fe center. The dual‐metal N3─Fe─N─Co site with a certain Fe─Co distance of 0.312 nm is constructed. It allows for manipulation of the positive shift of the Fe center charge state, driving the d‐band center up‐shift by 0.63 eV, thereby offering the optimal adsorption of intermediates. Benefiting from this structure, the as‐prepared Fe(Co2nd)‐NC enables an excellent ORR activity with a half‐wave potential of 0.948 V in 0.1 M KOH. As a cathode in ZABs, it delivered an outstanding peak power density of 218 mW cm−2 and a specific capacity of 915 mAh gZn−1 at 5 mA cm−2, respectively, with superior long‐term durability over 680 h. The second shell layer alignment regulation strategy shows great potential for energy storage applications.

Local Geometric Distortion to Stimulate Oxygen Reduction Activity of Atomically Dispersed Zn‐Nx Sites for Zn–Air Batteries

AbstractLocal geometric strain engineering is useful for modulating the performance of nitrogen‐coordinated transition metal‐carbon catalysts. However, realizing the nano‐level strain is technically challenging. Additionally, the structure‐property relationship between strain degree and performance remains poorly understood. Herein, it is conceptually predict that geometric bending induces more electron transfer from Zn to the coordinated N in Zn─N─C, leading to a positive shift of the d‐band center of the Zn atom, which promotes the adsorption reduction process of the O2 molecule and thus increases the intrinsic oxygen reduction reaction (ORR) activity. Moreover, a low‐temperature non‐saturated coordination strategy is proposed to prepare spherical porous carbon catalysts with surface‐enriched geometrically bent (20‐50°) Zn─N─C sites. Benefiting from the highly active Zn─N─C sites, large specific surface area and abundant pore structure, the optimized catalyst (S─Zn─N─C‐950) exhibited excellent intrinsic alkaline ORR activity (half‐wave potential E1/2 = 0.89 V) and high zinc‐air battery performance (peak power density of 229.2 mW cm−2), exceeding that of commercial Pt/C catalysts. Density functional theory (DFT) calculations show that when the geometrical bending angle is 30–45°, Zn centers with suitable charge transfer to the surrounding N can produce a moderate adsorption strength to the oxygen intermediate state, resulting in optimal ORR activity.

Electronic structure and spin state regulation of vanadium nitride via a sulfur doping strategy toward flexible zinc-air batteries

Owing to the distinctive structural characteristics, vanadium nitride (VN) is highly regarded as a catalyst for oxygen reduction reaction (ORR) in zinc-air batteries (ZABs). However, VN exhibits limited intrinsic ORR activity due to the weak adsorption ability to O-containing species. Here, the S-doped VN anchored on N, S-doped multi-dimensional carbon (S-VN/Co/NS-MC) was constructed using the solvothermal and in-situ doping methods. Incorporating sulfur atoms into VN species alters the electron spin state of vanadium in the S-VN/Co/NS-MC for regulating the adsorption energy of vanadium sites to oxygen molecules. The introduced sulfur atoms polarize the V 3dz2 electrons, shifting spin-down electrons closer to the Fermi level in the S-VN/Co/NS-MC. Consequently, the introduction of sulfur atoms into VN species enhances the adsorption energy of vanadium sites for oxygen molecules. The *OOH dissociation transitions from being unspontaneous on the VN surface to a spontaneous state on the S-doped VN surface. Then, the ORR barrier on the S-VN/Co/NS-MC surface is reduced. The S-VN/Co/NS-MC demonstrates a higher half-wave potential and limiting current density compared to the VN/Co/N-MC. The S-VN/Co/NS-MC-based liquid ZABs display a power density of 195.7 mW cm−2, a specific capacity of 815.7 mA h g−1, and a cycling stability exceeding 250 h. The S-VN/Co/NS-MC-based flexible ZABs are successfully employed to charge both a smart watch and a mobile phone. This approach holds promise for advancing the commercial utilization of VN-based catalysts in ZABs.

Hierarchically Porous, N, P‐Co‐Doped Carbon Structures with Embedded Pt Particles as Effective Electrocatalysts for the Oxygen Reduction Reaction

AbstractThe proton exchange membrane fuel cell now ranks as one of the best alternatives to fossil fuels. Two optimization techniques that have stirred up a lot of controversy include reducing the amount of precious metal Pt catalysts and boosting the kinetics of the cathodic oxygen reduction reaction (ORR). Herein, “template‐etching” method is used to create N−P co‐doped low‐Pt catalysts with hierarchical porous carbon nanospheres (Pt/NPC). The P atoms′ valence electrons, which serve to attach the Pt to the equally disseminated N atoms, further disperse the Pt inside the carbon nanospheres. As a result, the Pt is able to modify the electronic structure and alter the d‐band center, which raises the intrinsic ORR activity. The hierarchical porous structure of the carbon nanospheres, created by the phytic acid activation of the pores, can expose more active sites and efficiently enhance the transfer of oxygen and electrons, increasing the catalytic efficiency. The catalysts synthesized using this method had great stability, 9.87 wt % Pt concentration, and half‐wave potential of 0.832 V for acidic intermediates and 0.855 V for alkaline intermediates. Because of its entire pH ORR catalytic capabilities, this catalyst exhibits tremendous application potential for replacing conventional Pt/C catalysts.