Oxygen Electrocatalysts Research Articles

Modulation of electron transfer behavior on Fe2P-Co2P/NPC oxygen electrocatalyst by lattice cation substitution engineering and charge transport network design for rechargeable Zn-air batteries

Crystal structure modulation engineering on the lattice scale and charge transport network design on the micro/nano scale work together to endow oxygen electrocatalysts with high reactivity to fully release the capacity of Zn-air batteries (ZABs) as the next-generation green energy storage devices. Metal phosphide-based oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) electrocatalysts with tunable electronic structures, variable valence states, and moderate overpotentials are recognized as the most promising and ideal candidates for air cathodes. The cation substitution strategy overcomes the drawback that single metal phosphides with fewer active sites and high adsorption barriers are not sufficient to achieve satisfactory electrocatalytic performance. In this paper, the Fe2P-Co2P/NPC oxygen electrocatalyst employing lattice cation site substitution engineering and three-dimensional (3D) conductive network encapsulation strategies are constructed to successfully ensure fast electron transfer behavior and safe charge/discharge energy storage. Noteworthy, the presence of Schottky barriers at the interface of the two materials hinders the electron reflux, which promotes a unidirectional flow of electrons, and increases the electron condensation in the OER and ORR processes. Relying on these features, the Fe2P-Co2P/NPC-assembled liquid ZABs achieved power densities, specific capacities, and energy densities of 175.18 mW cm-2, 805.75 mAh gZn-1, and 958.84 Wh kg-1, respectively, and importantly good rate performances and stability were exhibited even under high-current-density operation. The corresponding flexible solid-state ZABs also possesses superior electrochemical activity and mechanical flexibility. This work paves the way for the construction of bifunctional oxygen electrocatalysts with high-speed electron transfer channels, thus advancing the development of wearable electronic devices.

N, F Co-Doped Carbon Derived from Spent Bleaching Earth Waste as Oxygen Electrocatalyst Support.

Affordable nitrogen and fluorine co-doped carbon nanostructure was prepared from the hazardous industrial waste of edible oil refinery, spent bleaching earth (SBE), and used as raw material for obtaining high-performance non-noble metal bifunctional oxygen electrocatalysts. Waste SBE contains 35 % residue non-saturated oil as a carbon source and the assistance of montmorillonite (MMT) as the template. This study converts waste SBE into a fluorine-doped carbon nanostructure through a pyrolysis process followed by removing the aluminosilicate layers of the MMT by HF etching. Furthermore, the impregnation of the support with Co and Fe nitrates readily gives rise to N, F co-doped carbon (NFC) electrocatalysts, as confirmed by XPS analysis. Electrochemical results evidenced that the Co-NFC catalyst proved to be a valuable bifunctional competitor for oxygen reduction reaction and oxygen evolution reaction in alkaline media, showing activity in both reactions and superior stability compared with the Fe-NFC catalyst in accelerated tests. This work offers a straightforward, economical, and eco-friendly strategy for designing N, F co-doped carbon-based electrocatalysts for oxygen reactions in electrochemical devices.

Aspartic acid/ thiourea − derived N and S − doped porous carbon as a metal-free electrocatalyst for oxygen and hydrogen evolution reactions

The preparation of high-efficiency electrocatalysts for the oxygen and hydrogen evolution process (OER and HER) using an easy, green, and facile preparation method is crucial for the effective and economical use of clean energy sources. Heteroatom-doped carbon nanomaterials are effective metal-free electrocatalysts for HER and OER reactions. Herein, N and S co-doped porous carbon nanocomposite (NS-PC) was constructed as a low-cost metal-free catalyst via pyrolysis of the Thiourea and L-aspartic acid. Doping heteroatoms (N and S) into the carbon structure can induce charge redistribution, expose many active sites, accelerate charge transfer, and thus effectively improve the catalytic activity. The NS-PC electrocatalyst demonstrates proper bifunctional electrocatalytic performance for HER and OER with long-term stability in KOH electrolytes. As a result, the NS-PC requires an overpotential of 139 mV and 315 mV in the current density of 10 mA cm– 2 and the Tafel slope of 59.6 and 69.8 mV dec−1 for HER and OER, respectively. As-papered NS-PC electrocatalyst offers the development of multi-functional electrocatalysts in the water splitting process using biological substances such as amino acids.

Promoting Electrocatalytic Oxygen Reactions Using Advanced Heterostructures for Rechargeable Zinc-Air Battery Applications.

In order to facilitate electrochemical oxygen reactions in electrically rechargeable zinc-air batteries (ZABs), there is a need to develop innovative approaches for efficient oxygen electrocatalysts. Due to their reliability, high energy density, material abundance, and ecofriendliness, rechargeable ZABs hold promise as next-generation energy storage and conversion devices. However, the large-scale application of ZABs is currently hindered by the slow kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). However, the development of heterostructure-based electrocatalysts has the potential to surpass the limitations imposed by the intrinsic properties of a single material. This Account begins with an explanation of the configurations of ZABs and the fundamentals of the oxygen electrochemistry of the air electrode. Then, we summarize recent progress with respect to the variety of heterostructures that exploit bifunctional electrocatalytic reactions and overview their impact on ZAB performance. The range of heterointerfacial engineering strategies for improving the ORR/OER and ZAB performance includes tailoring the surface chemistry, dimensionality of catalysts, interfacial charge transfer, mass and charge transport, and morphology. We highlight the multicomponent design approaches that take these features into account to create advanced highly active bifunctional catalysts. Finally, we discuss the challenges and future perspectives on this important topic that aim to enhance the bifunctional activity and performance of zinc-air batteries.

Co-CoSe heterogeneous fibers with strong interfacial built-in electric field as bifunctional electrocatalyst for high-performance Zn-air battery

The explorations of efficient electrocatalysts to accelerate oxygen reactions in a wide temperature range is a crucial issue to the development of zinc-air batteries (ZAB) for all-climate applications. Herein, the Co-CoSe heterogeneous furry fibers (Co-CoSe@NHF) are developed as a bifunctional oxygen electrocatalyst for ZAB towards wide-temperature range applications. The Co-CoSe heterostructure with large work function difference (ΔWF) endows interfacial electron redistribution, which builds strong interfacial built-in electric field (BIEF) and improves the oxygen reactions. Meanwhile, the Co-CoSe heterostructure is encapsulated by in-situ grown carbon nanotubes, and forms the hollow fiber (NHF) with furry surface and beads-on-string configuration. The highly porous and conductive NHF configuration facilitates the fast kinetics and favors to accommodates volume change during cycling. As a result, the Co-CoSe@NHF achieves the superior bifunctional properties and good reliability for oxygen reactions. Integrated with the Co-CoSe@NHF fiber, the ZAB cell delivers the superior power density (301 mW cm−2) and long-term cycling stability over 280 h at 25 °C, and maintains the power densities of 126 mW cm−2 even the temperature decreases to −25 °C. Moreover, the solid-state ZAB exhibits significant flexibility and superior properties in a wide temperature range. Therefore, this work not only proposes a new strategy to design the high-performance bifunctional electrocatalysts, but also propels the development of flexible power sources for all-climate applications.

(Invited) Graphene-Supported Fe/Ni Single Atoms and Feni Alloy Nanoparticles as Bifunctional Oxygen Electrocatalysts for Rechargeable Zinc-Air Batteries

To alleviate the severe energy crisis and environmental problems caused by the massive and unsustainable consumption of fossil fuels, it is urgent to develop renewable energy conversion and energy storage technologies to reform the traditional energy structure. Batteries are considered as one of the most promising energy storage technologies due to their sustainability, high efficiency and less pollution. Among various battery storage devices, rechargeable zinc-air batteries (ZABs) have attracted widespread attention on account of their high theoretical energy density (1086 Wh kg– 1), low cost, abundant zinc resources, low operating temperature, and good stability and safety in aqueous environments. However, the kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occurred on the air electrode during the discharging and charging processes are extremely sluggish, leading to low energy efficiency, which significantly limits the large-scale application of rechargeable ZABs. Pt-based electrocatalysts exhibit high ORR activities, while Ru- and Ir-based oxides are excellent OER electrocatalysts, but natural scarcity, high cost and poor durability seriously reduce the marketability and commercial competitiveness of rechargeable ZABs. Therefore, the development of robust, cost-effective and high-efficiency non-noble metal bifunctional ORR/OER electrocatalysts is of crucial significance for the practical application of rechargeable ZABs.As a promising alternative, earth-abundant transition metal (Fe, Co, Ni, etc.)-based materials have been extensively studied due to their relatively high electrocatalytic activity and durability. Thereinto, transition metal and nitrogen co-doped carbon (M-NC), especially Fe-NC, has been demonstrated to be the most effective ORR catalyst, and the active sites are generally considered as atomically dispersed metal coordinated to N atoms (M-Nx sites, x indicates the number of N atoms coordinating the metal). Nevertheless, M-NC catalysts only possess good ORR activity with poor OER performance. Bimetallic FeNi nanocomposites (metals, oxides, carbides, sulfides) are promising for OER. At high potentials, highly active FeNi oxyhydroxide species are generated on the surface of the FeNi-based electrocatalysts. Since ORR and OER depend on different catalytic active sites, an ideal bifunctional oxygen electrocatalysts should integrate M-NC complex with high ORR activity and bimetallic FeNi nanocomposite with a high OER activity to achieve bifunctionality. However, due to the intense competition between transition-metal single atoms and nanocomposites in the preparation process, it is challenging to combine them properly for superior bifunctional ORR/OER catalytic activity.Herein, we report a bifunctional oxygen electrocatalyst consisting of ZIF-derived carbon-anchored Fe/Ni single atoms and FeNi alloy nanoparticles; meanwhile, graphene is also introduced as carbon support to improve the uniformity of active sites (denoted as Fe/Ni-NC||FeNi@G). Benefiting from this unique composition and structure, Fe/Ni-NC||FeNi@G electrocatalyst displays excellent bifunctional ORR/OER activity and durability in rechargeable ZABs. This work provides an effective approach to designing highly efficient non-noble metal multifunctional catalysts for practical applications in rechargeable metal-air batteries. Acknowledgements Thanks for the financial support from the Shenzhen Science and Technology Innovation Committee (JCYJ20180507183818040).

Regulation of Transition Metal Doping into Double Perovskite Structure as for a Electrocatalyst in Water Electrolysis

Applying and combining of transition metals to perovskite structure is significantly dealt for improving the electrochemical property. The introduction of transition metals in the active B-site is considered as a useful pathway to regulate the chemical and electronic properties of the perovskites. In this study, a double perovskite structure (A2BB’O6) is designed to apply large ionic radius elements such as tungsten(W) that can not be doped into the general single perovskite structure(ABO3). Tungsten is normally equilibrium in the metallic phase, but tungsten ions rapidly move from 4+ state to the 6+ state in the oxide phase, boosting the electrochemical property. The W-based double perovskite materials are synthesized by a high temperature solid-state method. With a combination of Calcium (Ca) doped in the B-site for structural stabilization, transition metals (Ni, Co, etc.) are doped together as an active site to enhance the electrochemical performance. To analyze the physical and chemical structural characteristics, XRD with Rietveld refinement, XPS and XANES/EXAFS measurements are used. Rotating Disk Electrode (RDE) system is utilized to confirm the electrochemical performance of the prepared samples. Through cyclic voltammetry (CV) and linear sweep voltammetry (LSV) measurements, oxygen involved reactions are carried out to prove possibility on our W-based double perovskite materials as a high performance oxygen electrocatalyst with low-price.

Designing Switchable Transition Metal Nitrides/Carbides from High-Entropy PBA Derivative As Bifunctional Oxygen Electrocatalyst for Rechargeable Zinc-Air Batteries

In response to the growing energy and environmental challenges, considerable endeavors have been directed towards the development of sustainable and eco-friendly energy technologies as alternatives to fossil fuels. Moreover, rechargeable zinc-air batteries (RZABs) stand out due to their high energy density and environmental friendliness, although the sluggish cathode oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics restrict RZABs performance. Prussian blue analogues (PBAs), owing to their highly porous structure and tunable morphology, are often utilized as the precursors of the materials. Particularly, high-entropy PBAs (HEPBAs), formed by blending five or more metals in a random lattice, have achieved enhanced thermal and chemical stability via a robust structure with multiple transition metal ions. Meanwhile, transition metal carbides (TMCs) were investigated for ZAB applications due to their higher catalytic activity. Herein, we introduced CNT into HEPBA nanoparticles, followed by calcination processes, resulting in the synthesis of high-entropy metal carbides on CNT (HE-TMCs/CNT) which are effective for the bifunctional OER and ORR performance. HE-TMCs/CNT demonstrate superior activity towards the ORR (E1/2 = 0.77 V) in a 0.1 M KOH solution and OER (η = 330 mV @10 mA cm−2) in a 1 M KOH solution. The ZAB with HE-TMCs/CNT as the cathode demonstrated an open-circuit voltage of 1.39 V, providing a high energy density of 71 mW cm-2 under a current density of 102 mA cm-2. It exhibited the ability to be charged and discharged in cycles for up to 40 hours, revealing good stability under an applied current density of 5 mA cm-2. These results offer a straightforward pathway for the development of efficient bifunctional electrocatalysts for high-performance RZABs. Figure 1

Hydrothermally Synthesized rGO/MnO2/MoS2 Nanohybrids as Superior Bifunctional Electrocatalysts for Oxygen and Hydrogen Evolution Reactions.

This investigation delved into the field of bifunctional electrocatalyst water splitting, aimed at advancing sustainable energy by addressing the scarcity of efficient nonprecious electrocatalysts capable of facilitating both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). This study focused on nanohybrids consisting of hydrothermally synthesized rGO/MnO2/MoS2 composites and highlighted their efficacy as bifunctional electrocatalysts. The synergistic integration of rGO/MnO2/MoS2 enhanced the surface area, magnified electroactive sites, established a customized conductive arrangement, and provoked the efficiency in splitting of water. The nanohybrid displayed exceptional catalytic performance for the OER and HER, with significantly reduced overpotentials of 208 and 205 mV in 1 M KOH at 10 mA cm-2 current density, respectively. The findings underscore the potential of these cost-effective and environmentally friendly rGO/MnO2/MoS2 nanohybrids in advancing the field of electrocatalysis for renewable energy applications.

A Machine Learning‐Enhanced Framework for the Accelerated Development of Spinel Oxide Electrocatalysts

AbstractThe surging demand for sustainable energy has spurred intensive research into electrochemical conversion devices such as fuel cells, water splitting, and metal‐air batteries. The performance of oxygen electrocatalysts significantly impacts overall electrochemical efficiency. Recently, spinel oxides (AB2O4) have emerged as promising candidates; however, the scarcity of prior studies underscores the need for a thorough and comprehensive exploration. This study presents a computational framework that integrates machine learning and density functional theory (DFT) calculations for the systematic screening of 1240 spinel oxides. The data scarcity is addressed while enhancing prediction accuracy. Selected candidates are identified to outperform the benchmarking perovskite oxide. Additionally, their potential as mixed ionic and electronic conductors with a 3D network of ion diffusion pathways is highlighted. To further enhance the understanding and prediction of stability, catalytic activity, and reaction mechanisms, a new undemanding descriptor is introduced: the covalency indicator. This study offers a design principle for the development of high‐performance spinel oxide oxygen electrocatalysts.

Design of Industrially Important Ir–W-Based Electrocatalysts for Alkaline Bifunctional Oxygen and Hydrogen Evolution Reactions

Design of Industrially Important Ir–W-Based Electrocatalysts for Alkaline Bifunctional Oxygen and Hydrogen Evolution Reactions

Sandwiched heterostructure of NiFe2O4/TiO2 nanocrystals and MXene nanosheets for highly active oxygen electrocatalyst in rechargeable zinc-air batteries

Recent advancements in zinc-air batteries (ZABs) emphasize the need for efficient and sustainable oxygen electrocatalysts. Central to these efforts are metal-organic frameworks (MOFs), renowned for their bifunctional oxygen electrocatalytic capabilities. However, MOFs and their derivatives often exhibit subpar electrical conductivity and stability. Addressing this, we introduce an innovative approach involving MOFs-derived NiFe2O4/TiO2 nanocrystals sandwiched between 2D MXene nanosheets. This hybrid structure, NiFe2O4/TiO2@NC/Ti3C2, successfully enhances conductivity and active site accessibility, thereby enhancing oxygen reduction (ORR) and evolution (OER) reactions. The NiFe2O4/TiO2@Ti3C2–2 hybrid demonstrates excellent bifunctional activity, characterized by a notable ORR's half-wave potential of 0.846 V and an OER's onset potential of 1.5 V with a potential gap (ΔE) of 0.75 V. When employed in a ZAB, the battery achieves a peak power density of 164 mW cm−2 and maintains cycling stability for over 500 h at 10 mA cm−2. Beyond serving as conductive scaffolds, Ti3C2 MXene nanosheets have a vital role in preserving surface areas of the NiFe2O4/TiO2@NC materials. This study not only highlights a successful strategy for improving oxygen reactions in ZABs but also opens up new opportunities for the development of advanced MOF@MXene catalysts in energy conversion applications.

Coaxial MWCNTs/Co-N@N-doped carbon hierarchical porous nanowires as durable air electrode for aqueous Zn-air batteries

Aqueous zinc-air batteries can replace lithium-ion batteries to be used in the future large-scale application. However, efficient bifunctional oxygen catalyst used in air electrode for aqueous zinc-air batteries generally still meet serious challenge. The catalytic activity and stability of air electrode still far from satisfactory. In this work, we designed a series of coaxial MWCNTs/Co-N@N-doped carbon hierarchical porous nanowires (MWCNTs/Co-N@NC) as bifunctional oxygen electrocatalyst with different Co contents. The Co content can facilitate to form the Co-Nx and pyridinic-N to boost the bifunctional oxygen electrocatalysis. The optimal MWCNTs/Co-N@NC-1 delivers superior electrocatalysis for oxygen reduction reaction (ORR) with E1/2 of 0.86 V (vs. RHE) and rational performance for oxygen evolution reaction (OER) with Ej=10 of 1.59 V (vs. RHE) in 0.1 mol/L KOH. In addition, the MWCNTs/Co-N@NC-1-based Zn-air battery exhibits the discharge capacity of 898.84 mAh gZn−1 and a optimal power density of 158.1 mW cm−2 with cycling stability for 300 h. This study provides a strategy to construct robust durability air electrode for aqueous zinc-air batteries.

P-Block anion compressed d/p band center of bifunctional oxygen electrocatalysts for durable aqueous Zn–air batteries

Robust bifunctional electrocatalysts that accelerate the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are vital for rechargeable aqueous Zn–air batteries (AZABs). In this study, a three-dimensional foam-like N-doped carbon frameworks (NCFs) catalyst with abundant NCoTe2 active sites (CoTe2@NCFs) was successfully constructed using the carbon dots (CDs)-assisted strategy as the efficient bifunctional ORR/OER catalyst. In situ Raman spectra were used to monitor the formation of Co-OOH, which confirmed the dynamic change in oxygen intermediates on the surface of the CoTe2@NCFs catalyst. Both theoretical calculations and experimental results demonstrate that the integrated Te element in the p-block results in a reduction in the difference between d/p band centers (Δεd-p), which effectively enhances the rapid adsorption/desorption capability of *OOH/*OH, thereby improving the ORR/OER performance. Impressively, the CoTe2@NCFs catalyst shows excellent bifunctional oxygen catalytic performance (ΔE = 0.66 V). Moreover, the assembled CoTe2@NCFs-based rechargeable AZABs exhibit a high peak power density of 177.8 mW cm−2, substantial specific capacity of 793.4 mAh g−1, and excellent long-term cycling durability over 1000 cycles. The compressed d/p-band synergistic center provides novel insights into the design of bifunctional oxygen electrocatalysts for efficient energy storage and conversion devices.

The defect chemistry and machine learning study 5d transition metal doped on graphitic carbon nitride for bifunctional oxygen electrocatalyst with low overpotential

Searching for highly efficient bifunctional oxygen evolution reaction/oxygen reduction reaction (OER/ORR) electrocatalysts for sustainable and renewable clean energy is vital. However, these electrocatalyst designs remain cost-prohibitive for both experimental and computational studies. This paper systematically investigates 5d transition metal (5d TM) doped into graphitic carbon nitride (g-C3N3) as potential bifunctional OER/ORR electrocatalysts by considering the defect charge states through the defect chemistry study. Our formation energies results show that 33 kinds of 5d TM doped g-C3N3 have better stabilities in the different charge states. Among them, IrN×@C54N53 (Ir occupation N), IrN•@C54N53, PtN×@C54N53 (Pt occupation N), and Iri•@C54N54 (Ir interstitial sites) exhibit lower overpotentials. They are great candidates for bifunctional OER/ORR electrocatalysts. This is because adjusting the charge states of 5d-TM@g-C3N3 can tune the interaction strength of the oxygenated intermediates. Furthermore, machine learning shows that the charge transfer of TM atoms (Qe) and total magnetic moment (μB0) are the two most essential descriptors for OER and ORR overpotential, respectively. The charged defect adjusting of the bifunctional OER/ORR activity would develop the potential electrocatalysts for energy conversion applications.

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.

High-Performance Bifunctional Electrocatalysts for Flexible and Rechargeable Zn-Air Batteries: Recent Advances.

Flexible rechargeable Zn-air batteries (FZABs) exhibit high energy density, ultra-thin, lightweight, green, and safe features, and are considered as one of the ideal power sources for flexible wearable electronics. However, the slow and high overpotential oxygen reaction at the air cathode has become one of the key factors restricting the development of FZABs. The improvement of activity and stability of bifunctional catalysts has become a top priority. At the same time, FZABs should maintain the battery performance under different bending and twisting conditions, and the design of the overall structure of FZABs is also important. Based on the understanding of the three typical configurations and working principles of FZABs, this work highlights two common strategies for applying bifunctional catalysts to FZABs: 1) powder-based flexible air cathode and 2) flexible self-supported air cathode. It summarizes the recent advances in bifunctional oxygen electrocatalysts and explores the various types of catalyst structures as well as the related mechanistic understanding. Based on the latest catalyst research advances, this paper introduces and discusses various structure modulation strategies and expects to guide the synthesis and preparation of efficient bifunctional catalysts. Finally, the current status and challenges of bifunctional catalyst research in FZABs are summarized.

FeP nanoparticle embedded in N,P-doped 3D porous wood-derived carbon aerogel for oxygen reduction reaction

Metal-air batteries require the exploration of affordable electrocatalysts with exceptional catalytic performance for oxygen reduction reactions (ORR). One of the powerful ways to develop highly active and robust oxygen electrocatalysts is to load transition metal compounds onto a highly porous carbon aerogel. Here, we report a cell wall nanoengineering strategy to transform natural balsa wood into a wood-derived carbon aerogel (WCA), following by loading FeP nanoparticles inside the hierarchical N, P-doped WCA for ORR electrocatalysts. Wood nanotechnology is applied to manipulate the microstructure of the porous carbon aerogel with low-tortuosity, multichannel, and aligned pore, which benefits to the electron transportation for boosting the ORR. Under 0.1 M KOH conditions, the initial potential, half wave potential and limit current of FeP@N,P-WCA are 0.95 V, 0.84 V, and 5.20 mA cm−2 respectively, which are much higher than that of untreated wood and comparable to commercial Pt/C. The aqueous Zn-air batteries assembled with this catalyst exhibit a remarkable specific capacity of 775.5 mA h g−1 and better charge-discharge cycling stability. The excellent electrocatalytic activity demonstrated by FeP@N,P-WCA for ORR is attributed to the inherent tri-pathway (lumen, pit, and ray cell) porous structure of wood, the high conductivity and specific surface area of WCA (584.2 m2 g−1), and the highly dispersed FeP nanoparticles. This work provides a structural design concept for achieving high electrocatalytic biobased WCA reactors by combining wood nanotechnology and electrocatalysts chemistry for energy storage and conversion.

Conductive cobalt-organic framework nanoboxes for efficient electrochemical oxygen reduction

The development of efficient oxygen electrocatalysts and understanding their catalytic mechanism are vitally essential for sustainable energy technologies. Here, hollow conductive metal-organic frameworks nanoboxes (Co-MOF NBs) with quadrilateral Co-N4 units are well-designed and prepared via chemical etching and ligand exchange strategy, and serve as promising catalysts for oxygen reduction reaction (ORR). Atomically dispersed Co-N4 centers with single-electron occupation of the eg orbital (eg∼1) can readily penetrate the antibonding π-orbital of oxygen, thereby facilitating electron exchange between the Co sites and adsorbed oxygen and conferring high ORR activity. The hollow nanostructure ensures efficient charge/mass transfer and well-exposed active centers for Co-MOF NBs. The obtained Co-MOF NBs deliver superior ORR performance with high half-wave potential of 0.88 V and operation durability in 0.1 M KOH. The assembled zinc-air battery with Co-MOF NBs cathode catalyst achieves a maximum power density of 230 mW cm−2, which outperform commercial Pt/C and other reported MOF-based catalysts.

Bimetal Oxides Anchored on Carbon Nanotubes/Nanosheets as High-Efficiency and Durable Bifunctional Oxygen Catalyst for Advanced Zn-Air Battery: Experiments and DFT Calculations.

To meet increasing requirement for innovative energy storage and conversion technology, it is urgent to prepare effective, affordable, and long-term stable oxygen electrocatalysts to replace precious metal-based counterparts. Herein, a two-step pyrolysis strategy is developed for controlled synthesis of Fe2O3 and Mn3O4 anchored on carbon nanotubes/nanosheets (Fe2O3-Mn3O4-CNTs/NSs). The typical catalyst has a high half-wave potential (E1/2 = 0.87V) for oxygen reduction reaction (ORR), accompanied with a smaller overpotential (η10 = 290mV) for oxygen evolution reaction (OER), showing substantial improvement in the ORR and OER performances. As well, density functional theory calculations are performed to illustrate the catalytic mechanism, where the in situ generated Fe2O3 directly correlates to the reduced energy barrier, rather than Mn3O4. The Fe2O3-Mn3O4-CNTs/NSs-based Zn-air battery exhibits a high-power density (153mW cm-2) and satisfyingly long durability (1650 charge/discharge cycles/550h). This work provides a new reference for preparation of highly reversible oxygen conversion catalysts.