Coupling Fe3 C Nanoparticles and N-Doping on Wood-Derived Carbon to Construct Reversible Cathode for Zn-Air Batteries

Biomass-Derived Catalytically Active Carbon Materials for the Air Electrode of Zn-Air Batteries

Given the growing environmental and energy problems, developing clean, renewable electrochemical energy storage devices is of great interest. Zn-air batteries (ZABs) have broad prospects in energy storage because of their high specific capacity and environmental friendliness. The unavailability of cheap air electrode materials and effective and stable oxygen electrocatalysts to catalyze air electrodes are main barriers to large-scale implementation of ZABs. Due to the abundant biomass resources, self-doped heteroatoms, and unique pore structure, biomass-derived catalytically active carbon materials (CACs) have great potential to prepare carbon-based catalysts and porous electrodes with excellent performance for ZABs. This paper reviews the research progress of biomass-derived CACs applied to ZABs air electrodes. Specifically, the principle of ZABs and the source and preparation method of biomass-derived CACs are introduced. To prepare efficient biomass-based oxygen electrocatalysts, heteroatom doping and metal modification were introduced to improve the efficiency and stability of carbon materials. Finally, the effects of electron transfer number and H2O2 yield in ORR on the performance of ZABs were evaluated. This review aims to deepen the understanding of the advantages and challenges of biomass-derived CACs in the air electrodes of ZABs, promote more comprehensive research on biomass resources, and accelerate the commercial application of ZABs.

Iron Active Center Coordination Reconstruction in Iron Carbide Modified on Porous Carbon for Superior Overall Water Splitting

In this work, a novel liquid nitrogen quenching strategy is engineered to fulfill iron active center coordination reconstruction within iron carbide (Fe3C) modified on biomass-derived nitrogen-doped porous carbon (NC) for initiating rapid hydrogen and oxygen evolution, where the chrysanthemum tea (elm seeds, corn leaves, and shaddock peel, etc.) is treated as biomass carbon source within Fe3C and NC. Moreover, the original thermodynamic stability is changed through the corresponding force generated by liquid nitrogen quenching and the phase transformation is induced with rich carbon vacancies with the increasing instantaneous temperature drop amplitude. Noteworthy, the optimizing intermediate absorption/desorption is achieved by new phases, Fe coordination, and carbon vacancies. The Fe3C/NC-550 (550 refers to quenching temperature) demonstrates outstanding overpotential for hydrogen evolution reaction (26.3 mV at -10 mA cm-2) and oxygen evolution reaction (281.4 mV at 10 mA cm-2), favorable overall water splitting activity (1.57 V at 10 mA cm-2). Density functional theory (DFT) calculations further confirm that liquid nitrogen quenching treatment can enhance the intrinsic electrocatalytic activity efficiently by optimizing the adsorption free energy of reaction intermediates. Overall, the above results authenticate that liquid nitrogen quenching strategy open up new possibilities for obtaining highly active electrocatalysts for the new generation of green energy conversion systems.

Wood-Structured Nanomaterials as Highly Efficient, Self-Standing Electrocatalysts for Water Splitting

Electrocatalytic water splitting (EWS) driven by renewable energy is widely considered an environmentally friendly and sustainable approach for generating hydrogen (H2), an ideal energy carrier for the future. However, the efficiency and economic viability of large-scale water electrolysis depend on electrocatalysts that can efficiently accelerate the electrochemical reactions taking place at the two electrodes. Wood-derived nanomaterials are well-suited for serving as EWS catalysts because of their hierarchically porous structure with high surface area and low tortuosity, compositional tunability, cost-effectiveness, and self-standing integral electrode configuration. Here, recent advancements in the design and synthesis of wood-structured nanomaterials serving as advanced electrocatalysts for water splitting are summarized. First, the design principles and corresponding strategies toward highly effective wood-structured electrocatalysts (WSECs) are emphasized. Then, a comprehensive overview of current findings on WSECs, encompassing diverse structural designs and functionalities such as supported-metal nanoparticles (NPs), single-atom catalysts (SACs), metal compounds, and heterostructured electrocatalysts based on engineered wood hosts are presented. Subsequently, the application of these WSECs in various aspects of water splitting, including the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), overall water splitting (OWS), and hybrid water electrolysis (HWE) are explored. Finally, the prospects, challenges, and opportunities associated with the broad application of WSECs are briefly discussed. This review aims to provide a comprehensive understanding of the ongoing developments in water-splitting catalysts, along with outlining design principles for the future development of WSECs.

Developing Prussian blue/wood-derived biochar catalyst for persistent organic pollutant degradation: Preparation, characterization, and mechanism

Biomass-derived biochar shows broad promise for persistent organic pollutants (POPs) degradation and thus establishes a more sustainable homestead. However, effective catalytic performance is still challenging. Herein, an efficient catalyst (Prussian blue decorated wood-derived biochar, PBB) was constructed by introducing Prussian blue (PB) into wood-based biochar to activate peroxymonosulfate (PMS) for removing POPs. After anchoring of PB, the degradation performance of biochar was enhanced (degradation efficiency of methylene blue (MB, 20 mg/L) increased from 52% of biochar to 95% of PBB within 60 min). The PBB presents effective MB degradation performance with a wide pH value (3.0 < pH < 11.0) or co-existing diverse anions (Cl-, NO3-, H2PO4-, and HCO3-). Electron paramagnetic resonance (EPR) analysis as well as electrochemical tests confirmed that the non-radical pathway (1O2) is the key to biochar activation of PMS, but by restricting PB into the biochar, the radical pathway (SO4•- and •OH), the non-radical pathway (1O2), and direct electron transfer can work together to activate PMS. In addition, the degradation efficiency could remain about 80% after five-time cyclic tests. This work elucidates the role of PB nanoparticles in enhancing biochar catalysts, which can inspire the development of a carbon-neutralized, cost-effective, and effective strategy for POPs removal.

Precise Design and Modification Engineering of Single-Atom Catalytic Materials for Oxygen Reduction

Due to their unique electronic and structural properties, single-atom catalytic materials (SACMs) hold great promise for the oxygen reduction reaction (ORR). Coordinating environmental and engineering strategies is the key to improving the ORR performance of SACMs. This review summarizes the latest research progress and breakthroughs of SACMs in the field of ORR catalysis. First, the research progress on the catalytic mechanism of SACMs acting on ORR is reviewed, including the latest research results on the origin of SACMs activity and the analysis of pre-adsorption mechanism. The study of the pre-adsorption mechanism is an important breakthrough direction to explore the origin of the high activity of SACMs and the practical and theoretical understanding of the catalytic process. Precise coordination environment modification, including in-plane, axial, and adjacent site modifications, can enhance the intrinsic catalytic activity of SACMs and promote the ORR process. Additionally, several engineering strategies are discussed, including multiple SACMs, high loading, and atomic site confinement. Multiple SACMs synergistically enhance catalytic activity and selectivity, while high loading can provide more active sites for catalytic reactions. Overall, this review provides important insights into the design of advanced catalysts for ORR.

Fe3 C/nanocarbon-Enabled Lithium Dendrite Mitigation in Lithium-Sulfur batteries

Lithium dendrite-induced short circuits and material loss are two major obstacles to the commercialization of lithium-sulfur (Li-S) batteries. Here, a nanocarbon composite consisting of cotton-derived Fe3 C-encapsulated multiwalled carbon nanotubes (Fe3 C-MWCNTs) and graphene effectively traps polysulfides to suppress lithium dendrite growth is reported. Machine learning combined with molecular dynamics (MD) simulations unveils a new polysulfide-induced lithium dendrite formation mechanism: the migration of polysulfides away from the anode drags out lithium protrusions through localized lattice distortion of the lithium anode and traps lithium ions in the surrounding electrolyte, leading to lithium dendrite formation. The Li-S battery, constructed using the composite of cotton-derived Fe3 C-MWCNTs and graphene that serves as both the sulfur host and the anode interlayer, exhibits exceptional cycling stability, impressive capacity retention, and effective mitigation of lithium dendrite formation. The findings offer valuable strategies to prevent lithium dendrite formation and enhance understanding of lithium dendrite growth in Li-S batteries.

Oxygen vacancy engineering of mesoporous Bi-Fe2O3@NC multi-channel microspheres for remarkable oxygen reduction and aqueous/flexible Zn-air batteries

Designing multi-channel mesoporous structure and introducing oxygen vacancies to synergistically enhance oxygen reduction reaction (ORR) activity is crucial for the practical application of zinc-air batteries (ZABs) in the field of energy storage and conversion. Herein, a novel multi-channel mesoporous Bi-Fe2O3 microsphere with abundant oxygen vacancies supported on nitrogen-doped carbon (denoted as Bi-Fe2O3@NC) is constructed and the designated catalyst demonstrates a higher half-wave potential (0.88 V), large limiting current density (5.8 mA cm-2@0.4 V), and superior stability. Besides, the aqueous ZAB utilizing Bi-Fe2O3@NC cathode achieves a high power density of 198.6 mW cm-2 and maintains exceptional stability for 459 h at 5 mA cm-2, superior to most previously reported catalysts. Furthermore, a solid-state ZAB assembled with Bi-Fe2O3@NC shows a power density of 55.9 mW cm-2, highlighting its potential for flexible ZAB applications. The prominent ORR performance of Bi-Fe2O3@NC can be ascribed to its unique multi-channel mesoporous structure and abundant oxygen vacancies, which increase the exposure of active sites and facilitate efficient electron/mass transport. This work provides valuable insights for the rational design of advanced ORR catalysts for the practical requirements of aqueous/flexible ZABs in energy storage and conversion.

Construction of Metal Organic Framework-Derived Fe-N-C Oxidase Nanozyme for Rapid and Sensitive Detection of Alkaline Phosphatase

Alkaline phosphatase (ALP) is a phosphomonoester hydrolase and serves as a biomarker in various diseases. However, current detection methods for ALP rely on bulky instruments, extended time, and complex operations, which are particularly challenging in resource-limited regions. Herein, we synthesized a MOF-derived Fe-N-C nanozyme to create biosensors for the coulometric and visual detection of ALP. Specifically, we found the Fe-N-C nanozyme can efficiently oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue-colored tetramethyl benzidine (TMBox) without the need for H2O2. To construct the biosensor, we incorporated the ALP enzymatic catalytic reaction to inhibit the oxidation of TMB by Fe-N-C oxidase nanozyme. This biosensor showed rapid and highly sensitive detection of ALP in both buffer and clinical samples. The limit of detection (LOD) of our approach could be achieved at 3.38 U L-1, and the linear range was from 5 to 60 U L-1. Moreover, we also developed a visual detection for ALP by using a smartphone-based assay and facilitated practical and accessible point-and-care testing (POCT) in resource-limited areas. The visual detection method also achieved a similar LOD of 2.12 U L-1 and a linear range of 5-60 U L-1. Our approach presents potential applications for other biomarker detections by using ALP-based ELISA methods.

Interfacial Engineering of CoN/Co3 O4 Heterostructured Hollow Nanoparticles Embedded in N-Doped Carbon Nanowires as a Bifunctional Oxygen Electrocatalyst for Rechargeable Liquid and Flexible all-Solid-State Zn-Air Batteries

The design of economical, efficient, and robust bifunctional oxygen electrocatalysts is greatly imperative for the large-scale commercialization of rechargeable Zn-air battery (ZAB) technology. Herein, the neoteric design of an advanced bifunctional electrocatalyst composed of CoN/Co₃ O₄ heterojunction hollow nanoparticles in situ encapsulated in porous N-doped carbon nanowires (denoted as CoN/Co₃ O₄ HNPs@NCNWs hereafter) is reported. The simultaneous implementation of interfacial engineering, nanoscale hollowing design, and carbon-support hybridization renders the synthesized CoN/Co₃ O₄ HNPs@NCNWs with modified electronic structure, improved electric conductivity, enriched active sites, and shortened electron/reactant transport pathways. Density functional theory computations further demonstrate that the construction of a CoN/Co₃ O₄ heterojunction can optimize the reaction pathways and reduce the overall reaction barriers. Thanks to the composition and architectural superiorities, the CoN/Co₃ O₄ HNPs@NCNWs exhibit distinguished oxygen reduction reaction and oxygen evolution reaction performance with a low reversible overpotential of 0.725 V and outstanding stability in KOH medium. More encouragingly, the homemade rechargeable liquid and flexible all-solid-state ZABs utilizing CoN/Co₃ O₄ HNPs@NCNWs as the air-cathode deliver higher peak power densities, larger specific capacities, and robust cycling stability, exceeding the commercial Pt/C + RuO₂ benchmark counterparts. The concept of heterostructure-induced electronic modification herein may shed light on the rational design of advanced electrocatalysts for sustainable energy applications.

Ultrahigh-Loaded Fe Single Atoms and Fe3C Nanoparticle Catalysts as Air Cathodes for High-Performance Zn-Air Batteries

Fe-based materials containing Fe-Nx sites have emerged as promising electrocatalysts in the oxygen reduction reaction (ORR), but they still suffer structural instability which may lead to loss of catalytic activity. Herein, a novel electrocatalyst Fe₃C-FeSA@3DCN with the coexistence of Fe₃C nanoparticles and Fe single atoms (FeSA) in a three-dimensional conductive network (3DCN) is prepared via lattice confinement and defect trapping strategies with an Fe atomic loading of as high as 4.36%. In the ORR process, the limiting current density of Fe₃C-FeSA@3DCN reaches 5.72 mA cm^-2, with an onset potential of 0.926 V and a Tafel slope of 66 mV/decade, showing better catalytic activity and stability than Pt/C catalysts. Notably, its assembled aqueous and solid-state Zn-air batteries (ZABs) achieve peak power densities of 166 and 56 mW cm^-2, respectively, with a long service life of up to 200 h at a current density of 5 mA cm^-2. In addition, the assembled ZAB can provide a constant voltage on activated carbon electrodes to perform capacitive deionization to adsorb different ions. The importance of the Fe species active sites generated by Fe₃C and FeSA in the material for ORR activity to boost the electron transfer and mass transfer is demonstrated by a simple selective poisoning experiment.

Semi-Embedding Zn-Co3O4 Derived from Hybrid ZIFs into Wood-Derived Carbon for High-Performance Supercapacitors

Transition metal oxides (TMOs) can provide high theoretical capacitance due to the change of multiple valence states of transition metals. However, their intrinsic drawbacks, including poor electrical conductivity, lower energy density, and huge volume expansion, will result in the pulverization of electrode materials and restricted electrochemical kinetics, thus leading to poor rate capability and rapid capacity fading. Composite electrodes based on transition metal oxides and carbon-based materials are considered to be promising candidates for overcoming these limitations. Herein, we reported a preparation method of hybrid ZIFs derived Zn-doped Co3O4/carbon (Zn-Co3O4/C-230) particles semi-embedded in wood-derived carbon skeleton for integrated electrodes. A large specific surface area, excellent conductivity, and electrochemical stability provide a larger electrochemical activity and potential window for the electrode. Prepared Zn-Co3O4@CW-230 electrode (0.6 mm thick) displays ultrahigh area specific capacitances of 7.83 and 6.46 F cm-2 at the current densities of 5 and 30 mA cm-2, respectively. Moreover, a symmetric supercapacitor assembled by two identical Zn-Co3O4@CW-230 electrodes delivers a superior area-specific capacitance of 2.61 F cm-2 at the current densities of 5 mA cm-2 and great energy densities of 0.36 mWh cm-2 (6.0 mWh cm-3) at 2.5 mW cm-2, while maintaining 97.3% of initial capacitance over 10,000 cycles. It notably outperforms those of most carbon-based metal oxides, endowing the Zn-Co3O4@CW-230 with extensive prospects for practical application.

Synergistic Effect of Co9S8 and FeS2 Inlaid on N-Doped Carbon Nanofibers toward a Bifunctional Catalyst for Zn-Air Batteries

The development of economical and energy-efficient electrocatalysts is essential for the wide-scale application of secondary zinc-air batteries (ZABs). Herein, we prepared Co₉S₈ and FeS₂ nanoparticles inlaid on N-doped carbon nanofibers (Co₉S₈-FeS₂@N-CNFs), which were derived from the in situ growth of Fe-doped ZIF-67 nanosheet arrays on electrospun nanofibers and a subsequent sulfidation process. The Co₉S₈-FeS₂@N-CNFs display excellent electrocatalytic performances for OER (E_j=10, 330 mV) and ORR (E_1/2, 0.80 V) as well as a smaller charge and discharge gap (ΔE, 0.76 V) in KOH electrolyte, allowing it to be employed as an attractive air cathode bifunctional catalyst for secondary ZABs. The electrocatalytic performance of the composite materials (Co₉S₈-FeS₂@N-CNFs) is obviously better than that of the single-component materials (FeS₂@N-CNFs and Co₉S₈@N-CNFs). The improved catalytic performance is mainly attributed to the synergistic effect of the two transition-metal sulfides and the optimization of the structure. Furthermore, the peak power density of the assembled aqueous/solid-state ZABs based on Co₉S₈-FeS₂@N-CNFs can reach 214 and 91 mW cm^-2 with excellent stability, respectively, which outperforms the ones based on commercial precious-metal-based catalysts. We anticipate that our work will provide new inspiration for the design of MOF-derived sulfides as multifunctional catalysts.

Wood-Derived Monolithic Catalysts with the Ability of Activating Water Molecules for Oxygen Electrocatalysis

Oxygen reduction reaction (ORR) is the key reaction on cathode of rechargeable zinc-air batteries (ZABs). However, the lack of protons in alkaline conditions limits the rate of ORR. Herein, an activating water strategy is proposed to promote oxygen electrocatalytic activity by enhancing the proton production from water dissociation. FeP nanoparticles (NPs) are coupled on N-doped wood-derived catalytically active carbon (FeP-NWCC) to associate bifunctional active sites. In alkaline, FeP-NWCC possesses outstanding catalytic activities toward ORR (E_1/2  = 0.86 V) and Oxygen evolution reaction (OER) (overpotential is 310 mV at 10 mA cm^-2 ). The liquid ZABs assembled by FeP-NWCC deliver superior peak power density (144 mW cm^-2 ) and cycle stability (over 450 h). The quasi-solid-state ZABs based on FeP-NWCC also display excellent performances. Theoretical calculation illustrates that the superb bifunctional performance of FeP-NWCC results from the elevated dissociation efficiency of water via FeP NPs to assist the oxygen catalytic process. The strategy of activating water provides a new perspective for the design of ORR/OER bifunctional catalysts. This work is a model for the application of forest biomass.