Efficient Oxygen Electrocatalyst for Zn-Air Batteries: Carbon Dots and Co9S8 Nanoparticles in a N,S-Codoped Carbon Matrix

Carbon dots-supported Zn single atom nanozymes for the catalytic therapy of diabetic wounds

Diabetic wound treatment continues to be a significant clinical issue due to higher levels of oxidative stress, susceptibility to bacterial infections, and chronic inflammatory responses during healing. We rationally developed and synthesized an ultra-small carbon dots (C-dots) loaded with zinc single-atom nanozyme (Zn/C-dots) with the aim of promoting wounds healing by nanocatalytic treatment, especially targeting its complex pathological microenvironment. Zinc single atoms and C-dots form a dual catalytic system with higher enzymatic activity. Furthermore, the Zn/C-dots nanozyme effectively enters cells, accumulates at mitochondria, and removes excess ROS, protecting cells from oxidative stress damage and limiting the release of pro-inflammatory cytokines, hence reducing inflammation. Zinc can synergistically increase the antibacterial action of C-dots (the effective antibacterial rate of 100 µg/mL Zn/C-dots was above 90 %). Unlike traditional C-dots, Zn/C-dots can cause endothelial cell migration and the formation of new blood vessels. In vitro cytotoxicity, blood compatibility, and in vivo toxicity studies of Zn/C-dots show that they are biocompatible. We subsequently utilized the Zn/C-dots nanozymes to treat diabetic rats' chronic wounds for external use, combining them with ROS-responsive hydrogels to create an antioxidative system (H-Zn/C-dots). The hydrogels anchored the Zn/C-dots nanozymes to the wound, allowing for long-term treatment. The results revealed that H-Zn/C-dots can considerably reduce inflammation, accelerate angiogenesis, collagen deposition, and promote tissue remodeling at the diabetic wound site. After 14 days, the wound area had decreased to approximately 9.19 %, making it a potential treatment. STATEMENT OF SIGNIFICANCE: An ultra-small carbon dot with a zinc single-atom nanozyme was designed and manufactured. Zn/C-dots possess antibacterial, ROS-scavenging, and angiogenesis activities. In vivo, the multifunctional ROS-responsive hydrogel incorporating Zn/C-dots could speed up diabetic wound healing.

Nitrogen-Doped Carbon Dots Modified Fe-Co Sulfide Nanosheets as High-Efficiency Electrocatalysts toward Oxygen Evolution Reaction

Developing high-efficiency and stable oxygen evolution reaction (OER) electrocatalysts is an imperative requirement to produce green and clean hydrogen energy. In this work, the FeCoSy /NCDs composite with nitrogen-doped carbon dots (NCDs) modified Fe-Co sulfide (FeCoSy ) nanosheets is prepared by using a facile and mild one-pot solvothermal method. Benefiting from the low crystallinity and the synergistic effect between FeCoSy and NCDs, the optimal FeCoSy /NCDs-3 composite exhibits an overpotential of only 284 mV at 10 mA cm-2 , a small Tafel value of 52.1 mV dec-1 , and excellent electrochemical durability in alkaline solution. Remarkably, unlike ordinary metal sulfide electrocatalysts, the morphology, components, and structure of the FeCoSy /NCDs composite can be well retained after OER test. The NCDs modified FeCoSy composite with excellent electrocatalytic performance provides an effective approach to boost metal sulfide electrocatalysts for practical application.

N,S co-doped porous carbon with Co9S8 prepared with a Co-FF-derived Co3O4 template: a bi-functional electrocatalyst for rechargeable zinc-air batteries

To achieve broad commercialization of rechargeable metal-air batteries, the development of non-precious metal-based bi-functional oxygen electrocatalysts is critical. In this study, we prepared N,S co-doped porous carbon materials containing Co9S8 nanoparticles (Co9S8/NSC) through a one-step pyrolysis process. The process involved the pyrolysis of a polydopamine (PDA) coated Co-formic acid framework (Co-FF) derived Co3O4 and thiourea. The improved catalyst Co9S8/NSC-1 exhibited satisfactory long-term durability and superior oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity, the half-wave potential (E1/2) of the ORR reached 0.83 V, and the OER overpotential at 10 mA cm-2 (η10) was 300 mV. The zinc-air battery (ZAB) based on Co9S8/NSC-1 assembly had a maximum power density of 102.0 mW cm-2 and the cycle life reached 500 cycles. The material preparation method was simple, environmentally friendly and inexpensive, providing a feasible strategy for the development of non-precious metal-based electrocatalysts.

Surface state engineering of carbon dot/carbon nanotube heterojunctions for boosting oxygen reduction performance

Platinum-based (Pt) catalysts are the most common commercial catalysts for oxygen reduction reactions (ORR). Unfortunately, their high price, scarcity and poor durability hinder their further development. Therefore, the development of effective and economical ORR electrocatalysts has received increasing attention. Here, carbon dots (CDs) enriched in amino functional groups were successfully loaded onto carbon nanotubes (CNTs) with a large surface area and helical structure through a surface state engineering strategy. The resulting composites (CD/CNTs) are 0D/1D nano heterojunction structures. The CD/CNTs showed superior ORR activity compared with CNTs and CDs (E_oneset = 0.95 V, E_1/2 = 0.81 V and limiting current density = 4.74 mA cm^-2). In addition, the stability of CD/CNTs in an alkaline medium was up to 30000 s. The excellent ORR performance of CD/CNTs can be attributed to the dominant role of amino-N, the synergistic effect of heterojunctions formed by CDs and CNTs, and the high Lewis basicity. The composite electrocatalyst synthesized by the CD-regulated CNT strategy is expected to be a reliable cathode candidate for future energy conversion devices.

Nitrogen-Doped Carbon Dot as a Lubricant Additive in Polar and Non-polar Oils for Superior Tribological Properties via Condensation Reaction

Nitrogen-doped lubricating additives have been proved to be an effective strategy to improve the tribological properties of lubricating oil. However, the traditional preparation methods of nitrogen-doped lubricating additives have the defects including harsh preparation conditions and a time-consuming preparation process. Herein, we report a preparation method of nitrogen-doped carbon dot (NCD) lubricating additives in a short time by one-step aldehyde condensation reaction at room temperature. The small size effect and nitrogen-containing functional groups of NCD lubricating additives provide favorable conditions for their dispersion and low friction in base oil. The tribological properties of NCD lubricating additives in sunflower oil (SFO) and PAO10 were systematically evaluated. The results show that NCD lubricating additives could reduce the average friction coefficient of SFO from 0.15 to 0.06 and PAO10 oil from 0.12 to 0.06, and the wear width is also decreased by 50-60%. In particular, the friction curve is very stable, and the friction coefficient was maintained at about 0.06 even under the working time of 5 h. By analyzing the morphology and chemical properties of the worn surface, the lubrication effect of NCDs is attributed to its small size effect and adsorption, which was easy to enter the friction gap to fill and repair. Furthermore, the doping of nitrogen induces the occurrence of friction chemical reactions, forming a friction film of nitrides and metal oxides at the friction interface, which effectively reduces the friction and wear of the surface. These findings provide a possibility for the convenient and effective preparation of NCD lubricating additives.

Construction of three-dimensional cobalt sulfide/multi-heteroatom co-doped porous carbon as an efficient trifunctional electrocatalyst

Exploring cost-effective non-precious metal electrocatalysts is vital for the large-scale application of clean energy conversion devices (i.e., fuel cells, metal-air batteries and water electrolysers). Herein, we present the construction of a three-dimensional cobalt sulfide/multi-heteroatom co-doped carbon composite as a trifunctional electrocatalyst for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) through one-step sulfidation of zeolitic-imidazolate frameworks (ZIFs) using sulfur powder as a sulfur source. By virtue of the distinct periodic metal-nitrogen coordination structure and the abundant micropores within the ZIF precursor, sub-10 nm Co₉S₈ nanoparticles (NPs) are homogenously anchored on a Co, S and N multi-heteroatom co-doped carbon framework with a large specific surface area that exposes sufficient reactive sites for these electrocatalytic reactions. The optimized Co₉S₈/CoNSC exhibits outstanding ORR, OER and HER performance, comparable or even superior to those of commercial Pt/C and RuO₂. The small Co₉S₈ NPs and Co-N_x species embedded in the carbon matrix cooperatively catalyze the OER and ORR, while the HER catalysis is mainly contributed by Co₉S₈ NPs. Furthermore, the Co₉S₈/CoNSC shows outstanding anti-poisoning capability towards sulfur species during ORR catalysis with no obvious activity degradation observed in 0.1 M KOH containing 50 μM SO₃^2- species, significantly outperforming commercial Pt/C. The assembled rechargeable Zn-air battery using the Co₉S₈/CoNSC as a cathode shows a high power density (150 mW cm^-2) and the assembled water electrolyzer only requires 1.585 V at a current density of 10 mA cm^-2 when using this material as an anode and a cathode. This work provides an effective strategy to design and synthesize efficient, durable and anti-poisoning cobalt chalcogenide-based trifunctional electrocatalysts for the large-scale application of clean energy conversion devices.

Two-Dimensional Cobalt Sulfide/Iron-Nitrogen-Carbon Holey Sheets with Improved Durability for Oxygen Electrocatalysis

Transition-metal sulfide as a promising bifunctional oxygen electrocatalyst alternative to scarce platinum-group metals has attracted much attention, but it suffers activity loss over time owing to poor structural/compositional stability during catalysis. Herein, we report a self-template method for preparing a two-dimensional cobalt sulfide holey sheet superstructure with hierarchical porosity followed by the encapsulation of thin iron-nitrogen-carbon as a protective layer. The iron-nitrogen-carbon layer to some degree precludes the phase transition of cobalt sulfide underneath and preserves the structural integrity during catalysis, therefore rendering an exceptional durability in terms of no obvious activity loss after 10,000 cycles of the accelerated durability test. It also noticeably enhances the intrinsic activity of cobalt sulfide and does not influence its exposure into the electrolyte, resulting in showing an extraordinary electrochemical performance in terms of a potential difference of 0.69 V for the overall oxygen redox. A rechargeable zinc-air battery assembled by a cobalt sulfide/iron-nitrogen-carbon air cathode delivers approximately 4.2 times higher power density than that without an iron-nitrogen-carbon layer and stably operates for 300 h with a high voltaic efficiency. This work gives a facile and effective strategy for improving the long-term durability of transition-metal sulfide electrocatalysts.

In vitro and in vivo highly effective antibacterial activity of carbon dots-modified TiO2 nanorod arrays on titanium

Light-triggered antibacterial therapy has been proven to be a secure and effective way to treat bacterial infection. Nevertheless, the long-term security of the common photosensitizer remains to be seen in the body. In this work, carbon dots (CDs) with good biocompatibility are incorporated into TiO₂ nanorods to improve the photocatalytic and photothermal ability of titanium implants under the irradiation of visible light (VL) and near-infrared (NIR) light. The C-TiO₂ NR exhibit excellent in vitro and in vivo antimicrobial effect under 660 nm VL and 808 nm NIR light co-irradiation owing to the combined effect of hyperthermia, reactive oxygen species (ROS) and nanorod structure. Besides, C-TiO₂ NR can improve the adhesion and diffusion of bone marrow mesenchymal stem cells (BMSCs).

V. S, Menon RS, Panda SK, Sahu AK. In-situ fabrication of cobalt sulfide decorated N, S co-doped mesoporous carbon and its application as electrocatalyst for efficient oxygen reduction reaction

Designing an efficient electrocatalyst for facile oxygen reduction reaction (ORR) is essential to achieve higher fuel cell performance. Herein, we demonstrate the simple in-situ process to synthesize cobalt sulfide decorated...

Coordination regulated pyrolysis synthesis of ultrafine FeNi/(FeNi)9S8 nanoclusters/nitrogen, sulfur-codoped graphitic carbon nanosheets as efficient bifunctional oxygen electrocatalysts

Design of advanced carbon nanomaterials with high-efficiency oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities is still imperative yet challenging for searching green and renewable energies. Herein, we synthesized ultrafine FeNi/(FeNi)₉S₈ nanoclusters encapsulated in nitrogen, sulfur-codoped graphitic carbon nanosheets (FeNi/(FeNi)₉S₈/N,S-CNS) by coordination regulated pyrolyzing the mixture of the metal precursors, dithizone and g-C₃N₄ at 800 °C. The as-prepared FeNi/(FeNi)₉S₈/N,S-CNS exhibited distinct electrocatalytic activity and stability for the ORR with positive onset (E_onset) and half-wave (E_1/2) potentials (E_onset = 0.97 V; E_1/2 = 0.86 V) and OER with the small overpotential (η = 283 mV) at 10 mA cm^-2 in the alkaline media, outperforming commercial Pt/C and RuO₂ catalysts. This research provides some constructive guidelines for preparing efficient, low-cost and stable nanocatalysts for electrochemical energy devices.

A bifunctional nanozyme of carbon dots-mediated Co9S8 formation

Controlling the size of nanocrystals and inhibiting their agglomeration are of paramount importance for achieving ideal catalytic performance. Here we discovered that carbon dots (CDs) are not only able to serve as reductants but also as stabilizers of ultrasmall Co₉S₈ nanocrystals by means of their surface terminal groups. As a result, ultrasmall Co₉S₈ nanocrystals are incorporated into porous carbon nanosheets formed by splicing CDs. The resultant nanocomposites display a rich pore structure accompanying with large specific surface area and outstanding bifunctional performances to mimic the catalytic activity of peroxidase and oxidase without exerting any external energy. More importantly, the unique architecture endows Co₉S₈ nanocrystals with high stability and good durability. The nanocomposites have been demonstrated as a colorimetric sensor for detection of ascorbic acid with a superior anti-interference ability as well as a detection limit of 0.2 μM. Our findings open new synthetic opportunities by tuning the interaction of CDs with the surrounding environment and enable advanced applications such as biomedicine and catalytic transformations.

Advanced Oxygen Electrocatalyst for Air-Breathing Electrode in Zn-Air Batteries

The electrochemical reduction of oxygen to water and the evolution of oxygen from water are two important electrode reactions extensively studied for the development of electrochemical energy conversion and storage technologies based on oxygen electrocatalysis. The development of an inexpensive, highly active, and durable nonprecious-metal-based oxygen electrocatalyst is indispensable for emerging energy technologies, including anion exchange membrane fuel cells, metal-air batteries (MABs), water electrolyzers, etc. The activity of an oxygen electrocatalyst largely decides the overall energy storage performance of these devices. Although the catalytic activities of Pt and Ru/Ir-based catalysts toward an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER) are known, the high cost and lack of durability limit their extensive use for practical applications. This review article highlights the oxygen electrocatalytic activity of the emerging non-Pt and non-Ru/Ir oxygen electrocatalysts including transition-metal-based random alloys, intermetallics, metal-coordinated nitrogen-doped carbon (M-N-C), and transition metal phosphides, nitrides, etc., for the development of an air-breathing electrode for aqueous primary and secondary zinc-air batteries (ZABs). Rational surface and chemical engineering of these electrocatalysts is required to achieve the desired oxygen electrocatalytic activity. The surface engineering increases the number of active sites, whereas the chemical engineering enhances the intrinsic activity of the catalyst. The encapsulation or integration of the active catalyst with undoped or heteroatom-doped carbon nanostructures affords an enhanced durability to the active catalyst. In many cases, the synergistic effect between the heteroatom-doped carbon matrix and the active catalyst plays an important role in controlling the catalytic activity. The ORR activity of these catalysts is evaluated in terms of onset potential, number of electrons transferred, limiting current density, and durability. The bifunctional oxygen electrocatalytic activity and ZAB performance, on the other hand, are measured in terms of potential gap between the ORR and OER, ΔE = E_j10^OER - E_1/2^ORR, specific capacity, peak power density, open circuit voltage, voltaic efficiency, and charge-discharge cycling stability. The nonprecious metal electrocatalyst-based ZABs are very promising and they deliver high power density, specific capacity, and round-trip efficiency. The active site for oxygen electrocatalysis and challenges associated with carbon support is briefly addressed. Despite the considerable progress made with the emerging electrocatalysts in recent years, several issues are yet to be addressed to achieve the commercial potential of rechargeable ZAB for practical applications.

Electrocatalytic, Kinetic, and Mechanism Insights into the Oxygen-Reduction Catalyzed Based on the Biomass-Derived FeOx @N-Doped Porous Carbon Composites

A valid strategy for amplifying the oxygen reduction reaction (ORR) efficiency of non-noble electrocatalyst in both alkaline and acid electrolytes by decorated with a layer of biomass derivative nitrogen-doped carbon (NPC) is proposed. Herein, a top-down strategy for the generally fabricating NPC matrix decorated with trace of metal oxides nanoparticles (FeO_x NPs) by a dual-template assisted high-temperature pyrolysis process is reported. A high-activity FeO_x /FeNC (namely Hemin/NPC-900) ORR electrocatalyst is prepared via simply carbonizing the admixture of Mg₅ (OH)₂ (CO₃ )₄ and NaCl as dual-templates, melamine and acorn shells as nitrogen and carbon source, hemin as a natural iron and nitrogen source, respectively. Owing to its unique 3D porous construction, large BET areas (819.1 m² ∙g^-1 ), and evenly dispersed active sites (FeN_x , CN, and FeO parts), the optimized Hemin/NPC-900 catalyst displays comparable ORR catalytic activities, remarkable survivability to methanol, and preferable long-term stability in both alkali and acid electrolyte compared with benchmark Pt/C. More importantly, density function theory computations certify that the interaction between Fe₃ O₄ nanoparticles and arm-GN (graphitic N at armchair edge) active sites can effectually promote ORR electrocatalytic performance by a lower overpotential of 0.81 eV. Accordingly, the research provides some insight into design of low-cost non-precious metal ORR catalysts in theory and practice.

Kilogram-Scale Synthesis and Functionalization of Carbon Dots for Superior Electrochemical Potassium Storage

Carbon dot is a type of carbon material with an ultrasmall size of less than 10 nm for all three dimensions, which has attracted more and more attention due to its useful merits. Unfortunately, the complicated synthesis method and low yield largely limit its wide large-scale application. Herein, an inexpensive and high-efficiency aldol condensation method under ambient temperature and pressure was proposed for the large-scale synthesis of CDs, which can obtain products with 1.083 kg in 2 h and realize the functionalization of carbon dots doped with nitrogen (NCDs) and sulfur/nitrogen doubly (NSCDs), and then the mechanism and structure of CDs formation were explained. Moreover, utilizing the feature of controllable assembly of carbon dots, and combined with theoretical calculations, we have designed functionalized 1D carbon fibers (CF) to construct high-performance potassium storage anode materials through the assembly of carbon dots induced by a Zn compound. Benefitting from the microstructure and surface functional groups derived from CDs, the N-doped CF (NCF700) exhibits superior electrochemical energy storage performance for potassium ion batteries (PIBs). This study provides a low-cost and high-yield method to produce CDs and promotes the practical application of CDs in electrochemical energy storage.

Co/Co9S8@carbon nanotubes on a carbon sheet: facile controlled synthesis, and application to electrocatalysis in oxygen reduction/oxygen evolution reactions, and to a rechargeable Zn-air battery

A facile strategy to fabricate Co/Co₉S₈ nanoparticles-encapsulated in carbon nanotubes, on an N-doped porous graphene sheet (Co/Co₉S₈@CNTs) via pyrolysis of a mixture of Co(NO₃)₂, melamine and l-cysteine is reported.

Carbon Dots in Porous Materials: Host-Guest Synergy for Enhanced Performance

Carbon dots (CDs) are emerging as a new class of carbon nanomaterials, which have inspired growing interest for their widespread applications in anti-counterfeiting, sensing, bioimaging, optoelectronic and energy-related fields. In terms of the concept of host-guest assembly, immobilizing CDs into porous materials (PMs) has proven to be an effective strategy to avoid the aggregation of bare CDs in solid state, in particular, the host-guest synergy with both merits of CDs and PMs affords composites promising properties in afterglow and tunable emissions, as well as optimizes their performance in optics, catalysis, and energy storage. This Minireview summarizes the recent progress in the research of CDs@PMs, and highlights synthetic strategies of constructing composites and roles of porous matrices in boosting the applications of CDs in diverse areas. The prospect of future exploration and challenges are proposed for designing advanced CDs-based functional nanocomposite materials.

Exploiting a High-Performance "Double-Carbon" Structure Co9S8/GN Bifunctional Catalysts for Rechargeable Zn-Air Batteries

Rational synthesis of bifunctional electrocatalysts with high performance and strong durability is highly demanded rechargeable metal-air battery. In this work, ZIF-derived Co₉S₈/C coated with conductive graphene nanosheet (Co₉S₈/GN) was synthesized by a simple solvothermal method and formed a stable double-carbon structure. As expected, the prepared Co₉S₈/GN catalyst exhibits a high catalytic activity (ΔE: 0.88 V) and long-term durability toward both oxygen reduction reaction and oxygen evolution reaction (ORR and OER), which is even superior to the Pt/C + Ir/C mixture (0.91 V). In addition, the Zn-air battery with the Co₉S₈/GN catalyst showed higher power density (186 mW cm^-2) and more stable charge-discharge cycling performances (2000 cycles) than the Pt/C + Ir/C (118 mW cm^-2). Based on these analysis results, the favorable catalytic performance of ORR/OER should be illustrated by the following reasons: (i) large specific surface area and unique mesoporous structure, providing abundant active sites; (ii) good conductivity, accelerating the electrons transfer; and (iii) the unique stable "double-carbon" structures (metal-S-C-C), preventing the agglomeration of metal sulfide, building new quick transfer pathway, and forming the strong electron coupling ability and synergistic effect.

Dual-Shelled Multidoped Hollow Carbon Nanocages with Hierarchical Porosity for High-Performance Oxygen Reduction Reaction in Both Alkaline and Acidic Media

The rational design and facile synthesis of metal organic framework (MOF)-derived carbon materials with high oxygen reduction reaction (ORR) activity still remains challenging. Herein, we report on a simple yet robust route to dual-shelled Co, N, and S co-doped hollow carbon nanocages (denoted Co-N/S-DSHCN) with outstanding ORR performance. The concurrent compositional and structural engineering of the zeolitic imidazolate framework (ZIF-67), enabled by its coating with trithiocyanuric acid (TCA), yields core-shelled precursor particles which are subsequently carbonized into Co-N/S-DSHCN. Notably, Co-N/S-DSHCN-3.5 outperforms the commercial Pt/C, representing a +25 mV onset potential (E_on) and a +43 mV half-wave potential (E_1/2) in 0.1 M KOH and a comparable E_1/2 to Pt/C in 0.5 M H₂SO₄, respectively. Such impressive ORR activities of Co-N/S-DSHCN-3.5 originate from the effective synergy of Co, N, and S co-doping (i.e., a compositional tuning) in conjunction with a unique dual-shelled hollow architecture containing hierarchical porosity (i.e., a structural tailoring).

Recent Advances in Energy Conversion Applications of Carbon Dots: From Optoelectronic Devices to Electrocatalysis

Exploitation and utilization of sustainable energy sources has increasingly become the common theme of global social development, which has promoted tremendous development of energy conversion devices/technologies. Owing to excellent and unique optical/electrical properties, carbon dots (CDs) have attracted extensive research interest for numerous energy conversion applications. Strong absorption, downconversion photoluminescence, electron acceptor/donor characteristics, and excellent electron conductivity endow CDs with enormous potential for applications in optoelectronic devices. Furthermore, excellent electron transfers/transport capacities and easily manipulable structural defects of CDs offer distinct advantages for electrocatalytic applications. Recent advances in CD-based energy conversion applications, including optoelectronic devices such as light-emitting diodes and solar cells, and electrocatalytic reactions including the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, and carbon dioxide reduction reaction, are summarized. Finally, current challenges and future prospects for CD-based energy conversion applications are proposed, highlighting the importance of controllable structural design and modifications.

Pollen-derived porous carbon decorated with cobalt/iron sulfide hybrids as cathode catalysts for flexible all-solid-state rechargeable Zn-air batteries

The development of flexible all-solid-state rechargeable Zn-air batteries (FS-ZABs) for wearable applications faces challenges from the balance between performance and flexibility of the battery; efficient cathode catalyst and reasonable electrode construction design are key factors. Herein, a low-cost pollen derived N,S co-doped porous carbon decorated with Co9S8/Fe3S4 nanoparticle hybrids (Co-Fe-S@NSRPC) has been synthesized. Owing to the active Co9S8/Fe3S4 nanoparticles, N,S co-doping, and large specific area of the pollen derived porous carbon matrix, the Co-Fe-S@NSRPC composite exhibits an excellent bifunctional catalytic activity with a small potential gap (ΔE = 0.80 V) between the half-wave potential for the ORR (0.80 V) and the potential at 10 mA cm-2 for the OER (1.60 V), and endows a liquid Zn-air battery with a high power density of 138 mW cm-2, a larger specific capacity of 891 mA h g-1 and a stable rechargeability of up to 331 cycles. Based on the Co-Fe-S@NSRPC cathode catalyst, a 2D coplanar FS-ZAB has been fabricated with specially designed parallel narrow strip electrodes alternately arrayed on a polyacrylamide polyacrylic acid copolymer hydrogel solid electrolyte. The presented FS-ZAB exhibits excellent battery performance with high open-circuit-voltage (1.415 V), competitive peak power density (78 mW cm-2), large specific capacity (785 mA h g-1) and stable rechargeability (150 cycles), offers robust flexibility to maintain stable charge/discharge capacity under different bending deformations, and provides convenient coplanar integrability to realize parallel or series connection of multiple cells in a relatively small area.

Bifunctional Catalysts for Reversible Oxygen Evolution Reaction and Oxygen Reduction Reaction

Metal-air batteries (MABs) and reversible fuel cells (RFCs) rely on the bifunctional oxygen catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Finding efficient bifunctional oxygen catalysts is the ultimate goal and it has attracted a great deal of attention. The dilemma is that a good ORR catalyst is not necessarily efficient for OER, and vice versa. Thus, the development of a new type of bifunctional oxygen catalysts should ensure that the catalysts exhibit high activity for both OER and ORR. Composites with multicomponents for active centers supported on highly conductive matrices could be able to meet the challenges and offering new opportunities. In this Review, the evolution of bifunctional catalysts is summarized and discussed aiming to deliver high-performance bifunctional catalysts with low overpotentials.

Interfacial effect of Co4S3–Co9S8 nanoparticles hosted on rGO sheets derived from molecular precursor pyrolysis on enhancing electrochemical behaviour

Co₄S₃–Co₉S₈ nanoparticles with abundant interfaces hosted on reduced graphene oxide were synthesized via a monomolecular pyrolysis strategy to boost catalytic activity.

A cellulose dissolution and encapsulation strategy to prepare carbon nanospheres with ultra-small size and high nitrogen content for the oxygen reduction reaction

Space-confined pyrolysis of microcrystalline cellulose (MCC) to prepare ultra-small N-doped carbon nanospheres (NCNs) with high nitrogen content and superior ORR performance.

A Mini Review on Carbon Quantum Dots: Preparation, Properties, and Electrocatalytic Application

Luminescent carbon quantum dots (CQDs) represent a new form of nanocarbon materials which have gained widespread attention in recent years, especially in chemical sensor, bioimaging, nanomedicine, solar cells, light-emitting diode (LED), and electrocatalysis. CQDs can be prepared simply and inexpensively by multiple techniques, such as the arc-discharge method, microwave pyrolysis, hydrothermal method, and electrochemical synthesis. CQDs show excellent physical and chemical properties like high crystallization, good dispersibility, photoluminescence properties. In particular, the small size, superconductivity, and rapid electron transfer of CQDs endow the CQDs-based composite with improved electric conductivity and catalytic activity. Besides, CQDs have abundant functional groups on the surface which could facilitate the preparation of multi-component electrical active catalysts. The interactions inside these multi-component catalysts may further enhance the catalytic performance by promoting charge transfer which plays an important role in electrochemistry. Most recent researches on CQDs have focused on their fluorescence characteristics and photocatalytic properties. This review will summarize the primary advances of CQDs in the synthetic methods, excellent physical and electronic properties, and application in electrocatalysis, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reduction (HER), and CO2 reduction reaction (CO2RR).

Co/Co9S8 nanoparticles coupled with N,S-doped graphene-based mixed-dimensional heterostructures as bifunctional electrocatalysts for the overall oxygen electrode

A Co/Co₉S₈/rGO/MWCNT composite catalyst was designed and fabricated via a combined hydrothermal reaction with a calcination method for the ORR/OER.