Covalent entrapment of cobalt-iron sulfides in N-doped mesoporous carbon: extraordinary bifunctional electrocatalysts for oxygen reduction and evolution reactions

Topochemically synthesized Nb3VS6 as a stable anode for sodium-ion batteries

Ternary metal sulfides having layered morphology are considered as potential active materials for various applications. Herein, Nb3VS6 is synthesized topochemically for the first time using a Nb-V-HDA complex having a lamellar structure by employing H2S gas as the sulfidation agent. Nb3VS6, as an anode for SIBs, exhibited a specific capacity of 101.15 mA h g-1 at 0.5 A g-1, along with excellent cycling stability with 100% capacity retention after 2500 cycles.

Strong Carbon Layer-Encapsulated Cobalt Tin Sulfide-Based Nanoporous Material as a Bifunctional Electrocatalyst for Zinc-Air Batteries

Global demands for cost-effective, durable, highly active, and bifunctional catalysts for metal-air batteries are tremendously increasing in scientific research fields. In this work, a strategy for the rational fabrication of carbon layer-encapsulated cobalt tin sulfide nanopores (CoSnOH/S@C NPs) material as a bifunctional electrocatalyst for rechargeable zinc (Zn)-air batteries by a cost-effective and facile two-step hydrothermal method is reported. Moreover, the effect of metal elements on the morphology of CoSnOH nanodisks material via the hydrothermal method is investigated. Owing to its excellent nanostructure, exclusive porous network, and high specific surface area, the optimized CoSnOH/S@C NPs material reveals superior catalytic properties. The as-prepared CoSnOH/S@C NPs electrocatalyst reveals better properties of oxygen reduction reaction (half-wave potential of -0.88 V vs reversible hydrogen electrode) and oxygen evolution reaction (overpotential of 137 mV at 10 mA cm-2) when compared with commercial Pt/C and IrO2 catalyst materials. Most significantly, the CoSnO/S@C NPs-based Zn-air battery exhibits more excellent cycling stability than the Pt/C+IrO2 catalyst-based one. Consequently, the proposed material provides a new route for fabricating more active and stable multifunctional catalyst materials for energy conversion and storage systems.

First-row transition metal carbonates catalyze the electrochemical oxygen evolution reaction: iron is master of them all

In pursuing green hydrogen fuel, electrochemical water-splitting emerges as the optimal method. A critical challenge in advancing this process is identifying a cost-effective electrocatalyst for oxygen evolution on the anode. Recent research has demonstrated the efficacy of first-row transition metal carbonates as catalysts for various oxidation reactions. In this study, Earth-abundant first-row transition metal carbonates were electrodeposited onto nickel foam (NF) electrodes and evaluated for their performance in the oxygen evolution reaction. The investigation compares the activity of these carbonates on NF electrodes against bare NF electrodes. Notably, Fe2(CO3)3/NF exhibited superior oxygen evolution activity, characterized by low overpotential values, i.e. Iron is master of them all (R. Kipling, Cold Iron, Rewards and Fairies, Macmillan and Co. Ltd., 1910). Comprehensive catalytic stability and durability tests also indicate that these transition metal carbonates maintain stable activity, positioning them as durable and efficient electrocatalysts for the oxygen evolution reaction.

Peroxymonosulfate activation by nanocomposites towards the removal of sulfamethoxazole: Performance and mechanism

Heterogeneous activation of peroxomonosulfate (PMS) has been extensively studied for the degradation of antibiotics. The cobalt ferrite spinel exhibits good activity in the PMS activation, but suffers from the disadvantage of low PMS utilization efficiency. Herein, the nanocomposites including FeS, CoS2, CoFe2O4 and Fe2O3 were synthesized by hydrothermal method and used for the first time to activate PMS for the removal of sulfamethoxazole (SMX). The nanocomposites showed superior catalytic activity in which the SMX could be completely removed at 40 min, 0.1 g L-1 nanocomposites and 0.4 mM PMS with the first order kinetic constant of 0.2739 min-1. The PMS utilization efficiency was increased by 29.4% compared to CoFe2O4. Both radicals and non-radicals contributed to the SMX degradation in which high-valent metal oxo dominated. The mechanism analysis indicated that sulfur modification, on one hand, enhanced the adsorption of nanocomposites for PMS, and promoted the redox cycles of Fe2+/Fe3+ and Co2+/Co3+ on the other hand. This study provides new way to enhance the catalytic activity and PMS utilization efficiency of spinel cobalt ferrite.

A Review of Transition Metal Boride, Carbide, Pnictide, and Chalcogenide Water Oxidation Electrocatalysts

Transition metal borides, carbides, pnictides, and chalcogenides (X-ides) have emerged as a class of materials for the oxygen evolution reaction (OER). Because of their high earth abundance, electrical conductivity, and OER performance, these electrocatalysts have the potential to enable the practical application of green energy conversion and storage. Under OER potentials, X-ide electrocatalysts demonstrate various degrees of oxidation resistance due to their differences in chemical composition, crystal structure, and morphology. Depending on their resistance to oxidation, these catalysts will fall into one of three post-OER electrocatalyst categories: fully oxidized oxide/(oxy)hydroxide material, partially oxidized core@shell structure, and unoxidized material. In the past ten years (from 2013 to 2022), over 890 peer-reviewed research papers have focused on X-ide OER electrocatalysts. Previous review papers have provided limited conclusions and have omitted the significance of "catalytically active sites/species/phases" in X-ide OER electrocatalysts. In this review, a comprehensive summary of (i) experimental parameters (e.g., substrates, electrocatalyst loading amounts, geometric overpotentials, Tafel slopes, etc.) and (ii) electrochemical stability tests and post-analyses in X-ide OER electrocatalyst publications from 2013 to 2022 is provided. Both mono and polyanion X-ides are discussed and classified with respect to their material transformation during the OER. Special analytical techniques employed to study X-ide reconstruction are also evaluated. Additionally, future challenges and questions yet to be answered are provided in each section. This review aims to provide researchers with a toolkit to approach X-ide OER electrocatalyst research and to showcase necessary avenues for future investigation.

First-Row Transition Metals for Catalyzing Oxygen Redox

Rechargeable zinc-air batteries are widely recognized as a highly promising technology for energy conversion and storage, offering a cost-effective and viable alternative to commercial lithium-ion batteries due to their unique advantages. However, the practical application and commercialization of zinc-air batteries are hindered by the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Recently, extensive research has focused on the potential of first-row transition metals (Mn, Fe, Co, Ni, and Cu) as promising alternatives to noble metals in bifunctional ORR/OER electrocatalysts, leveraging their high-efficiency electrocatalytic activity and excellent durability. This review provides a comprehensive summary of the recent advancements in the mechanisms of ORR/OER, the performance of bifunctional electrocatalysts, and the preparation strategies employed for electrocatalysts based on first-row transition metals in alkaline media for zinc-air batteries. The paper concludes by proposing several challenges and highlighting emerging research trends for the future development of bifunctional electrocatalysts based on first-row transition metals.

Interfacial Electron Redistribution of FeCo2S4/N-S-rGO Boosting Bifunctional Oxygen Electrocatalysis Performance

Developing bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for the development of zinc–air batteries (ZABs), but several challenges remain in terms of bifunctional activity. FeCo2S4/N-S-rGO was prepared by in situ homogeneous growth of bimetallic sulfide FeCo2S4 on N, S-doped reduced graphene oxide. FeCo2S4/N-S-rGO exhibits a half-wave potential of 0.89 V for ORR and an overpotential of 0.26 V at 10 mA cm−2 for OER, showing significantly bifunctional activity superior to Pt/C (0.85 V) and RuO2 (0.41 V). Moreover, the FeCo2S4/N-S-rGO assembled ZAB shows a superior specific capacity and a power density of 259.13 mW cm−2. It is demonstrated that the interfacial electron redistribution between FeCo2S4 nanoparticles and heteroatom-doped rGO matrix can efficiently improve the electrochemical performance of the catalyst. The results provide new insights into the preparation of high-capability composite catalysts combining transition metal sulfides with carbon materials for applications in ZABs.

CuCo2S4@B,N-Doped Reduced Graphene Oxide Hybrid as a Bifunctional Electrocatalyst for Oxygen Reduction and Evolution Reactions

In this report, a facile synthetic route is adopted for typically designing a hybrid electrocatalyst containing boron, nitrogen dual-doped reduced graphene oxide (B,N-rGO) and thiospinel CuCo₂S₄ (CuCo₂S₄@B,N-rGO). The electrocatalytic activity of the hybrid catalyst is tested with respect to oxygen evolution (OER) and oxygen reduction (ORR) reactions in alkali. Physicochemical characterizations confirm the unique formation of a reduced graphene oxide-non-noble-metal sulfide hybrid. Electrochemical evaluation by cyclic voltammetry (CV) and linear-sweep voltammetry (LSV) reveals that the CuCo₂S₄@B,N-rGO hybrid possesses enhanced ORR and OER activity compared to the B,N-rGO-free CuCo₂S₄ catalyst. The synthesized CuCo₂S₄@B,N-rGO hybrid demonstrates remarkable enhancement in catalytic performance with an improved onset potential (1.50 and 0.88 V) and low Tafel slope (112 and 73 mV dec^-1) for both OER and ORR processes, respectively. In addition, the catalyst exhibits a diminutive potential difference (0.81 V) between the potential corresponding to the 10 mA cm^-2 current density for OER and the half-wave potential for ORR. The superior catalytic activity and high durability of the hybrid material may be attributed to the synergistic effect arising from the metal sulfide and dual-doped reduced graphene oxide. The present study illuminates the possibility of using the dual-doped graphene oxide and metal sulfide hybrid as a competent bifunctional cathode catalyst for renewable energy application.

CoFeS2@CoS2 Nanocubes Entangled with CNT for Efficient Bifunctional Performance for Oxygen Evolution and Oxygen Reduction Reactions

Exploring bifunctional electrocatalysts to lower the activation energy barriers for sluggish electrochemical reactions for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are of great importance in achieving lower energy consumption and higher conversion efficiency for future energy conversion and storage system. Despite the excellent performance of precious metal-based electrocatalysts for OER and ORR, their high cost and scarcity hamper their large-scale industrial application. As alternatives to precious metal-based electrocatalysts, the development of earth-abundant and efficient catalysts with excellent electrocatalytic performance in both the OER and the ORR is urgently required. Herein, we report a core–shell CoFeS₂@CoS₂ heterostructure entangled with carbon nanotubes as an efficient bifunctional electrocatalyst for both the OER and the ORR. The CoFeS₂@CoS₂ nanocubes entangled with carbon nanotubes show superior electrochemical performance for both the OER and the ORR: a potential of 1.5 V (vs. RHE) at a current density of 10 mA cm⁻² for the OER in alkaline medium and an onset potential of 0.976 V for the ORR. This work suggests a processing methodology for the development of the core–shell heterostructures with enhanced bifunctional performance for both the OER and the ORR.

Template free-synthesis of cobalt-iron chalcogenides [Co0.8Fe0.2L2, L = S, Se] and their robust bifunctional electrocatalysis for the water splitting reaction and Cr(vi) reduction

The ease of production of materials and showing multiple applications are appealing in this modern era of advanced technology. This paper reports the synthesis of a pair of novel cobalt-iron chalcogenides [Co0.8Fe0.2S2 and Co0.8Fe0.2Se2] with enhanced electro catalytic activities. These ternary metal chalcogenides were synthesized by a one-step template-free approach via a hexamethyldisilazane (HMDS)-assisted synthetic method. Transient photocurrent (TPC) studies and electrochemical impedance spectra (EIS) of these materials showed free electron mobility. Their bifunctional activities were verified in both the electrochemical oxygen evolution reaction (OER) and in the electrochemical reduction of toxic inorganic heavy metal ions [Cr(vi)] in polluted water. The materials showed robust catalytic ability in the oxygen evolution reaction with minimum possible over potential (345 and 350 mV @ η10) as determined by linear sweep voltammetry and the lower Tafel values (52.4 and 84.5 mV dec-1) for Co0.8Fe0.2Se2 and Co0.8Fe0.2S2 respectively. Surprisingly, both the materials also showed an excellent activity towards electrochemical Cr(vi) reduction to Cr(iii). Besides the maximum current achieved for Co0.8Fe0.2S2, a minimum value for the Limit of detection (LOD) was obtained for Co0.8Fe0.2S2 (0.159 μg L-1) compared to Co0.8Fe0.2Se2 (0.196 μg L-1). We tested the durability of catalysts, the critical factor for the prolonged use of catalysts, through the recyclability measurements of these materials as catalysts. Both the catalysts presented outstanding durability and balanced electro catalytic activities for up to 1500 CV cycles, and chronoamperometry studies also confirmed exceptional stability. The enhanced catalytic activities of these materials are ascribed to the free electron movement, evidenced by the increased TPC measured and EIS. Therefore, the template-free synthesis of these electro catalysts containing non-noble metal illustrates the practical approach to develop such types of catalysts for multiple functions.

Metal-Supported Biochar Catalysts for Sustainable Biorefinery, Electrocatalysis and Energy Storage Applications: A Review

Biochar (BCH) is a carbon-based bio-material produced from thermochemical conversion of biomass. Several activation or functionalization methods are usually used to improve physicochemical and functional properties of BCHs. In the context of green and sustainable future development, activated and functionalized biochars with abundant surface functional groups and large surface area can act as effective catalysts or catalyst supports for chemical transformation of a range of bioproducts in biorefineries. Above the well-known BCH applications, their use as adsorbents to remove pollutants are the mostly discussed, although their potential as catalysts or catalyst supports for advanced (electro)catalytic processes has not been comprehensively explored. In this review, the production/activation/functionalization of metal-supported biochar (M-BCH) are scrutinized, giving special emphasis to the metal-functionalized biochar-based (electro)catalysts as promising catalysts for bioenergy and bioproducts production. Their performance in the fields of biorefinery processes, and energy storage and conversion as electrode materials for oxygen and hydrogen evolutions, oxygen reduction, and supercapacitors, are also reviewed and discussed.

Electrocatalysis in Alkaline Media and Alkaline Membrane-Based Energy Technologies

Hydrogen energy-based electrochemical energy conversion technologies offer the promise of enabling a transition of the global energy landscape from fossil fuels to renewable energy. Here, we present a comprehensive review of the fundamentals of electrocatalysis in alkaline media and applications in alkaline-based energy technologies, particularly alkaline fuel cells and water electrolyzers. Anion exchange (alkaline) membrane fuel cells (AEMFCs) enable the use of nonprecious electrocatalysts for the sluggish oxygen reduction reaction (ORR), relative to proton exchange membrane fuel cells (PEMFCs), which require Pt-based electrocatalysts. However, the hydrogen oxidation reaction (HOR) kinetics is significantly slower in alkaline media than in acidic media. Understanding these phenomena requires applying theoretical and experimental methods to unravel molecular-level thermodynamics and kinetics of hydrogen and oxygen electrocatalysis and, particularly, the proton-coupled electron transfer (PCET) process that takes place in a proton-deficient alkaline media. Extensive electrochemical and spectroscopic studies, on single-crystal Pt and metal oxides, have contributed to the development of activity descriptors, as well as the identification of the nature of active sites, and the rate-determining steps of the HOR and ORR. Among these, the structure and reactivity of interfacial water serve as key potential and pH-dependent kinetic factors that are helping elucidate the origins of the HOR and ORR activity differences in acids and bases. Additionally, deliberately modulating and controlling catalyst-support interactions have provided valuable insights for enhancing catalyst accessibility and durability during operation. The design and synthesis of highly conductive and durable alkaline membranes/ionomers have enabled AEMFCs to reach initial performance metrics equal to or higher than those of PEMFCs. We emphasize the importance of using membrane electrode assemblies (MEAs) to integrate the often separately pursued/optimized electrocatalyst/support and membranes/ionomer components. Operando/in situ methods, at multiscales, and ab initio simulations provide a mechanistic understanding of electron, ion, and mass transport at catalyst/ionomer/membrane interfaces and the necessary guidance to achieve fuel cell operation in air over thousands of hours. We hope that this Review will serve as a roadmap for advancing the scientific understanding of the fundamental factors governing electrochemical energy conversion in alkaline media with the ultimate goal of achieving ultralow Pt or precious-metal-free high-performance and durable alkaline fuel cells and related technologies.

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.

High-efficiency degradation of p-arsanilic acid and arsenic immobilization with iron encapsulated B/N-doped carbon nanotubes at natural solution pH

p-arsanilic acid (p-ASA) is still widely applied as feed additive in many countries. Accompanied with chemical reactions in the environment, p-ASA will release more toxic inorganic arsenic. In order to safely and efficiently treat p-ASA flow washing into the environment, iron encapsulated B/N-doped carbon nanotubes (Fe@C-NB) were fabricated and used as the catalyst for the degradation of p-ASA. The calcination temperature and the dose of the iron salt have significant effects on the structure and properties of the catalysts. We have produced a series of catalysts of the same type to facilitate the degradation of p-ASA. Under optimal conditions of material (Fe@C-NB) syntheses, both 95% degradation of p-ASA and 86% total arsenic immobilization can be obtained with oxidant (Peroxymonosulfate, PMS) and catalyst (Fe@C-NB) treatment after 60 min. The effects of oxidant types (peroxydisulfate (PDS), PMS, hydrogen peroxide (H₂O₂)), amount, initial solution pH, inorganic anion, and other reaction conditions were studied in the p-ASA removal. In this Fenton-like reaction, the Fe@C-NB exhibits high efficiency and excellent stability without complex preparation methods; besides, the advantages of short reaction time and natural reaction conditions in Fe@C-NB/PMS system will promote the practical application of Fenton-like.

Carbon-Based Composites as Electrocatalysts for Oxygen Evolution Reaction in Alkaline Media

This review paper presents the most recent research progress on carbon-based composite electrocatalysts for the oxygen evolution reaction (OER), which are of interest for application in low temperature water electrolyzers for hydrogen production. The reviewed materials are primarily investigated as active and stable replacements aimed at lowering the cost of the metal electrocatalysts in liquid alkaline electrolyzers as well as potential electrocatalysts for an emerging technology like alkaline exchange membrane (AEM) electrolyzers. Low temperature electrolyzer technologies are first briefly introduced and the challenges thereof are presented. The non-carbon electrocatalysts are briefly overviewed, with an emphasis on the modes of action of different active phases. The main part of the review focuses on the role of carbon–metal compound active phase interfaces with an emphasis on the synergistic and additive effects. The procedures of carbon oxidative pretreatment and an overview of metal-free carbon catalysts for OER are presented. Then, the successful synthesis protocols of composite materials are presented with a discussion on the specific catalytic activity of carbon composites with metal hydroxides/oxyhydroxides/oxides, chalcogenides, nitrides and phosphides. Finally, a summary and outlook on carbon-based composites for low temperature water electrolysis are presented.

Enhanced Oxygen Evolution Reaction with a Ternary Hybrid of Patronite-Carbon Nanotube-Reduced Graphene Oxide: A Synergy between Experiments and Theory

This work reports the hybridization of patronite (VS₄) sheets with reduced graphene oxide and functionalized carbon nanotubes (RGO/FCNT/VS₄) through a hydrothermal method. The synergistic effect divulged by the individual components, i.e., RGO, FCNT, and VS₄, significantly improves the efficiency of the ternary (RGO/FCNT/VS₄) hybrid toward the oxygen evolution reaction (OER). The ternary composite exhibits an impressive electrocatalytic OER performance in 1 M KOH and requires only 230 mV overpotential to reach the state-of-the-art current density (10 mA cm^-2). Additionally, the hybrid shows an appreciable Tafel slope with a higher Faradaic efficiency (97.55 ± 2.3%) at an overpotential of 230 mV. Further, these experimental findings are corroborated by the state-of-the-art density functional theory by presenting adsorption configurations, the density of states, and the overpotential of these hybrid structures. Interestingly, the theoretical overpotential follows the qualitative trend RGO/FCNT/VS₄ < FCNT/VS₄ < RGO/VS₄, supporting the experimental findings.

Nanostructured Iron Sulfide/N, S Dual-Doped Carbon Nanotube-Graphene Composites as Efficient Electrocatalysts for Oxygen Reduction Reaction

Nanostructured FeS dispersed onto N, S dual-doped carbon nanotube-graphene composite support (FeS/N,S:CNT-GR) was prepared by a simple synthetic method. Annealing an ethanol slurry of Fe precursor, thiourea, carbon nanotube, and graphene oxide at 973 K under N2 atmosphere and subsequent acid treatment produced FeS nanoparticles distributed onto the N, S-doped carbon nanotube-graphene support. The synthesized FeS/N,S:CNT-GR catalyst exhibited significantly enhanced electrochemical performance in the oxygen reduction reaction (ORR) compared with bare FeS, FeS/N,S:GR, and FeS/N,S:CNT with a small half-wave potential (0.827 V) in an alkaline electrolyte. The improved ORR performance, comparable to that of commercial Pt/C, could be attributed to synergy between the small FeS nanoparticles with a high activity and the N, S-doped carbon nanotube-graphene composite support providing high electrical conductivity, large surface area, and additional active sites.

Solventless synthesis of nanospinel Ni1−xCoxFe2O4 (0 ≤ x ≤ 1) solid solutions for efficient electrochemical water splitting and supercapacitance

The formation of solid solutions represents a robust strategy for modulating the electronic properties and improving the electrochemical performance of spinel ferrites. However, solid solutions have been predominantly prepared via wet chemical routes, which involve the use of harmful and/or expensive chemicals. In the present study, a facile, inexpensive and environmentally benign solventless route is employed for the composition-controlled synthesis of nanoscopic Ni_1−xCo_xFe₂O₄ (0 ≤ x ≤ 1) solid solutions. The physicochemical characterization of the samples was performed by p-XRD, SEM, EDX, XPS, TEM, HRTEM and UV-Vis techniques. A systematic investigation was also carried out to elucidate the electrochemical performance of the prepared nanospinels towards energy generation and storage. Based on the results of CV, GCD, and stability tests, the Ni_0.4Co_0.6Fe₂O₄ electrode showed the highest performance for the supercapacitor electrode exhibiting a specific capacitance of 237 F g⁻¹, superior energy density of 10.3 W h kg⁻¹ and a high power density with a peak value of 4208 W kg⁻¹, and 100% of its charge storage capacity was retained after 4000 cycles with 97% coulombic efficiency. For HER, the Ni_0.6Co_0.4Fe₂O₄ and CoFe₂O₄ electrodes showed low overpotentials of 168 and 169 mV, respectively, indicating better catalytic activity. For OER, the Ni_0.8Co_0.2Fe₂O₄ electrode exhibited a lower overpotential of 320 mV at a current density of 10 mA cm⁻², with a Tafel slope of 79 mV dec⁻¹, demonstrating a fast and efficient process. These results indicated that nanospinel ferrite solid solutions could be employed as promising electrode materials for supercapacitor and water splitting applications.

The formation of solid solutions represents a robust strategy for modulating the electronic properties and improving the electrochemical performance of spinel ferrites.

MOF-derived Co/Cu-embedded N-doped carbon for trifunctional ORR/OER/HER catalysis in alkaline media

In this report, we demonstrate a bimetallic Co/Cu-embedded N-doped carbon structure for trifunctional catalysis of oxygen reduction, oxygen evolution and hydrogen evolution reactions in alkaline media. A hybrid catalyst synthesized through a metal-organic framework-based process (M-NC-CoCu) enables an active trifunctional catalysis due to its multi-faceted favorable characteristics. It is believed that a range of catalytically active sites are formed through the approach including well-dispersed tiny CuCo2O4 phases, a high concentration of pyridinic and graphitic N, and Cu-Ox, Cu-Nx and Co-Nx moieties. In addition, a high-surface-area morphology with a high concentration of sp2 bonding, which is beneficial for facilitated electron conduction, further contributes to the performance as an electrocatalyst.

Recent advances of noble-metal-free bifunctional oxygen reduction and evolution electrocatalysts

Bifunctional oxygen reduction and evolution constitute the core processes for sustainable energy storage. The advances on noble-metal-free bifunctional oxygen electrocatalysts are reviewed.

Copper- and Nitrogen-Codoped Graphene with Versatile Catalytic Performances for Fenton-Like Reactions and Oxygen Reduction Reaction

Copper- and nitrogen-codoped reduced graphene oxide material (Cu/N-rGO) was prepared with a hydrothermal method. Its versatile catalytic performances were demonstrated toward the oxidative degradation of rhodamine B (RhB) and oxygen reduction reaction (ORR). The Cu and N codoping of graphene enhanced not only its activation ability toward H2O2, but also its electrocatalytic ability for ORR. It was observed that the use of 3%Cu/N-rGO together with 40 mmol·L−1 H2O2 and 4 mmol·L−1 Na2CO3 could remove more than 94% of the added RhB (30 mg·L−1) in 20 min through a catalytic Fenton-like degradation. Quenching experiments and electron paramagnetic resonance (EPR) measurements indicated that the main reactive species generated in the catalytic oxidation process were surface-bound •OH. The modified graphene also showed good electrocatalytic activity for ORR reaction in alkaline media through a four-electron mechanism. On the electrode of Cu/N-rGO, the ORR reaction exhibited an onset potential of −0.1 V and a half-wave potential of −0.248 V, which were correspondingly close to those on a Pt/C electrode. In comparison with a Pt/C electrode, the 3%Cu/N-rGO electrode showed much greater tolerance to methanol. Such outstanding catalytic properties are attributed to the abundant active sites and the synergism between Cu and N in Cu/N-rGO.

Influences of Multilayer Graphene and Boron Decoration on the Structure and Combustion Heat of Al3Mg2 Alloy

To improve the engine-driven performance of propellants, high-energy alloys such as Al and Mg are usually adopted as annexing agents. However, there is still room for improvement in the potential full utilization of alloy energy. In this study, we investigated how to improve combustion efficiency by decorating Al₃Mg₂ alloy with multilayer graphene and amorphous boron. Scanning electron microscopy and Raman tests showed that decorating with multilayer graphene and amorphous boron promoted the dispersion of Al₃Mg₂ alloy. The results showed that decorating with 1% boron and 2% multilayer graphene improved the combustion heat of Al₃Mg₂ alloy to 32.8 and 30.5 MJ/kg, respectively. The coexistence of two phases improved the combustion efficiency of the matrix Al₃Mg₂ alloy.

A NiRhS fuel cell catalyst - lessons from hydrogenase

We present a novel fuel cell heterogeneous catalyst based on rhodium, nickel and sulfur with power densities 5-28% that of platinum. The NiRhS heterogeneous catalyst was developed via a homogeneous model complex of the [NiFe]hydrogenases (H₂ases) and can act as both the cathode and anode of a fuel cell.

Phase Engineering of Iron-Cobalt Sulfides for Zn-Air and Na-Ion Batteries

Rechargeable batteries are promising platforms for sustainable development of energy conversion and storage technologies. Highly efficient multifunctional electrodes based on bimetallic sulfides for rechargeable batteries are extremely desirable but still challenging to tailor with controllable phase and structure. Here, we report a colloidal strategy to fabricate FeCo-based bimetallic sulfides on reduced graphene oxide (rGO), which are expected to display highly efficient oxygen electrocatalysis and sodium storage performances. Specifically, as-screened FeCo₈S₈ nanosheets (NSs) on rGO originating from suitable tailoring of the Co₉S₈ matrix with Fe at the atomic level exhibited a very low potential difference (0.77 V) at 10 mA cm^-2 and negligible voltage loss after 200 cycles as an air electrode for Zn-air batteries. For Na-ion batteries, FeCo₈S₈ NS/rGO demonstrated a superior high-rate capability (188 mAh g^-1 at 20 A g^-1) with long-term cycling stability. The bifunctional electrocatalytic property and sodium storage performance are attributed to not only the synergistic effect of Fe/Co but also the optimized catalytic activity and ion transport ability by the in situ rGO hybrid. This work demonstrates the potential applications of FeCo-based bimetallic sulfides as efficient electrode materials for both rechargeable Zn-air and Na-ion batteries.

Molten-Salt Media Synthesis of N-Doped Carbon Tubes Containing Encapsulated Co Nanoparticles as a Bifunctional Air Cathode for Zinc-Air Batteries

Cost efficient bifunctional air cathodes possessing high electrocatalytic activity are of great importance for the development of secondary Zn-air batteries. In this work, cobalt nanoparticles are encapsulated within a 3D N-doped open network of carbon tubes (Co@N-CNTs) by a molten-salt synthesis procedure conducted at a high temperature. Physical characterization demonstrates that Co@N-CNTs are comprised of Co particle inserted carbon tubes with mesoporous tube walls, providing significant active surface area for electrochemical reactions. High electrocatalytic activity of Co@N-CNTs towards both oxygen evolution and oxygen reduction reactions is due to its well-developed active surface and a synergistic effect between N-doped carbon and Co nanoparticles. Both primary and secondary Zn-air battery cells assembled using Co@N-CNTs as an air cathode show higher electrochemical performance than similar cells containing commercial Pt/C and Pt/C +RuO₂ , making the newly developed material a promising alternative to existing metal-based air cathodes.

A Humidity-Induced Nontemplating Route toward Hierarchical Porous Carbon Fiber Hybrid for Efficient Bifunctional Oxygen Catalysis

Hierarchical porous carbons (HPCs) are highly efficient supports for various remarkable catalytic systems. However, templates are commonly utilized for the preparation of HPCs, and the postremoval of the templates is uneconomical, time-consuming, and harmful for the environment in most cases. Herein, a new humidity-induced nontemplating strategy is developed to prepare 1D HPC with rich topologies and interconnected cavities for catalysis and energy storage applications. Porous electrospun nanofibers as calcination precursors are prepared via a humidity-induced phase separation strategy. A nitrogen-doped hierarchical porous carbon nanofiber (HPCNF), loading Co/Co₃ O₄ hetero-nanoparticles as exemplary nonprecious-metal active substance (Co/Co₃ O₄ @HPCNF), is fabricated through the subsequent hydrothermal and pyrolysis treatment. The internal mesopore and cavity structure can be simply controlled by varying environment humidity during the electrospinning process. Benefiting from the unique topology, Co/Co₃ O₄ @HPCNF exhibits superior bifunctional activity when being used as electrocatalysts for oxygen reduction/evolution reactions. Moreover, the hybrid catalyst also demonstrates a remarkable power density of 102.5 mW cm^-2 , a high capacity of 748.5 mAh g_Zn ^-1 , and long cycle life in Zinc-air batteries. The developed approach offers a facile template-free route for the preparation of HPCNF hybrid and can be extended to other members of the large polymer family for catalyst design and energy storage applications.

An Ultra-Sensitive Electrochemical Sensor for the Detection of Carcinogen Oxidative Stress 4-Nitroquinoline N-Oxide in Biologic Matrices Based on Hierarchical Spinel Structured NiCo2O4 and NiCo2S4; A Comparative Study

Various factors leads to cancer; among them oxidative damage is believed to play an important role. Moreover, it is important to identify a method to detect the oxidative damage. Recently, electrochemical sensors have been considered as the one of the most important techniques to detect DNA damage, owing to its rapid detection. However, electrode materials play an important role in the properties of electrochemical sensor. Currently, researchers have aimed to develop novel electrode materials for low-level detection of biomarkers. Herein, we report the facile hydrothermal synthesis of NiCo₂O₄ micro flowers (MFs) and NiCo₂S₄ micro spheres (Ms) and evaluate their electrochemical properties for the detection of carcinogen-causing biomarker 4-nitroquinoline n-oxide (4-NQO) in human blood serum and saliva samples. Moreover, as-prepared composites were fabricated on a glass carbon electrode (GCE), and its electrochemical activities for the determination of 4-NQO were investigated by using various electrochemical techniques. Fascinatingly, the NiCo₂S₄-Ms showed a very low detection limit of 2.29 nM and a wider range of 0.005 to 596.64 µM for detecting 4-NQO. Finally, the practical applicability of NiCo₂S₄-Ms in the 4-NQO spiked human blood serum and saliva samples were also investigated.

A supersalt-type copper(i)-thiolate cluster with applications for mechano/thermochromism and the oxygen evolution reaction

A new copper(i)-thiolate (Cu-S) cluster with a CsCl unit (1, [Cu₁₂(μ₄-SCH₃)₆(NH₃)₁₂][Cu₁₂(μ₄-SCH₃)₆Cl₁₂]) exhibited interesting mechanochromic and thermochromic luminescence properties. Additionally, heteroatom-rich 1 could also be used as an electrocatalyst for the oxygen evolution reaction in alkaline media. The supersalt-type Cu-S cluster for the first time realized mechano/thermochromic and electrocatalytic applications.

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.

Co8FeS8 wrapped in Auricularia-derived N-doped carbon with a micron-size spherical structure as an efficient cathode catalyst for strengthening charge transfer and bioelectricity generation

The main issues regarding the practical application of microbial fuel cells (MFCs) are the poor activity and tolerance of oxygen reduction reaction (ORR) catalysts in wastewater. In this study, Auricularia chelated with Co, Fe and S ions is used as a nitrogen (N)-enriched carbon source to prepare N-doped bimetallic sulfide (Co₈FeS₈)-embedded carbon spheres (Co₈FeS₈/NSC) using a hydrothermal method. The effects of various temperatures (800-950 °C) on the structure and catalytic activity of Co₈FeS₈/NSC catalysts are investigated. The MFC with a Co₈FeS₈/NSC (900 °C) cathode obtained the maximum power density of 1.002 W m^-2, which is higher than that of Pt/C (0.88 W m^-2). After 1440 h of operation, the power density of the Co₈FeS₈/NSC (900 °C) cathode only declined by 5.49%, indicating that the Co₈FeS₈ activity, charge transfer and O₂ transport were slightly influenced by the attached microbes and poisonous substances in the wastewater. The electrochemical results indicate that Co₈FeS₈/NSC (900 °C) mainly proceeds by a 4e^- ORR pathway, indicating that Co₈FeS₈ (Co²⁺ and Fe²⁺) wrapped in NSCs (carbon spheres) can trigger synergistic effects to provide more active sites and high electrical conductivity to achieve the rapid kinetics required for the ORR. Moreover, the porous structures of the NSCs (220.97 m² g^-1) with incorporated pyridinic N, pyrrolic N and graphitic N can provide abundant available channels for O₂ and OH^- transport to ensure the preferential accessibility of the reactant molecules to active sites. This indicates that Auricularia-derived Co₈FeS₈/NSC catalysts have great potential as alternatives for precious metal-based catalysts in neutral electrolyte MFCs.

Nitrogen and Sulfur Co-Doped Mesoporous Carbon Embedded with Co9 S8 Nanoparticles: Efficient Electrocatalysts for Hydrogen Evolution

Co₉ S₈ embedded, N,S co-doepd mesoporous carbon materials were synthesized by adopting CoCl₂ as the molten salt. In details, CoCl₂ and glucose were used as cobalt and carbon precursors, respectively, and thiourea was utilized as sulfur and nitrogen precursors. This synthetic process involved three steps, including hand-milling, carbonation, and acid leaching. The results of characterization exhibited that the final products had mesoporous structures, which also showed high nitrogen and sulfur contents. Moreover, the Co₉ S₈ nanoparticles dispersed evenly in the carbonaceous matrix. Furthermore, the calcining temperature could affect the porosities of the final products and the contents of the heteroatoms, which could further determine the electrocatalytic activities of these catalysts. When used as the electrocatalysts for hydrogen evolution reaction, the optimal catalyst, GTCo900, exhibited superior catalytic activities under acidic condition. The overpotential is 62 mV to afford a current density of 10 mA cm^-2 . Moreover, it could also reveal excellent stability for 12 h.