In situ evolution of highly dispersed amorphous CoOx clusters for oxygen evolution reaction

Structural and Compositional Optimization of Fe-Co-Ni Ternary Amorphous Electrocatalysts for Efficient Oxygen Evolution in Anion Exchange Membrane Water Electrolysis

Anion exchange membrane water electrolysis (AEMWE) offers a sustainable path for hydrogen production with advantages such as high current density, dynamic responsiveness, and low-cost electrocatalysts. However, the development of efficient and durable oxygen evolution reaction (OER) electrocatalysts under operating conditions is crucial for achieving the AEMWE. This study systematically investigated Fe-Co-Ni ternary amorphous electrocatalysts for the OER in AEMWE through a comprehensive material library system comprising 21 composition series. The study aims to explore the relationship between composition, degree of crystallinity, and electrocatalytic activity using ternary contours and binary plots to derive optimal catalysts. The findings reveal that higher Co and lower Fe contents lead to increased structural disorder within the Fe-Co-Ni system, whereas an appropriate amount of Fe addition is necessary for OER activity. It is concluded that the amorphous structure of Fe-Co3-Ni possesses an optimal ternary composition and degree of crystallinity to facilitate the OER. Post-OER analyses reveal that the optimized ternary amorphous structure induces structural reconstruction into an OER-favorable OOH-rich surface. The Fe-Co3-Ni electrocatalysts exhibit outstanding performances in both half-cells and single-cells, with an overpotential of 256 mV at 10 mA cm- 2 and a current density of 2.0 A cm- 2 at 1.89 V, respectively.

Crystalline/Amorphous Mo-Ni(OH)2/FexNiy(OH)3x+2y hierarchical nanotubes as efficient electrocatalyst for overall water splitting

The development of efficient bifunctional catalysts for overall water splitting is highly desirable and essential for the advancement of hydrogen technology. In this work, Mo-Ni(OH)2/FexNiy(OH)3x+2y with hierarchical nanotube structure is constructed on flexible carbon cloth (CC) through simple electrochemical deposition and hydrothermal method. The hollow tube-structure is in favor of both exposing active sites and enhancing mass transfer capability. Moreover, the doping of Mo can enhance the electronic conductivity of heterostructures. The interfacial interaction between amorphous and crystal can enhance effectively the charge transfer kinetics across the interface. Therefore, Mo-Ni(OH)2/FexNiy(OH)3x+2y can achieve a low overpotential of 57 mV for hydrogen evolution reaction (HER) and 229 mV for oxygen evolution reaction (OER) at 10 mA·cm-2. In addition, Mo-Ni(OH)2/FexNiy(OH)3x+2y needs a potential of only 1.54 V at 10 mA·cm-2 for overall water splitting, and retains for a long period of time (60 h) reliable. The work will provide a valuable approach to the construction of highly efficient electrocatalysts for overall water splitting.

In situ growth of NiCo-MOF and the derived NiCo2O4/NiCo2O4/Ni foam composite with a wire-penetrated-cage hierarchical architecture for an efficient oxygen evolution reaction

A NiCo2O4/NiCo2O4/Ni foam (NCO/NCO/NF) hybrid composite with a wire-penetrated-cage hierarchical structure was synthesized by in situ growth of bimetallic NiCo metal-organic frameworks (NiCo-MOF) on a NiCo layered double hydroxide (NiCo-LDH) nanowire-modified Ni foam (NF) surface and subsequent heat treatment in air. The NCO/NCO/NF hybrid composite shows higher specific surface area and more active sites than its individual components. The wire-penetrated-cage hierarchical structure of NCO/NCO/NF and the synergistic coupling of NCO hollow nanocages (NCO HNCs), NCO nanowires (NCO NWs) and NF provide a fast electron transfer path, improve the conductivity, accelerate the kinetic reaction rate, and enhance the structural stability. When assessed as an electrode for the oxygen evolution reaction (OER), the NCO/NCO/NF hybrid composite exhibits a low overpotential of 310 mV at 10 mA cm-2 and current density retention of 91% after a 100 h oxidation reaction, which indicates that it has excellent catalytic activity and durability in the electrocatalytic OER.

Development of starch-based amorphous CoOx self-supporting carbon aerogel electrocatalyst for hydrogen evolution

Hydrogen energy is turning into a major research topic in this complex and changing world. In recent years, more and more research has been done on transition metal oxides and biomass composites. In this study, potato starch and amorphous cobalt oxide were assembled into carbon aerogel by sol-gel method and high-temperature annealing (CoOx/PSCA). The connected porous structure of the carbon aerogel is conducive to HER mass transfer, and its structure can avoid the agglomeration of transition metals. It also has great mechanical properties and can be directly used as a self-supporting catalyst for electrolysis with 1 M KOH for hydrogen evolution, which showed excellent HER activity and yielded the effective current density of 10 mA cm^-2 at 100 mV overpotential. Electrocatalytic experiments further showed that the better performance of CoOx/PSCA for HER can be attributed to the high electrical conductivity of carbon and the synergistic effect of unsaturated catalytic sites on the amorphous CoOx cluster. The catalyst comes from a wide range of sources, is easy to produce, and has good long-term stability, so it can be used in large-scale production. This paper provides a simple and easy method to make biomass-based transition metal oxide composites for electrolyzing water to produce hydrogen.

Emerging Phosphate-Functionalized Co3O4/Kaolinite Composites for Enhanced Activation of Peroxymonosulfate

The Fenton-like reaction, as one of the most efficient strategies to generate radical species for the degradation of environmental pollutants, has attracted considerable attention. However, engineering low-cost catalysts with excellent activity by phosphate surface functionalization has seldom been used for the activation of peroxymonosulfate (PMS). Herein, emerging phosphate-functionalized Co₃O₄/kaolinite (P-Co₃O₄/Kaol) catalysts have been prepared by hydrothermal and phosphorization. Kaolinite nanoclay with rich hydroxyl groups plays a vital role in realizing phosphate functionalization. The results indicate that P-Co₃O₄/Kaol shows superior catalytic performance and excellent stability to the degradation of Orange II, which could be attributed to the existence of phosphate that promotes the adsorption of PMS and the electron transfer of Co²⁺/Co³⁺ cycles. Furthermore, the ^•OH radical was identified as the dominating reactive species for the degradation of Orange II compared to the SO₄^•- radical. This work could offer a novel preparation strategy for emerging functionalized nanoclay-based catalysts for effective pollutant degradation.

Understanding the Surface Reconstruction on Ternary Wx CoBx for Water Oxidation and Zinc-Air Battery Applications

Here, the synthesis of a series of pure phase metal borides is reported, including WB, CoB, WCoB, and W₂ CoB₂ , and their surface reconstruction is studied under the electrochemical activation in alkaline solution. A cyclic voltammetric activation is found to enhance the activity of the CoB and W₂ CoB₂ precatalysts due to the transformation of their surfaces into the amorphous CoOOH layer with a thickness of 3-4 nm. However, such surface transformation does not happen on the WB and WCoB due to their superior structure stability under the applied voltage, highlighting the importance of metal components for the surface reconstruction process. It is found that, compared with CoB, the W₂ CoB₂ surface shows a quicker reconstruction with a larger active surface area due to the selective leaching of the W from its surface. In the meantime, the metallic W₂ CoB₂ core underneath the CoOOH layer shows a better promotion of its oxygen evolution reaction (OER) performance than CoB. Therefore, the ternary W₂ CoB₂ shows better OER performance than the CoB, as well as the WB and WCoB. It is also found that the mixture of W₂ CoB₂ with Pt/C as the catalysts in air electrode for rechargeable Zn-air battery (ZAB), shows better performance than the IrO₂ -Pt/C couple-based ZAB.

Integrated Bifunctional Electrodes Based on Amorphous Co-Ni-S Nanoflake Arrays with Atomic Dispersity of Active Sites for Overall Water Splitting

Fabrication of amorphous electrocatalysts without noble metals for cost-effective full water splitting is highly desired but remains a substantial challenge. In the present work, we report a facile strategy for exploring integrated bifunctional electrocatalysts based on amorphous cobalt/nickel sulfide nanoflake arrays self-supported on carbon cloth, by tailoring competitive coordination of metal ions between glucose and 2-aminoterephthalic acid. Ultrahigh dispersion of binary metal active sites with balanced atomic distribution enables the optimization of catalytic properties for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in an alkaline solution. The obtained catalyst exhibits remarkably enhanced OER and HER activities as compared with its oxide counterpart and analogues with different Co/Ni ratios. It requires overpotentials of 296 and 192 mV to deliver a current density of 10 mA cm^-2 for the OER and HER, respectively; it retains 96.6 and 96.9% activity after 32 h of OER and 36 h of HER tests at 10 mA cm^-2, respectively. As directly used an anode and a cathode in an alkaline electrolyzer, a low cell voltage of 1.60 V could endow a water splitting current of 10 mA cm^-2, outperforming the benchmark RuO₂ and Pt/C-based electrolyzer at 1.72 V@10 mA cm^-2. The current synthetic strategy may provide more opportunities for the design and direct synthesis of amorphous catalysts for overall water splitting and beyond.

Electronegativity-Induced Charge Balancing to Boost Stability and Activity of Amorphous Electrocatalysts

Amorphization is an efficient strategy to activate intrinsically inert catalysts. However, the low crystallinity of amorphous catalysts often causes high solubility and poor electrochemical stability in aqueous solution. Here, a different mechanism is developed to simultaneously stabilize and activate the water-soluble amorphous MoS_x O_y via a charge-balancing strategy, which is induced by different electronegativity between the co-dopants Rh (2.28) and Sn (1.96). The electron-rich Sn prefers to stabilize the unstable apical O sites in MoS_x O_y through charge transfer, which can prevent the H from attacking. Meanwhile, the Rh, as the charge regulator, shifts the main active sites on the basal plane from inert Sn to active apical Rh sites. As a result, the amorphous RhSn-MoS_x O_y exhibits drastic enhancement in electrochemical stability (η₁₀ increases only by 12 mV) after 1000 cycles and a distinct activity (η₁₀ : 26 mV and Tafel: 30.8 mV dec^-1 ) for the hydrogen evolution reaction in acidic solution. This work paves a route for turning impracticably water-soluble catalysts into treasure and inspires new ideas to design high-performance amorphous electrocatalysts.

Ternary Oxide CuWO4/BiVO4/FeCoOx Films for Photoelectrochemical Water Oxidation: Insights into the Electronic Structure and Interfacial Band Alignment

Photoelectrochemical (PEC) water oxidation using ternary oxide systems has been considered a promising approach for investigating the effective utilization of sunlight and the production of green fuel. Herein, we report a ternary-oxide-based CuWO4/BiVO4/FeCoOx film deposited entirely by RF-magnetron sputtering using homemade ceramic targets. Our CuWO4/BiVO4 photoanode exhibits a significant photocurrent density of 0.82 mA cm-2 at 1.23 V vs RHE under AM 1.5G illumination, which is a record 382% increase compared to that of the bare CuWO4 film. To further boost the PEC performance, we deposited an ultrathin layer of amorphous FeCoOx cocatalyst, resulting in a triple CuWO4/BiVO4/FeCoOx heterojunction with a significant reduction in onset potential and a 500% increase in the photocurrent density of bare CuWO4. Experimental and theoretical approaches were used to provide insights into the interfacial band alignment and photoinduced charge carrier pathway across heterojunctions. Our results reveal noticeable interface potential barriers for charge carriers at the CuWO4/BiVO4 heterojunction, potentially limiting its application in tandem systems. Conversely, the deposition of the FeCoOx ultrathin layer over the CuWO4/BiVO4 heterojunction induces a p-n junction on the BiVO4/FeCoOx interface, which, when combined with the abundant FeCoOx oxygen vacancies, results in improved charge separation and transport as well as enhanced photoelectrochemical stability. Our study provides a feasible strategy for producing photocatalytic heterojunction systems and introduces simple tools for investigating interface effects on photoinduced charge carrier pathways for PEC water splitting.

FeII, CoII and NiII complexes based on 1-chloro-3-(pyridin-2-yl)imidazo[1,5-a]pyridine: synthesis, structures, single-molecule magnetic and electrocatalytic properties

Three complexes [Fe2(L)2Cl4] (1), [Co2(L)2Cl4] (2) and [Ni(L)2Cl2]·CH2Cl2 (3) were synthesized and characterized. Complex 1 exhibits a slow magnetic relaxation behaviour. Complexes 1–3 are catalytically active toward the OER.

Reusable citric acid modified V/AC catalyst prepared by dielectric barrier discharge for hydroxylation of benzene to phenol

A reusable and efficient citric acid modified V/AC catalyst for benzene hydroxylation was prepared using an environmentally benign DBD method.

Stabilizing Hydrous β-NiOOH for Efficient Electrocatalytic Water Oxidation by Integrating Y and Co into Amorphous Ni-Based Nanoparticles

A two-stage ball milling process was used to synthesize amorphous Ni_79.2Nb_12.5Y_8.3 and Ni_74.2Co₅Nb_12.5Y_8.3 nanoparticles from elemental powders. The two-stage ball milling process provides a scalable and industrially applicable method for producing non-metalloid amorphous nanoparticles. The amorphous nanoparticles displayed excellent catalytic performance toward the oxygen evolution reaction (OER) in 1 M KOH, displaying lower overpotentials than IrO₂ at 10 mA cm^-2. The addition of Co in the amorphous alloy reduced the overpotential to 288 mV at 10 mA cm^-2. The pairing of X-ray photoelectron spectroscopy and in situ X-ray absorption spectroscopy revealed that the improved OER activity of amorphous Ni_74.2Co₅Nb_12.5Y_8.3 was attributed to the catalytic synergy between Y and Co. The integration of Y supported proton-coupled electron-transfer processes that assisted with the electrostatic adsorption of OH^- and formation of oxyhydroxide species, while Co sites enabled metal-oxo bonding to prevent Ni overcharging and the stabilization of β-NiOOH. The catalytic synergy between Y and Co reduces the amount of Co needed to enhance the OER activity of Ni-based alloys and lessens the dependence on Co, which is in high demand in many renewable energy and storage applications.

Interface Engineering of Heterogeneous CeO2-CoO Nanofibers with Rich Oxygen Vacancies for Enhanced Electrocatalytic Oxygen Evolution Performance

The development of highly efficient and cheap electrocatalysts for the oxygen evolution reaction (OER) is highly desirable in typical water-splitting electrolyzers to achieve renewable energy production, yet it still remains a huge challenge. Herein, we have presented a simple procedure to construct a new nanofibrous hybrid structure with the interface connecting the surface of CeO₂ and CoO as a high-performance electrocatalyst toward the OER through an electrospinning-calcination-reduction process. The resultant CeO₂-CoO nanofibers exhibit excellent electrocatalytic properties with a small overpotential of 296 mV at 10 mA cm^-2 for the OER, which is superior to many previously reported nonprecious metal-based and commercial RuO₂ catalysts. Furthermore, the prepared CeO₂-CoO nanofibers display remarkable long-term stability, which can be maintained for 130 h with nearly no attenuation of OER activity in an alkaline electrolyte. A combined experimental and theoretical investigation reveals that the excellent OER properties of CeO₂-CoO nanofibers are due to the unique interfacial architecture between CeO₂ and CoO, where abundant oxygen vacancies can be generated due to the incomplete matching of atomic positions of two parts, leading to the formation of many low-coordinated Co sites with high OER catalytic activity. This research provides a practical and promising opportunity for the application of heterostructured nonprecious metal oxide catalysts for high-efficiency electrochemical water oxidation.

Cobalt coordination controlled carbon nanospheres formation and inclusion of amorphous Co3O4 and AuNPs: strongly enhanced oxygen evolution reaction with excellent mass activity

Carbon nanospheres integrated with AuNPs and amorphous Co3O4 were fabricated by making use of cobalt coordination with AuNP surface ligands, which exhibited an enhanced oxygen evolution reaction (OER) with excellent mass activity. Co2+ coordination with AuNP surface functional molecules significantly influenced the nanostructure formation and OER activity. Nanospheres of carbon with an optimum concentration of AuNPs and Co3O4 (2) showed strong OER activity. 2 exhibited a high current density (358 mA cm-2 at an applied potential of 1.59 V) and required a low overpotential (256 mV) to generate a geometric current density (10 mA cm-2) compared to commercial RuO2 (363 mV). Importantly, 2 showed high mass activity (1352.5 mA mg-1), 14 times higher than RuO2 (93.87 mA mg-1). The low Tafel slope (52.4 mV dec-1) and charge transfer resistance along with large double layer capacitance (Cdl = 20.1) of 2 suggest strong electronic communication between the catalyst and the electrode surface and facilitated fast charge transport. Chronoamperometric studies confirmed the excellent stability of the catalyst. The present work demonstrates that the electrocatalytic activity of earth-abundant amorphous metal oxides can be strongly enhanced by integrating metallic nanoparticles (NPs) and optimizing nanostructures.

CoOx @Co-NC Catalyst with Dual Active Centers for Enhanced Oxygen Evolution: Breaking Trade-Off of Particle Size and Metal Loading

Increasing the metal loading and downsizing the metal particle size are two effective ways to boost the electrochemical performance of catalysts. However, it is difficult to simultaneously increase the metal loading and reduce the particle size since isolated individual atoms are easy to aggregate into nanoparticles when increasing the metal loading. To tackle this contradiction, we report a bottom-up ligand-mediated strategy to facilely prepare ultrafine CoO_x nanoclusters anchored on a Co-N-containing carbon matrix (CoO_x @Co-NC). The co-exist of N and O atoms prevent Co atoms agglomerating into large particles and allowing the formation of ultrafine dispersed Co species with large Co loading (up to 20 wt.%). Since the relationship between ultrasmall size and large metal loading is well balanced, the CoO_x nanoclusters have no inhibitory effect, but facilitate the catalytic performance of Co-N₄ sites during OER process. Consequently, due to the synergistic effect of ultrafine CoO_x nanoclusters and Co-N₄ macrocycles, the as-synthesized CoO_x @Co-NC exhibit promising OER activity (η₁₀ =370 mV, Tafel plot=40 mV/dec), bettering than that of benchmark RuO₂ (η₁₀ =411 mV, Tafel plot=72 mV/dec). This ligand-mediated strategy to synthesize carbonaceous materials containing dual active centers with large metal loading is promising for developing active and stable catalysts for electrocatalytic applications.

Co/CoOx heterojunctions encapsulated N-doped carbon sheets via a dual-template-guided strategy as efficient electrocatalysts for rechargeable Zn-air battery

Developing highly efficient oxygen electrocatalysts is of vital importance for rechargeable Zn-air batteries (ZABs). Herein, Co/CoO_x nano-heterojunctions encapsulated into nitrogen-doped carbon sheets (NCS@Co/CoO_x) are fabricated via a dual-template-guided approach by using zeolitic imidazolate frameworks (ZIFs) as templates. The synergistic integration of structural and compositional advantages endows such catalyst with superior catalytic properties to benchmark noble-metal catalysts. To be specific, the hierarchical micro/mesopores affords massive mass transport channels and maximizes the exposure of accessible active sites, whereas the NCS matrix accelerates electron transfer and prevents the self-aggregation of active species during the electrocatalytic reaction. Moreover, abundant and synergistic Co-based active sites (CoO, Co₃O₄, Co-N_x) greatly promote the catalytic activity. As the cathode of both liquid and flexible solid-state ZABs, excellent device properties are achieved, outperforming those assembled with commercial Pt/C+RuO₂ catalyst. This work presents a feasible and cost-effective strategy for developing oxygen electrocatalysts derived from ZIFs templates.

Enhancing the Capacity and Stability by CoFe2O4 Modified g-C3N4 Composite for Lithium-Oxygen Batteries

As society progresses, the task of developing new green energy brooks no delay. Li-O₂ batteries have high theoretical capacity, but are difficult to put into practical use due to problems such as high overvoltage, low charge-discharge efficiency, poor rate, and cycle performance. The development of high-efficiency catalysts to effectively solve the shortcomings of Li-O₂ batteries is of great significance to finding a solution for energy problems. Herein, we design CoFe₂O₄/g-C₃N₄ composites, and combine the advantages of the g-C₃N₄ material with the spinel-type metal oxide material. The flaky structure of g-C₃N₄ accelerates the transportation of oxygen and lithium ions and inhibits the accumulation of CoFe₂O₄ particles. The CoFe₂O₄ materials accelerate the decomposition of Li₂O₂ and reduce electrode polarization in the charge–discharge reaction. When CoFe₂O₄/g-C₃N₄ composites are used as catalysts in Li-O₂ batteries, the battery has a better discharge specific capacity of 9550 mA h g⁻¹ (catalyst mass), and the cycle stability of the battery has been improved, which is stable for 85 cycles.

Fe(III) Ions-Assisted Aniline Polymerization Strategy to Nitrogen-Doped Carbon-Supported Bimetallic CoFeP Nanospheres as Efficient Bifunctional Electrocatalysts toward Overall Water Splitting

It remains an urgent demand and challenging task to design and fabricate efficient, stable, and inexpensive catalysts toward sustainable electrochemical water splitting for hydrogen production. Herein, we explored the use of Fe(III) ion-assisted aniline polymerization strategy to embed bimetallic CoFeP nanospheres into the nitrogen-doped porous carbon framework (referred CoFeP-NC). The as-prepared CoFeP-NC possesses excellent hydrogen evolution reaction (HER) performance with the small overpotential (η₁₀) of 81 mV and 173 mV generated at a current density of 10 mA cm^-2 in acidic and alkaline media, respectively. Additionally, it can also efficiently catalyze water oxidation (OER), which shows an ideal overpotential (η₁₀) of 283 mV in alkaline electrolyte (pH = 14). The remarkable catalytic property of CoFeP-NC mainly stems from the strong synergetic effects of CoFeP nanospheres and carbon network. On the one hand, the interaction between the two can make better contact between the electrolyte and the catalyst, thereby providing a large number of available active sites. On the other hand, it can also form a network to offer better durability and electrical conductivity (8.64 × 10^-1 S cm^-1). This work demonstrates an efficient method to fabricate non-noble electrocatalyst towards overall water splitting, with great application prospect.

Co/Ni-polyoxotungstate photocatalysts as precursor materials for electrocatalytic water oxidation

An open-core cobalt polyoxometalate (POM) [(A-α-SiW9O34)Co4(OH)3(CH3COO)3]8-Co(1) and its isostructural Co/Ni-analogue [(A-α-SiW9O34)Co1.5Ni2.5(OH)3(CH3COO)3]8-CoNi(2) were synthesized and investigated for their photocatalytic and electrocatalytic performance. Co(1) shows high photocatalytic O2 yields, which are competitive with leading POM water oxidation catalysts (WOCs). Furthermore, Co(1) and CoNi(2) were employed as well-defined precursors for heterogeneous WOCs. Annealing at various temperatures afforded amorphous and crystalline CoWO4- and Co1.5Ni2.5WO4-related nanoparticles. CoWO4-related particles formed at 300 °C showed substantial electrocatalytic improvements and were superior to reference materials obtained from co-precipitation/annealing routes. Interestingly, no synergistic interactions between cobalt and nickel centers were observed for the mixed-metal POM precursor and the resulting tungstate catalysts. This stands in sharp contrast to a wide range of studies on various heterogeneous catalyst types which were notably improved through Co/Ni substitution. The results clearly demonstrate that readily accessible POMs are promising precursors for the convenient and low-temperature synthesis of amorphous heterogeneous water oxidation catalysts with enhanced performance compared to conventional approaches. This paves the way to tailoring polyoxometalates as molecular precursors with tuneable transition metal cores for high performance heterogeneous electrocatalysts. Our results furthermore illustrate the key influence of the synthetic history on the performance of oxide catalysts and highlight the dependence of synergistic metal interactions on the structural environment.

In Situ/Operando Electrocatalyst Characterization by X-ray Absorption Spectroscopy

During the last decades, X-ray absorption spectroscopy (XAS) has become an indispensable method for probing the structure and composition of heterogeneous catalysts, revealing the nature of the active sites and establishing links between structural motifs in a catalyst, local electronic structure, and catalytic properties. Here we discuss the fundamental principles of the XAS method and describe the progress in the instrumentation and data analysis approaches undertaken for deciphering X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra. Recent usages of XAS in the field of heterogeneous catalysis, with emphasis on examples concerning electrocatalysis, will be presented. The latter is a rapidly developing field with immense industrial applications but also unique challenges in terms of the experimental characterization restrictions and advanced modeling approaches required. This review will highlight the new insight that can be gained with XAS on complex real-world electrocatalysts including their working mechanisms and the dynamic processes taking place in the course of a chemical reaction. More specifically, we will discuss applications of in situ and operando XAS to probe the catalyst's interactions with the environment (support, electrolyte, ligands, adsorbates, reaction products, and intermediates) and its structural, chemical, and electronic transformations as it adapts to the reaction conditions.

Preparation of Cu–Cu2O–CuO by solid combustion ignited by dielectric barrier discharge and its activity towards p-nitrophenol reduction

Dielectric barrier discharge induces solid powder combustion at room temperature and atmosphere to prepare a high-activity catalyst for p-nitrophenol reduction.

Graphene oxide induced assembly and crumpling of Co3O4 nanoplates

Cobalt (II, III) oxide (Co₃O₄) has been widely studied and applied in various fields, however, it suffers from slow mass and electron transfer during applications. Herein, crumpled Co₃O₄ and Co₃O₄/reduced graphene oxide (rGO) with tunable 2D-in-3D structures were prepared by combining spray pyrolysis with a graphene oxide (GO) template. The 2D Co₃O₄ nanoplates were interconnected with each other to form a 3D ball with many wrinkles, resulting in defect enrichment on the abundant boundaries of the nanosheets, which provided more active sites for catalytic reactions. In addition, the unique 2D-in-3D structure allowed fast mass transfer and structural stability. Furthermore, the assembled structure could be understood as being composed of uniformly distributed oxygen-containing functional groups pinning metal cations on the GO surface through electrostatic interaction, and the 2D structure of the GO enabled the in situ converted Co₃O₄ to grow along the GO surface with excellent dispersion. Taking advantage of the above, the Co₃O₄/rGO balls demonstrated an excellent oxygen evolution reaction performance, an overpotential of 298 mV at a current density of 10.0 mA cm^-2 and a current density of 115.9 mA cm^-2 at the overpotential of η = 500 mV.

Amorphous Catalysts and Electrochemical Water Splitting: An Untold Story of Harmony

In the near future, sustainable energy conversion and storage will largely depend on the electrochemical splitting of water into hydrogen and oxygen. Perceiving this, countless research works focussing on the fundamentals of electrocatalysis of water splitting and on performance improvements are being reported everyday around the globe. Electrocatalysts of high activity, selectivity, and stability are anticipated as they directly determine energy- and cost efficiency of water electrolyzers. Amorphous electrocatalysts with several advantages over crystalline counterparts are found to perform better in electrocatalytic water splitting. There are plenty of studies witnessing performance enhancements in electrocatalysis of water splitting while employing amorphous materials as catalysts. The harmony between the flexibility of amorphous electrocatalysts and electrocatalysis of water splitting (both the oxygen evolution reaction [OER] and the hydrogen evolution reaction [HER]) is one of the untold and unsummarized stories in the field of electrocatalytic water splitting. This Review is devoted to comprehensively discussing the upsurge of amorphous electrocatalysts in electrochemical water splitting. In addition to that, the basics of electrocatalysis of water splitting are also elaborately introduced and the characteristics of a good electrocatalyst for OER and HER are discussed.

Amorphous Oxide Nanostructures for Advanced Electrocatalysis

Amorphous oxides have attracted special attention as advanced electrocatalysts owing to their unique local structural flexibility and attractive electrocatalytic properties. With abundant randomly oriented bonds and surface-exposed defects (e.g., oxygen vacancies) as active catalytic sites, the adsorption/desorption of reactants can be optimized, leading to superior catalytic activities. Amorphous oxide materials have found wide electrocatalytic applications ranging from hydrogen evolution and oxygen evolution to oxygen reduction, CO₂ electroreduction and nitrogen electroreduction. The amorphous oxide electrocatalysts even outperform their crystalline counterparts in terms of electrocatalytic activity and stability. Despite of the merits and achievements for amorphous oxide electrocatalysts, there are still issues and challenges existing for amorphous oxide electrocatalysts. There are rarely reviews specifically focusing on amorphous oxide electrocatalysts and therefore it is imperative to have a comprehensive overview of the research progress and to better understand the achievements and issues with amorphous oxide electrocatalysts. In this minireview, several general preparation methods for amorphous oxides are first introduced. Then, the achievements in amorphous oxides for several important electrocatalytic reactions are summarized. Finally, the challenges and perspectives for the development of amorphous oxide electrocatalysts are outlined.

Heterostructured CoO-Co3O4 nanoparticles anchored on nitrogen-doped hollow carbon spheres as cathode catalysts for Li-O2 batteries

Lithium-oxygen batteries have received extensive attention due to their high theoretical energy density and environmental friendliness. Herein, CoO-Co3O4 nanoparticles coated on nitrogen-doped hollow carbon spheres (N-HC@CoO-Co3O4) are prepared by a simple method, and N-HC@CoO-Co3O4 when used as the cathode material for a lithium-oxygen battery shows high catalytic performance. The nitrogen-doped hollow carbon spheres not only ensure an ultra-high specific surface area for the accommodation of the Li2O2 discharge products but also provide more reactive sites. CoO-Co3O4 nanoparticles supported on the surface of the nitrogen-doped hollow carbon spheres can effectively catalyze the formation and decomposition of worm-like Li2O2. The batteries assembled with N-HC@CoO-Co3O4 catalysts exhibit reduced overpotential, improved cycling performance, and high rate capability. Ultra-high discharge capacities of 24 265 mA h g-1 at a current density of 300 mA g-1 and 3622 mA h g-1 at a current density of 1000 mA g-1 are obtained. With a cutoff capacity of 500 mA h g-1, the battery with an N-HC@CoO-Co3O4 electrode can reach more than 112 cycles. This research offers new insights into the design of heterostructured oxide catalysts for Li-O2 batteries.

Combining Co3S4 and Ni:Co3S4 nanowires as efficient catalysts for overall water splitting: an experimental and theoretical study

In the quest for mass production of hydrogen from water electrolysis, to develop highly efficient, stable and low-cost catalysts is still the central challenge. When designing a novel catalyst, it is necessary to optimize the exposure and accessibility of its active sites as well as the reaction kinetics. This can be realized by combining an appropriate chemical composition of the material, including doping with metal elements, and a properly nanostructured morphology offering a high surface contact. We report here on the design and performances of cobalt-based oxide and sulfide nanowires as catalysts that can be used for both hydrogen and oxygen evolution reactions (denoted HER and OER respectively) in the same compatible electrolyte. Following a sulfuration process, Co3O4 nanowires are entirely converted into Co3S4 nanowires showing greatly improved OER catalytic performances with an overpotential of 283 mV (instead of 371 mV for Co3O4) to deliver a current density of 10 mA cm-2. Besides, when doping the surface of these Co3S4 nanowires with small amounts of nickel, the resulting Ni:Co3S4 nanowires exhibit an HER overpotential of 199 mV to reach 10 mA cm-2. But most importantly, two-electrode electrolyzer cells combining Co3S4 and Ni:Co3S4 electrodes show operating voltages as low as 1.70 V at 10 mA cm-2 over 40 hours, a value that competes advantageously with the best reported catalysts in 1.0 M KOH. Meanwhile, density functional theory (DFT) calculations show that the free energy of the intermediates has been reduced after the introduction of sulfur and nickel atoms, which have smaller overpotentials and corresponding enhanced electrocatalytic performance. Our results open a new avenue in the quest for overall water splitting using electrochemical systems.

Research Advances of Amorphous Metal Oxides in Electrochemical Energy Storage and Conversion

Amorphous metal oxides (AMOs) have aroused great enthusiasm across multiple energy areas over recent years due to their unique properties, such as the intrinsic isotropy, versatility in compositions, absence of grain boundaries, defect distribution, flexible nature, etc. Here, the materials engineering of AMOs is systematically reviewed in different electrochemical applications and recent advances in understanding and developing AMO-based high-performance electrodes are highlighted. Attention is focused on the important roles that AMOs play in various energy storage and conversion technologies, such as active materials in metal-ion batteries and supercapacitors as well as active catalysts in water splitting, metal-air batteries, and fuel cells. The improvements of electrochemical performance in metal-ion batteries and supercapacitors are reviewed regarding the enhancement in active sites, mechanical strength, and defect distribution of amorphous structures. Furthermore, the high electrochemical activities boosted by AMOs in various fundamental reactions are elaborated on and they are related to the electrocatalytic behaviors in water splitting, metal-air batteries, and fuel cells. The applications in electrochromism and high-conducting sensors are also briefly discussed. Finally, perspectives on the existing challenges of AMOs for electrochemical applications are proposed, together with several promising future research directions.