NiCo2O4 Research Articles

3D-stacked electrospun iron-doped nickel cobalt oxide nanofibers as integrated electrodes for anion exchange membrane water electrolysis

The commercialization of anion-exchange membrane water electrolysis (AEMWE) requires the development of highly active, stable, and cheap anode catalysts for the oxygen evolution reaction (OER). In this study, we proposed electrospun iron-doped NiCo2O4 (NCO) nanofibers on nickel foam (NF) and evaluated the performances of the resulting samples (FeX-NCO/NF; X = iron loading in NCO (0, 5, 10, and 15 at %)) as unitized anodes for the OER. Among the fabricated electrodes, Fe10-NCO/NF exhibited the lowest overpotential of 352 mV at a current density of 50 mA cm−2 in a half-cell test owing to its improved intrinsic activity. In an AEMWE single-cell test, Fe10-NCO/NF as anode showed high current density (932 mA cm-2 at 1.8 V) and long-term stability for 150 h The improved AEMWE performance of Fe10-NCO/NF was attributed to efficient mass transport enabled by superhydrophilic three-dimensional porous structure featuring stacked nanofibers.

Origin of magnetism via cation vacancy defects in non-stoichiometric NiCo2O4 nanoparticles: A synchrotron-based x-ray absorption and x-ray magnetic circular dichroism spectroscopic study

The present study probes the effect of cation distributions in the structural, optical, electronic, and magnetic properties of mixed-valent inverse-spinel NiCo2O4 (NCO) nanoparticles (NPs). NCO NPs were prepared using the sol–gel combustion method and the grain size was obtained in the magnetic exchange length range assumed to be from single-ion anisotropy. The Raman and photoluminescence spectroscopies confirm the presence of an inverse-spinel structure with different oxidation states, and vibrating sample magnetometry clarifies the existence of ferromagnetism with the presence of magnetic anisotropy among the cations. These NPs annealed at a higher grain-growth temperature accumulate ferrimagnetic properties and produce magneto-crystalline anisotropy making NCO an assuring material for spintronic applications. A detailed x-ray absorption spectroscopy and x-ray magnetic circular dichroism studies reveal an indestructible correlation between the distribution of the present cations and the element-specific origin of ferrimagnetic behavior. Ni is found to be accountable for the magnetic moment and electronic conduction, whereas Co is associated mainly with the generation of the magnetic anisotropy even in the polycrystalline NP form. This describes the anti-ferromagnetic coupling between Co and Ni ions that is pivotal in demonstrating the exchange interaction between these cations. The above result signifies the site-dependent cation valence states for the magnetic properties, and the extent of growing conditions are related to such cation-site dysfunction. This depicts further tunability in NCO as a functional oxide material.

Synthesis of Amorphous Nickel-Cobalt Hydroxides for Ni-Zn Batteries.

In this work we developed a hydrothermal method for synthesizing amorphous Ni-Co hydroxide (NC(OH)) and in the subsequent step crystalline NiCo2O4 (NCO) has been produced using water as the solvent. For nickel-zinc batteries, NC(OH) was found to have superior performance to its NCO prepared by two-step process. The thermal stability analysis exhibited the optimum temperature to obtain the NC(OH), and NCO electrode materials. The XRD pattern showed mixed phases containing both Ni and Co hydroxides (during the initial step) and in the subsequent step (calcined) the formation of cubic spinel structure was noticed. For NC(OH), aggregated particles with irregular morphology were observed while clustered nanorod-like shapes were noticed for NCO samples. To be noted, that the nanorod morphology was obtained through a facile approach without employing any structure-directing agent. Both NC(OH) and NCO were employed as cathodes for Ni-Zn battery studies against Zn foil anode with a polyamide-based separator soaked in 6 M KOH saturated with ZnO additive was used as electrolyte. The Ni-Zn cell was fabricated in CR2032 coin cell configuration. The electrochemical studies such as cyclic voltammetry (CV) showed the characteristic redox peaks for NC(OH) sample exhibiting high peak current compared to its NCO counterpart. The NC(OH) had a capacity of 268 mAh g-1 against 120 mAh g-1 for NCO at a current density of 1 Ag-1. The cell was able to retain 85 % of the capacity at the end of 500 cycles and showed remarkable rate capability. The Ni-Zn battery presents energy and power densities of 428.8 Wh Kg-1 and 2.68 kW Kg-1, respectively surpassing the normal values reported for aqueous rechargeable batteries. Owing to the presence of Ni and Co in hydroxide form (reduced crystallinity) the NC(OH) sample showed improved electrochemical activity. This work provides a facile approach and effective strategy for developing bimetallic hydroxides for optimal energy storage performance.

Graphene Oxide Decorated with Nickel Cobaltite Nanoparticles as an Adsorbent for Cationic Methyl Green Dye: Kinetic, Isotherm, and Thermodynamic Studies

‎تم في هذه الدراسة ، تزيين ‏رقائق أكسيد الجرافين (‏GO‏) بجسيمات ‏كوبلتيت النيكل النانوية ‏NiCo2O4‎‏(‏NC‏) عن طريق الترسيب في ‏الموقع ، وتم استخدام المتراكب ‏المحضر (‏NC: GO‏) كسطح ماز لإزالة ‏صبغة الميثيل الخضراء ( ‏MG‏) من ‏المحاليل المائية. تم التحقق من ‏التغطية الناجحة لأوكسيد الجرافين ‏بجزيئات كوبلتيت النيكل النانوية ‏‏(‏NC‏) باستخدام دراسات ‏FT-IR‏ وحيود ‏الأشعة السينية (‏XRD‏). كانت أحجام ‏الجسيمات البلورية لل ‏NC‏ و ‏ لل ‏GO‏ المزين ب NCهي ‏‎10.53‎‏ نانوميتر ‏‏9.30 نانومتر على التوالي. تم دراسة ‏تأثير العديد من العوامل التجريبية ‏، بما في ذلك زمن التلامس ، وكمية ‏السطح الماز ، ودرجة الحرارة. كان ‏وقت التلامس الأمثل وكمية السطح 120 ‏دقيقة و 3 مجم / لتر على التوالي. ‏تتلائم بيانات الامتزاز بشكل أفضل مع ‏ايزوثيرم ‏Freundlich‏. تم استخدام ‏أربعة نماذج حركية لتتبع عملية ‏الامتزاز: معادلة زائفة من الدرجة ‏الأولى ، ومعادلة زائفة من الدرجة ‏الثانية ، ومعادلة الانتشار داخل ‏الجسيمات ، ومعادلة بويد. أظهرت ‏نمذجة البيانات التجريبية أن حركية ‏الامتزاز كانت ممثلة بشكل جيد ‏بنموذج الرتبة الثانية الزائفة (‏R2 ‎‎= 0.9945‎‏) مع معدل ثابت سرعة يبلغ 3.2 ‏‏× 10 - 3 (جم / مجم. دقيقة). يتم ‏امتصاص صبغة ‏MG‏ تدريجيًا بواسطة ‏الجسيمات النانوية ‏NC‏ من خلال ‏الانتشار داخل الجسيمات ويتم ‏الاحتفاظ بها بعد ذلك في مسام أصغر. ‏أظهرت قيم التحليل الديناميكي ‏الحراري أن عملية امتزاز صبغة ‏MG‏ ‏كانت ماصة للحرارة بطبيعتها ، و ‏تلقائية وعملية الامتزاز فيزيائية. الكلمات المفتاحية: الانتشار داخل الجسيمات ، المسافات البينية، النموذج الزائف من الدرجة الأولى ، معادلة بويد

Enhanced catalytic activity of novel sea urchin-like spinel for advanced electrochemical energy conversion

Through precise morphological engineering, novel sea urchin-like spinel NiCo2O4 (NCO) was successfully synthesized and thoroughly investigated as a bifunctional electrode for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In contrast to traditional NCO, the distinctive scattered nanofiber microstructure of NCO prepared via hydrothermal at 100 ℃ (HT100) increases the specific surface area, introduces more oxygen vacancies, reduces the bandgap, enhances the diffusion, adsorption, and dissociation processes of oxygen molecules, thereby promoting rapid electron transfer and augmenting the number of active sites for both ORR and OER. At 800 °C, under the ORR model, NCO-HT100 exhibits an impressive output performance of 920 mW cm−2, surpassing traditional NCO by 47.8 %. Simultaneously, under the OER model, NCO-HT100 achieves a current density of 134.29 mA cm−2. Compared with conventional NCO, sea urchin-like NCO-HT100 displays lower Tafel slopes and overpotentials in alkaline solution at room temperature, indicating superior OER performance. These findings highlight that the sea urchin-like NCO-HT100 stands out as an advanced bifunctional electrode material for both ORR and OER. The insights gained from this research provide pivotal guidance for the future development of multifunctional electrode materials in energy conversion device applications.

Oxygen Vacancy-Induced Low-Valence reactive species enabling High-Efficient nonenzymatic glucose detection

NiCo2O4 (NCO), a typical spinel-type transition metal oxide, emerges as a promising candidate for non-electroenzymatic glucose sensors because of its stable structure and low overpotential. However, the practical applications of NCO are hindered by its limited intrinsic activity for glucose detection. Herein, we intentionally incorporated low-valence redox species into NCO nanowires by modulating the oxygen vacancies (VO-NCO NWs), thereby facilitating glucose oxidation reactivity. The concentration of low-valence species increases with the generated oxygen vacancies, which enriches the reactive redox species and enhances the intrinsic electrical conductivity, thereby improving the catalytic activity. Consequently, the optimized VO-NCO NWs exhibit highly efficient glucose detection with high sensitivity up to 19.65 mA·mM−1·cm−2, which is 4.6 times higher than that of the pristine NCO NWs, as well as a low limit of detection (LOD) of 0.15 μM. Furthermore, a flexible miniaturized three electrode (FMTE) assembled with optimized VO-NCO NWs provides a high sensitivity of 15.89 mA·mM−1·cm−2 and a low LOD of 0.18 μM in synthetic sweat. Under various bending conditions, the FMTE demonstrates good mechanical flexibility, with no discernible alterations in the response current. These findings provide a promising protocol for the dynamic monitoring of sweat composition to reveal human physiological health status.

High‐Performance NiCo2O4/Graphene Quantum Dots for Asymmetric and Symmetric Supercapacitors with Enhanced Energy Efficiency

AbstractFor the sustainable growth of future generations, energy storage technologies like supercapacitors and batteries are becoming more and more common. However, reliable and high‐performance materials’ design and development is the key for the widespread adoption of batteries and supercapacitors. Quantum dots with fascinating and unusual properties are expected to revolutionize future technologies. However, while the recent discovery of quantum dots honored with a Nobel prize in Chemistry, their benefits for the tenacious problem of energy are not realized yet. In this context, herein, chemical‐composition tuning enabled exceptional performance of NiCo2O4(NCO)/graphene quantum dots (GQDs) is reported, which outperform the existing similar materials, in supercapacitors. A comprehensive study is performed on the synthesis, characterization, and electrochemical performance evaluation of highly functional NCO/GQDs in supercapacitors delivering enhanced energy efficiency. The high‐performance, functional NCO/GQDs electrode materials are synthesized by the incorporation of GQDs into NCO. The effect of variable amount of GQDs on the energy performance characteristics of NCO/GQDs in supercapacitors is studied systematically. In‐depth structural and chemical bonding analyses using X‐ray diffraction (XRD) and Raman spectroscopic studies indicate that all the NCO/GQDs composites crystallize in the spinel cubic phase of NiCo2O4 while graphene integration evident in all the NCO/GQDs. The scanning electron microscopy imaging analysis reveals homogeneously distributed spherical particles with a size distribution of 5–9 nm validating the formation of QDs. The high‐resolution transmission electron microscopy analyses reveal that the NCOQDs are anchored on graphene sheets, which provide a high surface area of 42.27 m2g−1 and high mesoporosity for the composition of NCO/GQDs‐10%. In addition to establishing reliable electrical connection to graphene sheets, the NCOQDs provide reliable 3D‐conductive channels for rapid transport throughout the electrode as well as synergistic effects. Chemical‐composition tuning, and optimization yields NCO/GQDs‐10% to deliver the best specific capacitance of 3940 Fg−1 at 0.5 Ag−1, where the electrodes retain ≈98% capacitance after 5000 cycles. The NCO/GQD‐10%//AC asymmetric supercapacitor device demonstrates outstanding energy density and power density values of 118.04 Wh kg−1 and 798.76 W kg−1, respectively. The NCO/GQDs‐10%//NCO/GQDs‐10% symmetric supercapacitor device delivers excellent energy and power density of 24.30 Wh kg−1 and 500 W kg−1, respectively. These results demonstrate and conclude that NCO/GQDs are exceptional and prospective candidates for developing next‐generation high‐performance and sustainable energy storage devices.

The impact of temperature and frequency on negative capacitance and dielectric attributes in NiCo2O4 bulk ceramic

This paper presents a complete analysis of the electrical and dielectric characteristics of NiCo2O4 (NCO) bulk ceramic synthesized by the co-precipitation process as a future electronic device material. The structural analysis following the synthesis process revealed the formation of cubic-phase spinel NCO in the shape of nanospheres, with an approximate diameter of 25 nm. The present study aimed to examine the relationship between capacitance and conductance for the NCO under investigation, focusing on their frequency and temperature dependencies. The frequency range of interest ranged from 100 Hz to 1.5 MHz, while the temperature range considered was from 300 K to 450 K. The C/f plot has exhibited the phenomenon of negative capacitance, which may be attributed to the augmentation of polarization and the incorporation of additional minority carriers inside the structure. The dielectric parameters, such as permittivity, dielectric loss, alternating current conductance, and electrical modulus, were determined by capacitance and conductance measurements, taking into account their frequency and temperature reliance. All dielectric calculations were influenced by negative capacitance measurements. The negative capacitance feature of NiCo2O4 is attributed to the ferroelectric properties of the Ni and Co elements in its composition. In conclusion, this paper has made a valuable contribution to the existing body of literature by enhancing our comprehension of the negative capacitance behavior and dielectric characteristics of the NCO.

Robust room temperature perpendicular magnetic anisotropy and anomalous Hall effect of sputtered NiCo2O4 film

Inverse spinel ferrimagnetic NiCo2O4 (NCO) exhibits volatile physical properties due to the complex ion/valence occupation, which complicates the study its intrinsic properties. In this work, robust room temperature perpendicular magnetic anisotropy (PMA) is distinctly observed in high-quality RF-sputtered NCO film down to 3 uc (2.4 nm), confirmed by the room temperature anomalous Hall effect. The NCO films show a good metallic conductivity with a dimensional driven metal-insulator transition. The scaling relation between anomalous Hall conductivity ( σxy ) and the longitudinal conductivity ( σxx ) reveals the dirty metal behavior in conjunction with the contribution of intrinsic Berry phase or disorder-enhanced electron correlation contribute to the anomalous Hall effect for thick films while the dirty scaling law dominates for the thin films. This work introduces an oxide candidate with robust room temperature PMA as well as massive production ability for the functional spintronic applications.

Synergistic effects of defects and surface engineering in Ni-Co metal oxides to improve the high performance of Zn-ion hybrid supercapacitors

NiCo2O4 (NCO) is an auspicious pseudocapacitor material for high energy density zinc-ion hybrid supercapacitors (ZHSCs), but its low intrinsic conductivity and significant volume expansion seriously hinder its electrochemical performance. Here, we develop a nitrogen (N) doped and oxygen-vacancy-rich (Ov) NiCo oxide nanolines grown in-situ on the carbon cloth (CC) named N-Ov-NCO@CC. The morphology and structure of N-Ov-NCO@CC were characterized by XRD, XPS, EPR, SEM and TEM. It can be clearly observed that N-Ov-NCO@CC nanowires are composed of many tiny nanoparticles, and this unique structure provides abundant gaps at the microscopic scale, providing ample sites for the attachment of electrolyte ions. Due to N-functionalization, synergistic effects of doping, defect and surface engineering are realized. As a result, N-Ov-NCO@CC exhibits significantly enhanced electrochemical performance. The N-Ov-NCO@CC single electrode exhibits a high capacitance of 993.0 F/g (496.5C/g) at 1 A/g and excellent cycle stability with a capacitance retention rate of 98 % after 5000 cycles. In addition, the assembled N-Ov-NCO@CC//Zn-ZHSC operates stably in the voltage range of 1.2–2.0 V. A high specific capacitance of 484.4 F/g is available at current densities of 1 A/g. In addition, it still has a high cycle life with a capacitance retention rate of 97.1 % after 10,000 cycles and a high specific energy/power (50.3 Wh/kg at 300.2 W/kg). Density function theory (DFT) verification shows that N-Ov-NCO has higher conductivity than Ov-NCO and pristine NCO, which is conducive to improving electrochemical performance. This work provides a new idea for developing stable electrode materials for new ZHSCs.

Dual efficiency enhancement in overall water splitting with defect-rich and Ru atom-doped NiFe LDH nanosheets on NiCo2O4 nanowires

The development of layered double hydroxides (LDHs) as bifunctional catalysts for efficient overall water splitting by controlling the composition and structure of the material remains challenging. In this study, defect-rich and Ru-doped NiFe LDH nanosheet shells on NiCo2O4 (NCO) nanowires were successfully synthesized using a hydrothermal method, followed by alkaline etching. The resulting def-Ru-NiFe LDH/NCO (def = defects) catalyst exhibited remarkable catalytic activity with overpotentials of 122 and 225 mV for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, at a current density of 10 mA cm−2. Density functional theory calculations demonstrated that atomic vacancy defects and the rational incorporation of Ru single atoms in def-Ru-NiFe LDH/NCO induced the regulation of the electronic structure and optimized the adsorption energies, thus enhancing the OER and HER performances. Particularly, an electrolyzer utilizing def-Ru-NiFe LDH/NCO exhibited exceptional performance, achieving cell voltages of 1.58 and 1.46 V in 1 M KOH at 25 and 75 °C, respectively. Moreover, the catalyst exhibited outstanding stability during 60 h of operation at a high applied voltage and temperature (75 °C). These results highlight the potential of def-Ru-NiFe LDH/NCO for hydrogen production.

Tunable anomalous Hall effect and Curie temperature in perpendicular magnetic anisotropic lanthanum doped NiCo2O4 film

Perpendicular magnetic anisotropic NiCo2O4 (NCO) films show volatile physical properties due to the complicated ion occupation/valence disproportion, making it feasible to be manipulated. In this work, the tunable anomalous Hall effect is observed in high-quality lanthanum (La) doped NCO films grown by the off-axis RF sputtering technique. It reveals that the longitudinal resistance (Rxx) significantly increases as the growth of La doping level, while the Curie temperature (TC) decreases with the rising of La doping level. A universal scaling law between the longitudinal conductance (σxx) and the anomalous Hall conductance (σxy), including the terms of dirty scaling mechanism, intrinsic contribution, and side jump, is proposed to explain the observed anomalous Hall effect. Additionally, an intrinsic linear relation between σxx and TC is revealed. The evolution of anomalous Hall resistance (RA), TC, and Rxx is closely related to the complex valence state/occupation of Ni ions induced by La doping. This work provides a strategy to manipulate the physical properties of NCO film, making it a potential material for spintronic applications.

NiCo2O4/MXene Hybrid as an Efficient Bifunctional Electrocatalyst for Oxygen Evolution and Reduction Reaction

AbstractFor the advancement of electrochemical energy conversion and storage technologies, bifunctional electrocatalysts are crucial for efficiently driving both the oxygen evolution (OER) and reduction reactions (ORR). Cobalt‐based spinel oxides are a class of promising bifunctional electrocatalysts. However their low electrical conductivity and stability may hinder further improvement. A novel composite material composed of NiCo2O4 nanoparticles integrated with emerging two dimensional MXene nanosheets (NiCo2O4/MXene) was developed. The successful integration of NiCo2O4 with MXene brings about a number of attractive structural features. This includes synergistic effects between NiCo2O4 and MXene, highly accessible surface areas, complete exposure of numerous active sites, and excellent electronic conductivity, all of which collectively contribute to the desirability of composite material for OER and ORR. The synthesized NiCo2O4/MXene composite showed extraordinary OER electrocatalytic activity with a lower overpotential of 360 mV at a current density of 10 mA/cm2, and a small Tafel slope of 64 mV/dec compared to NiCo2O4, MXene and NiCo2O4+MXene (physically mixed). Additionally, NiCo2O4/MXene displays an ORR limiting current density of −4 mA/cm2 and exhibited highest onset potential and half wave potential of 0.92 V and 0.72 V vs. RHE, respectively, for the ORR in alkaline media compared to NiCo2O4, MXene and NiCo2O4+MXene (physically mixed).

Atomic-Scale Structural Properties in NiCo2O4/CuFe2O4 Bilayer Heterostructures on (001)-MgAl2O4 Substrate Regulated by Film Thickness.

Changing film thickness to manipulate microstructural properties has been considered as a potential method in practical application. Here, we report that atomic-scale structural properties are regulated by film thickness in an NiCO2O4(NCO)/CuFe2O4(CFO) bilayer heterostructure prepared on (001)-MgAl2O4 (MAO) substrate by means of aberration-corrected scanning transmission electron microscopy (STEM). The misfit dislocations at the NCO/CFO interface and antiphase boundaries (APBs) bound to dislocations within the films are both found in NCO (40 nm)/CFO (40 nm)/MAO heterostructures, contributing to the relaxation of mismatch lattice strain. In addition, the non-overlapping a/4[101]-APB is found and the structural transformation of this kind of APB is resolved at the atomic scale. In contrast, only the interfacial dislocations form at the interface without the formation of APBs within the films in NCO (10 nm)/CFO (40 nm)/MAO heterostructures. Our results provide evidence that the formation of microstructural defects can be regulated by changing film thickness to tune the magnetic properties of epitaxial bilayer spinel oxide films.

A versatile non-precious metal based electrode material endowed by layer-on-layer structure for methanol oxidation and supercapacitor applications

A high-performance non-noble metal-based electrode is the need of the hour to resolve the challenge of huge energy demand. Energy conversion and storage devices are the two ways to tackle this challenge. In this context, porous and non-noble metal-based electrodes NiCo2O4 (NCO), NiCo2O4/NiO (CNO) and NiCo2O4/NiO/rGO (CNOG) are developed as a bifunctional electrode for supercapacitor and methanol fuel cell applications. The binary composite of NiCo2O4 with NiO increases the redox sites and enhances its electrochemical activity. The low conductivity and problem of aggregation of transition metal oxides are overcome by developing a hybrid nanocomposite of NiCo2O4/NiO with reduced graphene oxide (rGO). The layer-on-layer morphology of CNOG, and the interfacial interactions among NiCo2O4 nanoflakes, NiO nanoparticles and rGO nanosheets increase the specific surface area of the hybrid, which leads to enhanced ion penetration into the active sites. CNOG acts as a potential anode catalyst for methanol oxidation with excellent structural stability. It exhibits a high methanol oxidation current density with low onset potential and faster kinetics. Symmetric supercapacitor CNOG//CNOG delivers specific capacitance of 59.4989 F/g, energy and power density of 6.69 Wh/kg and 698 W/kg respectively at 3 M KOH aqueous electrolyte. The solid-state symmetric supercapacitor (SSSC) using PVA/KOH electrolyte allows broader potential window, thereby outperforming the aqueous electrolyte. The SSSC exhibits specific capacitance of 88.8 F/g, energy and power density 20.84 Wh/kg and 1003 W/kg respectively at the same current density.

Spin reorientation transition in (110)-oriented NiCo2O4 epitaxial thin films

Magnetic anisotropy is an important character for magnetic materials. In this work, magnetic anisotropy of (110)-oriented ferrimagnetic NiCo2O4 (NCO) thin films deposited epitaxially on MgAl2O4 substrates by pulsed laser deposition is studied and compared with (001)-oriented NCO films. While the (001)-oriented films show a perpendicular magnetic anisotropy with the out-of-plane [001] direction as the magnetic easy axis, a jump in magnetic hysteresis loop is observed for the (110)-oriented films with a field applied vertically along the out-of-plane [110] direction. This jump in hysteresis loop is associated with a spin reorientation transition, depending on the applied field and temperature. Magnetic force microscopy reveals that this spin reorientation develops as domains nucleate, grow, and coalesce. This spin reorientation transition is discussed in terms of the competition between different magnetic anisotropy in an external field.

Asymmetric Electrode Design for High-Area Capacity and High-Energy Efficiency Hybrid Zn Batteries.

Compared to Zn-air batteries, by integrating Zn-transition metal compound reactions and oxygen redox reactions at the cell level, hybrid Zn batteries are proposed to achieve higher energy density and energy efficiency. However, attaining relatively higher energy efficiency relies on controlling the discharge capacity. At high area capacities, the proportion of the high voltage section can be neglected, resulting in a lower energy efficiency similar to that of Zn-air batteries. Here, a high-loading integrated electrode with an asymmetric structure and asymmetric wettability is fabricated, which consists of a thick nickel hydroxide (Ni(OH)2) electrode layer with vertical array channels achieving high capacity and high utilization, and a thin NiCo2O4 nanopartical-decorated N-doped graphene nanosheets (NiCo2O4/N-G)catalyst layer with superior oxygen catalytic activity. The asymmetric wettability satisfies the wettability requirements for both Zn-Ni and Zn-air reactions. The hybrid Zn battery with the integrated electrode exhibits a remarkable peak power density of 141.9mWcm-2, superior rate performance with an energy efficiency of 71.4% even at 20mAcm-2, and exceptional cycling stability maintaining a stable energy efficiency of ≈84% at 2mAcm-2 over 100 cycles (400 h).

Design and investigation of photoelectrochemical water treatment using self-standing Fe3O4/NiCo2O4 photoanode: In-situ H2O2 generation and fenton-like activation

Photoelectrocatalytic advanced oxidation processes (PEC AOPs) show great promise for solar-driven water treatment due to their energy efficiency and environmental compatibility. This study focuses on two key aspects: 1) creating an efficient photoanode and 2) utilizing the cathodic process simultaneously to enhance water treatment. Herein, a self-standing photoanode with stemmed nanospikes made from Fe3O4@NiCo2O4 (FNCO) was developed and seamlessly integrated into a PEC system. FNCO photoanode significantly improves PEC cell performance, using half the energy (12 Wh/g-pollutant) and achieving a four-fold higher rate constant (7.9×10−2 s−1) compared to NiCo2O4 (NCO). The in-situ generation of H2O2 and its Fenton-like activation amplifies the generation of reactive oxygen species (ROS), contributing to the PEC degradation activity. Detailed analysis reveals that the presence of surface-Fe3O4 enhances surface hydrophilicity and contributes to the high density of catalytically active sites in FNCO. We conducted a comprehensive investigation into the in-situ formation and activation pathways of H2O2 molecules through a series of experiments. The designed PEC water treatment system achieved almost 60 % total organic carbon (TOC) removal efficiency with consistent performance across a range of real-world water treatment scenarios, underscoring its versatility and robustness.

Structure and Electron Engineering for Nitrate Electrocatalysis to Ammonia: Identification and Modification of Active Sites in Spinel Oxides.

Cobalt spinel oxides, which consist of tetrahedral site (AO4) and octahedral site (BO6), are a potential group of transition metal oxides (TMO) for electrocatalytic nitrate reduction reactions to ammonia (NRA). Identifying the true active site in spinel oxides is crucial to designing advanced catalysts. This work reveals that the CoO6 site is the dominant site for NRA through the site substitution strategy. The suitable electronic configuration of Co at the octahedral site leads to a stronger interaction between the Co d-orbital and the O p-orbital in O-containing intermediates, resulting in a high-efficiency nitrate-to-ammonia reduction. Furthermore, the substitution of metallic elements at the AO4 site can affect the charge density at the BO6 site via the structure of A-O-B. Thereafter, Ni and Cu are introduced to replace the tetrahedral site in spinel oxides and optimize the electronic structure of CoO6. As a result, NiCo2O4 exhibits the best activity for NRA with an outstanding yield of NH3 (15.49mgcm-2h-1) and FE (99.89%). This study introduces a novel paradigm for identifying the active site and proposes an approach for constructing high-efficiency electrocatalysts for NRA.

NiCo2O4 on monolithic 3DGF/CNT for high performance hybrid zinc batteries

Hybrid Zn-Air and Zn-MX (MX refers to metal species with cation redox properties) batteries that combine the merits of both types are attracting increasing interest. However, the low areal capacity of the Zn-MX segment hinders their applications toward power resilience. Increasing the electrochemically active material loading is critical to achieving sufficient capacity but poses a challenge for conventional electrodes to maintain fast gas diffusion, which is necessary for the Zn-air function. Herein, we report an advanced, monolithic, carbon-based current collector by growing carbon nanotubes (CNT) onto a 3D graphene network (3DGF). The porous and highly conductive current collector readily accommodates more electrochemically active material, NiCo2O4 (NCO), thereby improving the Zn-NCO segment’s capacity without sacrificing the Zn-air segment’s performance. The 3DGF/CNT/NCO electrode was fabricated into a hybrid Zn battery which achieved a superior areal specific capacity of 2.87 mAh cm−2 at 5 mA cm−2, almost threefold of previously reported values, and an impressive rate capability and cycling stability with 98% of original capacity retained after 1000 cycles at 20 mA cm−2 charging/discharging current density. This work showcases 3DGF/CNT as an advanced current collector architecture for new and novel batteries.