Electrochemical Reaction Sites Research Articles

MXene‐Enhanced Metal–Organic Framework‐Derived CoP Nanocomposites as Highly Efficient Trifunctional Electrocatalysts for OER, HER, and ORR

Developing robust active electrocatalysts from readily available earth‐abundant elements for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR) remains an unresolved challenge. Herein, Ti3C2Tx MXene‐containing metal–organic framework‐derived CoP nanocomposite electrocatalysts are successfully prepared by phosphidation of in situ‐produced ZIF‐67/MXene composite precursor at various heat treatment temperatures. The obtained nanocomposite catalysts are characterized by X‐ray diffraction, Brunauer–Emmett–Teller, X‐ray photoelectron spectroscopy, field emission‐scanning electron microscope/energy dispersive X‐ray spectroscopy (EDS), and high‐resolution transmission electron microscopy/EDS. In the produced composites, Ti3C2Tx MXene functions as a supportive substrate to facilitate mass transfer, as well as ion transport, and to improve electrical conductivity. Moreover, the introduction of MXene into the heterostructured CoP@C/Ti3C2Tx enables it to expose and provide extra active sites for electrochemical reactions. The as‐prepared CoP@C/MXene‐360 (abbreviated as CPMX‐360) nanocomposite is a promising trifunctional electrocatalyst toward OER, HER, and ORR. CPMX‐360 exhibits excellent electrocatalytic activity with an overpotential of 235 mV at 10 mA cm−2 in OER, an overpotential of 220 mV at −10 mA cm−2 in HER, and an Eonset and E1/2 of 0.82 and 0.74 V in ORR, respectively. This research provides a viable method to develop nonprecious trifunctional electrocatalyst via phosphidation of metal–organic framework and MXene with excellent performance for OER, HER, and ORR.

Bifunctional heterostructure ZnWO4@ZnO nanocomposite for high-performance electrocatalysis and supercapacitor applications

Earth-abundant transition metal oxides (TMOs) represent a versatile class of electrode materials that excel in energy and environmental applications. Strategically incorporating additional metal oxides to form heterostructures significantly enhances electrical conductivity and cyclic stability, paving the way for better performance in energy storage and conversion technologies. In this study, we developed a ZnWO4@ZnO nanocomposite heterostructure using a straightforward solid-state synthesis method, positioning it as a bifunctional electroactive material for supercapacitor and catalytic applications. Importantly, the heterostructure’s increased surface area allows for more active sites for electrochemical reactions, which can boost current generation. The synergistic interaction between ZnO and ZnWO4 significantly enhances the electrochemical properties of the heterostructure, resulting in an impressive specific capacitance of 363 Fg−1 and exceptional cyclic stability over 10,000 charge–discharge cycles. These results underscore the potential of this material in energy storage and conversion technologies, making it a compelling candidate for high-performance supercapacitor and catalytic applications.

Carbon-Embedded Pt Alloy Cluster Catalyst: Properties and Oxygen Reduction Activity

Carbon-embedded PtFe alloy cluster catalysts have emerged as promising candidates for enhancing the performance and durability of oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). These catalysts, synthesized through a multi-step process involving carbonization of hyper-crosslinked polystyrene particles with Fe precursors, doping of nitrogen species, deposition of Pt precursors, and subsequent reduction, exhibit remarkable properties and catalytic activity.Advanced imaging techniques, including aberration-corrected scanning transmission electron microscopy (ADF-STEM) and scanning electron microscopy (SEM), have revealed that the metal clusters are embedded beneath the carbon support surface. X-ray absorption fine structure (XAFS) analysis further confirmed the Pt-Fe alloy structure of the metal clusters, which are approximately 1.5 nm in size. The carbon-embedded PtFe alloy cluster catalysts demonstrate high mass activity and exceptional durability for the ORR. Despite being embedded within the carbon matrix, the Pt sites within the clusters serve as active sites for electrochemical reactions. Co-adsorption of Br- ions with protons alters cyclic voltammetry (CV) curves similarly to typical Pt/C catalysts, indicating the accessibility of Pt sites. Moreover, small molecules such as protons formic acid, and methanol can effectively diffuse through the carbon layer to reach the Pt surface.When applied in the cathode of PEMFCs with a low Pt loading of 0.05 mg Pt cm-2, the PtFe cluster catalysts exhibit high current density at 0.65 V and excellent durability. After 30,000 cycles, the current density remains nearly unchanged, highlighting the superior performance of these catalysts compared to conventional Pt/C or PtFe/C catalysts. Density functional theory (DFT) calculations further elucidate the catalytic mechanism of the carbon-embedded PtFe alloy clusters. Carbon atoms stably adsorb on Fe sites of PtFe clusters, making nearby Pt sites active for ORR with optimal adsorption strength of oxygen intermediates. This comprehensive understanding of the catalytic behavior and properties of carbon-embedded PtFe alloy cluster catalysts opens up new avenues for the development of highly active and durable ORR catalysts in PEMFCs, with minimized Pt usage. Figure 1

Insights into the Negative Impact of Carbon Binder Domains in Lithium-Ion Battery Electrode through 3D Microstructure Resolved Model

The lithium-ion battery (LIB) electrode consists of an active material, a conductive additive, and a binder, with the pores filled with a liquid electrolyte. The conductive additive compensates for the intrinsic low electrical conductivity of the active material, while the binder enhances mechanical bonding between components. These constituents collectively form the carbon binder domain (CBD). CBD assumes a passive role in electrochemical behavior; however, it exerts adverse effects at the microscale, obstructing Li-ion transport pathways and reducing electrochemical reaction sites. However, the heterogeneous nature of LIB electrode microstructures poses challenges for in-depth analysis. In this study, we systematically investigate the impact of CBD on LIB performance using a three-dimensional microstructure resolved model. Electrochemical modeling enables the visualization of experimentally inaccessible information, such as mass transport and electrochemical reaction characteristics. Our findings offer promising insights for advancing electrode design methodologies.

Development of CuFe2O4 microspheres/carbon sheets composite materials as a sensitive electrochemical sensorfor determination of bisphenol A.

A composite material based on CuFe-ZIF-derived CuFe2O4 nano-microspheres grown in situ and well-ordered on carbon sheets (CS) was prepared and applied for highly effective determination of bisphenol A (BPA). The composite material possessed inherently high redox activity due to the presence of both Cu and Fe ions with various oxidation states (Cu²⁺/Cu⁺ and Fe³⁺/Fe²⁺), high specific surface area, uniform distribution of Cu and Fe ions, and a robust framework imparted by its precursor CuFe-ZIF. Thisled to increased active sites for electrochemical reactions, improved electron transfer efficiency, and structural integrity during electrochemical cycling. Furthermore, combining CS with CuFe2O4 not only provided a large surface area to support well-ordered CuFe₂O₄ nano-microspheres without aggregation, but also enhanced the conductivity and mechanical stability of the CuFe₂O₄/CS composite. This results in synergistic effects that enhanced the overall performance of the composite material. In addition, both copper and iron are relatively non-toxic and abundant, making CuFe₂O₄/CS safe and cost-effective for large-scale applications. Consequently, the CuFe2O4/CS-modified electrode shows highly efficient electrochemical sensing properties with a wider detection range of 0.009-168 µM and lower detection limit of 0.0027 µM (S/N = 3) compared withmost reported BPA sensors. It also hasanoptimized current at pH 7 which is convenient for real world applications. This CuFe2O4/CS modified electrode as a highly sensitive electrochemical platform can be applied to monitor BPA concentrations in bottled water with good recovery (97.2-102.2%).

Stabilization of High‐Valent Molecular Cobalt Sites through Oxidized Phosphorus in Reduced Graphene Oxide for Enhanced Oxygen Evolution Catalysis

AbstractHeterogeneous molecular cobalt (Co) sites represent one type of classical catalytic sites for electrochemical oxygen evolution reaction (OER) in alkaline solutions. There are dynamic equilibriums between Co2+, Co3+ and Co4+ states coupling with OH−/H+ interaction before and during the OER event. Since the emergence of Co2+ sites is detrimental to the OER cycle, the stabilization of high‐valent Co sites to shift away from the equilibrium becomes critical and is proposed as a new strategy to enhance OER. Herein, phosphorus (P) atoms were doped into reduced graphene oxide to link molecular Co2+ acetylacetonate toward synthesizing a novel heterogeneous molecular catalyst. By increasing the oxidation states of P heteroatoms, the linked Co sites were spontaneously oxidized from 2+ to 3+ states in a KOH solution through OH− ions coupling at an open circuit condition. With excluding the Co2+ sites, the as‐derived Co sites with 3+ initial states exhibited intrinsically high OER activity, validating the effectiveness of the strategy of stabilizing high valence Co sites.

Hierarchically Ordered Pore Engineering of Carbon Supports with High-Density Edge-Type Single-Atom Sites to Boost Electrochemical CO2 Reduction.

Metal sites at the edge of the carbon matrix possess unique geometric and electronic structures, exhibiting higher intrinsic activity than in-plane sites. However, creating single-atom catalysts with high-density edge sites remains challenging. Herein, the hierarchically ordered pore engineering of metal-organic framework-based materials to construct high-density edge-type single-atomic Ni sites for electrochemical CO2 reduction reaction (CO2RR) is reported. The created ordered macroporous structure can expose enriched edges, further increased by hollowing the pore walls, which overcomes the low edge percentage in the traditional microporous substrates. The prepared single-atomic Ni sites on the ordered macroporous carbon with ultra-thin hollow walls (Ni/H-OMC) exhibit Faraday efficiencies of CO above 90% in an ultra-wide potential window of 600mV and a turnover frequency of 3.4×104h-1, much superior than that of the microporous material with dominant plane-type sites. Theory calculations reveal that NiN4 sites at the edges have a significantly disrupted charge distribution, forming electron-rich Ni centers with enhanced adsorption ability with *COOH, thereby boosting CO2RR efficiency. Furthermore, a Zn-CO2 battery using the Ni/H-OMC cathode shows an unprecedentedly high power density of 15.9mW cm-2 and maintains an exceptionally stable charge-discharge performance over 100h.

Porous N, P co-doping Ti3C2Tx MXene for high-performance capacitive deionization

The emerging energy-saving and environmentally friendly capacitive deionization (CDI) technology has attracted more and more attention. However, it remains a great challenge to develop CDI electrode materials with excellent comprehensive properties. Herein, the porous N, P co-doping Ti3C2Tx MXene (N, P-Ti3C2Tx) was prepared successfully by combining simple flocculation with an annealing process. Benefitting from the synergistic effect of the combination of porous structure and co-doping of N and P heteroatoms, the N, P-Ti3C2Tx exhibits substantial specific surface area, which provides more surface bounding active sites for electrochemical reactions, thus assisting to boost the CDI performance. As a result, the N, P-Ti3C2Tx exhibited an admirable salt (Na+) adsorption capacity of 53.3 mg g−1 and exceptional recycling property. Impressively, the N, P-Ti3C2Tx also exhibited superior desalination performance of Pb2+, characterized by an exceptionally high desalination capacity of up to 168.2 mg g−1 at 1.2 V, and the corresponding desalination rate reached 0.047 mg g−1 s−1. Additionally, the deionization mechanism involved was elucidated through a series of characterizations. This work will furnish an effective avenue for the innovative design of MXene-based electrode materials toward high-performance CDI.

Impact of ultrasonic treatment duration on the microstructure and electrochemical performance of NiZnCo2O4 electrode materials for supercapacitors

This work investigates the impact of different ultrasonic treatment durations on the synthesis and electrochemical performance of NiZnCo2O4 (NZC) supercapacitor electrodes. Optimizing treatment to 20 min resulted in a uniform, compact NiZnCo2O4 layer with improved nanostructures, which increased the surface area and active sites for electrochemical reactions. X-ray diffraction (XRD) confirmed successful NiZnCo2O4 synthesis, revealing distinct crystalline phases of NiO, ZnCo2O4, and Co3O4, with improved crystallinity. Electrochemical tests, conducted using a 1.0 M KOH electrolyte, demonstrated that the NZC-2 electrode treated for 20 min achieved the highest 5.678 F/cm3 volumetric capacitance at 0.5 mA/cm2 current density along with 70.5 Wh/kg an energy density at 260 W/kg power density. The galvanostatic charge-discharge and cyclic voltammetry tests revealed that NZC-2 maintained superior charge-discharge efficiency, showing the longest discharge time at 1 mA/cm². Electrochemical impedance spectroscopy (EIS) measurements demonstrated that NZC-2 exhibited the lowest total impedance, thereby enhancing ion transport efficiency. The NZC-2/AC asymmetric supercapacitor showed excellent long-term stability, retaining 64.2% of its capacity after 20,000 charge-discharge cycles. It successfully powered a 1.2 V small fan, demonstrating its practical applicability. The results highlight the crucial importance of ultrasonic treatment in greatly improving the structural and electrochemical characteristics of NiZnCo2O4 electrodes, which opens up possibilities for the advancement of high-performance supercapacitors.

Amplifying energy storage and production efficiency: Utilizing BaS3: Ni2S3: Sb2S3 synthesized from dithiocarbamate precursors for enhanced and sustainable energy solutions

During this period of increasing energy use, the scientific community and energy stakeholders have been closely monitoring electrochemical energy storage. In an attempt to enhance the functionality of charge storage devices, diethyldithiocarbamate ligand is employed as a chelating agent during the production of the novel BaS3: Ni2S3: Sb2S3. The semiconductor BaS3: Ni2S3: Sb2S3, which was made in an environmentally friendly manner, showed good photoactivity due to its 2.97 eV energy band gap and light absorption. The resultant chalcogenide had an average crystallite size of 19.69 nm and displayed outstanding crystallinity with mixed crystallographic phases. Furthermore, infrared spectroscopy was used to investigate metallic sulfide connections, and the findings indicated that they varied between 500 and 875 cm−1. This chalcogenide featured varied sites for electrochemical reactions due to its morphology. The electrochemical performance of BaS3: Ni2S3: Sb2S3 was assessed using a conventional three-electrode setup. With a specific capacitance of up to 1019.4 F g−1 and a power density of 11931.26 W kg−1, BaS3: Ni2S3: Sb2S3 has proven to be an excellent electrode material for energy storage. This remarkable electrochemical performance was further reinforced by the comparable series resistance (Rs) of 0.57 Ω. During electrocatalysis, the electrode produced an OER overpotential with a Tafel slope of 348 mV and 119 mV dec−1. In contrast, the overpotential and Tafel slope in terms of the HER activity and were 211 mV and 100 mV/dec, respectively.

Stabilization of High-Valent Molecular Cobalt Sites through Oxidized Phosphorus in Reduced Graphene Oxide for Enhanced Oxygen Evolution Catalysis.

Heterogeneous molecular cobalt (Co) sites represent one type of classical catalytic sites for electrochemical oxygen evolution reaction (OER) in alkaline solutions. There are dynamic equilibriums between Co2+, Co3+ and Co4+ states coupling with OH-/H+ interaction before and during the OER event. Since the emergence of Co2+ sites is detrimental to the OER cycle, the stabilization of high-valent Co sites to shift away from the equilibrium becomes critical and is proposed as a new strategy to enhance OER. Herein, phosphorus (P) atoms were doped into reduced graphene oxide to link molecular Co2+ acetylacetonate toward synthesizing a novel heterogeneous molecular catalyst. By increasing the oxidation states of P heteroatoms, the linked Co sites were spontaneously oxidized from 2+ to 3+ states in a KOH solution through OH- ions coupling at an open circuit condition. With excluding the Co2+ sites, the as-derived Co sites with 3+ initial states exhibited intrinsically high OER activity, validating the effectiveness of the strategy of stabilizing high valence Co sites.

Ce-doped NiCo-layered double hydroxide based self-supporting tremella-shaped nanoflower heterostructure as efficient electrocatalyst for the oxygen evolution reaction

NiCo-layered double hydroxide (NiCo-LDH) catalysts, which indicate a profound prospect of oxygen evolution reaction (OER) under alkaline conditions, are facing great challenges in terms of low electrical conductivity, restricted by poor conductivity, limited electrochemical reaction sites, and low-density of edge sites. The authors developed a simple and convenient in-situ one-pot self-assembly method. The Ce-doped defective NiCo-LDH hexagonal nanosheets and nitrogen-doped graphene fabricated the NiCoCe-LDH/RNF electrocatalyst on the nickel foam (NF) substrate, which demonstrated excellent OER activity under alkaline conditions, only needed 299 mV overvoltage to achieve 50 mA cm−2 current intensity, could last for 6 hours at 20 mA cm−2. The highly active OER benefited from the structural advantages of the novelty three-dimensional array structure. The novel geometric structure of tremella-shaped nanoflower integrated with curved nanosheets and curled edges loaded on NF provides more electrochemical reaction sites for intermediate coordination. The nitrogen-doped reduced graphene oxide accommodated better interaction between active materials and charge carriers, enhancing the conductivity and electron transfer performance of nanostructures. The effective synergistic between the heterostructures promoted the excellent OER electrocatalytic activity of NiFeCe-LDH/RNF nanocomposites. DFT calculations at the atomic level of pristine and Ce-doped NiCo-LDH exhibited that Ce-doping can reduce the Gibbs free energy of the potential-determining step and improve the catalytic activity of OER. This work has broadened the horizons for developing simple and highly available OER electrocatalysts.

Enhanced dopamine detection using Ti3C2Tx/rGO/Pt ternary composite synthesized via microwave-assisted hydrothermal method

A novel electrochemical sensing platform for dopamine (DA) detection was developed by fabricating the ternary composite of Ti3C2Tx MXene (M) and reduced graphene oxide (rGO) with platinum nanoparticles (Pt NPs) through microwave-assisted hydrothermal heating. The exceptional electrical conductivity and rich surface chemistry of MXene provide abundant active catalytic sites for electrochemical reactions, while the large surface area of rGO facilitates ion and electron pathways. The integration of rGO in the MXene sheet, forming MXene-rGO (M_rGO) heterostructure composite, imparts long-term stability to the 2D heterostructure while providing additional electron pathways and significantly enhancing conductivity. Pt NPs synergistically increased the electrocatalytic activity of the electrochemical sensor's performance. Ternary nanocomposites were fabricated with different weight percentages (wt.%) of Pt NPs, ranging from 5 to 20. Characterizations of the samples (rGO, M, M_rGO, and 5–20 wt% Pt@M_rGO) were conducted through X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RAMAN), and X-ray spectroscopy (XPS). Electrochemical evaluations of the samples were investigated in 0.1 M phosphate buffer solution (PBS) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) analyses. The analysis revealed that the ternary composite with 5 wt% of Pt NPs (5% Pt@M_rGO) exhibited a uniform well-distribution of Pt NPs and the highest oxidation peak for DA oxidation in CV studies. The presence of metal nanoparticles, aided by the synergistic effects between the MXene and rGO, resulted in an excellent DA sensor with a 0.147 μM detection limit from 1 to 14 μM linearity range. The sensor demonstrated outstanding selectivity, reproducibility (RSD values of 8.10%), repeatability (RSD value of 2.46%) and, excellent stability over 14 days. In human urine samples, the sensor exhibited excellent DA recovery (88.62–110.65%). This study significantly advances the development of electrochemical sensors for DA detection by introducing a rapid, facile and, efficient method for fabricating ternary composites. The fabricated sensor exhibited high sensitivity, excellent selectivity, and robust electrochemical performance, offering valuable insights into human and behavioral health advancements.

Achieving Complete Conversion from Nickel Foam to Nickel Sulfide Foam for a Freestanding Hybrid‐Supercapacitor Electrode

AbstractWe present a unique, one‐step, hydrothermal process to prepare nickel sulfide (Ni3S2) foam by a simple and direct conversion from nickel foam, which contributes both as a scaffold for the reaction and as reactant. The Ni3S2 foam exhibits remarkable mechanical stability, retaining the structural integrity of the foam and excellent crystallinity even after ultrasonication at 200 W for 30 mins. We document the transformation of the nickel foam template into a Ni3S2 foam, highlighting the role of synthesis duration on the phase evolution and unique morphology of Ni3S2. PXRD and SEM analyses reveal a complete transformation after 24 hours from the nickel foam to a pure Ni3S2 foam, which has a highly porous and interconnected ultra‐thin nanosheet architecture. This significantly enhances the surface area and provides many electrochemical reaction sites. In a three‐electrode cell, the capacity of the Ni3S2 foam electrode is 3.9 C cm−2 at 8 mA cm−2, which is higher than previous reports for Ni3S2. In a hybrid supercapacitor device, the Ni3S2 foam demonstrates significant increase in capacitance through 500 cycles and the capacitance plateaus after 2000 cycles. Even after 8500 continued charge‐discharge cycles, the device exhibits excellent cycle stability indicating improvement with age.

Research on the tri-block copolymer-directed self-assembly synthesis of bicontinuous structures for electrical energy storage

The burgeoning demand for more efficient energy storage systems necessitates advancements in electrode material technologies. Bicontinuous structures, synthesized using tri-block copolymers, present a promising avenue due to their unique properties that can enhance battery performance. This study aims to explore the potential of tri-block copolymer-directed self-assembly in synthesizing bicontinuous structures and to assess their application as innovative electrode materials in electrical energy storage systems. It was found that the synthesized bicontinuous structures demonstrate superior ionic pathways, resulting in enhanced ion transport and improved electrochemical performance compared to traditional electrode materials. The copolymers contribute to the formation of a highly ordered mesoporous architecture, leading to increased surface area and more active sites for electrochemical reactions. Furthermore, these structures exhibit significant stability during cycling, attributed to their ability to accommodate volume expansions and distribute mechanical stress effectively. Future research should focus on the extension of the synthesis process and the further optimization of the electrochemical properties in order to make the transition from laboratory studies to practical applications.

Phosphate ions functionalized metal-organic framework-derived cobalt oxide with improved redox reactivity for high-performance alkaline aqueous Zn-ion batteries

Alkaline aqueous Zn/Co3O4 batteries (AZCBs) have captured significant attention within the field of scalable grid energy storage due to their high output voltage (>1.8 V), superior safety profile, and low manufacturing cost. Nevertheless, the intrinsic Co3O4 material experiences limitations in terms of low electronic conductivity and insufficient active sites, consequently constraining its electrochemical performance in AZCBs. To address this challenge, this investigation focuses on the use of phosphate ions functionalized Co3O4 (referred to as PCO) material derived from cobalt-based metal-organic frameworks (Co-MOFs) as a cathode electrode in AZCBs. Both theory calculations and experimental verification illustrate that the functionalization with phosphate ion enhances the active sites for electrochemical redox reactions and increases the electrical conductivity of intrinsic Co3O4. Consequently, a pouch cell configuration of PCO-2||Zn with the optimized PCO-2 sample as cathode exhibits a high capacity of 162.0 mAh g−1, a maximum energy density of 265.7 Wh kg−1, a maximum power density of 16.39 kW kg−1. Furthermore, excellent long-term stability is observed, with the capacity retention rate reaching 92.3 % over 5000 cycles at a high current density of 5 A g−1. Additionally, the constructed fibrous flexible solid-state device also demonstrates notable long-term stability, with a capacity retention of 96 % after 2000 cycles under a high current density of 10 mA cm−2, and performs well under different deformation statuses. This successful approach may hold potential for the exploration of other cathode materials, such as Mn or V-based compounds, which may exhibit high performance in aqueous zinc-based batteries.

Rapid electrosynthesis of low-loaded platinum nanosheet catalysts for high-performance hydrogen oxidation reactions

The development of fuel cells is urgently needed, leading to increasing demand for electrodes with low catalyst loading, high utilization, and straightforward fabrication. In this work, we successfully designed and synthesized Pt nanosheet electrocatalysts grown in situ on treated carbon cloth (Pt/CC) using a simple and rapid electrodeposition technique. At a pulse peak current density of 300 mA cm−2, the catalyst exhibited impressive Pt surface coverage uniformity, ultralow Pt loading, and an ultrathin nanosheet structure, providing a large number of active sites for electrochemical reactions. With a Pt loading of only 0.02 mg cm−2, Pt/CC-300 provides an 11-fold improvement in hydrogen oxidation reaction (HOR) performance over commercial Pt/C catalysts. The electrode can be directly employed as an anode electrode without any additives or secondary treatment. This not only simplifies the production process but also paves the way for more economical and efficient fuel cell technology.

Emerging detection of carbon-based gases with multiple bonds by activating Mo[dbnd]O bonding in Na, Sb-codoped NiMoO4

Exhausting carbon-based gases from building construction or comfortable household supplies have caused the main pollution gas species for the indoor air environment. Given the variety of indoor activities, many reports have been challenged to find room-temperature operational and harmless materials. Here, we report that the activating MoO vibration mode in Na,Sb doped-NiMoO4 micro-sized powder reveals the high response of CO and VOC, occupying multiple bonds at room temperature. We performed Na and Sb doping in the α-NiMoO4 crystal structure, such as introducing the Sb in Ni and interstitial doping of Na in around 4 Å of free space in the NiMoO4 crystal structure that manipulates the partial β-NiMoO4 phase. The Na,Sb-codoped NiMoO4 generates the higher MoO vibration mode from FT-IR measurement and enables carbon-based gas detection with 38 responses to CO and nearly 20 responses to VOC under 20 ppm of each analyte gases environment. Furthermore, the n-type gas sensing behavior of Na,Sb doped-NiMoO4 chemiresistor exhibits an immediate sensing response instead of a none-of response than intrinsic or single element doped NiMoO4. These results suggest that Na,Sb codoped-NiMoO4 is the applicable material for emergent warning against carbon-based gas exposure in the indoor environment. In addition, activating the electrochemical reaction site of MoO4–2 in NiMoO4 is tailorable by a simple doping process.

Constructing graphene oxide-wrapped wolframite-type 3D cube-like CuWO4 composite as a promising redox-active electrode for battery-type supercapacitors

The electronics industry's increasing demand for swift energy storage solutions drives researchers to invest significant resources into enhancing electrode materials. Achieving optimal efficiency throughout the charging process requires meticulous attention to the designing of the morphological, structure and chemical compositions of the electrode materials. Understanding the synergies among elements and structural dynamics is pivotal for maximizing the electrodes' performance. To address these challenges, we propose a groundbreaking approach through a straightforward and cost-effective solid-state reaction method followed by an impregnation technique to design a graphene oxide-wrapped wolframite-type 3D cube-like CuWO4 (GW-CuWO4) composite matrix. This design substantially increases the electrode's surface area (5 times greater than pristine CuWO4 and 12 times greater than sphere-like Na2WO4) and enhances its mesoporous characteristics. We extensively analyzed the physicochemical properties of GW-CuWO4 and compared them with pristine CuWO4 and Na2WO4 using various analytical techniques. The electrochemical performance of all electrodes exhibited battery-type characteristics, with the supercapacitive performance thoroughly investigated and compared. The specific capacity of the GW-CuWO4 composite electrode demonstrated significant results, reaching 520.8 C g−1 at 1.0 A g−1, with outstanding rate capability retaining 93 % capacity even at a high rate of charging current of 10 A g−1. In contrast, the specific capacity and rate capability of pristine CuWO4 were 392.1 C g−1 and 87 %, respectively, and Na2WO4 showed 295.8 C g−1 and 64 %. Additionally, the GW-CuWO4 electrode displayed excellent cyclic performance, retaining 95 % capacity at 10 A g−1 compared to CuWO4 (84 %). The GW-CuWO4 electrode exhibits enhanced electrochemical performance due to the synergistic interactions between its constituent parts and its distinct 3D mesoporous composite network. High conductivity, rich redox reactions, easy electron transfer, short ion diffusion lengths, quick kinetics, and an abundance of active sites for electrochemical reactions are all made possible by this network. Presenting this cutting-edge electrode design builds a fresh framework for producing effective electrodes suited for the upcoming wave of high-performance energy storage devices.

Enhancing ammonia sensing performance of Ag2MoO4-based mixed-potential sensor by introducing ionic and electronic conductance

The breath ammonia detection is crucial for the evaluation of the pathological state. Among the existing ammonia detection technologies, the mixed potential sensor exhibits promising potential owing to its high stability, good selectivity and small size. However, it remains challenging in application due to its insufficient limit of detection (LOD). To improve the performance of such sensor, a novel sensing material Ag2MoO4 was synthesized in this work. The electrode morphology was tuned for optimum performance by adjusting the sintering temperature. The response to 5 ppm NH3 at 425 °C is about −29.86 mV with response/recover times of 105/96 s and sensitivity of −49.55 mV/decade. In addition, the sensor exhibits good selectivity and outstanding detection capability of trace-level NH3 as low as 400 ppb. High concentrations of water vapor and CO2 can greatly affect its performance, but it can be easily eliminated by a filter. The research of its sensing mechanism reveals that Ag2MoO4 has both ionic conductance and electronic conductance, which transforms the electrochemical reaction site from two-dimensional three-phase boundaries (TPB) to a three-dimensional one distributed within the sensing material. Specifically, the sensor shows excellent NH3 detection ability with the number of reaction sites increases.