Heterostructure of Fe-Doped CoMoOx/CoMoOx as an Efficient Electrocatalyst for Oxygen Evolution Reaction

Oxygen evolution reaction (OER) plays a crucial role as a counter half-reaction for both electrochemical hydrogen production through water splitting and the generation of valuable carbon compounds via CO2 reduction. To overcome the sluggish kinetics of the OER, significant efforts have been devoted to developing cost-effective, sustainable, and efficient electrocatalysts, with transition-metal-based catalysts emerging as promising candidates. Herein, we successfully synthesized a core-shell type nanostructure of Fe-doped CoMoOx/CoMoOx (CMFO), which exhibits excellent electrocatalytic properties for OER. The presence of an amorphous layer of Fe-doped CoMoOx with abundant oxygen vacancies, along with the stability of a key OER intermediate, *O, contributes to the enhanced activity of CMFO catalyst compared to pristine CoMoOx (CMO). The optimized catalyst of CMFO-550 achieved much lower overpotential and Tafel slope and also exhibited better remarkable long-term stability for over 90 h compared to CMO-550. These findings highlight the potential of CMFO-550 as a cost-effective and highly efficient electrocatalyst for the OER. The successful development of this core-shell nanostructure opens up a new opportunity for the design and synthesis of advanced electrocatalysts for the OER, with implications for various applications in energy conversion and storage.

Exploring the Effects of Various Two-Dimensional Supporting Materials on the Water Electrolysis of Co-Mo Sulfide/Oxide Heterostructure

In this study, various two-dimensional (2D) materials were used as supporting materials for the bimetallic Co and Mo sulfide/oxide (CMSO) heterostructure. The water electrolysis activity of CMSO supported on reduced graphene oxide (rGO), graphite carbon nitride (gC3N4), and siloxene (SiSh) was better than that of pristine CMSO. In particular, rGO-supported CMSO (CMSO@rGO) exhibited a large surface area and a low interface charge-transfer resistance, leading to a low overpotential and a Tafel slope of 259 mV (10 mA/cm2) and 85 mV/dec, respectively, with excellent long-term stability over 40 h of continuous operation in the oxygen evolution reaction.

Synthesis of Flower-Like Cobalt-Molybdenum Mixed-Oxide Microspheres for Deep Aerobic Oxidative Desulfurization of Fuel

Flower-like cobalt-molybdenum mixed-oxide microspheres (CoMo-FMs) with hierarchical architecture were successfully synthesized via a hydrothermal process and subsequent calcination step. The characterization results show that CoMo-FMs were assembled from ultrathin mesoporous nanosheets with thicknesses of around 4.0 nm, providing the composite with a large pore volume and a massive surface area. The synthesized CoMo-FMs were employed as catalysts for the aerobic oxidative desulfurization (AODS) of fuel, and the reaction results show that the optimal catalyst (CoMo-FM-2) demonstrated an outstanding catalytic performance. Over CoMo-FM-2, various thiophenic sulfides could be effective removed at 80-110 °C under an atmospheric pressure, and a complete conversion of sulfides could be achieved in at least six consecutive cycles without a detectable change in chemical compositions. Further, the catalytic mechanism was explored by conducting systemic radical trapping and transformation experiments, and the excellent catalytic performance for CoMo-FMs should be mainly due to the synergistic effect of Mo and Co elements.

Anchoring cobalt molybdenum nickel alloy nanoparticles on molybdenum dioxide nanosheets as efficient and stable self-supported catalyst for overall water splitting at high current density

Developing bifunctional electrocatalysts with efficient and stable catalytic performance at high current density to improve the productivity of water splitting is important for relieving the environmental pollution and energy crisis. Herein, the Ni₄Mo and Co₃Mo alloy nanoparticles were anchored on MoO₂ nanosheets (H-NMO/CMO/CF-450) by annealing the NiMoO₄/CoMoO₄/CF (CF: self-made cobalt foam) under Ar/H₂ atmosphere. Benefitting from the nanosheets structure, synergistic effect of the alloys, existence of oxygen vacancy and the cobalt foam with smaller pore sizes as conductive substrate, the self-supported H-NMO/CMO/CF-450 catalyst demonstrates outstanding electrocatalytic performance, which delivers small overpotential of 87 (270) mV at 100 (1000) mA·cm^-2 for HER and 281 (336) mV at 100 (500) mA·cm^-2 for OER in 1 M KOH. Meanwhile, the H-NMO/CMO/CF-450 catalyst is used as working electrodes for overall water splitting, which just require 1.46 V @ 10 mA·cm^-2 and 1.71 V @ 100 mA·cm^-2, respectively. More importantly, the H-NMO/CMO/CF-450 catalyst can stabilize for 300 h at 100 mA·cm^-2 in both HER and OER. This research provides an idea for the preparation of stable and efficient catalysts at high current density.

CoMoO4-modified hematite with oxygen vacancies for high-efficiency solar water splitting

Hematite is a potential photoelectrode for photoelectrochemical (PEC) water splitting. Nevertheless, its water oxidation efficiency is highly limited by its significant photogenerated carrier recombination, poor conductivity and slow water oxidation kinetics. Herein, under low-vacuum (LV) conditions, we fabricated a CoMoO₄ layer on oxygen-vacancy-modified hematite (CoMo-Fe₂O₃ (LV)) for the first time for efficient solar water splitting. The existence of oxygen vacancies can significantly facilitate the electrical conductivity, while the large onset potential along with oxygen vacancies can be lowered by the CoMoO₄ with accelerated water oxidation kinetics. Therefore, a high photocurrent density of 3.53 mA cm^-2 at 1.23 V_RHE was obtained for the CoMo-Fe₂O₃ (LV) photoanode. Moreover, it can be further coupled with the FeNiOOH co-catalyst to reach a benchmark photocurrent of 4.18 mA cm^-2 at 1.23 V_RHE, which is increased around 4-fold compared with bare hematite (0.90 mA cm^-2). The combination of CoMoO₄, FeNiOOH, and oxygen vacancies may be used as a reasonable strategy for developing high-efficiency hematite-based photoelectrodes for solar water oxidation.

Multilayered Molybdate Microflowers Fabricated by One-Pot Reaction for Efficient Water Splitting

The development of high-performance, low-cost and rapid-production bifunctional electrocatalysts towards overall water splitting still poses huge challenges. Herein, the authors utilize a facile hydrothermal method to synthesize a novel structure of Co-doped ammonium lanthanum molybdate on Ni foams (Co-ALMO@NF) as self-supported electrocatalysts. Owing to large active surfaces, lattice defect and conductive channel for rapid charge transport, Co-ALMO@NF exhibits good electrocatalytic performances which requires only 349/341 mV to achieve a high current density of 600 mA cm^-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Besides, a low cell voltage of 1.52 V is required to reach the current density of 10 mA cm^-2 in alkaline medium along with an excellent long-term stability for two-electrode configurations. Density functional theory calculations are performed to reveal the reaction mechanism on Co-ALMO@NF, which shows that the Mo site is the most favorable ones for HER, while the introduction of Co is beneficial to reduce the adsorption intensity on the surface of Co-ALMO@NF, thus accelerating OER process. This work highlighted the importance of the structural design for self-supporting electrocatalysts.

Construction of Cobalt Molybdenum Diselenide Three-phase Heterojunctions for Electrocatalytic Hydrogen Evolution in Acid Medium

Molybdenum diselenide and cobalt diselenide have been commonly implemented in electrocatalytic hydrogen evolution reaction (HER). However, there have been few research on the creation of their three-phase heterojunctions and the associated HER process. Herein, we constructed a three-phase heterostructure sample consisting of orthorhombic CoSe₂ , cubic CoSe₂ and MoSe₂ and we investigated its HER performance. The sample shows microsphere morphology composed of nanosheets with interfacial interactions between the components. It possesses an overpotential of -136 mV at -10 mA cm^-2 in acid medium, which is superior to that of single component and most two-phase heterostructures. Especially, the overpotential at -200 mA cm^-2 is smaller than that of Pt/C. The excellent performance can be attributed to the d-orbital upshift of the Co active sites due to charge redistribution between the three-phase heterojunction and the optimization of the hydrogen free energy. This work provides inspiration for exploring the application of other multi-component heterojunctions in electrocatalytic hydrogen evolution.

Non-radical-dominated catalytic degradation of methylene blue by magnetic CoMoO4/CoFe2O4 composite peroxymonosulfate activators

In this study, magnetic CoMoO₄/CoFe₂O₄ (CMO/CFO) nanospheres with a core-shell structure were synthesized via two-step hydrothermal methods. The obtained particles were employed as catalysts to activate peroxymonosulfate (PMS) and degrade methylene blue (MB). The physico-chemical characterizations of the synthesized CMO/CFO showed that the CMO shell contributed to the enhancement of redox conversion and the increase in the concentration of oxygen vacancies (OVs). By examining reactive oxygen species (ROS) in the CMO/CFO/PMS system, the MB degradation was dominated by a non-radical pathway, and ¹O₂ was identified as the most abundant ROS. Besides, the CMO/CFO exhibited faster reaction kinetics than the pristine CFO. Moreover, the magnetic properties guaranteed the recycling and reuse of CMO/CFO, and the removal rate of MB was maintained at ∼94% after continuous use five times. Both the tolerance to SO₄^2-and the wide pH range where the material is applicable make it a promising catalyst for dyeing wastewater treatment.

Unraveling spongy Co3O4 mediated activation of peroxymonosulfate: Overlooked involvement of instantaneously produced high-valent-cobalt-oxo

Peroxymonosulfate (PMS) activation induced by tricobalt tetroxide spinel (Co₃O₄) has been confirmed as a typical Haber-Weiss reaction, while free radicals were once considered as the dominated reactive species in the previous studies. However, the catalytic mechanism of the spongy Co₃O₄ driven PMS activation was surprisingly found as a radical/nonradical mixed process rather than a pure radical process in the present work. The important role of sulfate radical (SO₄^-) was confirmed through the quenching experiments. Despite the inhibition of furfuryl alcohol (FFA) and 1,4-benzoquinone (BQ) on degradation was generally accepted as the evidence to support the existence of ¹O₂ and O₂^-, additional experiments using methyl phenyl sulfoxide (PMSO) as the indicator indeed verified high-valent-cobalt-oxo rather than ¹O₂ and O₂^- dominated the very early reaction stage. Notably, instead of homogeneous Co³⁺, heterogeneous Co(IV) = O on catalyst surface was believed to be responsible for the oxidation of organics. Spongy Co₃O₄ not only possessed stronger catalytic ability than commercial Co₃O₄ (k_{[spongy Co3O4]} = 0.74 min^-1, k_[Co3O4] = 0.08 min^-1), but also owned preferable stability. The performance of catalytic system was barely affected by the solution pH under the near neutral condition. Besides, little suppression of the widely existing anions on the degradation indicated the potential application of spongy Co₃O₄/PMS system. This study provides a reliable oxidation technology for the removal of organic pollutants, and sheds new light on the cobalt oxide triggered PMS activation process.

Coupling Interface Construction of Ni(OH)2/MoS2 Composite Electrode for Efficient Alkaline Oxygen Evolution Reaction

The transition metal-based catalysts have excellent electrochemical oxygen evolution reaction catalytic activity in alkaline electrolytes, attracting a significant number of researchers’ attention. Herein, we used two-step hydrothermal and solvothermal methods to prepare a Ni(OH)2/MoS2/NF electrocatalyst. The electrocatalyst displayed outstanding OER activity in 1.0 M KOH electrolyte with lower overpotential (296 mV at 50 mA·cm−2) and remarkable durability. Comprehensive analysis shows that reinforcement of the catalytic function is due to the synergistic effect between Ni(OH)2 and MoS2, which can provide more highly active sites for the catalyst. This also provides a reliable strategy for the application of heterogeneous interface engineering in energy catalysis.

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.

The electrochemical immunosensor of the "signal on" strategy that activates MMoO4 (M = Co, Ni) peroxidase with Cu2+ to achieve ultrasensitive detection of CEA

A new type of ultrasensitive electrochemical immunosensor with "signal on" strategy was designed for quantitative detection of CEA. The sensing strategy design is based on the following principles: We use HMSNs-Cu²⁺@HA as the signal probe, the structure of HA is destroyed under acidic conditions, and the released Cu²⁺ activates the substrate material MMoO₄ (M = Co, Ni) Peroxidase activity initiates the reaction of catalytic H₂O₂ and realizes the "signal on" condition of electrical signals. This strategy has the following advantages: (1) HA coating of HMSNs-Cu²⁺ can prevent Cu²⁺ leakage, has good biocompatibility and can be connected with more antibodies. (2) The prepared sensor has the characteristics of high sensitivity and a low detection limit. When the electrode substrate was CoMoO₄, the detection range of the immunosensor was 0.01 pg/mL-40 ng/mL, and the detection limit was 0.0035 pg/mL (S/N = 3). This work innovatively applies the catalytic activity of metal ion-activated nanozymes in the detection of CEA, providing a new perspective for the monitoring and analysis of cancer markers.

Electronic Structure Tuning of 2D Metal (Hydr)oxides Nanosheets for Electrocatalysis

2D metal (hydr)oxide nanosheets have captured increasing interest in electrocatalytic applications aroused by their high specific surface areas, enriched chemically active sites, tunable physiochemical properties, etc. In particular, the electrocatalytic reactivities of materials greatly rely on their surface electronic structures. Generally speaking, the electronic structures of catalysts can be well adjusted via controlling their morphologies, defects, and heterostructures. In this Review, the latest advances in 2D metal (hydr)oxide nanosheets are first reviewed, including the applications in electrocatalysis for the hydrogen evolution reaction, oxygen reduction reaction, and oxygen evolution reaction. Then, the electronic structure-property relationships of 2D metal (hydr)oxide nanosheets are discussed to draw a picture of enhancing the electrocatalysis performances through a series of electronic structure tuning strategies. Finally, perspectives on the current challenges and the trends for the future design of 2D metal (hydr)oxide electrocatalysts with prominent catalytic activity are outlined. It is expected that this Review can shed some light on the design of next generation electrocatalysts.

Boosting OER performance of IrO2 in acid via urchin-like hierarchical-structure design

Urchin-like hierarchical IrO2 nanostructures, which are obtained by a surfactant-free, wet-chemical approach, show boosted OER performance in acid with an overpotential of 260 mV @10 mA cm-2geo under optimal pocessing conditions. The overpotential @10 mA cm-2geo can be kept below 285 mV for over 30 hours.

Flexible Co-Mo-N/Au Electrodes with a Hierarchical Nanoporous Architecture as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction

Designing highly active and robust electrocatalysts for oxygen evolution reaction (OER) is crucial for many renewable energy storage and conversion devices. Here, self-supported monolithic hybrid electrodes that are composed of bimetallic cobalt-molybdenum nitride nanosheets vertically aligned on 3D and bicontinuous nanoporous gold (NP Au/CoMoN_x ) are reported as highly efficient electrocatalysts to boost the sluggish reaction kinetics of water oxidation in alkaline media. By virtue of the constituent CoMoN_x nanosheets having large accessible CoMoO_x surface with remarkably enhanced electrocatalytic activity and the nanoporous Au skeleton facilitating electron transfer and mass transport, the NP Au/CoMoN_x electrode exhibits superior OER electrocatalysis in 1 m KOH, with low onset overpotential (166 mV) and Tafel slope (46 mV dec^-1 ). It only takes a low overpotential of 370 mV to reach ultrahigh current density of 1156 mA cm^-2 , ≈140-fold higher than free CoMoN_x nanosheets. The electrocatalytic performance makes it an attractive candidate as the OER catalyst in the water electrolysis.

MOF-derived ZnCo2O4 porous micro-rice with enhanced electro-catalytic activity for the oxygen evolution reaction and glucose oxidation

A porous ZnCo₂O₄ micro-rice like microstructure was synthesized via calcination of a Zn–Co MOF precursor at an appropriate temperature. The as-prepared ZnCo₂O₄ sample presented good electrocatalytic oxygen evolution reaction performance with a small overpotential (η₁₀ = 389 mV) and high stability in basic electrolyte. Furthermore, in basic medium, the as-synthesized ZnCo₂O₄ micro-rice also showed good electrocatalytic activity for glucose oxidation. A ZnCo₂O₄ micro-rice modified glass carbon electrode may be used as a potential non-enzymatic glucose sensor. The excellent electrocatalytic OER and glucose oxidation performances of ZnCo₂O₄ might be attributed to the unique porous structure formed by the nanoparticles. The porous architecture of the micro-rice can provide a large number of electrocatalytically active sites and high electrochemical surface area (ECSA). The result may offer a new way to prepare low-cost and high performance oxygen evolution reaction and glucose oxidation electrocatalysts.

A porous ZnCo₂O₄ micro-rice like microstructure was synthesized via calcination of a Zn–Co MOF precursor at an appropriate temperature.

Synergistic engineering of architecture and composition in NixCo1-xMoO4@CoMoO4 nanobrush arrays towards efficient overall water splitting electrocatalysis

Implementing the hierarchical structures of non-noble-metal-based electrocatalysts and modulating their composition can help accelerate surface reactions and fulfill the promise of renewable energy devices via water splitting. Herein, molybdenum-based compounds are constructed on activated nickel foam (act-NF) by a one-step hydrothermal growth. The product generated on the act-NF is Ni_xCo_1-xMoO₄@CoMoO₄, with a novel 3D hierarchical heterostructure, wherein the one-dimensional CoMoO₄ nanorods are hierarchically integrated with the two-dimensional Ni_xCo_1-xMoO₄ nanosheets (NCMO@CMO/act-NF). The formation of Ni_xCo_1-xMoO₄@CoMoO₄ attributes to the release and diffusion of Ni²⁺ from act-NF. Heterogeneous Ni_xCo_1-xMoO₄@CoMoO₄ has compositional differences, and synergistic interaction between cobalt and nickel results in the modulated electronic states. Meanwhile, the hierarchical structure facilitates the exposure of active sites. Combining these two advantages, NCMO@CMO/act-NF presents a low η₁₀ value of 61 and 180 mV in 1.0 M KOH for the HER and OER, respectively, and it shows a low cell voltage of 1.46 V for overall water splitting with robust stability. DFT calculations reveal that Ni doping leads to the charge depletion of Co, which further optimizes the d-band center of metal sites and tunes the adsorption of adsorbates to facilitate the water splitting reaction. Thus, a promising strategy of incorporating the nanostructure design with compositional modulation is presented to develop functional materials for energy conversion.

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.

Cu0.4Co0.6MoO4 Nanorods Supported on Graphitic Carbon Nitride as a Highly Active Catalyst for the Hydrolytic Dehydrogenation of Ammonia Borane

As a typical chemical hydride, ammonia borane (AB) has received extensive attention because of its safety and high hydrogen storage capacity. The aim of this work was to develop a cost-efficient and highly reactive catalyst for hydrolyzing AB. Herein, we synthesized a series of CuxCo1–xMoO4 dispersed on graphitic carbon nitride (g-C3N4) to dehydrogenate AB. Among those CuxCo1–xMoO4/g-C3N4 catalysts, Cu0.4Co0.6MoO4/g-C3N4 exhibited the highest site time yield (STY) value of 75.7 m o l H 2 m o l c a t − 1   m i n − 1 with a low activation energy of 14.46 kJ mol−1. The STY value for Cu0.4Co0.6MoO4/g-C3N4 was about 4.3 times as high as that for the unsupported Cu0.4Co0.6MoO4, indicating that the g-C3N4 support plays a crucial role in improving the catalytic activity. Considering its low cost and high catalytic activity, our Cu0.4Co0.6MoO4/g-C3N4 catalyst is a strong candidate for AB hydrolysis for hydrogen production in practical applications.

PBA@POM Hybrids as Efficient Electrocatalysts for the Oxygen Evolution Reaction

To realize the effective conversion of renewable energy through water decomposition, efficient electrocatalysts for the oxygen evolution reaction (OER) are essential. In this article, PBA@POM was successfully prepared with a Prussian blue analogue (PBA) as the initial structure. A facile hydrothermal process is reported for obtaining PBA@POM by etching the cubic PBA with a strong Brønsted acid, H₃ PMo₁₂ O₄₀ (HPMo). The hollow cube structure not only exposes more active sites but also promotes electron transport, which results in excellent electrocatalytic activity for the OER. Compared with the PBA, which initially simply adhered to POM, the optimum PBA@POM hybrids display remarkably enhanced OER catalytic activity, with an almost constant overpotential of 440 mV at a current density of 10 mA cm^-2 and a small Tafel slope (23.45 mV dec^-1 ). The facilely prepared PBA@POM with good electrochemical activity and stability promises great potential for the OER.

Kinetic and Electrochemical Reaction Mechanism Investigations of Rodlike CoMoO4 Anode Material for Sodium-Ion Batteries

Sodium-ion batteries are considered the most promising power source for electrical energy storage systems because of the abundance of sodium and their significant cost advantages. However, high-performance electrode materials are required for their successful application. Herein, we report a monoclinic-type CoMoO₄ material which is synthesized by a simple solution method. An optimized calcination temperature with a high crystallinity and a rodlike morphology of the material are selected after analyzing the as-synthesized powder by temperature-dependent time-resolved X-ray diffraction. The CoMoO₄ rods exhibit initial discharge and charge capacities of 537 and 410 mA h g^-1, respectively, when used as an anode for sodium-ion batteries. The sodium diffusion coefficient in the bimetallic CoMoO₄ anode is measured using the galvanostatic intermittent titration technique and calculated in the range of 1.565 × 10^-15 to 4.447 × 10^-18 cm² s^-1 during the initial cycle. Further, the reaction mechanism is investigated using ex situ X-ray diffraction and X-ray absorption spectroscopy, and the obtained results suggest an amorphous-like structure and reduction/oxidation of Co and Mo during the sodium insertion/extraction process. Ex situ transmission electron microscopy and energy-dispersive spectroscopy images of the CoMoO₄ anode in fully discharged and recharged state reveal the rodlike morphology with homogenous element distribution.

Efficient aerobic oxidative desulfurization over Co–Mo–O bimetallic oxide catalysts

Co–Mo–O bimetallic oxides were prepared as efficient catalysts for aerobic oxidative desulfurization with oxygen in air as the oxidant.

Humid atmospheric pressure plasma jets exposed micro-defects on CoMoO4 nanosheets with enhanced OER performance

A novel humid APPJs method was adopted to treat CoMoO₄ nanosheet arrays resulting in micro-defects and more reaction intermediates that led to an enhanced OER property.

Oxygen vacancy-confined CoMoO4@CoNiO2 nanorod arrays for oxygen evolution with improved performance

Experimental and DFT calculation results show that the presence of oxygen vacancies can decrease the adsorption energy of intermediates at active sites and facilitate the adsorption of intermediates, thus improving the catalytic properties.

Enhanced Photoelectrochemical Water Oxidation Performance on BiVO4 by Coupling of CoMoO4 as a Hole-Transfer and Conversion Cocatalyst

Manipulation of interfacial charge separation and transfer is one of the primary breakthroughs to improve the water oxidation activity and stability of BiVO₄ photoanode. In the present work, a CoMoO₄-coupled BiVO₄ (BiVO₄/CoMoO₄) film was designed and prepared as the photoanode for photoelectrochemical (PEC) water oxidation. Compared with the bare BiVO₄ film, obviously improved PEC water oxidation performance was observed on the BiVO₄/CoMoO₄ film. Specifically, a higher water oxidation photocurrent density of 3.04 mA/cm² at 1.23 V versus RHE was achieved on the BiVO₄/CoMoO₄ photoanode, which is of about 220% improvement over bare BiVO₄ photoanode (1.34 mA/cm² at 1.23 V vs RHE). In addition, the BiVO₄/CoMoO₄ film photoanode was of better stability and faster hole-to-oxygen kinetics for water oxidation, without significant activity attenuation for 6 h of reaction at 0.65 V versus RHE. The enhanced water oxidation performance on the BiVO₄/CoMoO₄ film photoanode can be ascribed to the synergistic effect of the following factors: (i) thermodynamically, the photogenerated holes of BiVO₄ are directionally transferred to CoMoO₄ through their physical coupling interface and valance band potential matching; and (ii) kinetically, the transferred holes induce the formation of Co³⁺-active sites on CoMoO₄ that could synergistically oxidize H₂O to molecular O₂ with stable activity.

Hedgehog-inspired nanostructures for hydrogel-based all-solid-state hybrid supercapacitors with excellent flexibility and electrochemical performance

High-security deformable energy-storage devices that are mechanically robust, with considerable energy and power densities are becoming desirable for smart wearable electronics. Here, a highly flexible hydrogel-based all-solid-state hybrid supercapacitor was rationally designed and assembled, with unique NiCo2O4@NixCoyMoO4 (x : y = 3 : 1) nanostructures as the electrode, which was bio-inspired by the curling up and relaxation of hedgehogs. The hybrid supercapacitor shows no obvious decay in capacitance during bending to different states, indicating its outstanding flexibility and mechanical stability. The capacitance was still maintained at 92.0% of the initial value, even after continuous bending for 3000 cycles. The highly monodisperse NiCo2O4@NixCoyMoO4 nanostructures releasing stress during bending is responsible for the favorable stability and flexibility. Furthermore, the hybrid supercapacitor displayed outstanding electrochemical performance, with a high specific capacitance of 207 F g-1 at 1 A g-1, a high energy density of 64.7 W h kg-1 at 749.6 W kg-1, and favorable cycling stability (nearly 100% after 10 000 cycles). The flexible hybrid supercapacitor could be charged with a solar cell and served as the power source to light up LEDs. This simple and reliable hybrid supercapacitor, with extraordinary mechanical stability and electrochemical performance, is a promising power source for smart wearable electronics.

Cobalt Oxide Materials for Oxygen Evolution Catalysis via Single-Source Precursor Chemistry

The utilization of metal alkoxides as single-source precursors for (mixed-)oxide materials offers remarkable benefits, such as the possibility to precisely control the metal ratio in the resulting material, highly homogeneous distribution of the elements in the film, and the low temperatures required for film processing. Herein we report on the isolation and characterization of the bimetallic Co-Mo alkoxide [Co₃ Mo₄ O₁₀ (OCH₃ )₁₀ (dmf)₄ ] (Co₃ Mo₄ ; dmf=N,N-dimethylformamide), which was prepared by the anion metathesis reaction of the corresponding metal chlorides. The Co-Mo alkoxide was explored as a well-defined precursor of cobalt oxide catalysts for the oxygen evolution reaction (OER) in alkaline electrolyte MOH. The catalysts demonstrated excellent activity in the OER, manifested in low onset potentials and Tafel slopes and superb stability under the operating conditions both in alkaline and nearly neutral media. It was observed that the nature of the metal cation of the alkaline electrolyte MOH (M⁺ =Li⁺ , Na⁺ , K⁺ , Cs⁺ ) greatly affected the catalytic performance of the material. We propose that the positive effect of larger metal cations on the film activity in the OER could be explained by the higher hydration enthalpies of larger ions and enhanced mass transport within a larger interlayer space between the [CoO₂ ]^δ-_∞ sheets of the in situ formed binary oxides. It may be deduced that this trend is universal and may be extended to other types of metal oxides forming layered structures during the OER.

Two-Dimensional Mn-Co LDH/Graphene Composite towards High-Performance Water Splitting

The oxygen evolution reaction (OER) is a complex multi-step four-electron process showing sluggish kinetics. Layered double hydroxides (LDH) were reported as promising catalysts for the OER, but their low electrical conductivity restricts their widespread applications. To overcome this problem, a composite material containing Mn-Co LDH ultrathin nanosheet and highly conductive graphene was synthesized for the first time. Benefited from the high electrocatalytic activity and the superior charge transfer ability induced by these components, the new material shows superior OER activity. Used as the OER catalyst, a high current density of 461 mA cm−2 at 2.0 V vs. RHE (reversible hydrogen electrode) was measured besides shows a low overpotential of 0.33 V at 10 mA cm−2. Moreover, the new composite also shows a superior bifunctional water splitting performance as catalyst for the OER and HER (hydrogen evolution reaction) catalysts. Our results indicate that the presented material is a promising candidate for water splitting which is cheap and efficient.

Electrodeposited Amorphous Tungsten-doped Cobalt Oxide as an Efficient Catalyst for the Oxygen Evolution Reaction

Thin film of amorphous tungsten-doped cobalt oxide (W:CoO) was successfully grown on a conducting electrode via an electrochemical oxidation process employing a [Co(WS₄ )₂ ]^2- deposition bath. The W:CoO catalyst displays an attractive performance for the oxygen evolution reaction in an alkaline solution. In an NaOH solution of pH 13, W:CoO operates with a moderate onset overpotential of 230 mV and requires 320 mV overpotential to generate a catalytic current density of 10 mA cm^-2 . A low Tafel slope of 45 mV decade^-1 was determined, indicating a rapid O₂ -evolving kinetics. The as-prepared W:CoO belongs to the best cobalt oxide-based catalysts ever reported for the oxygen evolution (OER) reaction.

CaMoO4 nanosheet arrays for efficient and durable water oxidation electrocatalysis under alkaline conditions

It is highly desirable to design and develop earth-abundant electrocatalysts for efficient and durable oxygen evolution reaction (OER) under alkaline conditions. In this communication, we demonstrate the development of CaMoO4 nanosheet arrays on nickel foam (CaMoO4/NF) as a durable high-performance non-noble-metal electrocatalyst for the OER. CaMoO4/NF shows high catalytic activity and needs an overpotential of only 345 mV to attain a geometrical catalytic current density of 50 mA cm-2 in 1.0 M KOH. Notably, it also shows high long-term electrochemical durability for at least 25 h.