KOH Solution Research Articles

Integration of a Bismuth-Based Tris-Mononuclear Complex with 2D Functional Materials for Highly Efficient and Durable Aqueous Electrocatalytic Hydrogen Evolution.

The eminence of transitioning from traditional fossil fuel-based energy resources to renewable and sustainable energy sources is most evidently crucial. The potential of hydrogen as an alternative energy source has specifically focuses the electrocatalytic water splitting (EWS) as a promising technique for generating hydrogen. Development of efficient electrocatalysts to facilitate the EWS process while rationalizing the limitations of noble metal catalysts like platinum has become one of the daunting tasks. Consequently, porous functional materials such as metal complexes (MCs) and graphene oxide (GO) can act as potential catalysts for EWS. Therefore, a composite of GO and a mononuclear bismuth metal complex is synthesized through in situ facile synthesis, which is further utilized as an efficient electrocatalyst for the hydrogen evolution reaction (HER). Several potential electrocatalytic MC@GO composite (BMGO-3,5,7) materials were prepared with compositional variation of GO (3, 5, and 7 wt %). The experimental results demonstrate that the BMGO5 composite exhibits excellent HER activity with a low overpotential value of 105 mV at 10 mA cm-2 and a low Tafel slope of 44 mV dec-1 in 1 M KOH solution. Furthermore, a comprehensive investigation on the potentiality of the BMC-GO composite for hydrogen evolution from river water splitting was performed in order to address the issue of freshwater depletion. Inclusion of a mononuclear MC for facile synthesis of functional GO-based efficient electrocatalyst material is very scanty in the literature. This unique approach could assist future research endeavors toward designing efficient electrocatalysts for sustainable renewable energy generation. This is one of the first of its kind, where mononuclear MCs were utilized to develop GO-based functional composite materials for efficient electrocatalysis toward sustainable renewable energy generation.

Heterojunction engineering via in-situ electrochemical reconstruction for boosting electrocatalytic biomass upgrading-coupled hydrogen production

Rationally designing and constructing high-performance electrocatalysts is critical for environmental and sustainable electrocatalytic biomass upgrading coupled with hydrogen evolution. Herein, we developed a novel in-situ electrochemical reconstruction strategy to fabricate heterostructured electrocatalysts for efficient biomass upgrading-coupled hydrogen production. Through in-situ anodic and cathodic electrochemical reconstructions, Ni(OH)2-CuO nanorods assembled by nanosheets with abundant low-crystalline Ni(OH)2/crystalline CuO heterojunctions on Cu foam (Ni(OH)2-CuO/CF) and S-doped Ni(OH)2-Cu2O nanofoam formed by cross-linked nanoparticles on CF (Ni(OH)2-Cu2O(S)/CF) were respectively constructed for electrocatalytic 5-hydroxymethylfurfural oxidation reaction (HMFOR) and hydrogen evolution reaction (HER). For the Ni(OH)2-CuO/CF, the overall configuration of nanorods assembled by self-standing nanosheets ensures good conductivity, full exposure of active sites, and fast mass/electron transfer. The abundant Ni(OH)2/CuO heterojunctions provide dual active sites of Ni and Cu to simultaneously adsorb and activate hydroxyl and aldehyde groups in HMF. The electronic interaction between Ni(OH)2 and CuO accelerates the reversible conversion of Ni2+↔Ni3+ to generate more Ni3+ active species and enhances the intrinsic activity of dual active sites to reduce the reaction energy barrier of the rate-determining step. As a result, the Ni(OH)2-CuO/CF shows superior HMFOR performance, with a HMF conversion of 99.3%, a FDCA yield of 98.1%, and stability for 50 cycles in 10 mM HMF+1.0 M KOH medium. Meanwhile, the Ni(OH)2-Cu2O(S)/CF also exhibits remarkable HER activity with an overpotential of only 64.7 mV at 10 mA cm−2 in 1.0 M KOH solution due to its unique structure and composition. When coupling a two-electrode system, the HMFOR-HER system achieves a current density of 10 mA cm−2 at 1.44 V, 221 mV lower than that of the OER-HER system. This work provides an in-situ electrochemical reconstruction strategy for designing advanced heterojunction-rich electrocatalysts for various electrocatalytic applications.

Tailoring Spinel with Perovskite: Sr Substitution in the Perovskite Phase of CoFe2O4–LaCoO3 Nanocomposite for Oxygen Evolution and Methanol Oxidation in Alkaline Medium

CoFe2O4–La1−xSrxCoO3 (x = 0.2, 0.6, 0.8) composites have been synthesized using a two‐step, low‐temperature wet chemical approach that combines coprecipitation and sol–gel techniques. The composite materials have been physicochemically analyzed using Fourier‐transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscope. The electrocatalytic properties of the composite materials have been assessed in terms of their performance in oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) in alkaline medium. Cyclic voltammetry has been used for analyzing the redox behavior of the materials in 1 M KOH solution. The electrocatalytic activity of the materials has been assessed using anodic polarization curves on Ni substrate and the CoFe2O4–La0.2Sr0.8CoO3 film electrode demonstrates excellent activity, with current densities of 11.1 mA cm−2 for OER and 47.4 mA cm−2 for MOR at 650 mV. Also, the CoFe2O4–La0.2Sr0.8CoO3 film electrode has the maximum specific activity of 1.1 × 103 mA cm−2 g−1 at 650 mV toward OER. The electrodes’ stability has been assessed through chronoamperometric experiments and additional insight into the enhancement of electrocatalytic activity gained through the electrochemical surface area estimations using electrochemical impedance spectroscopy. From chronoamperometric experiment, it has been observed that the CoFe2O4–La0.2Sr0.8CoO3 film electrode attains stability within 114 s with a current density of 108.7 mA cm−2. Furthermore, the thermodynamic parameters, including the standard enthalpy of activation (ΔH°#), standard entropy of activation (ΔS°#), and standard electrochemical energy of activation (), have been estimated by anodic polarization curve recorded in KOH as well as KOH with CH3OH solutions at various temperatures.

Exploring multifaceted properties of Polypyrrole-Cobalt ferrite nanocomposites: A comprehensive study

The remarkable properties of Polypyrrole (PY) hold immense potential for revolutionizing electronic device technologies. From flexible electronics to high-performance sensors, PY and its nanocomposites offer a plethora of opportunities to engineer advanced electronic components with enhanced functionalities. The properties of Polypyrrole (PY), Cobalt ferrite (CF) and their nanocomposites (PY1, PY2, PY3, PY4) have been explored with increasing amount of Cobalt ferrite. Their synthesis and nano size are confirmed by X-ray diffraction and Fourier transform infrared spectroscopy. SEM confirmed the Walnut morphology of PY and it is maintained in nanocomposites but size of particles has been increased. Consequently, optical band gap (Eg) and thermal stability of samples observed from UV-Visible Spectroscopy and Thermogravimetric analysis get affected. A. C. Conductivity shows the dispersive nature and a significant increase can be seen from PY1 to PY4 i.e. ac conductivity increases with cobalt ferrite composition into the nanocomposites. Dielectric losses were explained using polarization effect and conductivity values of materials. Diamagnetic nature of PY changes into ferromagnetic in the nanocomposites. Electrodes of each sample were prepared using slurry method and their electrochemical analyses were done in 2 M KOH solution. By enhancing thermal stability, electrical conductivity, and capacitance while simultaneously reducing the optical band gap, the integration of Cobalt ferrite into the PY matrix unlocks new avenues for electronic device design. These advancements pave the way for the development of more efficient and sustainable electronic devices.

Nano-Sheets of CsNiVF6 Pyrochlore Electrocatalyst for Enhanced Urea Oxidation and Hydrogen Green Production Reactions

This study presents the successful synthesis of a cesium–nickel–vanadium fluoride (CsNiVF6) pyrochlore nano-sheet catalyst via solid-phase synthesis and its electrochemical performance in green hydrogen production through urea electrolysis in alkaline media. The physicochemical characterizations revealed that the CsNiVF6 exhibits a pyrochlore-type structure consisting of a disordered cubic corner-shared (Ni, V)F6 octahedra structure and nano-sheet morphology with a thickness ranging from 10 to 20 nm. Using the CsNiVF6 catalyst, the electrochemical analysis, conducted through cyclic voltammetry, demonstrates a current mass activity of ~1500 mA mg−1, recorded at 1.8 V vs. RHE, along with low-resistance (3.25 ohm) charge transfer and good long-term stability for 0.33 M urea oxidation in an alkaline solution. Moreover, the volumetric hydrogen production rate at the cathode (bare nickel foam) is increased from 12.25 to 39.15 µmol/min upon the addition of 0.33 M urea to a 1.0 KOH solution and at a bias potential of 2.0 V. The addition of urea to the electrolyte solution enhances hydrogen production at the cathode, especially at lower voltages, surpassing the volumes produced in pure 1.0 M KOH solution. This utilization of a CsNiVF6 pyrochlore nano-sheet catalyst and renewable urea as a feedstock contributes to the development of a green and sustainable hydrogen economy. Overall, this research underscores the potential use of CsNiVF6 as a cost-effective nickel-based pyrochlore electrocatalyst for advancing renewable and sustainable urea electrolysis processes toward green hydrogen production.

Construction of a p-p heterojunction Co3O4/MoS2 electrocatalyst for boosting hydrogen evolution reaction

Building p-p heterojunctions with Fermi level difference, due to the motion of energy levels, band bending, and internal electric field generation, can effectively improve the electronic structure of the interface, enrich the active sites of heterojunctions, and promote the adsorption of reaction intermediates, which is an effective approach to constructing high-performance electrocatalysts. In this study, a Co3O4/MoS2 p-p heterojunction catalyst with nano-particle/nano-flower structure was designed, inducing charge transfer from Co3O4 to MoS2, thereby increasing the negative charge of MoS2, improving *H adsorption through electrostatic interaction, enhancing electrocatalytic kinetics, and reducing reaction overpotential. The catalytic performance of MoS2 for hydrogen evolution reaction was effectively enhanced. In 1 M KOH solution, the current density was 10 mA cm−2, and the overpotential was 156 mV, with good stability after 40 h of operation. This work provides a new direction for the design of p-p heterojunction electrocatalysts and offers more choices for promoting the development of high-performance non-noble metal catalysts.

On the van der Waals Heteroepitaxy and Hydroxylation/Oxidation States of Au@Muscovite by Pulsed Laser Ablation in Water and Recovery in Aqueous KOH Solution

On the van der Waals Heteroepitaxy and Hydroxylation/Oxidation States of Au@Muscovite by Pulsed Laser Ablation in Water and Recovery in Aqueous KOH Solution

Revealing the origin of single‐atom W activity in H2O2 electrocatalytic production: Charge symmetry‐breaking

AbstractThe low‐energy electrochemical production of hydrogen peroxide (H2O2) has garnered significant attention as a viable alternative to traditional industrial routes, with the goal of achieving carbon neutrality. For their H2O2 selectivity in the two‐electron oxygen reduction reaction (ORR), the coordination environment of tungsten (W)‐based materials is critical. In this study, atomically dispersed W single atoms were immobilized on N‐doped carbon substrates by a facile pyrolysis method to obtain a W single‐atom catalyst (W‐SAC). The coordination environment of an isolated W single atom with a tetra‐coordinated porphyrin‐like structure in W‐SAC was determined by X‐ray photoelectron spectroscopy and X‐ray absorption spectroscopy analysis. Notably, the as‐prepared W‐SAC showed superior two‐electron ORR activity in 0.1 M KOH solution, including high onset potential (0.89 V), high H2O2 selectivity (82.5%), and excellent stability. By using differential phase contrast‐scanning transmission electron microscopy and density functional theory calculations, it is revealed that the charge symmetry‐breaking of W atoms changes the adsorption behavior of the intermediates, leading to enhanced reactivity and selectivity for two‐electron ORR. This work broadens the avenue for understanding the charge transfer of W‐based electrocatalytic materials and the in‐depth reaction mechanism of SACs in two‐electron ORR.

Anisotropic polyphenylene-based anion-exchange membranes with flexible side-chains via click reaction for high-performance water electrolysis

Anion-exchange membrane water electrolysis (AEMWE) represents a promising and cost-effective electrochemical energy conversion system for green hydrogen production owing to its utilization of earth-abundant metals for various cell components (catalysts, porous transport layers, bipolar plates) and the zero-gap design. However, the lack of high-performance anion-exchange membranes (AEMs) has hampered the advancement of AEMWE technology. Here, by using colon coupling and click reactions, the ether-free polyphenylene-based AEMs (QPPBTF-TMA-w) with flexible side-chains containing triazole linkers. The QPPBTF-TMA-w membranes stand out for their lower activation energy for hydroxide conduction which is attributed to the well-structured ion-conducting channels via distinct phase separation facilitated by the triazole linker, which optimizes hydrophilicity and ensures efficient ion transport within the membrane. In addition, the QPPBTF-TMA-w membranes exhibit unique anisotropic swelling and ion-conduction behaviors, such as lower in-plane swelling and higher through-plane conductivity, which are advantageous for practical cell applications. Therefore, despite having a modest ion exchange capacity (IEC) value of 2.0, the QPPBTF-TMA-w membrane delivers high-performance in anion-exchange membrane water electrolysis (AEMWE), achieving 6.4 A/cm2 at 2.0 V at 70 °C using a 1.0 M KOH solution.

Convenient construction of electrocatalysts via combustion-assisted corrosion engineering for efficient water oxidation

Developing an efficient strategy for the universal synthesis of electrocatalysts is crucial for advancing the industrialization of water splitting, yet it remains a significant challenge. In this study, we propose combustion-assisted corrosion engineering as a rapid method to fabricate electrocatalysts for the oxygen evolution reaction (OER) within seconds. By utilizing a three-dimensional framework composed of nickel foam and the unique structure of the active species, we enable swift electrolyte diffusion and gas release. Consequently, the optimized S–NiO/NF exhibits remarkable OER catalytic activity, requiring a low overpotential of 236 mV to achieve a current density of 50 mA cm−2 in 1.0 M KOH solution. Notably, the reconfiguration during the OER process leads to the formation of actual catalytic active species, enhancing the number of active centers and thereby improving the catalyst's performance. This research presents a versatile method for industrially fabricating non-noble metal self-supporting electrodes with high efficiency, offering a practical solution for energy conversion and storage.

Zn-Doped MnO2 microflake pseudocapacitive cathode on Ni(OH)2/Ni-Foam substrate as a promising charge storage material

Zn-doped MnO2 microflakes cathode material on Ni(OH)2/Ni foam has been synthesized and characterized as well as tested its electrochemical performances in 3 M KOH solution. The present work varies the amounts of Zn dopant in MnO2 system to improve its capability in energy storage. Material identification has been simply confirmed with XRD, SEM, TEM, and XPS analysis. It is expected the Zn dopant will induce surface defects such as ZnMn2- or ZnMn0 and oxygen vacancy, leading to enhanced charge storage efficiency. In addition, XPS analysis reveals the existence of positively charged oxygen vacancy and the surface charge of ZnMn2- or ZnMn0 induce different surface oxidation states of Mn2+ and Mn4+. The oxidation states of Mn could accommodate the redox reactions involving ion adsorption and intercalation during pseudocapacitive charge and discharge processes. Substituting Zn into Mn sites is optimized with MnZn-1.5 which reaches a specific capacitance of 1601F/g at a 0.4 VAg/AgCl in KOH solution. This work demonstrates a promising material system for supercapacitor applications using Zn doping with a simple preparation process to support a large-scale application.

One-step hydrothermal synthesis of nanowire-like W/Mo-Ni3S2/NF electrocatalysts for highly efficient hydrogen evolution reactions

The design of nanostructures and the adjustment of components are very important to improve the performance of hydrogen evolution electrocatalysts. In this paper, Ni, W and Mo trimetallic catalysts are studied from the aspects of morphology, structure and electronic transfer, and a better combination of hydrogen reaction efficiency is obtained. The W/Mo co-doped nickel sulfide electrocatalyst was synthesized on Ni foam by one-step hydrothermal method. As anticipated, the individual incorporation of either tungsten (W) or molybdenum (Mo) into the electrocatalyst did not yield satisfactory enhancements in hydrogen evolution reaction (HER) performance. However, when both W and Mo were co-doped onto the electrocatalyst, a significant improvement in catalyst material performance was observed. Hence, the coexistence of W and Mo is the key to improve HER electrocatalytic activity. In 1 M KOH solution, the W/Mo-Ni3S2/NF electrocatalyst exhibited exceptional HER activity with an overpotential of only 136 mV at a current density of 10 mA·cm−2 and demonstrated excellent cycle stability exceeding 20 hours. In this paper, the strategy of bimental co-doping composite is adopted to adjust the structure of nickel sulfide, which provides reference value for the design of reasonable and efficient HER electrocatalyst.

Optimizing photocatalytic and supercapacitive performance by β-Bi2O3@BiFeO3 modification with PVDF polymer based nanocomposites

The PVDF (Poly-Vinyl-difloride) membrane modified with Bismuth oxide (β-Bi2O3)/Bismuth Ferrite (BiFeO3) p-n heterojunction synthesized via hydrothermal process to explore its energy storage and conversion applications. The PVDF-Bi2O3/BiFeO3 nanocomposites (NCs) prepared in this study were subjected to analysis using PXRD, FTIR, UV-Vis DRS, FE-SEM with EDX, TEM, and transient photocurrent response techniques, individually. The as-prepared materials were evaluated for their photocatalytic performance in the visible light-induced degradation of Methylene Blue (MB) and Rhodamine-B (RhB) dyes. The photocatalytic performance demonstrates degradation efficiencies of 95% for MB dye and 83% for RhB dye when utilizing the PVDF-β-Bi2O3@BiFeO3 nanocatalyst. The enhancement in the photocatalytic performance of the PVDF-Bi2O3/BiFeO3 heterojunction was a result of improved visible light absorption, suppression of photogenerated electron-hole pair recombination, accelerated separation and migration of photogenerated charges. The capacitance behavior of PVDF-β-Bi2O3@BiFeO3 is significantly higher than β-Bi2O3@BiFeO3 in 3 M KOH solution which has specific capacitance of 300 F g−1at 1 A g−1 of current density and fabricated a symmetric device has10.08 Wh kg−1 and 999.39 W kg−1 specific energy and specific power at 0.5 A g−1 of current density with the 88.7% of capacitance retention and 94.12% of coulombic efficiency up to 10000 cycles.

Preparation and electrocatalytic oxygen evolution of bimetallic phosphates (NiFe)2P/NF

Abstract The energy and environmental crisis pose a great challenge to human development in the 21st century. The design and development of clean and renewable energy and the solution for environmental pollution have become a hotspot in the current research. Based on the preparation of transition metal phosphates, transition metals were used as raw materials, Prussian blue-like NiFe(CN)6 as a precursor, which was in situ grown on nickel foam (NF) substrate. After low temperature phosphating treatment, a bimetallic phosphide electrocatalyst (NiFe)2P/NF was prepared on NF substrate. Using 1 mol·L−1 KOH solution as a basic electrolyte, based on the electrochemical workstation of a three-electrode system, the electrochemical catalytic oxygen evolution performance of the material was tested and evaluated. Experiments show that (NiFe)2P/NF catalyst has excellent oxygen evolution performance. In an alkaline medium, the overpotential required to obtain the catalytic current density of 10 mA·cm−2 is only 220 mV, and the Tafel slope is 67 mV·dec−1. This is largely due to: (1) (NiFe)2p/NF nanocatalysts were well dispersed on NF substrates, which increased the number of active sites exposed; (2) the hollow heterostructure of bimetallic phosphates promotes the electron interaction between (NiFe)2P and NF, increased the rate of charge transfer, and the electrical conductivity of the material is improved; and (3) theoretical calculations show that (NiFe)2P/NF hollow heterostructure can effectively reduce the dissociation barrier of water, promote the dissociation of water; furthermore, the kinetic reaction rate of electrocatalytic oxygen evolution is accelerated. Meanwhile, the catalyst still has high activity and high stability in 30 wt% concentrated alkali solution. Therefore, the construction of (NiFe)2P/NF electrocatalysts enriches the application of non-noble metal nanomaterials in the field of oxygen production from electrolytic water.

Preparation and characterization of high-ash coal slime-based soil amendment as well as investigations of its adsorption performance and mechanisms towards heavy metals in soil

In this study, high-ash coal slime-based mineral soil amendment (MSA) was prepared via the hydrothermal method using high-ash coal slime as raw material, supplemented with activator calcium oxide and additive KOH solution. After hydrothermal treatment at 230 °C for 5 h, the original crystalline phase (quartz and kaolinite) of the high-ash slime was completely transformed into hydrotalcite zeolite, tobermorite, and silicate of potassium aluminosilicate, which has the largest specific surface area. The adsorption of Pb2+ and Cd2+ was adherent to the kinetic equation of secondary adsorption and Freundlich models, and the removal of Pb2+ and Cd2+ reached up to 362.58 mg g−1 and 64.67 mg g−1. The successive releases of SiO2 and CaO from MSA conformed to the Elovich equation, whereas the releases of SiO2 in Cd-containing environments and CaO in Pb- and Cd-containing environments more closely conformed to the power function; the releases of K2O all conformed to the first-order kinetic equation. The presence of Pb2+ and Cd2+ in the environment promotes the release of potassium and calcium elements with MSA's ion-exchange ability, and attenuates the release of silicon elements. Combining Pb2+ and Cd2+ with silicon resulted in the intolerant precipitation of 3PbO·2SiO2 and Cd2SiO4. The mineral precipitation mechanism is the most important mechanism of MSA in immobilizing heavy metals, accounting for 72.7%–80.5% of the total adsorption. Further contaminated soil immobilization experiments also showed that the application of MSA significantly reduced the bioavailability of soil heavy metals. When the MSA addition amount was 1.6%, the residual state increased by 63.58%. In conclusion, preparing MSA may effectively utilize coal-based solid waste with high added value.

Enhancement in capacitive performance of Co3O4 with MnTiO3 via composite (MnTiO3/Co3O4) strategy developed by ultrasonication route

The specific surface area, conductivity and cyclic stability of nanomaterials significantly impact a pseudocapacitor electrode's performance. The Co3O4 is economically viable and widely available but has limited surface area and conductivity. However, MnTiO3 has a greater surface area and exhibits superior ion conductivity, resulting in better specific capacitance (Cs). Herein, a novel MnTiO3/Co3O4 nanocomposite is manufactured to enhance the properties of Co3O4 using an ultrasonication technique for application in supercapacitors. Several analytical methods were utilized to examine synthesized materials' textural, structural and morphological characteristics. The MnTiO3/Co3O4 nanocomposite demonstrated notable Cs of 1534.67 F/g, specific energy (SE, 64.05 Wh/kg) and specific power (SP, 274.1 W/kg) at current density (Cd) of 1 A/g in 2.0 M KOH solution, according to electrochemical experiments. Additionally, after 5000th cycles, the nanocomposite exhibits excellent cyclic stability than pristine materials. This study not only showcases the significant capabilities of the commercially accessible MnTiO3/Co3O4 nanocomposite but also presents a novel approach for developing cost-effective, high-performing composite materials with multiple potential applications in the energy field.

Enhancing oxygen evolution reaction performance of Ruddlesden–Popper perovskite oxide through heteroatom incorporation

Prior studies have demonstrated that Ruddlesden–Popper (RP) type perovskite oxides exhibit promising electrocatalytic properties for oxygen evolution reaction (OER). However, the limited electrocatalytic activity has impeded their widespread utilization. The incorporation of heteroatoms into the Ruddlesden–Popper type structure has been identified as an effective strategy to enhance the electrocatalytic performance. This research presents the systematic design and synthesis of RP type perovskite oxide LaSrFeO4 (LSFO), followed by the optimization of electrocatalytic activity through Ni substitution at the Fe site of SLFO to create LaSrFe1-xNixO4 (LSFNO-x, x = 0.2, 0.4, and 0.5). Therein, the LSFNO-0.4 sample achieved a current density of 10 mA·cm−2 with an overpotential of only 340 mV. Additionally, it displayed exceptional stability over 120 h in a 1.0 M KOH solution. Both experimental and theoretical studies suggest that the addition of Ni cation increases the Fe − O covalency, and impacts the morphology and surface electron density of LSFO. This substitution results in a greater electrochemically active surface area, improved electron transfer, and optimization of hydrogen/water absorption free energy. This study presents a successful approach for enhancing the OER performance of Ruddlesden–Popper LSFO through the deliberate control of Fe − O covalent bonding.

A rigid free-standing supercapacitor electrode material made from fat coal-based activated carbon foam

A free-standing electrode material is a competitive candidate for supercapacitor due to its excellent capacity and volumetric energy density. Currently, most of the studies are focused on the preparations and performances of flexible free-standing electrode materials, whereas few on the development of rigid free-standing electrode materials. Herein, a vitrinite concentrate of fat coal is used as a raw material and carbon black as an addition agent to prepare a carbon foam by way of high-pressure pyrolysis. The prepared carbon foam is activated by KOH solution to further achieve an activated carbon foam by which we have fabricated a rigid free-standing electrode material. The assembled symmetric device with the rigid free-standing electrode material demonstrates an extremely high areal specific capacitance of 2304.41 mF cm−2 at 4 mA cm−2, an outstanding cycling stability of 100 % after 40 000 cycles, and an excellent volume energy density of 10.23 mWh cm−3 at 31.78 mW cm−3. These fascinating electrochemical performances of the electrode material are attributed to unique 3D interconnected porous structure of the activated carbon foam. The micron-sized 3D interconnected pores facilitate the transport of electrolyte ions within the electrodes. Meanwhile, micropores on the 3D interconnected pore wall provide abundant active sites for electrolyte ions.

Regulating the electronic state of SnO2@NiFe-LDH heterojunction: Activating lattice oxygen for efficient oxygen evolution reaction

In Oxygen Evolution Reaction (OER), catalysts with lattice oxygen, utilizing the Lattice Oxygen Mechanism (LOM), directly participate in oxygen evolution, effectively reducing activation energy. NiFe-Layered Double Hydroxides (NiFe-LDHs), rich in surface hydroxyls, are potential for LOM. However, their stability is challenged in alkaline conditions due to metal cation dissolution from the lattice, limiting catalytic efficiency. In this work, we modify NiFe-LDH by combining hydrothermal and electrodeposition techniques, coupling NiFe-LDH with the metal oxide SnO2. This process creates a heterojunction enriched with oxygen vacancies through interfacial and defect engineering. In 1 M KOH solution, this modified catalyst exhibits an OER overpotential of just 209 mV at a current density of 10 mA cm−2. Furthermore, when the current density is increased to 100 mA cm−2, the overpotential only increases by a modest 46 mV. Subsequent DFT investigations reveal that in the heterostructured system, there is an enhanced overlap between the O 2p and metal 3d orbitals, which optimizes the covalency of the metal–oxygen bond and promotes the participation of lattice oxygen in the reduction reaction. The heterojunction, in concert with oxygen vacancies, aligns the energy bands of oxygen and metal closer to the Fermi level, resulting in improved continuity of electronic orbitals near the Fermi level. This synergistic arrangement significantly reduces the energy barrier for the rate-determining step of the OER, substantiating the improved performance and activation of lattice oxygen.

Dealloying of Mg-based alloys for production of self-supporting metallic nanostructures

Dealloying is a proficient technique in the fabrication of nanostructured metals, particularly nanoporous materials, with promising potential for diverse applications. However, the development of robust and self-standing nanostructured metal foils through dealloying presents significant challenges. By generating an alloy layer on the surface of the metal foil, nanostructures can be generated on the metal foil surface through subsequent dealloying. This approach utilizes the inherent flexibility and ductility of the metal foil to ensure self-support. It also allows for the tailoring of the structure and composition of the dealloyed nanostructured metal by manipulation of the phase constitution in the surface alloy layer. In this study, we report a strategy for generating alloy layers on metal foil surfaces through the thermal evaporation of magnesium (Mg) followed by annealing. Upon dealloying the surface alloy layer, we successfully obtain self-supported nanostructured metal foils. Employing copper (Cu) as an example, we demonstrate that Mg can form a Mg–Cu alloy layer on the surface of a Cu foil, where the control over the alloy layer's phase composition and thickness is achieved by adjusting the annealing duration. Furthermore, we investigated the feasibility of this method on nickel (Ni) substrates, including Ni foils and Ni foams. Moreover, by further functionalizing the resulting nanostructured Ni foil, we transformed it into Ni(OH)2/Ni foil and explored its performance in the electrocatalytic oxygen evolution reaction (OER). The resulting catalyst achieved a current density of 10 mA cm−2 at a potential of only 349 mV in a 1 M KOH solution, exhibiting a Tafel slope of 84.52 mV dec−1. Following 10 h of stability testing, the catalyst exhibited negligible degradation in performance. This study provides a convenient and versatile pathway for preparing self-supported nanostructured metals.