Tuning the Nanoparticle Interfacial Properties and Stability of the Core-Shell Structure in Zn-Doped NiMoO4@AWO4

Engineering Lattice Strain in Co-Doped NiMoO4 for boosting Methanol Oxidation Reaction

Nickel-based molybdates have attracted considerable attention owing to their distinctive isomorphous structure. In this study, pristine NiMoO4 and Co-doped Ni1-xCoxMoO4 were synthesized and investigated for their electrocatalytic activity in methanol oxidation and methanol-assisted water splitting reactions. Through a comprehensive exploration of the structure-property relationship, it was found that the optimal coexistence of α and β molybdate phases, induced by Co doping, led to lattice strain and facilitated the presence of essential catalytic descriptors such as higher oxidation states of Ni and surface oxygen vacancies within the lattice. These factors contributed to the enhanced electrocatalytic activity of Ni0.7Co0.3MoO4 in methanol oxidation and hydrogen evolution reaction. Detailed kinetic studies were conducted to further elucidate the mechanisms involved. Overall, these findings highlight the promising potential of Ni0.7Co0.3MoO4 as an effective catalyst for electrochemical methanol upgrading in conjunction with water splitting, with implications for sustainable energy conversion technologies.

MOF-Mediated Construction of NiCoMn-LDH Nanoflakes Assembled Co(OH)F Nanorods for Improved Supercapacitive Performance

The application of transition metal hydroxides has long been plagued by its poor conductivity and stability as well as severe aggregation tendency. In this paper, a novel hierarchical core-shell architecture, using an F-doped Co(OH)2 nanorod array (Co(OH)F) as the core and Mn/Ni co-doped Co(OH)2 nanosheets (NiCoMn-LDH) as the shell, was constructed via an MOF-mediated in situ generation method. The obtained Co(OH)F@ NiCoMn-LDH composites exhibited excellent supercapacitive performance with large specific capacitance as well as improved rate capability and long-term stability. The effect of the Ni/Mn ratio on the supercapacitive performance and energy storage kinetics was systematically investigated and the related mechanism was revealed.

Molybdenum disulfide (MoS2) along with graphene nanoplatelets (GNPs) utilized to enhance the capacitance of conducting polymers (PANI and PPy)

Hybrid composites of molybdenum disulfide (MoS2), graphene nanoplatelets (GNPs) and polyaniline (PANI)/polypyrrole (PPy) have been synthesized as cost-effective electrode materials for supercapacitors. We have produced MoS2 from molybdenum dithiocarbamate by a melt method in an inert environment and then used a liquid exfoliation method to form its composite with graphene nanoplatelets (GNPs) and polymers (PANI and PPy). The MoS2 melt/GNP ratio in the resultant composites was 1 : 3 and the polymer was 10% by wt. of the original composite. XRD (X-ray diffraction analysis) confirmed the formation of MoS2 and SEM (scanning electron microscopy) revealed the morphology of the synthesized materials. The electrochemical charge storage performance of the synthesized composite materials was assessed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge (GCCD) measurements. Resultant composites showed enhanced electrochemical performances (specific capacitance = 236.23 F g-1, energy density = 64.31 W h kg-1 and power density = 3858.42 W kg-1 for MoS2 melt 5 mPP at a current density of 0.57 A g-1 and had 91.87% capacitance retention after 10 000 charge-discharge cycles) as compared to the produced MoS2; thus, they can be utilized as electrode materials for supercapacitors.

A Facile Two-Step Hydrothermal Synthesis of Co(OH)2@NiCo2O4 Nanosheet Nanocomposites for Supercapacitor Electrodes

The composites of NiCo₂O₄ with unique structures were substantially investigated as promising electrodes. In this study, the unique structured nanosheets anchored on nickel foam (Ni foam) were prepared under the hydrothermal technique of NiCo₂O₄ and subsequent preparation of Co(OH)₂. The Co(OH)₂@NiCo₂O₄ nanosheet composite has demonstrated higher specific capacitances owing to its excellent specific surface region, enhanced rate properties, and outstanding electrical conductivities. Moreover, the electrochemical properties were analyzed in a three-electrode configuration to study the sample material. The as-designed Co(OH)₂@NiCo₂O₄ nanosheet achieves higher specific capacitances of 1308 F·g^-1 at 0.5 A·g^-1 and notable long cycles with 92.83% capacity retention over 6000 cycles. The Co(OH)₂@NiCo₂O₄ nanosheet electrode exhibits a long life span and high capacitances compared with the NiCo₂O₄ and Co(OH)₂ electrodes, respectively. These outstanding electrochemical properties are mainly because of their porous construction and the synergistic effects between NiCo₂O₄ and Co(OH)₂. Such unique Co(OH)₂@NiCo₂O₄ nanosheets not only display promising applications in renewable storage but also reiterate to scientists of the unlimited potential of high-performance materials.

Review of NiS-Based Electrode Nanomaterials for Supercapacitors

As a new type of energy storage device, supercapacitors have the advantages of high-power densities, high safety factors, and low maintenance costs, so they have attracted widespread attention among researchers. However, a major problem with supercapacitors is that their energy densities are not high enough, which limits their application. Therefore, it is crucial to expand the application scenarios of supercapacitors to increase their energy density as much as possible without diminishing their advantages. The classification and working principles of supercapacitors are introduced in this paper. The electrochemical properties of pure NiS materials, NiS composites with carbon materials, NiS composites with sulfide materials, and NiS composites with transition metal oxides for supercapacitors are summarized. This paper may assist in the design of new electrode materials for NiS-based supercapacitors.

Tunable Electronic Properties of Two-Dimensional GaSe1-xTex Alloys

In this work, we performed a theoretical study on the electronic properties of monolayer GaSe1-xTex alloys using the first-principles calculations. The substitution of Se by Te results in the modification of a geometric structure, charge redistribution, and bandgap variation. These remarkable effects originate from the complex orbital hybridizations. We demonstrate that the energy bands, the spatial charge density, and the projected density of states (PDOS) of this alloy are strongly dependent on the substituted Te concentration.

Sulfur Nanoparticle-Decorated Nickel Cobalt Sulfide Hetero-Nanostructures with Enhanced Energy Storage for High-Performance Supercapacitors

Transition-metal sulfides exaggerate higher theoretical capacities and were considered a type of prospective nanomaterials for energy storage; their inherent weaker conductivities and lower electrochemical active sites limited the commercial applications of the electrodes. The sheet-like nickel cobalt sulfide nanoparticles with richer sulfur vacancies were fabricated by a two-step hydrothermal technique. The sheet-like nanoparticles self-combination by ultrathin nanoparticles brought active electrodes entirely contacted with the electrolytes, benefiting ion diffusion and charges/discharges. Nevertheless, defect engineers of sulfur vacancy at the atomic level raise the intrinsic conductivities and improve the active sites for energy storage functions. As a result, the gained sulfur-deficient NiCo2S4 nanosheets consist of good specific capacitances of 971 F g-1 at 2 A g-1 and an excellent cycle span, retaining 88.7% of the initial capacitance over 3500 cyclings. Moreover, the values of capacitance results exhibited that the fulfilling characteristic of the sample was a combination of the hydrothermal procedure and the surface capacitances behavior. This novel investigation proposes a new perspective to importantly improve the electrochemical performances of the electrode by the absolute engineering of defects and morphologies in the supercapacitor field.

Two-Dimensional Core-Shell Structure of Cobalt-Doped@MnO2 Nanosheets Grown on Nickel Foam as a Binder-Free Battery-Type Electrode for Supercapacitor Application

Herein, we present an interfacial engineering strategy to construct an efficient hydrothermal approach by in situ growing cobalt-doped@MnO₂ nanocomposite on highly conductive nickel foam (Ni foam) for supercapacitors (SCs). The remarkably high specific surface area of Co dopant provides a larger contacting area for MnO₂. In the meantime, the excellent retentions of the hierarchical phase-based pore architecture of the cobalt-doped surface could beneficially condense the electron transportation pathways. In addition, the nickel foam (Ni foam) nanosheets provide charge-transport channels that lead to the outstanding improved electrochemical activities of cobalt-doped@MnO₂. The unique cobalt-doped@MnO₂ nanocomposite electrode facilitates stable electrochemical architecture, multi-active electrochemical sites, and rapid electro-transports channels; which act as a key factor in enhancing the specific capacitances, stability, and rate capacities. As a result, the cobalt-doped@MnO₂ nanocomposite electrode delivered superior electrochemical activities with a specific capacitance of 337.8 F g^-1 at 0.5 A g^-1; this is greater than pristine MnO₂ (277.9 F g^-1). The results demonstrate a worthy approach for the designing of high-performance SCs by the grouping of the nanostructured dopant material and metal oxides.

Conductive PPy@cellulosic Paper Hybrid Electrodes with a Redox Active Dopant for High Capacitance and Cycling Stability

Polypyrrole@cellulose fibers (PPy@CFs) electrode materials are promising candidates in the energy storage. Various strategies have been pursued to improve their electrochemical performance. However, the poor conductivity, specific capacitance, and cyclic stability still hindered its application. Compared with the previous studies, we selected AQS with electrochemical activity as a dopant to improve these defects. It exhibits a high capacitance of 829.8 F g⁻¹ at a current density of 0.2 A g⁻¹, which is much higher than that of PPy@CFs electrode material (261.9 F g⁻¹). Moreover, the capacitance retention of PPy:AQS/p-PTSA@CFs reaches up to 96.01% after 1000 cycles, indicating superior cyclic stability. Therefore, this work provides an efficient strategy for constructing high-performance electrode materials for energy storage.

Polyaniline inside the pores of high surface area mesoporous silicon as composite electrode material for supercapacitors

Mesoporous silicon (mSi) obtained by the magnesiothermic reduction of mesoporous silica was used to deposit polyaniline (PANI) in its pores, the composite was tested for its charge storage application for high performance supercapacitor electrodes. The mesoporous silica as confirmed by Small Angle X-ray Scattering (SAXS) has a Brunauer-Emmett-Teller (BET) surface area of 724 m2g-1 and mean pore size of 5 nm. After magnesiothermic reduction to mSi, the BET surface area is reduced to 348 m2g-1 but the mesoporousity is retained with a mean pore size of 10 nm. The BET surface area of mesoporous silicon is among the highest for porous silicon prepared/reduced from silica. In situ polymerization of PANI inside the pores of mSi was achieved by controlling the polymerization conditions. As a supercapacitor electrode, the mSi-PANI composite exhibits better charge storage performance as compared to pure PANI and mesoporous silica-PANI composite electrodes. Enhanced electrochemical performance of the mSi-PANI composite is attributed to the high surface mesoporous morphology of mSi with a network structure containing abundant mesopores enwrapped by an electrochemically permeable polyaniline matrix.

Advances in Engineered Metal Oxide Thin Films by Low-Cost, Solution-Based Techniques for Green Hydrogen Production

Functional oxide materials have become crucial in the continuous development of various fields, including those for energy applications. In this aspect, the synthesis of nanomaterials for low-cost green hydrogen production represents a huge challenge that needs to be overcome to move toward the next generation of efficient systems and devices. This perspective presents a critical assessment of hydrothermal and polymeric precursor methods as potential approaches to designing photoelectrodes for future industrial implementation. The main conditions that can affect the photoanode's physical and chemical characteristics, such as morphology, particle size, defects chemistry, dimensionality, and crystal orientation, and how they influence the photoelectrochemical performance are highlighted in this report. Strategies to tune and engineer photoelectrode and an outlook for developing efficient solar-to-hydrogen conversion using an inexpensive and stable material will also be addressed.

Fabrication of Mn3O4-CeO2-rGO as Nanocatalyst for Electro-Oxidation of Methanol

Recently, the use of metal oxides as inexpensive and efficient catalysts has been considered by researchers. In this work, we introduce a new nanocatalyst including a mixed metal oxide, consisting of manganese oxide, cerium oxide, and reduced graphene oxide (Mn₃O₄-CeO₂-rGO) by the hydrothermal method. The synthesized nanocatalyst was evaluated for the methanol oxidation reaction. The synergetic effect of metal oxides on the surface of rGO was investigated. Mn₃O₄-CeO₂-rGO showed an oxidation current density of 17.7 mA/cm² in overpotential of 0.51 V and 91% stability after 500 consecutive rounds of cyclic voltammetry. According to these results, the synthesized nanocatalyst can be an attractive and efficient option in the methanol oxidation reaction process.

Successful Manufacturing Protocols of N-Rich Carbon Electrodes Ensuring High ORR Activity: A Review

The exploration and development of different carbon nanomaterials happening over the past years have established carbon electrodes as an important electrocatalyst for oxygen reduction reaction. Metal-free catalysts are especially promising potential alternatives for replacing Pt-based catalysts. This article describes recent advances and challenges in the three main synthesis manners (i.e., pyrolysis, hydrothermal method, and chemical vapor deposition) as effective methods for the production of metal-free carbon-based catalysts. To improve the catalytic activity, heteroatom doping the structure of graphene, carbon nanotubes, porous carbons, and carbon nanofibers is important and makes them a prospective candidate for commercial applications. Special attention is paid to providing an overview on the recent major works about nitrogen-doped carbon electrodes with various concentrations and chemical environments of the heteroatom active sites. A detailed discussion and summary of catalytic properties in aqueous electrolytes is given for graphene and porous carbon-based catalysts in particular, including recent studies performed in the authors’ research group. Finally, we discuss pathways and development opportunities approaching the practical use of mainly graphene-based catalysts for metal–air batteries and fuel cells.

Electrochemical Behavior of Symmetric Electrical Double-Layer Capacitors and Pseudocapacitors and Identification of Transport Anomalies in the Interconnected Ionic and Electronic Phases Using the Impedance Technique

A double-channel transmission line impedance model was applied to the study of supercapacitors to investigate the charge transport characteristics in the ionic and electronic conductors forming the electrode/solution interface. The macro homogeneous description of two closely mixed phases (Paasch-Micka-Gersdorf model) was applied to study the influence of disordered materials on the charge transport anomalies during the interfacial charge-discharge process. Different ex situ techniques were used to characterize the electrode materials used in electrical double-layer (EDLC) and pseudocapacitor (PC) devices. Two time constants in the impedance model were adequate to represent the charge transport in the different phases. The interfacial impedance considering frequency dispersion and blocked charge transfer conditions adequately described the charge storage at the interface. Deviations from the normal (Fickian) transport involving the ionic and electronic charge carriers were identified by the dispersive parameters (e.g., n and s exponents) used in the impedance model. The ionic and electronic transports were affected when the carbon-based electrical double-layer capacitor was converted into a composite with strong pseudocapacitive characteristics after the decoration process using NiO. The overall capacitance increased from 2.62 F g-1 to 536 F g-1 after the decoration. For the first time, the charge transport anomalies were unequivocally identified in porous materials used in supercapacitors with the impedance technique.

Non-aqueous synthesis of high-quality Prussian blue analogues for Na-ion batteries

A microwave-assisted solvothermal (MW-ST) method was developed to synthesize high-quality Prussian blue analogues. The tuned NaFeHCF exhibits low water content as well as good thermal stability. It delivers a high...