Ni and Zn co-substituted Co(CO3)0.5OH self-assembled flowers array for asymmetric supercapacitors

Robust and Corrosion-Resistant Overall Water Splitting Electrode Enabled by Additive Manufacturing

Electrolysis of water has emerged as a prominent area of research in recent years. As a promising catalyst support, copper foam is widely investigated for electrolytic water, yet the insufficient mechanical strength and corrosion resistance render it less suitable for harsh working conditions. To exploit high-performance catalyst supports, various metal supports are comprehensively evaluated, and Ti6 Al4 V (Ti64) support exhibited outstanding compression and corrosion resistance. With this in mind, a 3D porous Ti64 catalyst support is fabricated using the selective laser sintering (SLM) 3D printing technology, and a conductive layer of nickel (Ni) is coated to increase the electrical conductivity and facilitate the deposition of catalysts. Subsequently, Co0.8 Ni0.2 (CO3 )0.5 (OH)·0.11H2 O (CoNiCH) nanoneedles are deposited. The resulting porous Ti64/Ni/CoNiCH electrode displayed an impressive performance in the oxygen evolution reaction (OER) and reached 30 mA cm-2 at an overpotential of only 200 mV. Remarkably, even after being compressed at 15.04 MPa, no obvious structural deformation is observed, and the attenuation of its catalytic efficiency is negligible. Based on the computational analysis, the CoNiCH catalyst demonstrated superior catalytic activity at the Ni site in comparison to the Co site. Furthermore, the electrode reached 30 mA cm-2 at 1.75 V in full water splitting conditions and showed no significant performance degradation even after 60 h of continuous operation. This study presents an innovative approach to robust and corrosion-resistant catalyst design.

A Se-induced heterostructure electrode with polymetallic-CoNiFe towards high performance supercapacitors

Rational regulation of electrode materials with high conductivity and unexceptionable cycling stability is crucial to meet the requirements of high-performance supercapacitors (SCs). Herein, a hierarchical porous kebab-like heterostructure (CoNiFe-Se) is prepared by a facile solvothermal reaction and selenization step. Both experimental and computational results demonstrate that incorporating Se via hydrothermal reaction contributes to modulating the morphology and electronic structure of transition metal carbonate hydroxides. The heterostructured electrode with abundant active sites composed of electroactive polymetallic-CoNiFe imparts excellent charge storage. Additionally, the unique structure of CoNiFe-Se with its heterogeneous interface, oxygen vacancies and cavities improves electrochemical activity, accelerates electron transfer and suppresses the volume expansion during the cycling. As a result, the CoNiFe-Se exhibits excellent electrochemical performance of 5040 mF cm-2 at 1 mA cm-2 and long-term durability with 85.7% retained capacitance after 10 000 cycles. Interestingly, an integrated asymmetric supercapacitor performs well for energy storage. This finding opens a new avenue for developing transition metal carbonate hydroxides using selenization strategies in the field of SCs.

Magnetically Triggered Interplay of Capacitive and Diffusion Contributions for Boosted Supercapacitor Performance

The chemistry involved in supercapacitors in terms of their mechanistic contributions leading to improved specific capacity will aid in easy commercialization. The main contributory factors in a supercapacitor are either capacitive (non-diffusion controlled) or ion-diffusion behavior, which results in enhanced charge-discharge characteristics of a supercapacitor reflected in its power density, whereas ion-diffusion behavior will lead to the enhanced energy density of a supercapacitor. In this context, the present article attempts to understand the use of external magnetic fields, leading to the interplay between capacitive and ion-diffusion behavior in a high-performance supercapacitor. The model system chosen in the present study, nickel cobalt copper carbonate hydroxide (NiCoCuCH), can effectively address the interplay between capacitive and ion diffusion contributions by varying total magnetic effects involving magnetic dilution. The magneto-enhancement of the electrodes nickel cobalt copper carbonate hydroxide (NiCoCuCH) and aluminum-doped nickel cobalt copper carbonate hydroxide (Al-NiCoCuCH) was demonstrated under the magnetic field from 0 to 250 mT. Both NiCoCuCH and Al-NiCoCuCH show dominant non-diffusion-controlled (capacitive) and diffusion-controlled behavior as a function of the applied external magnetic field. Under the influence of the external magnetic field, ferromagnetic coupling between metal-oxygen-metal centers via oxygen 2p orbitals enhances, leading to a facile redox pathway. To further control the charge-discharge behavior of the electrode via the interplay between diffusive and capacitive, a non-magnetic ion, Al3+, was doped into the bare metal carbonate hydroxide crystal lattice. The Al3+ ion not only alters the crystal symmetry but also restricts the alignment of the magnetic domains in the electrode, leading to a sluggish redox pathway, effectively increasing the capacitive contribution, and leading to improved charge-discharge characteristics at the expense of energy density. We have constructed an asymmetric device with the best-performing (110 mT) NiCoCuCH electrode as a positive electrode and activated carbon as a negative electrode. The NiCoCuCH/AC ASC device at 110 mT has the largest specific capacity (1100 C g-1 at 2 A g-1) at 110 mT, leading to a high energy density (250 W h kg-1) and a power density (1.7 kW kg-1) of the electrode.

High-performance asymmetric supercapacitor based on a CdCO3/CdO/Co3O4 composite supported on Ni foam – part II: a three-electrode electrochemical study†

A binder-free CdCO₃/CdO/Co₃O₄ compound with a micro-cube-like morphology on a nickel foam (NF) made via a facile two-step hydrothermal + annealing procedure has been developed. The morphological, structural and electrochemical behavior of both the single compounds constituting this final product and the final product itself has been studied. The synergistic contribution effect of the single compounds in the final compounded resulting specific capacitance values are presented and discussed. The CdCO₃/CdO/Co₃O₄@NF electrode exhibits excellent supercapacitive performance with a high specific capacitance (C_S) of 1.759 × 10³ F g⁻¹ at a current density of 1 mA cm⁻² and a C_S value of 792.3 F g⁻¹ at a current density of 50 mA cm⁻² with a very good rate capability. The CdCO₃/CdO/Co₃O₄@NF electrode also demonstrates a high coulombic efficiency of 96% at a current density as high as 50 mA cm⁻² and also exhibits a good cycle stability with capacitance retention of ca. 100% after 1000 cycles at a current density of 10 mA cm⁻² along with a potential window of 0.4 V. The obtained results suggest that the facilely synthesized CdCO₃/CdO/Co₃O₄ compound has great potential in high-performance electrochemical supercapacitor devices.

Schematic illustration of the two-step process involved in the preparation of the different chemical compounds supported on the nickel foam substrates.

Effect of Intrinsic Pore Distribution on Ion Diffusion Kinetics of Supercapacitor Electrode Surface

The electrolyte ion diffusion kinetics have an important impact on electrochemical energy storage. Herein, we report the effect of the intrinsic porosity of NiCoP on accelerating electrolyte ion diffusion kinetics and accommodating volume expansion during the charge/discharge process. The pore distribution model of electrode/electrolyte was designed and optimized by the finite element simulation, demonstrating the visualization and quantitative analysis of the diffusion process of the electrode/electrolyte interface with intrinsic porous structure. When the pore area ratio reached 50.01%, the theoretical diffusion coefficient of 1.41 × 10^-11 m² s^-1 would be conducive to the rapid diffusion of electrolytes. The electrode gained a specific capacity of 2805 F g^-1 at a current density of 1 A g^-1 based on the measured diffusion coefficient (1.79 × 10^-10 m² s^-1), superior to 1.44-times that of the pristine electrode. The diffusion barriers of intrinsic porous NiCoP (3.19 eV) and conventional NiCoP (47.10 eV) were calculated by the density functional theory calculations, respectively. The intrinsic porous NiCoP was prepared by the hydrothermal treatment, annealing, and phosphating processes. The pore distribution was regulated by the concentration of NaHCO₃ as a pore-forming additive. This work combines simulations and experiments to form a method to optimize diffusion kinetics at the electrode/electrolyte interface.

New nickel-rich ternary carbonate hydroxide two-dimensional porous sheets for high-performance aqueous asymmetric supercapattery

Transition metal carbonate hydroxides (M-CHs) are promising candidates for electrode materials in supercapattery, due to their low-cost preparation and high-energy features. However, they also suffer from ionic kinetics bottlenecks without efficient morphological design. Tailoring the chemical compositions and nanostructures of electrode materials to realize high performance is significant for meeting the current demand for electrical energy storage devices. Therefore, we present a simple hydrothermal method for constructing better electrochemically active M-CHs with ternary metal components and hierarchical nanostructures that are assembled by interwoven nanosheets. Benefiting from higher contents of Ni species and superior two-dimensional/three-dimensional (2D/3D) pore structures, the fabricated cobalt-nickel-zinc carbonate hydroxides with Co/Ni/Zn molar ratios of 2:3:1 (CoNiZn-231) delivered the best specific capacity of 1130.8 C g^-1 at 1 A g^-1, decent rate performance (67.2% in 1-10 A g^-1), and excellent cycling performance (92.6% over 10,000 cycles) in comparison with the majority of mono/bimetallic materials. Then, an alkaline hybrid (CoNiZn-231//activated carbon (AC)) device is developed, which shows a high energy density of 31.62 Wh kg^-1 at a power density of 646 W kg^-1 and an excellent capacity retention of 99.27% after 10,000 cycles. Herein, the rational design of trimetallic compositions and hierarchical structures of carbonate hydroxides is described, which provides good choices for the synthesis of high-performance electrode materials in electrochemical energy storage applications.

Design of a Scalable Dendritic Copper@Ni2+, Zn2+ Cation-Substituted Cobalt Carbonate Hydroxide Electrode for Efficient Energy Storage

Design and fabrication of novel electrode materials with excellent specific capacitance and cycle stability are urgent for advanced energy storage devices, and the combinability of multiple modification methods is still insufficient. Herein, Ni²⁺, Zn²⁺ double-cation-substitution Co carbonate hydroxide (NiZnCo-CH) nanosheets arrays were established on 3D copper with controllable morphology (3DCu@NiZnCo-CH). The self-standing scalable dendritic copper offers a large surface area and promotes fast electron transport. The 3DCu@NiZnCo-CH electrode shows a markedly improved electrochemical performance with a high specific capacity of ∼1008 C g^-1 at 1 A g^-1 (3.2, 2.83, and 1.26 times larger than Co-CH, ZnCo-CH, and NiCo-CH, respectively) and outstanding rate capability (828.8 C g^-1 at 20 A g^-1) due to its compositional and structural advantages. Density functional theory (DFT) calculation results illustrate that cation doping adjusts the adsorption process and optimizes the charge transfer kinetics. Moreover, an aqueous hybrid supercapacitor based on 3DCu@NiZnCo-CH and rGO demonstrates a high energy density of 42.29 Wh kg^-1 at a power density of 376.37 W kg^-1, along with superior cycling performance (retained 86.7% of the initial specific capacitance after 10,000 cycles). Impressively, these optimized 3DCu@NiZnCo-CH//rGO devices with ionic liquid can be operated stably in a large potential range of 4 V with greatly enhanced energy density and power capability (110.12 Wh kg^-1 at a power density of 71.69 W kg^-1). These findings may shed some light on the rational design of transition-metal compounds with tunable architectures by multiple modification methods for efficient energy storage.

Tailoring NiCoAl layered double hydroxide nanosheets for assembly of high-performance asymmetric supercapacitors

NiCoAl layered double hydroxide nanosheets (NiCoAl-LDHNs) were prepared by a one-step solvothermal method. The shape and size of the obtained nanosheets are optimized by adjusting the solvothermal time and the molar concentration ratio of Ni²⁺/Co²⁺ to obtain the electrode material with the best performance. When the solvothermal time is 9 h and the molar concentration ratio of Ni²⁺/Co²⁺ is 1:1, NiCoAl-LDHNs has the best morphology and electrochemical performance. When assembled into a supercapacitor, NiCoAl-LDHN-9 has a high specific capacitance of 1228.5 F g^-1 at 1 A g^-1. As the current density is increased to 20 A g^-1, the specific capacitance is 1001.8 F g^-1, which still has a high capacitance retention of 81.6%. When NiCoAl-LDHN-9 was assembled into an asymmetric supercapacitor, NiCoAl-LDHN-9//AC has a specific capacitance of 102.1 F g^-1 at 0.5 A g^-1. The asymmetric supercapacitor devices also show excellent electrochemical performance in terms of energy density (35.9 Wh kg^-1 at 225.8 W kg^-1), power density (4.8 kW kg^-1 at 22.2 Wh kg^-1) and cycle life (capacitance retention rate after 10,000 cycles is 87.1%). Those results indicate that NiCoAl-LDHN have the potential to be promising electrode materials for high performance supercapacitors.