A versatile ionic liquid-assisted approach to synthesize hierarchical structures of β-Ni(OH) 2 nanosheets for high performance pseudocapacitor

A high-performance histidine-functionalized MWCNT-GONR/Co–Ni LDH flower cluster structural composite via a microwave synthesis for supercapacitors

A flower cluster structural histidine-functionalized multi-walled carbon nanotube-graphene oxide nanoribbon/Co–Ni LDH (His-MW/LDH) composite was synthesized via the microwave method.

PVP-Assisted Synthesis of Self-Supported Ni2P@Carbon for High-Performance Supercapacitor

Highly conductive and stable electrode materials are usually the focus of high-performance supercapacitors. In this work, a unique design of Ni₂P@carbon self-supported composite nanowires directly grown on Ni foam was applied for a supercapacitor. The Co₃O₄ nanowire array was first synthesized on the Ni foam substrate, and the resulting Ni₂P@carbon nanocomposite was obtained by hydrothermally coating Co₃O₄ with the Ni-ethylene glycol complex followed by gaseous phosphorization. We have discovered that the molecular weight of surfactant polyvinylpyrrolidone (PVP) used in the hydrothermal step, as well as the temperature for phosphorization, played very important roles in determining the electrochemical properties of the samples. Specifically, the sample synthesized using PVP with 10 k molecular weight and phosphorized at 300°C demonstrated the best supercapacitive performance among the different samples, with the highest capacitance and most stable cyclic retention. When an asymmetric supercapacitor (ASC) was assembled with this Ni₂P@carbon sample as the cathode and activated carbon (AC) as the anode, the ASC device showed excellent capacitances of 3.7 and 1.6 F cm⁻² at 2 and 50 mA cm⁻², respectively, and it kept a high capacitance of 1.2 F cm⁻² after 5000 cycles at a current rate of 25 mA cm⁻². In addition, the ASC could reach a high energy density of about 122.8 Wh kg⁻¹ at a power density of 0.15 kW kg⁻¹ and 53.3 Wh kg⁻¹ at the highest power density of 3.78 kW kg⁻¹. Additionally, this device also had the ability to power up 16 red LEDs effortlessly, making it a strong candidate in electrochemical energy storage for practical usage.

Ionic Liquids as Environmentally Benign Electrolytes for High-Performance Supercapacitors

Electrochemical capacitors (ECs) are a vital class of electrical energy storage (EES) devices that display the capacity of rapid charging and provide high power density. In the current era, interest in using ionic liquids (ILs) in high-performance EES devices has grown exponentially, as this novel versatile electrolyte media is associated with high thermal stability, excellent ionic conductivity, and the capability to withstand high voltages without undergoing decomposition. ILs are therefore potentially useful materials for improving the energy/power performances of ECs without compromising on safety, cyclic stability, and power density. The current review article underscores the importance of ILs as sustainable and high-performance electrolytes for electrochemical capacitors.

Electrochemical phase diagrams of Ni from ab initio simulations: role of exchange interactions on accuracy

The stabilities of Ni metal and its derived compounds, including oxides, hydroxides, and oxyhydroxides under electrochemical conditions, can be readily predicted from the Ni Pourbaix diagram, where the formation free energies of the involved species are utilized to construct the phase stability map with respect to electrode potential and pH. We calculate and analyze the crystal structures, electronic structures, and thermodynamic energies of Ni metal and its compounds using different exchange-correlation functionals to density-functional-theory (DFT), including the semilocal LDA and GGA density functionals, the nonlocal metaGGA, and the hybrid density functionals. Next, we simulate the corresponding Ni Pourbaix diagrams to compare systematically the performance of the functional to each other and to experimental observations. We show that the structures and energies obtained from experimental databases may not be sufficiently accurate to describe direct electrochemical observations, and we explain how the electronic exchange within the density functionals plays a key role in determining the accuracy of the DFT calculated electronic, thermodynamic, and electrochemical properties. We find that only the hybrid density functional produces reliable results owing to the fractional contribution of exact Fock exchange included therein. Last, based on our accurate Ni Pourbaix diagram, we construct band-gap and magnetic electrochemical maps which can facilitate more experimental measurements and property assessments under variable potential and pH in the future.

Rational Design of Self-Supported Ni3S2 Nanosheets Array for Advanced Asymmetric Supercapacitor with a Superior Energy Density

We report a rationally designed two-step method to fabricate self-supported Ni₃S₂ nanosheet arrays. We first used 2-methylimidazole (2-MI), an organic molecule commonly served as organic linkers in metal-organic frameworks (MOFs), to synthesize an α-Ni(OH)₂ nanosheet array as a precursor, followed by its hydrothermal sulfidization into Ni₃S₂. The resulting Ni₃S₂ nanosheet array demonstrated superior supercapacitance properties, with a very high capacitance of about 1,000 F g^-1 being delivered at a high current density of 50 A g^-1 for 20,000 charge-discharge cycles. This performance is unparalleled by other reported nickel sulfide-based supercapacitors and is also advantageous compared to other nickel-based materials such as NiO and Ni(OH)₂. An asymmetric supercapacitor was then established, exhibiting a very stable capacitance of about 200 F g^-1 at a high current density of 10 A g^-1 for 10,000 cycles and a surprisingly high energy density of 202 W h kg^-1. This value is comparable to that of the lithium-ion batteries, i.e., 180 W h kg^-1. The potential of the material for practical applications was evaluated by building a quasi-solid-state asymmetric supercapacitor which showed good flexibility and power output, and two of these devices connected in series were able to power up 18 green light-emitting diodes.