High-rate transition metal-based cathode materials for battery-supercapacitor hybrid devices

Efficient improvement in the electrochemical performance of petal-like lamellar NiMn-LDHs with affluent oxygen vacancies derived from Mn MOF-74

Supercapacitors (SCs) as a kind of novel energy storage devices have emerged to meet the urgent requirement of environmentally friendly clean energy storage equipment. However, unsatisfactory energy density and low operating voltage tremendously restrict their practical application. Herein, petal-like lamellar NiMn-layered double hydroxide (NiMn-LDH) was successfully fabricated through a simple Ni(NO3)2 etching method with Mn MOF-74 as a sacrificial template. This NiMn-LDH 3/NF electrode exhibited an improved specific capacitance of 1410.2 F g-1 at a current density of 1 A g-1 (Mn MOF-74/NF: 172.2) owing to its high redox activity, compositional flexibility and intercalating capability. Importantly, NiMn-LDH was further optimized via a facile hydroperoxide treatment to harvest NiMn-LDH (O-LDH) with abundant oxygen vacancies, exhibiting remarkable improvement in specific capacitance (990%) compared to original MOF-74 before modification. The preparation of O-LDH enriches the electrode material engineering strategy and achieves improved electrochemical performance for application in new-generation SCs.

Modular Cluster Circuits for the Variational Quantum Eigensolver

The variational quantum eigensolver algorithm recently became a popular method to compute the quantum chemical properties of molecules on noisy intermediate scale quantum (NISQ) devices. In order to avoid noise accumulation from the NISQ device in the quantum circuit, it is important to keep the so-called quantum depth of the circuit at a minimum, defined as the minimum number of quantum gates that must be operated sequentially. In the present work, we introduce a modular 2-qubit cluster circuit that allows for the design of a shallow-depth quantum circuit compared to previously proposed architectures without loss of chemical accuracy. Moreover, by virtue of the simplicity of the cluster circuit, it is possible to assign a valence bond chemical interpretation to the cluster circuit. The design was tested on the H2, (H2)2, and LiH molecules, as well as the finite-size transverse-field Ising model, as the latter provides additional insights into the construction of the circuit in a resonating valence bond picture.

Superior cyclability of high surface area vanadium nitride in salt electrolytes

High surface area vanadium nitrides (VNs) have been extensively studied as materials for aqueous supercapacitors due to the high initial capacitance in alkaline media at low scan rates. However, low capacitance retention and safety limit their implementation. The use of neutral aqueous salt solutions has the potential to mitigate both of these concerns, but is limited in analysis. Hence, we report on the synthesis and characterization of high surface area VN as a supercapacitor material in a wide variety of aqueous chlorides and sulfates using Mg²⁺, Ca²⁺, Na⁺, K⁺, and Li⁺ ions. We observe the following trend in the salt electrolytes: Mg²⁺ > Li⁺ > K⁺ > Na⁺ > Ca²⁺. Mg²⁺ systems provide the best performance at higher scan rates with areal capacitances of 294 μF cm^-2 in 1 M MgSO₄ over a 1.35 V operating window at 2000 mV s^-1. Furthermore, VN in 1 M MgSO₄ maintained a 36% capacitance retention from 2 to 2000 mV s^-1 compared to 7% in 1 M KOH. Capacitance in 1 M MgSO₄ and 1 M MgCl₂ increased to 121% and 110% of their original values after 500 cycles and maintained capacitances of 589 and 508 μF cm^-2 at 50 mV s^-1 after 1000 cycles, respectively. In contrast, in 1 M KOH the capacitance decreases to 37% of its original value, reaching only 29 F g^-1 at 50 mV s^-1 after 1000 cycles. The superior performance of the Mg system is attributed to a reversible surface 2 e^- transfer pseudocapacitive mechanism between Mg²⁺ and VN_xO_y. These findings can be used to further the field of aqueous supercapacitors to build safer and more stable energy storage systems that can charge quicker compared to KOH systems.

Electrode Materials for Supercapacitors in Hybrid Electric Vehicles: Challenges and Current Progress

For hybrid electric vehicles, supercapacitors are an attractive technology which, when used in conjunction with the batteries as a hybrid system, could solve the shortcomings of the battery. Supercapacitors would allow hybrid electric vehicles to achieve high efficiency and better power control. Supercapacitors possess very good power density. Besides this, their charge-discharge cycling stability and comparatively reasonable cost make them an incredible energy-storing device. The manufacturing strategy and the major parts like electrodes, current collector, binder, separator, and electrolyte define the performance of a supercapacitor. Among these, electrode materials play an important role when it comes to the performance of supercapacitors. They resolve the charge storage in the device and thus decide the capacitance. Porous carbon, conductive polymers, metal hydroxide, and metal oxides, which are some of the usual materials used for the electrodes in the supercapacitors, have some limits when it comes to energy density and stability. Major research in supercapacitors has focused on the design of stable, highly efficient electrodes with low cost. In this review, the most recent electrode materials used in supercapacitors are discussed. The challenges, current progress, and future development of supercapacitors are discussed as well. This study clearly shows that the performance of supercapacitors has increased considerably over the years and this has made them a promising alternative in the energy sector.