Supercapacitor: 2D metallic conductor CrSe₂ synthesized at scale as crystalline powder remains stable in acidic conditions and outperforms high surface area carbon in supercapacitor applications

Abstract

Supercapacitors are energy storage devices with the ability to rapidly charge and discharge, making them a valuable complement to battery systems. To maximize their fast-charging capabilities, identifying materials and methods to enhance their energy density is crucial. In this work, we carried out a comprehensive study of an emerging 2D dichalcogenide, CrSe₂, as a supercapacitor material. We demonstrate that CrSe₂ can be obtained at ambient temperature through deintercalation of a relevant KCrSe₂ precursor using a 0.5 M solution of I₂ in acetonitrile. Although CrSe₂ decomposed in 1 M KOH, it was found to be chemically stable in common electrolytes such as H₂SO₄, Li₂SO₄, and Na₂SO₄. Despite low surface area CrSe₂ reached a specific capacitance of 27 F g⁻¹ in 1 M H₂SO₄ and, thus consistently outperformed high surface carbon black. Computational studies suggested that the metallic conductivity of CrSe₂ was likely the primary factor contributing to the superior performance of this 2D chalcogenide over high surface carbon analogues.

Supercapacitors are interesting energy storage devices in terms of power density and lifetime. Organic electrolytes are frequently applied in commercial supercapacitor devices. However, their water-based counterparts are much more sustainable, cost-effective and safer. Therefore, aqueous energy storage devices are interesting alternatives. Here, aqueous Ammonium and tartrate-based electrolytes are introduced as possible candidates for applications in aqueous supercapacitors.

Abstract

Supercapacitors are promising energy storage devices in terms of power density and lifetime. Organic electrolytes are frequently applied in commercial supercapacitor devices. However, their water-based counterparts are much safer, more sustainable and cost-effective. In this study we therefore present, for the first time, aqueous tartrate-based electrolytes (sodium tartrate / ammonium tartrate) for supercapacitor applications, and relate them to well-known inorganic aqueous electrolytes like Na₂SO₄. Additionally, the influence of the cation on the electrochemical performance of supercapacitors is investigated using sodium and ammonium cations for comparison. We demonstrate the electrochemical performance and physicochemical properties of ammonium tartrate / sulfate and sodium tartrate / sulfate. An improvement of the conductivity in the range of 40–60 % was achieved by the exchange of sodium cation with ammonium cation. Carbon electrodes in newly introduced aqueous tartrate-based electrolytes deliver high specific capacitances up to 117 Fg⁻¹. Furthermore, electrical double layer capacitors (EDLCs) containing 1 M ammonium tartrate display a high energy density at 0.1 Ag⁻¹ and at 10 Ag⁻¹ (9.88 Whkg⁻¹ and 1.14 Whkg⁻¹, respectively). Floating tests show excellent long-term performance. Tartrate-based EDLCs retain >80 % of their initial capacitance at 1.6 V cell voltage (120 h floating time). In the case of ammonium tartrate electrolyte, a novel metal-free and non-toxic concept for an eco-friendly supercapacitor device is proposed.

The Front Cover illustrates a chimney made of Sn-modified geopolymer-bricks. Functionalized geopolymers can be applied as hybrid material for construction and as an electrode for CO₂ electrolysis to formate. The cover was designed by one of the authors Jürgen Schuster and the designer Verena Stöckl. More information can be found in the Research Article by J. Schuster et al.

Noble-free 3D anode: 3D-printed Ti-6Al-4V electrode was evaluated for its anodic behavior in alkaline solutions with a novel electrochemical approach. According to the ECSA results from voltammetry, 3D Ti-6Al-4V provides 42 times more active surface area than flat plate anodes. It enables effective charge transfer of 911 mA cm⁻² from almost non-conductive anodic behavior of a plate structure.

Abstract

Electrochemical processes use expensive noble metal-based anodes which limit industrial implementation. In this study, a noble-metal-free Ti-6Al-4V anode is introduced in an advanced flow reactor. We demonstrate that the 3D additively manufactured electrode can provide a more projected surface area and facilitate anodic reactions under controlled electrolyte conditions. Alkaline NaOH and KOH electrolytes act as anodic electrolytes that are toxic compounds-free and enable corrosion control. Impedance and voltammetry responses to electrochemical reactions are studied. The electrochemical active surface area of the 4 rods scaffold geometry is 42 times higher than a flat plate anode. Therefore, improved charge transfer is achieved in the flow reactor incorporating the 3D Ti-6Al-4V electrode due to the increased surface area and wettability. The structure of almost non-conductive passivation on a flat plate anode is changed to unstable passivation due to the 3D scaffold structure. This enables effective charge transfer of 911 mA cm⁻² at higher potentials up to 5 V for 1.5 m KOH in a non-flow condition. Furthermore, a 1 m KOH solution delays metal ion dissolution from the anode surface by acting as a corrosion-controlling medium. 3D Ti-6Al-4V is likely to be an affordable alternative anode in alkaline environmentally friendly electrochemical applications.

The Cover Feature shows the Al-air battery test cell prepared for the 3D Al-porous electrode. There are also clues about the reaction on the porous electrode surface in contact with the solution. Porous electrodes can positively affect battery performance by providing additional active surface area in NaOH solution. The battery performance of the electrodes is analyzed in comparison with a smooth surface electrode. Cover design by Osman Kahveci. More information can be found in the Research Article by O. Kahveci.

This work provides a comprehensive review of the current progress on the mechanism, influencing factors, product detection methods, performance evaluation methods and strategies used to design efficient electrocatalysts for the electrochemical synthesis of ammonia from nitrate. Additionally, it briefly predicts the future research direction with the aim of offering a certain reference for the development of green and environmentally friendly nitrogen fixation technology.

Abstract

The presence of nitrate in industrial, domestic and agricultural wastewater has a detrimental impact on both ecosystem and human health, as remediation and purification efforts are slow, challenging and difficult, given the high solubility and stability of this pollutant. Taking nitrate into high value-added ammonia by electrochemical reduction can overcome high pollution and energy consumption limit of Haber-Bosch process with long-term significance of environmental protection and energy saving. This review summarized the research progress on the electrocatalytic reduction of nitrate to ammonia, with a focus on the reaction mechanisms, influencing factors, product detection methods, performance evaluation methods and the research status of electrocatalysts up to now. The review reported the latest strategies employed to design efficient electrocatalysts, such as pore structure regulation, alloying, heterostructure construction, defect and interface engineering, crystal surface regulation and microenvironment modulation of single-atom catalysts. It highlights critical factors that determin the performance in terms of nitrate adsorption, exposed active sites, mass transfer rate, intermediates barrier and side reactions, as well as the stability of electrocatalysts and recovery of ammonia. In addition, the future direction of technology for electrocatalytic reduction of nitrate to ammonia has also been proposed.

Polymers for batteries: A linear polymer with micro and Nano pores with azo and carbonyl functionalities renders increased accessibility to Li ions after preconditioning. During charge-discharge experiment Azo-Carb-PDI electrode had impressive discharge capacity of 469 mA h/g after 500 cycle which is almost 15 times higher than the monomer (Azo-PDI-Azo, 30 mA h/g after 100 cycle).

Abstract

Organic materials with carbonyl, azo, nitrile and imine moieties are widely used in lithium batteries. The solubility of these materials in battery electrolytes is an issue. Aggregation of the organic molecules can suppress the solubility, but the accessibility of lithium-ion is hindered. Therefore, insoluble porous organic materials are desired. Herein, we synthesized a linear polymer with carbonyl and azo functionalities. Due to the presence of easily isomerizable azo moiety, a porous polymer was obtained. The polymer showed nano and micropores. The battery with the porous polymer showed an impressive specific capacity of 400 mA h/g at 0.2 A/g. If the battery is pre-conditioned, the specific capacity increased to 615 mA h/g at the same current density. The post-mortem analysis of the battery confirmed that the polymer didn't dissolve in the battery electrolyte. The control material is a small molecule with carbonyl and azo moieties that showed a poor specific capacity of 40 mA h/g indicating the necessity to have a hierarchically porous dual-functional polymer.

Nano-XCT analysis for batteries: This study compares scanning electron microscopy images and nano X-ray computed tomography scans of pristine and cycle-aged battery electrodes. Structural changes over the cycle life are determined, and a quantitative analysis of the active material‘s gray scale value distribution reveals severe degradation near the separator interface, with a reciprocal relationship to particle radius.

Abstract

LiNi_0.8Co_0.1Mn_0.1O₂ has emerged as a promising electrode material for automotive lithium-ion batteries due to its high specific discharge capacity, cost-effectiveness, and reduced cobalt content. However, despite all mentioned beneficial attributes, the widespread adoption of this material class is impeded by active material degradation during cycling operation, which is linked to performance loss. This study compares scanning electron microscopy images and nano X-ray computed tomography scans with a 3D reconstruction of pristine and cycle-aged battery electrodes to determine structural changes over cycle life. Although a very moderate current rate was chosen for the cycle test, which suggests a homogeneous load across the entire electrode, particle fracture varied across electrode thickness and particle size. A quantitative analysis of the active material‘s gray scale value distribution reveals severe degradation near the separator interface with a reciprocal relationship to particle radius. Remarkably, particle shape and size remain relatively unchanged despite cracking, eliminating the need to adjust these parameters in aging simulations. Moreover, it underscores the practical significance of particle cracking, as it can significantly impact the electrode‘s performance. Thus, analyzing changes in particle shape and size alone is insufficient, and a comprehensive exploration of the particle interior using nano-XCT is necessary.

The inner potential φ experienced by an ion differs greatly from the average electrostatic potential as calculated by DFT. The problem is caused by the divergence of the potential at the sites of the nuclei. DFT-based tight binding gives results in line with values estimated from experiment or from other models, and allows a uniform quantum-mechanical modeling of electrode and solution.

Abstract

In modelling electrochemical interfaces it is important to treat electrode and electrolyte at the same level of theory. Density functional theory, which is usually the method of choice, suffers from a distinct disadvantage: The inner potential is calculated as the average of the total electrostatic potential. This includes the highly localized potential generated from the nuclei. The resulting inner potential is far too high, of the order of 3.5 V, and not relevant for electrochemistry. In the density functional based tight binding (DFTB) method the electrostatic potential is much smoother, as it stems from atomic charge fluctuations with respect to neutral reference atoms. The resulting values for the electrochemical inner potential are much lower and compare well with those obtained by other, elaborate methods. Thus DFTB recommends itself as a method for treating the electrochemical interface including the inner potential.

In this paper, the PWCM electrode prepared from polymer wastes in recent years was reviewed, and the effect of different preparation methods on the electrode performance was compared.

Abstract

Due to the high power density, fast charging speed, and long cycling stability, supercapacitors have been developed rapidly in the area of electrical energy storage devices in the past decades. During the application of supercapacitors, it was found that the properties of the electrode material can greatly affect the supercapacitor performance. Recently, electrode materials based on polymer waste-derived carbon materials (PWCM) have attracted much attention because of the low preparation cost, good electrode performance, and great benefits for environmental protection. This review aims to describe the recent research development and summarize the investigation state in the field of the PWCM electrodes prepared from polyethylene, polypropylene, polyethylene terephthalate, polystyrene, etc. The preparation method and the electrode performance of the PWCM electrodes are compared. The relationship among the preparation methods, material structure, and electrochemical performance of the PWCM electrodes was explored. Furthermore, the prospects for the application of the PWCMs were provided.