Capacitance response in an aqueous electrolyte of Nb2O5 nanochannel layers anodically grown in pure molten o-H3PO4

Hybrid and Asymmetric Supercapacitors: Achieving Balanced Stored Charge across Electrode Materials

An electrochemical capacitor configuration extends its operational potential window by leveraging diverse charge storage mechanisms on the positive and negative electrodes. Beyond harnessing capacitive, pseudocapacitive, or Faradaic energy storage mechanisms and enhancing electrochemical performance at high rates, achieving a balance of stored charge across electrodes poses a significant challenge over a wide range of charge-discharge currents or sweep rates. Consequently, fabricating hybrid and asymmetric supercapacitors demands precise electrochemical evaluations of electrode materials and the development of a reliable methodology. This work provides an overview of fundamental aspects related to charge-storage mechanisms and electrochemical methods, aiming to discern the contribution of each process. Subsequently, the electrochemical properties, including the working potential windows, rate capability profiles, and stabilities, of various families of electrode materials are explored. It is then demonstrated, how charge balancing between electrodes falters across a broad range of charge-discharge currents or sweep rates. Finally, a methodology for achieving charge balance in hybrid and asymmetric supercapacitors is proposed, outlining multiple conditions dependent on loaded mass and charge-discharge current. Two step-by-step tutorials and model examples for applying this methodology are also provided. The proposed methodology is anticipated to stimulate continued dialogue among researchers, fostering advancements in achieving stable and high-performance supercapacitor devices.

Recent Progress of Self-Supported Metal Oxide Nano-Porous Arrays in Energy Storage Applications

The demand for high-performance and cost-effective energy storage solutions for mobile electronic devices and electric vehicles has been a driving force for technological advancements. Among the various options available, transitional metal oxides (TMOs) have emerged as a promising candidates due to their exceptional energy storage capabilities and affordability. In particular, TMO nanoporous arrays fabricated by electrochemical anodization technique demonstrate unrivaled advantages including large specific surface area, short ion transport paths, hollow structures that reduce bulk expansion of materials, and so on, which have garnered significant research attention in recent decades. However, there is a lack of comprehensive reviews that discuss the progress of anodized TMO nanoporous arrays and their applications in energy storage. Therefore, this review aims to provide a systematic detailed overview of recent advancements in understanding the ion storage mechanisms and behavior of self-organized anodic TMO nanoporous arrays in various energy storage devices, including alkali metal ion batteries, Mg/Al-ion batteries, Li/Na metal batteries, and supercapacitors. This review also explores modification strategies, redox mechanisms, and outlines future prospects for TMO nanoporous arrays in energy storage.

A long-term stable aqueous aluminum battery electrode based on one-dimensional molybdenum-tantalum oxide nanotube arrays

Aluminum ion aqueous batteries (AIBs) are among the most promising candidates for high energy density devices due to the multivalent redox processes associated with Al³⁺ ion intercalation. However, only a few stable AIB electrode materials have been reported so far. MoO₃ is a very promising electrode material due to its octahedral layered crystal structure which can accommodate multivalent cation by intercalation. However, the poor electrochemical stability of MoO₃ and the sluggish intercalation kinetics of Al³⁺ ion in Mo oxides electrodes limit its practical application. In this work, we propose a strategy to overcome such shortcomings of MoO₃ by fabricating electrodes composed of self-ordered one-dimensional (1D) MoTaO_x nanotubes synthesized via electrochemical anodization of Mo-Ta alloy substrates. We show that this approach allows for direct incorporation of Ta in the Mo oxide nanotubes. The resulting MoTaO_x nanotubes, composed of octahedral MoO₃ and rhombohedral Mo₂Ta₂O₁₁ phases, exhibit remarkable electrochemical stability and Al-ion storage properties in aqueous electrolytes that are superior to that of pristine Mo oxide or other most efficient electrode materials reported to date. Such MoTaO_x nanotube-based electrodes can achieve a specific capacity of 1180 mA h cm^-3 (337 mA h g^-1, 141 μA h cm^-2) at 1.25 A cm^-3 (∼0.35 A g^-1, 0.15 mA cm^-2). More importantly, the capacity retention of such nanotube array electrodes remains above 83% of the initial capacity after 3000 cycles.

The Use of Anodic Oxides in Practical and Sustainable Devices for Energy Conversion and Storage

This review addresses the main contributions of anodic oxide films synthesized and designed to overcome the current limitations of practical applications in energy conversion and storage devices. We present some strategies adopted to improve the efficiency, stability, and overall performance of these sustainable technologies operating via photo, photoelectrochemical, and electrochemical processes. The facile and scalable synthesis with strict control of the properties combined with the low-cost, high surface area, chemical stability, and unidirectional orientation of these nanostructures make the anodized oxides attractive for these applications. Assuming different functionalities, TiO2-NT is the widely explored anodic oxide in dye-sensitized solar cells, PEC water-splitting systems, fuel cells, supercapacitors, and batteries. However, other nanostructured anodic films based on WO3, CuxO, ZnO, NiO, SnO, Fe2O3, ZrO2, Nb2O5, and Ta2O5 are also explored and act as the respective active layers in several devices. The use of AAO as a structural material to guide the synthesis is also reported. Although in the development stage, the proof-of-concept of these devices demonstrates the feasibility of using the anodic oxide as a component and opens up new perspectives for the industrial and commercial utilization of these technologies.

An Accurate Growth Mechanism and Photocatalytic Degradation Rhodamine B of Crystalline Nb2O5 Nanotube Arrays

To effectively improve photocatalytic activity, the morphology and crystallinity of semiconductor photocatalysts must be precisely controlled during the formation process. Self-aligned Nb2O5 nanotube arrays have been successfully fabricated using the electrochemical anodization method. A novel growth mechanism of Nb2O5 nanotubes has been proposed. Starting from the initial oxidation process, the “multi-point” corrosion of fluoride ions is a key factor in the formation of nanotube arrays. The inner diameter and wall thickness of the nanotubes present a gradually increasing trend with increased dissociative fluorine ion concentration and water content in the electrolyte. With dehydroxylation and lattice recombination, the increased crystallinity of Nb2O5 represents a reduction of lattice defects, which effectively facilitates the separation and suppresses the recombination of photo-generated carriers to enhance their catalytic degradation activity.

Electrochemical preparation of Nb2O5 nanochannel photoelectrodes for enhanced photoelectrocatalytic performance in removal of RR120 dye

The present work describes the synthesis of niobium oxide nanochannels (Nb₂O₅NCs) with high surface area, porosity, photocurrent density, and photoelectrochemical stability as photocatalyst. The Nb₂O₅NCs were prepared by electrochemical anodization of niobium foil in different electrolytes: 1 M H₂SO₄ containing 0.4 wt% HF (S1); glycerol containing 0.4 M NH₄F (S2); 0.25 g NH₄F with 4 vol% water in glycol at 50 °C (S3); and glycerol containing 10 wt% K₂HPO₄, at 130 °C (S4, annealed in air; S5, annealed in N₂). All the Nb₂O₅NCs showed well-organized arrays of nanochannels grown on the Nb foil, with tube diameters in the order S4<S2<S1<S3 and film thicknesses in the order S1<S2<S3<S4, as determined using FEG-SEM analyses. The samples were also characterized using XRD, EDX, DRS, XPS, EIS, Mott-Schottky analysis, and LSV curves. But, best results were obtained only when phosphorus (about 1% doping) was incorporated into the electrodes samples prepared in glycerol containing 10 wt% K₂HPO₄ at 130 °C (i.e. S4 and S5). This procedure enhances the absorption intensity in the UV-Vis regions, the conductivity, the charge carrier density, and the photocurrent density. The Nb₂O₅NC sample S5 was tested for the degradation of Procion Red HE-3B (RR120) dye, as a model pollutant, achieving efficient photoelectrodegradation with nearly 2 times higher mineralization efficiency compared to photolysis (PT) and photocatalysis (PC). Thus, the results indicate that the modification of Nb₂O₅NC thin film photoelectrodes by phosphorous doping can be a powerful and efficient alternative to usual approaches applied to the treatment of complex reactive dyes.

Phosphorylation of Polymeric Carbon Nitride Photoanodes with Increased Surface Valence Electrons for Solar Water Splitting

Overcoming the sluggish kinetics of the water oxidation is the key to a high performance for solar water splitting. Herein, phosphorylated polymeric carbon nitride (PCN) photoanodes were developed and showed enhanced photocurrent densities for solar water splitting. A photocatalytic efficiency of 120 μA cm^-2 was achieved in the basic solution (1.0 m NaOH) without sacrificial agents. In this system, phosphates were ionically anchored on the surface of PCN, and the modified films showed significantly increased density of valence electrons, and thus promoting photocatalytic efficiency.

Ultrasound assisted synthesis of Bi2NbO5F/rectorite composite and its photocatalytic mechanism insights

Enhancing the adsorbability of the photocatalysts is an effective way to improve the photocatalytic performance. Herein, we firstly synthesized a novel Bi₂NbO₅F/rectorite (BF/R) composite photocatalyst with high adsorption capacity via the ultrasound assisted route. The X-ray photoelectron spectrometer (XPS) analysis has demonstrated that the Bi₂NbO₅F and rectorite were connected with each other by weak chemical bonds. The introduced rectorite in the composite provided rich adsorption active sites for the adsorption of rhodamine B (RhB). The catalytic activity of the BF/R catalyst was evaluated by degrading RhB (5 mg/L) under UV-light irradiation. The BF/R composite with 32% rectorite exhibited the best photocatalytic degradation efficiency for degrading RhB in aqueous solution, which was 6.6 times higher than that of the bare BF sample. The improved activity of the BF/R composite can be ascribed to its strong adsorbability and enhanced light absorption. More importantly, the BF/R catalyst still showed good stability and high activity for degrading RhB after four recycles. Lastly, a possible photocatalytic mechanism on the BF/R composite was proposed. This work would provide helpful insights into the synthesis of the clay combined with Bi-based adjustable structure materials via ultrasound method.