Energy release from RuO2//RuO2 supercapacitors under dynamic discharge conditions

Application of an Electrochemical Sensor Based on Nitrogen-Doped Biochar Loaded with Ruthenium Oxide for Heavy Metal Detection

Cotton is a widely cultivated cash crop and represents one of the most significant raw materials for textiles on a global scale. The rapid development of the cotton industry has resulted in the production of substantial amounts of cotton husks, which are frequently underutilized or discarded. This study utilizes agricultural waste, specifically cotton shells, as a precursor for biochar, which is subsequently carbonized and nitrogen-doped with ruthenium oxide to synthesize an innovative composite material known as RuO2-NC. An electrochemical sensor was developed using this composite material to detect heavy metals, particularly lead and copper ions. The results demonstrate that the electrochemical sensor can accurately quantify concentrations of lead and copper ions across a wide linear range, exhibiting exceptional sensitivity. Furthermore, the sensor was tested on samples from Viola tianshanica Maxim (Violaceae) collected from the Xinjiang Uygur Autonomous Region (XUAR) in China, showing commendable accuracy and sensitivity. This approach promotes eco-friendly recycling of agricultural waste while offering advantages such as straightforward operation and reduced costs, thereby presenting promising prospects for practical applications.

ZnO-MnO2 co-modified hierarchical porous carbon nanofiber film electrodes for high-energy density supercapacitors

This study focuses on preparing composite hierarchical porous carbon nanofiber film that includes ZnO and MnO2. Using electrospinning technology, hierarchical porous structure was introduced into the nanofibers, enhancing energy density through the synergistic effect of zinc oxide and manganese dioxide. The zinc-manganese dioxide co-modified hierarchical porous carbon nanofiber film (ZnMnO-HPC) exhibits outstanding electrochemical performance when used as supercapacitor electrode, with a specific capacity reaching 401.77 C/g at 0.5 A/g, and 201.29 C/g at high current density of 5 A/g. ZnMnO-HPC also exhibits remarkable energy density when assembled with activated carbon electrode into asymmetric capacitor, reaching 38.37 Wh/kg at a power density of 407 W/kg and 19.5 Wh/kg at a power density of 12,800 W/kg, indicating promising applications in the high-energy-density supercapacitor field.

Solar reduced graphene oxide decorated with manganese dioxide nanostructures for brackish water desalination using asymmetric capacitive deionization

Capacitive deionization (CDI) has emerged as a low-cost, reagent-free technique for the desalination of water. This technique is based on the immobilization of dissolved ions on the electrically charged electrodes, by the electrosorption phenomenon. The electrosorption of dissolved ions by using CDI is limited for feed water having a low concentration of salts. To address this problem, we employ an asymmetric capacitive deionization (Asy-CDI) architecture having solar reduced graphene oxide decorated with manganese dioxide nanostructures (SRGO-MnO2 composite). The Asy-CDI possesses an SRGO-MnO2 composite as the cathode and SRGO as the anode with an anion exchange membrane. The cathode formed from the SRGO-MnO2 composite serves the purpose of immobilization of cations, whereas the anode formed from SRGO is responsible for anion removal. The crystal structure, chemical composition and morphology of the as-synthesized SRGO-MnO2 composite electrode materials are characterized by several techniques, confirming that the surface of SRGO is successfully loaded with α-MnO2 nanostructures. The electrochemical characterization reveals a high specific capacitance of the as-synthesized SRGO-MnO2 composite (419.9 F g-1) at 100 mV s-1. The Asy-CDI provides a higher salt adsorption capacity (40.2 mg g-1) compared to Sy-CDI (28.3 mg g-1) with feed water containing a salt concentration of 2000 mg L-1. These results indicate that the Asy-CDI may be employed as an efficient technique for the desalination of high concentration salt water.

Electrospray Deposition of PEDOT:PSS on Carbon Yarn Electrodes for Solid-State Flexible Supercapacitors

The increasing demand for flexible electronic devices has risen due to the high interest in electronic textiles (e-textiles). Consequently, the urge to power e-textiles has sparked enormous interest in flexible energy storage devices. One-dimensional (1D) configuration supercapacitors are the most promising technology for textile applications, but often their production involves complex synthesis techniques and expensive materials. This work unveils the use of the novel electrospray deposition (ESD) technique for the deposition of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS). This deposition methodology on conductive carbon yarns creates flexible electrodes with a high surface area. The deposition conditions of PEDOT:PSS were optimized, and their influence on the electrochemical performance of a 1D symmetric supercapacitor with a cellulose-based gel as an electrolyte and a separator was evaluated. The tests herein reported show that these capacitors exhibited a high specific capacitance of 72 mF g^-1, an excellent cyclability of more than 85% capacitance retention after 1500 cycles, and an outstanding capability of bending.

Pseudocapacitive Effects of Multi-Walled Carbon Nanotubes-Functionalised Spinel Copper Manganese Oxide

Spinel copper manganese oxide nanoparticles combined with acid-treated multi-walled carbon nanotubes (CuMn₂O₄/MWCNTs) were used in the development of electrodes for pseudocapacitor applications. The CuMn₂O₄/MWCNTs preparation involved initial synthesis of Mn₃O₄ and CuMn₂O₄ precursors followed by an energy efficient reflux growth method for the CuMn₂O₄/MWCNTs. The CuMn₂O₄/MWCNTs in a three-electrode cell assembly and in 3 M LiOH aqueous electrolyte exhibited a specific capacitance of 1652.91 F g^-1 at 0.5 A g^-1 current load. Similar investigation in 3 M KOH aqueous electrolyte delivered a specific capacitance of 653.41 F g^-1 at 0.5 A g^-1 current load. Stability studies showed that after 6000 cycles, the CuMn₂O₄/MWCNTs electrode exhibited a higher capacitance retention (88%) in LiOH than in KOH (64%). The higher capacitance retention and cycling stability with a Coulombic efficiency of 99.6% observed in the LiOH is an indication of a better charge storage behaviour in this electrolyte than in the KOH electrolyte with a Coulombic efficiency of 97.3%. This superior performance in the LiOH electrolyte than in the KOH electrolyte is attributed to an intercalation/de-intercalation mechanism which occurs more easily in the LiOH electrolyte than in the KOH electrolyte.

The Characteristics Analysis of a Microfluid-Based EGFET Biosensor with On-Chip Sensing Film for Lactic Acid Detection

In this research, a microfluid-based extended gate field-effect transistor (EGFET) biosensor with an on-chip sensing window (OCSW) was fabricated. The detection window was composed of six metal layers, and a ruthenium dioxide (RuO₂) film was spattered on the surface and functionalized with lactase to detect lactic acid (LA). To detect LA in a more diversified way, a microfluidic system was integrated with the biosensor. Moreover, a special package was used to seal the sensing window and microfluidic tube and insulate it from other parts to prevent water molecule invasion and chip damage. The sensitivity analysis of the EGFET biosensor was studied by a semiconductor parameter analyzer (SPA). The static and dynamic measurements of the EGFET with sensing windows on a chip were analyzed. The sensing characteristics of the EGFET biosensor were verified by the experimental results. The proposed biosensor is suitable for wearable applications due to the advantages of its low weight, low voltage, and simple manufacturing process.

Synergy of Bi2 O3 and RuO2 Nanocatalysts for Low-Overpotential and Wide pH-Window Electrochemical Ammonia Synthesis

Electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions is still seriously impeded by the inferior NH₃ yield and low Faradaic efficiency, especially at low overpotentials. Herein, we report the synthesis of nano-sized RuO₂ and Bi₂ O₃ particles grown on functionalized exfoliated graphene (FEG) through in situ electrodeposition, denoted as RuO₂ -Bi₂ O₃ /FEG. The prepared self-supporting RuO₂ -Bi₂ O₃ /FEG hybrid with a Bi mass loading of 0.70 wt% and Ru mass loading of 0.04 wt% shows excellent NRR performance at low overpotentials in acidic, neutral and alkaline electrolytes. It achieves a large NH₃ yield of 4.58±0.16 μg_NH3  h^-1  cm^-2 with a high Faradaic efficiency of 14.6 % at -0.2 V versus reversible hydrogen electrode in 0.1 M Na₂ SO₄ electrolyte. This performance benefits from the synergistic effect between Bi₂ O₃ and RuO₂ which respectively have a fairly strong interaction of Bi 6p orbitals with the N 2p band and abundant supply of *H, as well as the binder-free characteristic and the convenient electron transfer via graphene nanosheets. This work highlights a new electrocatalyst design strategy that combines transition and main-group metal elements, which may provide some inspirations for designing low-cost and high-performance NRR electrocatalysts in the future.

Functionalized and tip-open carbon nanotubes for high-performance symmetric supercapacitors

Carbon nanotubes (CNTs) have been widely studied for use in supercapacitor electrodes because of their excellent conductivity, high aspect ratio, excellent mechanical properties, chemical stability, and large specific surface area. However, the electrochemical performance of CNTs is usually limited by their closed tips and fewer active sites. Therefore, a facile and efficient chemical-acid-etching method was employed to open the tips of CNTs and introduce functional groups. Different types of ions (Li⁺, Na⁺, and Mg²⁺) in aqueous electrolytes were investigated using the functionalized and tip-open CNTs (FTO-CNTs), and the Li⁺-based electrolyte has the best electrochemical performance. The areal capacitance when using FTO-CNTs as positive and negative electrodes could reach 542 mF cm^-2 and 410 mF cm^-2, respectively, at a scan rate of 10 mV s^-1, and the positive electrode reached the highest areal capacitance of 903 mF cm^-2 at a current density of 1 mA cm^-2. The symmetric supercapacitor-based FTO-CNTs electrode delivered a superior areal energy density of 39 μW h cm^-2 and an areal power density of 10.2 mW cm^-2, with remarkable cycling stability.