In Situ Grown Ultrafine RuO2 Nanoparticles on GeP5 Nanosheets as the Electrode Material for Flexible Planar Micro-Supercapacitors with High Specific Capacitance and Cyclability

3D Binder-Free Mo@CoO Electrodes Directly Manufactured in One Step via Electric Discharge Machining for In-Plane Microsupercapacitor Application

Cobalt oxide-based in-plane microsupercapacitors (IPMSCs) stand out as a favorable choice for various applications in energy sources for the Internet of Things (IoT) and other microelectronic devices due to their abundant natural resources and high theoretical specific capacitance. However, the low electronic conductivity of cobalt oxide greatly hinders its further application in energy storage devices. Herein, a new manufacturing method of electric discharging machining (EDM), which is simple, safe, efficient, and environment-friendly, has been developed for synthesizing Mo-doped and oxygen-vacancy-enriched Co-CoO (Mo@Co-CoO) integrated microelectrodes for efficiently constructing Mo@Co-CoO IPMSCs with customized structures in a single step for the first time. The Mo@Co-CoO IPMSCs with three loops (IPMSCs3) exhibited a maximum areal capacitance of 30.4 mF cm-2 at 2 mV s-1. Moreover, the Mo@Co-CoO IPMSCs3 showed good capacitive behavior at a super-high scanning rate of 100 V s-1, which is around 500-1000 times higher than most reported CoO-based electrodes. It is important to note that the IPMSCs were fabricated using a one-step EDM process without any assistance of other material processing techniques, toxic chemicals, low conductivity binders, exceptional current collectors, and conductive fillers. This novel fabrication method developed in this research opens a new avenue to simplify material synthesis, providing a novel way for realizing intelligent, digital, and green manufacturing of various metal oxide materials, microelectrodes, and microdevices.

An Ultrasensitive SPR biosensor for RNA detection based on robust GeP5 nanosheets

Ultrasensitive and rapid detection of biomarkers is among the upmost priorities in promoting healthcare advancements. Improved sensitivity of photonic sensors based on two-dimensional (2D) materials have brought exciting prospects for achieving real-time and label-free biosensing at dilute target concentrations. Here, we report a high-sensitivity surface plasmon resonance (SPR) RNA sensor using metallic 2D GeP5 nanosheets as the sensing material. Theoretical evaluations revealed that the presence of GeP5 nanosheets can greatly enhance the plasmonic electric field of the Au film thereby boosting sensing sensitivity, and that optimal sensitivity (146° RIU-1) can be achieved with 3-nm-thick GeP5. By functionalizing GeP5 nanosheets with specific cDNA probes, detection of SARS-CoV-2 RNA sequences were achieved using the GeP5-based SPR sensor, with high sensitivity down to a detection limit of 10 aM and excellent selectivity. This work demonstrates the immense potential of GeP5-based SPR sensors for advanced biosensing applications and paves the way for utilizing GeP5 nanosheets in novel sensor devices.

Environmentally sustainable implementations of two-dimensional nanomaterials

Rapid advancement in nanotechnology has led to the development of a myriad of useful nanomaterials that have novel characteristics resulting from their small size and engineered properties. In particular, two-dimensional (2D) materials have become a major focus in material science and chemistry research worldwide with substantial efforts centered on their synthesis, property characterization, and technological, and environmental applications. Environmental applications of these nanomaterials include but are not limited to adsorbents for wastewater and drinking water treatment, membranes for desalination, and coating materials for filtration. However, it is also important to address the environmental interactions and implications of these nanomaterials in order to develop strategies that minimize their environmental and public health risks. Towards this end, this review covers the most recent literature on the environmental implementations of emerging 2D nanomaterials, thereby providing insights into the future of this fast-evolving field including strategies for ensuring sustainable development of 2D nanomaterials.

Hollow Nanowire Constructed by NiCo Doped RuO2 Nanoparticles for Robust Hydrogen Evolution at High-Current-Density

Large-current-density electrocatalytic water splitting is essential for industrial hydrogen production, but it is currently hindered by lacking active and robust hydrogen evolution reaction (HER) catalysts. Herein, a novel electrode of hollow nanowire arrays constructed by NiCo modified RuO₂ nanoparticles on Ni foam (NiCo@RuO₂ HNAs/NF) for high-performance HER was reported. Such efficient electrode was fabricated by ion exchange with NF-supported Ni modified cobalt carbonate hydroxide nanowire arrays template (Ni@CoCH NAs/NF). The formed NiCo@RuO₂ HNAs/NF only needed overpotentials of 148.5 and 236.1 mV to deliver 500 and 1000 mA cm^-2 , respectively, along with excellent stability at the high-current-density for 300 h. Such remarkable HER performance was mainly attributed to the hollow structure with high surface area, hydrophilic feature, and NiCo@RuO₂ with optimized hydrogen evolution kinetics. After coupling with anodic Ni@CoCH NAs/NF, our electrolyzer outperformed Pt/C-IrO₂ and most other Ru-based electrolyzers. This work provides a promising Pt alternative catalyst for profitable H₂ production.

Spectroscopic Monitoring of the Electrode Process of MnO2@rGO Nanospheres and Its Application in High-Performance Flexible Micro-Supercapacitors

Structural instability is a major obstacle to realizing the high performance of a MnO₂-based pseudocapacitor material. Understanding its structure transformation in the process of electrochemical reaction, therefore, plays an important role in the efficient enhancement of rate capacity and stability. Herein, a stable MnO₂@rGO core-shell nanosphere is first synthesized by a liquid-liquid interface deposition further combined with the electrostatic self-assembly method. The structural transformation process of the MnO₂@rGO electrode is monitored by ex situ Raman and X-ray diffraction spectroscopy during the charging-discharging process. It is found in the first discharging process that layered-MnO₂ transforms into the spinel-Mn₃O₄ phase with K⁺ ion intercalation. From the second charging, the spinel-Mn₃O₄ phase is gradually adjusted to a more stable λ-MnO₂ with a three-dimensional tunnel structure, finally realizing the reversible intercalation/deintercalation of K⁺ ions in the λ-MnO₂ tunnel structure during subsequent cycling, which can be attributed to the presence of oxygen vacancies formed by the lengthening of the Mn-O bond and losing oxygen in the MnO₆ octahedral unit with K⁺ ion intercalation/deintercalation. Meanwhile, the MnO₂@rGO electrode demonstrates a high specific capacitance of 378 F g^-1 at 1 A g^-1 and excellent cycling stability with a capacitance retention of up to 89.5% after 10 000 cycles at 10 A g^-1. Furthermore, the assembled symmetric micro-supercapacitor delivers a high areal energy density of 1.01 μWh cm^-2, superior cycling stability with no significant capacity decay after 8700 cycles, and a capacity retention rate of almost 100% after 2000 bending cycles, showing great mechanical flexibility and practicability.

High-Performance MnO2 Nanowire/MoS2 Nanosheet Composite for a Symmetrical Solid-State Supercapacitor

To improve the production rate of MoS₂ nanosheets as an excellent supercapacitor (SC) material and enhance the performance of the MoS₂-based solid-state SC, a liquid phase exfoliation method is used to prepare MoS₂ nanosheets on a large scale. Then, the MnO₂ nanowire sample is synthesized by a one-step hydrothermal method to make a composite with the as-synthesized MoS₂ nanosheets to achieve a better performance of the solid-state SC. The interaction between the MoS₂ nanosheets and MnO₂ nanowires produces a synergistic effect, resulting in a decent energy storage performance. For practical applications, all-solid-state SC devices are fabricated with different molar ratios of MoS₂ nanosheets and MnO₂ nanowires. From the experimental results, it can be seen that the synthesized nanocomposite with a 1:4 M ratio of MoS₂ nanosheets and MnO₂ nanowires exhibits a high Brunauer-Emmett-Teller surface area (∼118 m²/g), optimum pore size distribution, a specific capacitance value of 212 F/g at 0.8 A/g, an energy density of 29.5 W h/kg, and a power density of 1316 W/kg. Besides, cyclic charging-discharging and retention tests manifest significant cycling stability with 84.1% capacitive retention after completing 5000 rapid charge-discharge cycles. It is believed that this unique, symmetric, lightweight, solid-state SC device may help accomplish a scalable approach toward powering forthcoming portable energy storage applications.