Hollow Few-Layer Graphene-Based Structures from Parafilm Waste for Flexible Transparent Supercapacitors and Oil Spill Cleanup

Free-Standing, Interwoven Tubular Graphene Mesh-Supported Binary AuPt Nanocatalysts: An Innovative and High-Performance Anode Methanol Oxidation Catalyst

Pt-based alloy or bimetallic anode catalysts have been developed to reduce the carbon monoxide (CO) poisoning effect and the usage of Pt in direct methanol fuel cells (DMFCs), where the second metal plays a role as CO poisoning inhibitor on Pt. Furthermore, better performance in DMFCs can be achieved by improving the catalytic dispersion and using high-performance supporting materials. In this work, we introduced a free-standing, macroscopic, interwoven tubular graphene (TG) mesh as a supporting material because of its high surface area, favorable chemical inertness, and excellent conductivity. Particularly, binary AuPt nanoparticles (NPs) can be easily immobilized on both outer and inner walls of the TG mesh with a highly dispersive distribution by a simple and efficient chemical reduction method. The TG mesh, whose outer and inner walls were decorated with optimized loading of binary AuPt NPs, exhibited a remarkably catalytic performance in DMFCs. Its methanol oxidation reaction (MOR) activity was 10.09 and 2.20 times higher than those of the TG electrodes with only outer wall immobilized with pure Pt NPs and binary AuPt NPs, respectively. Furthermore, the catalyst also displayed a great stability in methanol oxidation after 200 scanning cycles, implying the excellent tolerance toward the CO poisoning effect.

Human Exhalation CO2 Sensor Based on the PEI-PEG/ZnO/NUNCD/Si Heterojunction Electrode

Gas sensors based on semiconductors have outstanding sensitivity compared with the oxide-based devices; however, the high operation temperature greatly hinders its development in practical applications. Chronic obstructive pulmonary disease (COPD) is one of the leading causes of death worldwide, and the patients with severe COPD with or without exacerbation tend to have airflow obstruction, which results in an increase of CO2 concentration and subsequent hypercapnic respiratory failure. At present, COPD detection relies on professional operation; however, the patients suffer great discomfort during the arterial blood sampling. All these facts reduce patient's willingness to test their physical health. Thus, noninvasive monitoring of CO2 levels is crucial for the early diagnosis of high-risk COPD patients. A nitrogen-incorporated ultrananocrystalline diamond (NUNCD) film exhibits excellent properties in biosensing and polyetherimide-polyethylene glycol (PEI-PEG) polymer possesses a great capability of CO2 capturing. By incorporating NUNCD into PEI-PEG film, this work focuses on ameliorating the sensitivity and selectivity of the present semiconductor CO2 sensor. From the theoretical regression analyses of the experimental results, it is found that the excellent performance of the PEI-PEG/ZnO/NUNCD/Si electrode is contributed by two main reaction layers, the adsorption layer (PEI-PEG) and the electric transfer layer (ZnO/NUNCD). The selectivity is dominated by the PEI-PEG adsorption layer and the sensitivity is directly related to the changes in the work function of the ZnO/NUNCD interface. The high aspect ratio (>10) of the flower-like ZnO structure, growth from ZnO nanoparticles, can provide a more active adsorption area, as a result, extremely enhancing the sensitivity of the CO2 sensor.

Edge-Rich Interconnected Graphene Mesh Electrode with High Electrochemical Reactivity Applicable for Glucose Detection

The development of graphene structures with controlled edges is greatly desired for understanding heterogeneous electrochemical (EC) transfer and boosting EC applications of graphene-based electrodes. We herein report a facile, scalable, and robust method to produce graphene mesh (GM) electrodes with tailorable edge lengths. Specifically, the GMs were fabricated at 850 °C under a vacuum level of 0.6 Pa using catalytic nickel templates obtained based on a crack lithography. As the edge lengths of the GM electrodes increased from 5.48 to 24.04 m, their electron transfer rates linearly increased from 0.08 to 0.16 cm∙s⁻¹, which are considerably greater than that (0.056 ± 0.007 cm∙s⁻¹) of basal graphene structures (defined as zero edge length electrodes). To illustrate the EC sensing potentiality of the GM, a high-sensitivity glucose detection was conducted on the graphene/Ni hybrid mesh with the longest edge length. At a detection potential of 0.6 V, the edge-rich graphene/Ni hybrid mesh sensor exhibited a wide linear response range from 10.0 μM to 2.5 mM with a limit of detection of 1.8 μM and a high sensitivity of 1118.9 μA∙mM⁻¹∙cm⁻². Our findings suggest that edge-rich GMs can be valuable platforms in various graphene applications such as graphene-based EC sensors with controlled and improved performance.

Controlling Electrode Spacing by Polystyrene Microsphere Spacers for Highly Stable and Flexible Transparent Supercapacitors

Transparent polymer electrolytes such as poly(vinyl alcohol)-based H⁺, Li⁺, K⁺, and Na⁺ gels have been widely used as both an electrolyte and a separator for flexible transparent supercapacitors (FTSCs). However, these gels sandwiched between the electrodes in FTSCs are easily compressed under bending and compression due to their viscous flow behavior, resulting in the deformation of electrode spacing and the unstable capacitance performance. To resolve this issue, herein, we introduce monodispersed polystyrene (PS) microspheres into PVA-LiCl polymer gel electrolytes as spacers to precisely control the electrode spacing during the assembly of FTSCs using single-walled carbon nanotubes/indium tin oxide-polyethylene terephthalate (ITO-PET) or MnO₂/multiwalled carbon nanotubes/ITO-PET as transparent electrodes. The electrode spacing could be tuned by varying the diameter of PS microspheres, for example, 20, 40, and 80 μm. More importantly, the PS microsphere spacers protect the gel electrolyte from the squeeze when bending takes place, allowing the stable performance output by FTSCs under a bending state. After repeating bending tests, the capacitance remains 95.6%, indicating the high stability and flexibility of the devices with the assistance of PS microsphere spacers.

Controllable synthesis of carbon nanosheets derived from oxidative polymerisation of m-phenylenediamine

Synthesis of high-quality carbon nanosheets with superior physicochemical properties is of particular importance for environmental and catalytic applications. In this research, carbon nanosheets with tunable porosity were successfully synthesized using two-dimensional (2D) poly(m-phenylenediamine) (PmPD) as precursor. The flat polymer precursor was acquired by oxidative polymerisation of m-phenylenediamine coupled with iron ions coordination, which confined an anisotropic growth of polymer within the 2D directions. Moreover, the addition of H₂O after the polymerisation is able to indirectly regulate the porosity of the carbon nanosheets. The carbon nanosheets with controllable porosity realize comparable electrocatalytic activity for oxygen reduction reaction as compared with commercial Pt/C, indicative of great potential to serve as noble metals candidates in the application of zinc/air batteries.

Percolating Film of Pillared Graphene Layer Integrated with Silver Nanowire Network for Transparent and Flexible Supercapacitors

Transparent and flexible supercapacitors (TFSCs) are viable power sources for next-generation wearable electronics. The ingenious design of the transparent electrode determines the performance of TFSCs. A percolating film of a pillared graphene layer integrated with a silver nanowire network as the transparent electrode was prepared, by which TFSC devices exhibit a significantly improved performance contrastively. Under the condition of the same transmittance, about 27-72% improvement in the areal capacitance can be achieved. On the one hand, the pillars of carbon nanotube (CNT) were distributed in the graphene layer uniformly, enlarging the inner distance of adjacent graphene layers and providing an open structure for extra ion transport and storage of TFSCs. On the other hand, the introduced CNT could facilitate the electron transport at the direction perpendicular to the graphene basal plane, enhancing the electronic conductivity of the graphene layer. More importantly, the formed percolating film ensures an efficient transport of electron along with the silver nanowire when it encounters the obstacle within the graphene layer, resulting in a highly conductive electrode. The TFSC device with a good compatibility indicates a reliable practicability, which provides a facile route toward the design of high-performance TFSCs.