Tuning polar discrimination between side chains to improve the performance of anion exchange membranes

Anion exchange membranes (AEMs) are the heart of alkaline fuel cells and water electrolysis, and have made a great progress in recent years. However, AEMs are still unable to satisfy the needs of high conductivity and stability, hindering their widespread commercialization. Side chain regulations have been widely used to prepare highly conductive and durable AEMs. Here, we construct a series of polyaromatic AEMs grafted with fluorinated cation side chains and cation-free alkyl chains with different end groups to explore the polar discrimination of side chains on membrane performance. This work demonstrates that AEMs grafting the cation side chains with superhydrophobic fluorine pendent and alkyl side chains with hydrophilic pendent enhance water content and ion conductivity. This is due to the strong immiscibility between the hydrophilic and hydrophobic head groups which promotes the establishments of microphase separation and ion highways. Specifically, poly(binaphthyl-co-terphenyl piperidinium) containing fluorinated piperidinium side chains and alkyl chains with methoxy pendent (QBNTP-QFM) possesses a satisficed OH- conductivity (170.6 mS cm-1 at 80 °C) and can tolerate 5 M hot NaOH for 2100 h with only 3.4 % conductivity loss. Expectedly, the single cell with QBNTP-QFM yields a prominent maximum power density of 1.62 W cm-2 and the water electrolysis cell with QBNTP-QFM achieves a pronounced current density of 3.0 A cm-2 at 1.8 V, both cells also display a prominent durability for 120 h operation. The results prove that this side chain optimization can improve ion conductivity and is a promising method for AEM development.

Room-temperature sulfur doped NiMoO4 with enhanced conductivity and catalytic activity for efficient hydrogen evolution reaction in alkaline media

Transition metal oxides have been acknowledged for their exceptional water splitting capabilities in alkaline electrolytes, however, their catalytic activity is limited by low conductivity. The introduction of sulfur (S) into nickel molybdate (NiMoO4) at room temperature leads to the formation of sulfur-doped NiMoO4 (S-NiMoO4), thereby significantly enhancing the conductivity and facilitating electron transfer in NiMoO4. Furthermore, the introduction of S effectively modulates the electron density state of NiMoO4 and facilitates the formation of highly active catalytic sites characterized by a significantly reduced hydrogen absorption Gibbs free energy (ΔGH*) value of -0.09 eV. The electrocatalyst S-NiMoO4 exhibits remarkable catalytic performance in promoting the hydrogen evolution reaction (HER), displaying a significantly reduced overpotential of 84 mV at a current density of 10 mA cm-2 and maintaining excellent durability at 68 mA cm-2 for 10 h (h). Furthermore, by utilizing the anodic sulfide oxidation reaction (SOR) instead of the sluggish oxygen evolution reaction (OER), the assembled electrolyzer employing S-NiMoO4 as both the cathode and anode need merely 0.8 V to achieve 105 mA cm-2, while simultaneously producing hydrogen gas (H2) and S monomer. This work paves the way for improving electron transfer and activating active sites of metal oxides, thereby enhancing their HER activity.

Cellulose nanofiber hydrogel with high conductivity electrolytes for high voltage flexible supercapacitors

Although flexible double layer capacitors based on hydrogels overcome the drawbacks of commercial double layer capacitors such as low safety and non-deformability, it is still considered as attractive challenges to achieve high conductivity for hydrogel electrolytes as well as high operating voltages for hydrogel flexible supercapacitors. In this paper, ion migration channels were engineered by immobilizing positive and negative charges on polymer skeleton and dispersing cellulose nanofibers in the polymerized polyelectrolyte network, providing ultra-high ionic conductivity (103 mS cm-1). In addition, K3[Fe(CN)6] was introduced through a soaking method, leading to redox reactions on the surface of carbon electrode during charging and discharging, supporting a relatively wide voltage window (1.8 V). Moreover, the specific capacitance at high current remained 55 % of the specific capacitance at low current, indicating excellent rate performance. In addition, the device displayed high cycling stability (80.05 % after 10,000 cycles). Notably, we successfully light up the red LED with only one device. Accordingly, this work provides a feasible design concept for the development of cellulose nanofibers (CNF) hydrogel-based solid-state electrolyte with high conductivity for flexible supercapacitors with wide potential window and high energy density.

Design of co-continuous structure of cellulose/PAA-based alkaline solid polyelectrolyte for flexible zinc-air battery

In order to prepare high ionic conductivity and robust mechanical properties of alkaline solid polyelectrolyte (ASPE) for applications in flexible wearable devices, a co-continuous structure membrane was designed using in-situ polymerization to introduce cross-linked polyacrylic acid (N-PAA) into the cellulose network constructed by regenerated degreasing cotton (RDC). The resultant ASPE membrane showed high ionic conductivity (430 mS·cm^-1 at 25 °C), strong mechanical properties, and excellent alkaline stabilities, proving the viability of cellulose for use in energy storage systems. Surprisingly, the sandwich-shaped zinc-air battery assembled using RDC/N-PAA/KOH membranes as electrolytes exhibits superior values of cycling stability, discharge time, specific capacity (731.5 mAh·g^-1), peak power density (40.25 mW·cm^-2), and mechanical flexibility. Even under bending conditions, the zinc-air batteries still possess stable energy supply performance, suggesting this novel solid polyelectrolyte has promising application for wearable technology.

Yarn-ball-shaped CNF/MWCNT microspheres intercalating Ti3C2Tx MXene for electromagnetic interference shielding films

Ti₃C₂T_x MXenes with excellent metallic conductivity have proved promising in its application of electromagnetic interference (EMI) shielding. A hierarchical hybrid film with ultrathin thickness composed of Ti₃C₂T_x MXene layers embedded with yarn-ball-shaped microspheres of cellulose nanofibrils (CNF) and multiwalled carbon nanotube (MWCNT) was designed to improve the absorption of electromagnetic waves (EMWs). The addition of yarn-ball-shaped microspheres is to shield more EMWs via multiple reflections in the inner space and reduce the undesirable emissions into the air. After thermal annealing treatment, the ultrathin film with intercalation of the carbonized yarn-ball-shaped CNF/MWCNT microspheres exhibited enhanced EMWs absorption as an important part of shielding effectiveness (45.1±0.9 dB) as well as excellent mechanical stability (≈0.9 million bending times). Thus, the well-designed structure of multilayered hybrid films with intercalated conductive microspheres can be a good candidate for higher absorption in EMI shielding effectiveness and outstanding mechanical properties.

High conductive graphene assembled films with porous micro-structure for freestanding and ultra-low power strain sensors

Graphene emerges as an ideal material for constructing high-performance strain sensors, due to its superior mechanical property and high conductivity. However, in the process of assembling graphene into macroscopic materials, its conductivity decreases significantly. Also, tedious fabrication process hinders the application of graphene-based strain sensors. In this work, we report a freestanding graphene assembled film (GAF) with high conductivity ((2.32 ± 0.08) × 10⁵ S m^-1). For the sensitive materials of strain sensors, it is higher than most of reported carbon nanotube and graphene materials. These advantages enable the GAF to be an ultra-low power consumption strain sensor for detecting airflow and vocal vibrations. The resistance of the GAF remains unchanged with increasing temperature (20-100 ℃), exhibiting a good thermal stability. Also, the GAF can be used as a strain sensor directly without any flexible substrates, which greatly simplifies the fabrication process in comparison with most reported strain sensors. Additionally, the GAF used as a pressure sensor with only ~4.7 μW power is investigated. This work provides a new direction for the preparation of advanced sensors with ultra-low power consumption, and the development of flexible and energy-saving electronic devices.

Highly conductive graphene/carbon black screen printing inks for flexible electronics

The industrial scale production and application of liquid conductive nanomaterials with well-defined conductive properties, printing adaptability and mechanical properties are crucial for the flexible electronic devices. Although graphene can be used as an attractive liquid nanoink platform for electronic devices, it is still a major challenge to prepare graphene conductive inks with high concentration, conductivity and stability with graphene powders as raw materials and improve the post-treatment process for printed patterns. Here, a novel graphene-based screen printing conductive ink employing liquid-exfoliated graphene powders produced by jet cavitation and carbon black jointly as conductive filler is presented. The inks with graphene powders containing thicker smaller-area flakes and carbon black fraction of 15% in the total conductive fillers exhibit printability down to lines of 90 μm in width and printed pattern electrical conductivity of 2.15 × 10⁴ S/m at 7 μm thickness along with outstanding mechanical properties. Also, special post-treatment, i.e. heating-compression rolling-heating, makes the conductive ink formulation compatible with a wide range of substrates and suitable for Roll-to-Roll applications. Overall, this paper provides a new solution to high-efficiency, low-cost, large-scale production of printed flexible electronics.

3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices

Flexible and Personalizable battery is a promising candidate for energy storage, but suffers from the weldablity and large-scale producibility of the electrode. To address the issues, we design a nickel foam catalyzed electroless deposition (NFED) derived 3D-metal-pattern embroidered electrodes. This is the first attempt to utilize this type of electrode in battery field. It is found that the current collector can be embroidered on any selected areas of any complex-shape electrodes, with high controllability and economical feasibility. As a result, the electronic conductivity of the flexible electrodes can be improved by nearly one order of magnitude, which can be easily and firmly weldded to the metal tab using the industry generic ultrasonic heating process. The embroidered electrodes could substantially promote the electrochemical performance under bending deformation, with both Li-S and Li-LiFePO₄ batteries as the models. This innovation is also suitable to embroider all the VIII group elements on any electrodes with personalized shapes, which is widely attractive for the development of next generation flexible and personalizable energy storage devices.

Reduced Graphene Oxide Films with Ultrahigh Conductivity as Li-Ion Battery Current Collectors

Solution processed, highly conductive films are extremely attractive for a range of electronic devices, especially for printed macroelectronics. For example, replacing heavy, metal-based current collectors with thin, light, flexible, and highly conductive films will further improve the energy density of such devices. Films with two-dimensional building blocks, such as graphene or reduced graphene oxide (RGO) nanosheets, are particularly promising due to their low percolation threshold with a high aspect ratio, excellent flexibility, and low cost. However, the electrical conductivity of these films is low, typically less than 1000 S/cm. In this work, we for the first time report a RGO film with an electrical conductivity of up to 3112 S/cm. We achieve high conductivity in RGO films through an electrical current-induced annealing process at high temperature of up to 2750 K in less than 1 min of anneal time. We studied in detail the unique Joule heating process at ultrahigh temperature. Through a combination of experimental and computational studies, we investigated the fundamental mechanism behind the formation of a highly conductive three-dimensional structure composed of well-connected RGO layers. The highly conductive RGO film with high direct current conductivity, low thickness (∼4 μm) and low sheet resistance (0.8 Ω/sq.) was used as a lightweight current collector in Li-ion batteries.