Proton exchange membranes (PEMs), which are crucial fuel cell parts, play an important role in the field of energy science. However, the further development of conventional PEMs based on synthetic polymers is greatly limited by high energy consumption and difficult degradation. In this work, we reported the fabrication of a novel viscose-based PEM via cationic modification and dyeing treatment with the reactive dyes KE-7B1. High-efficiency proton transmission channels can be constructed due to the formation of the complex internal three-dimensional network of the as-prepared viscose-based PEM. H⁺ conductivity ( ${\sigma }_{\mathrm{H}}^{+}$) and water uptake are intensively investigated by changing the cationic agents and KE-7B1, and the maximum ${\sigma }_{\mathrm{H}}^{+}$ reaches 44.19 mS/cm at 80 °C and 98% relative humidity (RH). Furthermore, the prepared membrane shows the lowest calculated activation energy value (12.25 kJ/mol), indicating that both Grotthuss and Vehicle mechanisms play an important role in ionic transport. The membrane chemical structure and micromorphology are analyzed and the proton transmission modes are explored in detail, supplemented with research on the hydrophilic/hydrophobic characteristics and crystallinity of the membranes. The application stability of the membranes is also evaluated analyzing the thermal, mechanical, and oxygen resistance properties, and the results show that all the prepared membranes can maintain good thermal stability within 200 °C. The maximum tensile strength reaches 42.12 MPa, and the mass losses of the membranes soaked in 30% (in mass, same below) H₂O₂ solution for 120 h can be restricted to 10%. Therefore, as a novel PEM, the obtained dye viscose-based membranes show great potential for application in fuel cells.

The processes of photocatalytic CO₂ reduction (pCO₂R) and electrochemical CO₂ reduction (ECO₂R) have attracted considerable interest owing to their high potential to address many environmental and energy-related issues. In this aspect, a single Cu atom decorated on a carbon nitride (CN) surface (Cu–CN) has gained increasing popularity because of its unique advantages, such as excellent atom utilization and ultrahigh catalytic activity. CN—particularly graphitic CN (g-C₃N₄)—is a photo- and electrocatalyst and used as an important support material for single Cu atom-based catalysts. These key functions of Cu–CN-based catalysts can improve the catalytic performance and stability in the pCO₂R and ECO₂R during the application process. In this review, we focus on Cu as a single metal atom decorated on CN for efficient photoelectrochemical CO₂ reduction (pECO₂R), where ECO₂R increases the electrocatalytic active area and promotes electron transfer, while pCO₂R enhances the surface redox reaction by efficiently using photogenerated charges and offering integral activity as well as an active interface between Cu and CN. Interactions of single Cu atom-based photo-, electro-, and photoelectrochemical catalysts with g-C₃N₄ are discussed. Moreover, for a deeper understanding of the history of the development of pCO₂R and ECO₂R, the basics of CO₂ reduction, including pCO₂R and ECO₂R over g-C₃N₄, as well as the structural composition, characterization, unique design, and mechanism of a single atom site are reviewed in detail. Finally, some future prospects and key challenges are discussed.

The electrochemical carbon dioxide reduction reaction (CO₂RR) is a promising approach to produce liquid fuels and industrial chemicals by utilizing intermittent renewable electricity for mitigating environmental problems. However, the traditional H-type reactor seriously limits the electrochemical performance of CO₂RR due to the low CO₂ solubility in electrolyte, and high ohmic resistance caused by the large distance between two electrodes, which is unbeneficial for industrial application. Herein, we demonstrated a high-performance continuous flow membranes electrode assembly (MEA) reactor based on a self-growing Cu/Sn bimetallic electrocatalyst in 0.5 mol·L^-1 KHCO₃ for converting CO₂ to formate. Compared with an H-type cell, the MEA reactor not only shows the excellent current density (66.41 mA·cm^-2 at -1.11 V_RHE), but also maintains high Faraday efficiency of formate (89.56%) with the steady work around 20 h. Notably, we also designed the new CO₂RR system to effectively separate the gaseous/liquid production. Surprisingly, the production rate of formate reached 163 μmol·h^-1·cm^-2 at -0.91 V_RHE with the cell voltage of 3.17 V. This study provides a promising path to overcome mass transport limitations of the electrochemical CO₂RR and to separate liquid from gas products.

A nanocomposite of polyaniline/graphene (PAN/GN) was prepared using reverse-phase polymerization. The nanocomposite material was dropcast onto a glassy carbon electrode (GCE). Then, a single-stranded DNA (ssDNA) probe for HIV-1 gene detection was immobilized on the modified electrode, and the negative charged phosphate backbone of the HIV-1 was bound to the modified electrode surface via π-π^* stacking interactions. The hybridization between the ssDNA probe and the target HIV-1 formed double-stranded DNA (dsDNA), and the electron transfer resistance of the electrode was measured using impedimetric studies with a [Fe(CN)₆]^3-/4- redox couple. Under the optimized experimental conditions, the change of the impedance value was linearly related to the logarithm of the concentration of HIV genes in the range from 5.0 × 10⁻¹⁶ M to 1.0 × 10⁻¹⁰ M (R = 0.9930), and the HIV sensor exhibited a lower detection limit of 1.0 × 10⁻¹⁶ M (S/N = 3). The results show that this biosensor presented wonderful selectivity, sensitivity and specificity for HIV-1 gene detection. Thus, this biosensor provides a new method for the detection of HIV gene fragments.

Hydroxyl anion conducting membrane composed of poly(vinyl alcohol) (PVA), poly(diallyldimethylammonium chloride) (PDDA), and hydroxylated multiwalled carbon nanotubes (MWCNTs-OH) have been synthesized via a facile blending-casting method assisted by a hot-chemical cross-linking process. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) showed that PDDA and MWCNTs-OH were successfully introduced into the PVA matrix and MWCNTs-OH could effectively improve the network structure of the membrane. With the addition of MWCNTs-OH, many properties of the membranes such as thermal, chemical, mechanical stability and swelling property were improved significantly. Most prominent is the improvement of mechanical property, where the PVA/PDDA/MWCNTs-OH(1:0.5/3 wt.%) membrane showed high tensile strength of 40.3 MPa, tensile elongation of 12.3% and high Young's modulus of 782.8 MPa. Moreover, MWCNTs-OH bound the polymer chains in the membranes more compactly, resulting in decreased water uptake. By tuning the mass fraction of PVA, PDDA, and MWCNTs-OH in the membrane, the maximum OH⁻ conductivity (0.030 S cm⁻¹ at room temperature) was achieved for the composition of 0.5 wt.% MWCNTs-OH doped with the PVA: PDDA (1:0.5 by mass) blend. The membranes showed excellent oxidative stability when treated with both a solution of H₂O₂ (30 wt.%) at room temperature and in a hot KOH solution (8 M) at 80 °C. Based on the full aliphatic structure membrane (PVA/PDDA-OH/1 wt.%MWCNTs-OH), membrane electrode assemblies (MEAs) fabricated with Pt/C cathode catalyst can achieve power densities of 41.3 mW cm⁻² and 66.4 mW cm⁻² in a H₂/O₂ system at room temperature and 40 °C, respectively. Using CoPc as the Pt-free cathode catalyst, power densities of 9.1 mW cm⁻² and 14.0 mW cm⁻² at room temperature and 40 °C were obtained, respectively.

In this paper, Nafion membrane was firstly modified by copper phthalocyanine tetrasulfonic acid tetrasodium salt (CuTSPc) to prepare the Nafion/CuTSPc-x composite membranes. FTIR, XRD and SEM results revealed the successful incorporation of CuTSPc into Nafion and good compatibility between the two composites. The proton conductivities of the Nafion/CuTSPc-x composite membranes were evidently higher than pure cast Nafion membrane, and increased with CuTSPc contents. Among them, the Nafion/CuTSPc-6% membrane with the highest ion exchange capacity (1.14 mequiv•g⁻¹) exhibited the highest proton conductivity of 0.084 S cm⁻¹ at 30 ℃ and 0.131 S cm⁻¹ at 80 ℃, respectively. When fabricated of a membrane electrode assembly (MEA), the Nafion/CuTSPc-4.5% membrane displayed an initial fuel cell performance with a power density of 43.3 mW cm⁻² at room temperature, close to that for pure cast Nafion membrane. Benefiting from the compact structure, high proton conductivity and outstanding stability, the Nafion/CuTSPc-x composite membranes show promising potentials for fuel cell applications.