This study describes the reverse of the well-known double layer effects on charge transfer kinetics in the relationship between a cause and an effect. The reversible redox reaction of a ferrocenyl derivative decreased the capacitive values of the double layer impedance up to negative values, corresponding to an inductive component. This observation was disclosed by the subtraction of the real admittance from the imaginary admittance, which can extract the net double layer capacitance from the Warburg impedance. The inductance-like behavior is caused due to two reasons: (i) the double layer capacitance in the polarized potential domain is determined by the low concentrations of the field-oriented solvent dipoles that are considered as the conventionally employed redox concentrations and (ii) the double layer capacitance is caused by the orientation of the dipoles in the same direction as that of the electric field, whereas the redox reaction generates charge in the direction opposite to the field. The faradaic effect was demonstrated via the ac-impedance data obtained for the ferrocenyl compound in a KCl solution in the unpolarized potential domain between 1 Hz and 3 kHz frequency. The negative admittance was proportional to the frequency. The theory of negative capacitance was presented by combining the mirror-image surface charge with the Nernst equation.

The extraction of double-layer capacitance (DLC) is proposed using the electrochemical impedance spectroscopy (EIS) technique. By the concept of the frequency-dependent DLC, the DLC of polyaniline (PANI)-coated platinum wire is separated from the total capacitance at different DC potentials. The high conducting oxidized PANI is less frequency dependent. The DLC at the frequency of 1 Hz is the same as that of separation from the faradic current by cyclic voltammetry technology, exhibiting S-shaped curve at different DC potential. The process of the oxidation of PANI during the electrochemical impedance measurement is similar to the diffusion control.

Flaky particles of polyaniline (PANI)-graphene (GN) with rectangular size of 1.0-1.5 mm are dispersed in aqueous solution so that their suspension is stable for one day without aggregation. The weight fraction of PANI in the particle is 75 %, which is independent of the loaded fraction of PANI in the synthesis. The PANI-GN film made of the suspension forms a self-standing, elastic, conductive film. The PANI-GN suspension exhibits both the reduction and the oxidation waves at potentials similar to those of PANI adsorbed on an electrode, whereas the PANI-GO suspension shows only the voltammetric reduction wave. The redox peak currents are controlled by diffusion of PANI-GN flakes. The PANI-GN film cast on the electrode shows voltammetric peaks for PANI, of which redox charge is larger than that of the electrochemically polymerized PANI film with the common weight of PANI. This fact can be explained in terms of the electrochemically exhaustive oxidation of PANI through the electric conduction of GN.

Membrane separation technology is extensively used in water treatment. However, during long-term operation, biofouling caused by bacteria and other microorganisms significantly limits the service life of membranes. Introducing antibacterial nanomaterials onto the membrane surface or into the internal structure is an effective way to combat biofouling. This review systematically summarizes recent progress in antibacterial membranes modified with different nanomaterials. First, we classify antibacterial nanomaterials by dimensionality and highlight their physicochemical properties and effects on overall membrane performance. Furthermore, we summarize the advantages, disadvantages, and applicability of three antibacterial nanomaterial modification strategies for membranes, including surface coating, grafting, and blending. Subsequently, we analyze in depth the main antibacterial mechanisms that enhance membrane performance, including metal ion release, reactive oxygen species oxidation, physical contact disruption, and anti-adhesion, as well as their synergistic effects. Finally, we critically evaluate the remaining challenges, such as interfacial compatibility between nanomaterials and polymers, controlled release of metal ions, and environmental safety. This review provides a reference for the rational design of high-performance antibacterial membranes.