Capacitive deionization (CDI) has attracted huge interest as an energy-efficient and eco-friendly desalination strategy. Its development is presently limited due to the relatively low CDI capacitances of carbon materials. Herein, hierarchical porous carbon materials (HPCs) derived from ethylenediaminetetraacetic acid (EDTA) upon annealing were used, which showed impressive CDI performance with a maximum desalination capacity of 34.27 mg g⁻¹ in 40 mg L⁻¹ NaCl aqueous solution. Such capability was attributed to the appropriate hierarchical pore structure, high specific surface area (2185.71 m² g⁻¹), large pore volume (1.368 cm³ g⁻¹) and reasonable graphitization degree, which were also confirmed by the high specific capacitances of 182 F g⁻¹ in 1 mol L⁻¹ NaCl and 260 F g⁻¹ in 6 mol L⁻¹ KOH. Since the physisorption capacity was nearly 0, and the regeneration process was facile and complete, such economical HPCs materials show potential for practical desalination applications in the future. Moreover, the HPCs electrodes presented ion selectivity in competitive multi-ionic solutions by kinetic behavior difference or static capacitance difference.

Controlling and understanding the electrochemical properties of electroactive polymeric colloids is a highly topical but still a rather unexplored field of research. This is especially true when considering more complex particle architectures like stimuli-responsive microgels, which would entail different kinetic constraints for charge transport within one particle. We synthesize and electrochemically address dual stimuli responsive core–shell microgels, where the temperature-responsiveness modulates not only the internal structure, but also the microgel electroactivity both on an internal and on a global scale. In detail, a facile one-step precipitation polymerization results in architecturally advanced poly(N-isopropylacrylamide-co-vinylferrocene) P(NIPAM-co-VFc) microgels with a ferrocene (Fc)-enriched (collapsed/hard) core and a NIPAM-rich shell. While the remaining Fc units in the shell are electrochemically accessible, the electrochemical activity of Fc in the core is limited due to the restricted mobility of redox active sites and therefore restricted electron transfer in the compact core domain. Still, prolonged electrochemical action and/or chemical oxidation enable a reversible adjustment of the internal microgel structure from core–shell microgels with a dense core to completely oxidized microgels with a highly swollen core and a denser corona. The combination of thermo-sensitive and redox-responsive units being part of the network allows for efficient amplification of the redox response on the overall microgel dimension, which is mainly governed by the shell. Further, it allows for an electrochemical switching of polarity (hydrophilicity/hydrophobicity) of the microgel, enabling an electrochemically triggered uptake and release of active guest molecules. Hence, bactericidal drugs can be released to effectively kill bacteria. In addition, good biocompatibility of the microgels in cell tests suggests suitability of the new microgel system for future biomedical applications.

LiNi_0.5Mn_1.5O₄ (LNMO) spinel has been extensively investigated as one of the most promising high-voltage cathode candidates for lithium-ion batteries. The electrochemical performance of LNMO, especially its rate performance, seems to be governed by its crystallographic structure, which is strongly influenced by the preparation methods. Conventionally, LNMO materials are prepared via solid-state reactions, which typically lead to microscaled particles with only limited control over the particle size and morphology. In this work, we prepared Ni-doped LiMn₂O₄ (LMO) spinel via the polyol method. The cycling stability and rate capability of the synthesized material are found to be comparable to the ones reported in literature. Furthermore, its electronic charge transport properties were investigated by local electrical transport measurements on individual particles by means of a nanorobotics setup in a scanning electron microscope, as well as by performing DFT calculations. We found that the scarcity of Mn³⁺ in the LNMO leads to a significant decrease in electronic conductivity as compared to undoped LMO, which had no obvious effect on the rate capability of the two materials. Our results suggest that the rate capability of LNMO and LMO materials is not limited by the electronic conductivity of the fully lithiated materials.