Effects of central metal ions in porphyrin-sensitized solar cells were investigated by using 5-(4-carboxyphenyl)-10,15,20-tris(2,4,6-trimethylphenyl)porphyrins as sensitizers and I−/I3− or Br−/Br3− as redox mediators. Zn(II), Cu(II), Pd(II), and free-base porphyrins were synthesized, and the properties of them and the photovoltaic performances of the dye-sensitized solar cells (DSSCs) using them are compared. The electron injection processes from the dyes into TiO2 were investigated by changing Li+ concentration in the electrolytes. The regeneration processes of the dyes were examined by comparing the electrolytes with different redox potentials (I−/I3− or Br−/Br3−). With the Br−/Br3− redox mediator, palladium porphyrin yielded both higher short-circuit current density (Jsc) and open-circuit voltage (Voc) than that with the I−/I3− mediator and achieved the highest power conversion efficiency among all combinations in this study.
Solid electrolyte interphase (SEI) layer that forms on the graphite negative electrodes of lithium-ion batteries (LIBs) has a crucial role in inhibiting the excess decomposition of electrolyte solutions. While this passivating ability is essential for improving the durability of LIBs, the relationship between the passivating ability and the surface structure of the graphite is not yet fully understood. In this study, we investigate the solvent co-intercalation behavior in the presence of SEI layers formed on various types of graphite surface structures. The amount of edge sites on each graphite sample is determined using electric double layer capacitance. The co-intercalation reactions of untreated, ethylene-carbonate-treated, and vinylene-carbonate-treated graphite samples in dimethoxyethane-based electrolyte solutions are compared. The co-intercalation reactions commence at approximately 1 V vs. Li/Li+ for all untreated samples, but the onset potentials are lowered by the presence of SEI layers, and the extent of this lowering depends on the sample. The SEI layer formed on the edge-rich surface effectively suppresses the co-intercalation reaction, and the additive is also more effective for the edge-rich sample.
Carbon dioxide electrochemical reduction (CO2ER) has attracted considerable attention as a technology to recycle CO2 into raw materials for chemicals using renewable energies. We recently found that Zn-Al layered double hydroxides (Zn-Al LDH) have the CO-forming CO2ER activity. However, the activity was only evaluated by using the liquid-phase CO2ER. In this study, Ni-Al and Ni-Fe LDHs as well as Zn-Al LDH were synthesized using a facile coprecipitation process and the gas-phase CO2ER with the LDH-loaded gas-diffusion electrode (GDE) was examined. The products were characterized by XRD, STEM-EDX, BF-TEM and ATR-IR spectroscopy. In the ATR-IR results, the interaction of CO2 with Zn-Al LDH showed a different carbonates evolution with respect to other LDHs, suggesting a different electrocatalytic activity. The LDH-loaded GDE was prepared by simple drop-casting of a catalyst ink onto carbon paper. For gas-phase CO2ER, only Zn-Al LDH exhibited the CO2ER activity for carbon monoxide (CO) formation. By using different potassium salt electrolytes affording neutral to strongly basic conditions, such as KCl, KHCO3 and KOH, the gas-phase CO2ER with Zn-Al LDH-loaded GDE showed 1.3 to 2.1 times higher partial current density for CO formation than the liquid-phase CO2ER.