Searching High-Potential Dihydroxynaphthalene Cathode for Rocking-Chair All-Organic Aqueous Proton Batteries

The lack of acid-proof high-potential cathode largely limits the development and competitiveness of proton batteries. Herein, the authors systematically investigated six dihydroxynaphthalenes (DHNs) and found that 2,6-DHN delivered the best cathode performance in proton battery with the highest redox potential (0.84 V, vs SHE) and a specific capacity of 91.6 mAh g-1 at 1 A g-1 . In situ solid-state electropolymerization of DHNs is responsible for the voltage and capacity fading of DHNs, and 2,6-DHN's excellent electrochemical performance is derived from its high polymerization energy barrier. By compounding with rGO, the 2,6-DHN/rGO electrode can maintain a specific capacity of 89 mAh g-1 even after 12 000 cycles at 5 A g-1 . When it is paired with the 2,6-dihydroxyanthraquinone (DHAQ) anode, the assembled rocking-chair all-organic proton battery exhibited a high cell voltage of 0.85 V, and excellent energy/power densities (70.8 Wh kg-1 /850 W kg-1 ). This study showcases a new-type high-potential proton-containing organic cathode and paves the way for constructing a high-voltage rocking-chair proton battery. Also, in situ solid-state electropolymerization will inspire the further study of phenol-based small-molecule electrodes.

Hydroxyl-Functionalized Covalent Organic Frameworks as High-Performance Supercapacitors

Covalent organic frameworks (COFs) have attracted significant interest because of their heteroatom-containing architectures, high porous networks, large surface areas, and capacity to include redox-active units, which can provide good electrochemical efficiency in energy applications. In this research, we synthesized two novel hydroxy-functionalized COFs-TAPT-2,3-NA(OH)_2, TAPT-2,6-NA(OH)₂ COFs-through Schiff-base [3 + 2] polycondensations of 1,3,5-tris-(4-aminophenyl)triazine (TAPT-3NH₂) with 2,3-dihydroxynaphthalene-1,4-dicarbaldehyde (2,3-NADC) and 2,6-dihydroxynaphthalene-1,5-dicarbaldehyde (2,6-NADC), respectively. The resultant hydroxy-functionalized COFs featured high BET-specific surface areas up to 1089 m² g^-1, excellent crystallinity, and superior thermal stability up to 60.44% char yield. When used as supercapacitor electrodes, the hydroxy-functionalized COFs exhibited electrochemical redox activity due to the presence of redox-active 2,3-dihydroxynaphthalene and 2,6-dihydroxynaphthalene in their COF skeletons. The hydroxy-functionalized COFs showed specific capacitance of 271 F g^-1 at a current density of 0.5 A g^-1 with excellent stability after 2000 cycles of 86.5% capacitance retention. Well-known pore features and high surface areas of such COFs, together with their superior supercapacitor performance, make them suitable electrode materials for use in practical applications.

Removal of naphthols and analogues by the combined use of an oxidoreductase polyphenol oxidase and a biopolymer chitosan from aqueous solutions

In this study, the combined use of an amino group-containing polymer chitosan and an oxidoreductase polyphenol oxidase (PPO) was applied to the removal of naphthols and dihydroxynaphthalenes (DHNs) from aqueous solutions. The process parameters, such as the pH value, temperature and enzyme dose, were discussed for PPO-catalysed oxidation of 1-naphthol. The optimum conditions of enzymatic oxidation of 1-naphthol were determined to be pH 8.0 and 40 °C. Under the optimum conditions, PPO-catalysed oxidation of 1-naphthol increased with an increase in the enzyme dose. Quinone derivatives enzymatically generated were chemisorbed on chitosan beads and the initial velocity of PPO-catalysed oxidation increased with an increase in the amount of added chitosan beads. A specific initial velocity of 0.0675 μmol/U·min was obtained in the PPO concentration range below 200 U/cm³ and 1-naphthol was completely removed within 24 h by quinone adsorption on chitosan beads (0.20 cm³/cm³) at a PPO concentration of 100 U/cm³. The removal time was shortened by increasing the enzyme dose or the amount of added chitosan beads. 2-Naphthol was also completely removed at an initial concentration of 0.05 mM or less by prolonging the reaction time, since PPO-catalysed oxidation of 2-naphthol was much slower than that of 1-naphthol. In addition, this procedure was also applied to the removal of DHNs. These results revealed that the procedure constructed in this study was an effective technique to remove naphthols and DHNs from the aqueous medium.