Search

Lithium-oxygen batteries have attracted widespread attention owing to their superior theoretical energy density. However, they are obstructed by sluggish oxygen reduction (ORR) and evolution reaction (OER) kinetics at air cathodes. Herein, different from using single solid or soluble catalysts, solid-soluble synergistic catalysis is proposed to conjointly enhance ORR/OER performances. During discharge, single-atomic zinc/cobalt embedded in nitrogen-doped carbon (Zn, Co-N/C) is judiciously engineered as a solid catalyst to regulate the growth pathway of Li2O2and promote ORR kinetics. During charge, a typical redox mediator (RM, LiI) is added as a soluble catalyst to permit efficient oxidation of Li2O2. Of note is that the atomic Zn/Co-Nxsites can chemically adsorb oxidized iodine (I2) and accelerate OER kinetics, which plays a decisive role in eliminating the shuttle effect of I3–/I2to the Li anode. Coupling a single-atomic catalyst with restricted oxidized iodine offers an exceptional discharge capacity, remarkably low polarization, and superior long-term cycling stability.

The concept of high-performance excited-state intramolecular proton transfer (ESIPT)-based fluorescent metal–organic framework (MOF) probes for Al3+is proposed in this work. By regulating the hydroxyl groups on the organic linker step by step, new fluorescent magnesium–organic framework (Mg–MOF) probes for Al3+ions were established based on the ESIPT fluorescence mechanism. It is observed for the first time that the number of intramolecular hydrogen bonds between adjacent hydroxyl and carboxyl groups can effectively adjust the ESIPT process and lead to tunable fluorescence sensing performance. Together with the well-designed porous and anionic framework, the Mg–TPP–DHBDC probe decorating with a pair of intramolecular hydrogen bonds exhibits extra-high quantitative fluorescence response to Al3+through an unusual turn-off (0–1.2 μM) and turn-on (4.2–15 μM) luminescence sensing mechanism. Notably, the 28 nM limit of detection value represents the lowest record among all reported MOF-based Al3+fluorescent sensors up to now. Benefited from the unique turn–off–on ESIPT fluorescence detection process, the Mg–TPP–DHBDC MOF sensor exhibits single Al3+detection compared with other 16 common metal ions including Ga3+, In3+, Fe3+, Cr3+, Ca2+, and Mg2+. Impressively, such an Al3+selective sensing process can even be fulfilled by the reusable MOF test paper detected by naked eyes. Overall, the quantitative Al3+detection, together with the extraordinary sensitivity, selectivity, fast response, and good reusability, strongly supports our concept of ESIPT-based fluorescent MOF Al3+probes and makes Mg–TPP–DHBDC one of the most powerful Al3+fluorescent sensors.