Photo-/Electroinduced Irreversible Isomerization of 2,2'-Azobispyridine Ligands in Arene Ruthenium(II) Complexes.

Novel arene RuII complexes containing 2,2'-azobispyridine ligands were synthesized and characterized by using 1 H and 13 C NMR spectroscopy, UV/vis spectroscopy, electrochemistry, DFT calculations and single-crystal X-ray diffraction. Z-configured complexes featuring unprecedented seven-membered chelate rings involving the nitrogen atom of both pyridines were isolated and were shown to undergo irreversible isomerization to the corresponding E-configured five-membered chelate complexes in response to light or electrochemical stimulus.

Metal Ion-/Proton-Coupled Electron Transfer (MPCET) on ortho-Quinone.

Quinol/quinone equilibria are ubiquitous in nature and find multiple technological applications, most recently in electrical charge storage. Much research has been devoted to proton-coupled electron transfer (PCET) in such systems and to bidentate complexation of ortho-quinol (catechol) ligands with multivalent metal ions but rarely to the interplay of these two reactions. Here, we investigate the impact of a redox-inactive metal ion, as a complexing and charge-compensating agent, on redox processes of catechol in aqueous solutions, that is, in the presence of proton equilibria. We pay separate attention to their thermodynamics and kinetics, which can be regulated by the pH and buffer capacity. As the proton buffer concentration decreases, proton equilibria during catechol PCET are slower to establish, thus kinetically prioritizing the participation of the metal ion rather than the proton in the redox charge compensation. Making use of this kinetic interplay can be a general strategy to conceive organic battery cathodes for proton-free metal-ion aqueous batteries.

Does Water-in-Salt Electrolyte Subdue Issues of Zn Batteries?

Zn-metal batteries (ZnBs) are safe and sustainable because of their operability in aqueous electrolytes, abundance of Zn, and recyclability. However, the thermodynamic instability of Zn metal in aqueous electrolytes is a major bottleneck for its commercialization. As such, Zn deposition (Zn2+ → Zn(s)) is continuously accompanied by the hydrogen evolution reaction (HER) (2H+ → H2 ) and dendritic growth that further accentuate the HER. Consequently, the local pH around the Zn electrode increases and promotes the formation of inactive and/or poorly conductive Zn passivation species (Zn + 2H2 O → Zn(OH)2 + H2 ) on the Zn. This aggravates the consumption of Zn and electrolyte and degrades the performance of ZnB. To propel HER beyond its thermodynamic potential (0 V vs standard hydrogen electrode (SHE) at pH 0), the concept of water-in-salt-electrolyte (WISE) has been employed in ZnBs. Since the publication of the first article on WISE for ZnB in 2016, this research area has progressed continuously. Here, an overview and discussion on this promising research direction for accelerating the maturity of ZnBs is provided. The review briefly describes the current issues with conventional aqueous electrolyte in ZnBs, including a historic overview and basic understanding of WISE. Furthermore, the application scenarios of WISE in ZnBs are detailed, with the description of various key mechanisms (e.g., side reactions, Zn electrodeposition, anions or cations intercalation in metal oxide or graphite, and ion transport at low temperature).