Unveiling the occurrence of Co(III) in NiCo layered electroactive hydroxides. The role of distorted environments

DIEGO HUNT; MATIAS JOBBAGY; MARTÍN MIZRAHI ; VICTOR OESTREICHER; FÉLIX G REQUEJO ; DIEGO HUNT; MATIAS JOBBAGY; MARTÍN MIZRAHI ; VICTOR OESTREICHER; FÉLIX G REQUEJO

CHEMISTRY-A EUROPEAN JOURNAL

WILEY-V C H VERLAG GMBH

Año: 2020

0947-6539

P { margin-bottom: 0.08in; }A:link { }Co‐ and Ni‐based layered hydroxidesconstitute a unique class of two‐dimensional inorganic materialswith exceptional chemical diversity, physicochemical properties andoutstanding performance as supercapacitors and overall watersplitting catalysts. Recently, the occurrence of Co(III) in thesephases has been proposed as a key factor that enhance theirelectrochemical performance. However, the origin of this centers andcontrol over its contents remains as an open question. We employedthe Epoxide Route to synthesize a whole set of α‐NiCo layeredhydroxides. The PXRD and XAS characterization alert about theoccurrence of Co(III) as a consequence of the increment in the Nicontent. DFT+U simulation suggest that the shortening of the Co?Odistance promotes a structural distortion in the Co environments,resulting in a double degeneration in the octahedral Co 3d orbitals.Hence, a strong modification of the electronic properties leaves thesystem prone to oxidation, by the appearance of Co localizedelectronic states on the Fermi level. This work combines amicroscopic interpretation supported by a multiscalecrystallochemical analysis, regarding the so called synergistic redoxbehavior of Co and Ni, offering fundamental tools for thecontrollable design of highly efficient electroactive materials. Tothe best of our knowledge this is the firstcomputational‐experimental investigation of the electronic andstructural details of α‐NiCo hydroxides, laying the foundation forthe fine tuning of electronic properties in layered hydroxides.