2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/139274We report a successful tuning of Co valence state in cobalt oxyhydrate superconductor via a facile post reduction using NaOH as reducing agent. The change in Co valence was precisely determined by measuring the volume of the released oxygen. The possible hydronium-incorporation was greatly suppressed in concentrated NaOH solution, making the absolute Co valence determinable. As a result, an updated superconducting phase diagram was obtained, which shows that the superconducting transition temperature increases monotonically with increasing Co valence in a narrow range from +3.58 to +3.65.17 pages, 5 figures and 1 table. Chem. Mat. in pressSuperconductivityStrongly Correlated Electronstext