Synthesis of hierarchical transition metal oxyhydroxides in aqueous solution at ambient temperature and their application as OER electrocatalysts

CoOOH: Synthesis and Application in Alkaline Electrochemical Oxygen Evolution Reaction

“…Preparation of CoOOH by wet-chemical oxidation methods involves the use of low-valence Co salts or compounds as Co source and conventional oxidative reagents such as NaClO, [50,[67][68][69]75] H 2 O 2 , [51,66,76,77] K 2 S 2 O 8 , [65] Na 2 CrO 4 , [78] and Na 2 MoO 4 . [79] Wetchemical oxidation is easy to control and does not require harsh conditions like high temperature or high pressure.…”

“…For instance, Cölfen et al adopted an environmentally friendly one-step co-precipitation route to synthesize hierarchical CoOOH spheres. [65] Co 2+ and ammonium hydroxide solution are co-precipitated under the presence of K 2 S 2 O 8 as oxidizing agent (Figure 2f). The authors demonstrated that the K 2 S 2 O 8 is the key for the one-step formation of CoOOH, while Co(OH) 2 -Cl, one kind of basic salt, [72] Copyright 2021, American Chemical Society.…”

“…Preparation of CoOOH usually involves a oxidation process due to the relatively high valence state of Co species. Generally, CoOOH can be prepared through wet-chemical oxidation methods, [54,[65][66][67][68][69] electrochemical oxidation methods [64,[70][71][72][73] and calcination method, [74] etc. In this part, we will review the control synthesis of CoOOH-based electrocatalysts according to the synthetic methods, and discuss their impact on the structure of CoOOH.…”

Toward Understanding the Formation Mechanism and OER Catalytic Mechanism of Hydroxides by In Situ and Operando Techniques

“…Conversely, a rapid increase in OH − concentration can facilitate the successful formation of Ni(OH) 2 with doped Fe irrespective of the specific Fe species involved [11] . The second example is to investigate the mechanism of valence change of metal cations during the formation process of CoOOH via an eco‐friendly and facile one‐step coprecipitation route, which involves the diffusion of NH 3 vapor originating from an ammonium hydroxide solution into aqueous solution to generate OH − ions that can react with Co 2+ ions under the influence of the oxidizing agent K 2 S 2 O 8 [70] . Based on ex situ XRD and UV/Vis spectroscopy results, the authors concluded that K 2 S 2 O 8 cannot make the already formed crystalline Co(OH) 2 totally oxidized, suggesting that, under the reaction condition in this study, the oxidation of cobalt species is finished before the formation of the crystalline hydroxide.…”

Auf dem Weg zum Verständnis des Bildungs‐ und OER‐Katalysemechanismus von Hydroxiden durch In situ‐ und Operando‐Techniken

“…[11] Das zweite Beispiel ist die Untersuchung des Mechanismus der Valenzänderung von Metallkationen während der Bildung von CoOOH durch eine umweltfreundliche und einfache einstufige Kopräzipitation, bei der NH 3 -Dampf aus einer Ammoniumhydroxidlösung in eine wässrige Lösung diffundiert, um OH À -Ionen zu erzeugen, die unter dem Einfluss des Oxidationsmittels K 2 S 2 O 8 mit Co 2 + -Ionen reagieren können. [70] Basierend auf den Ergebnissen der Ex situ-XRD und UV/Vis-Spektroskopie schließen die Autoren, dass [71] Die erzielten Ergebnisse zeigen, dass die Bildung der ultradünnen Morphologie auf der Hemmung des Wachstums in z-Richtung durch die -NH2-Gruppen der Formamidmoleküle beruht, was zur Entwicklung alternativer, kostengünstiger und ungiftiger Formamid-Ersatzstoffe führt und gleichzeitig Einblicke in die universelle Synthese einschichtiger Hydroxide bei Raumtemperatur liefert.…”