Mechanism, decomposition pathway and new evidence for self-healing of manganese oxides as efficient water oxidizing catalysts: new insights

Abstract

The electrochemical water-oxidation reaction usually requires a catalyst to reduce the overpotential and Earth-abundant catalysts, like MnO2, are attracting much attention. Here we use chemometric analysis, EPR and UV-Vis spectroscopies to track Mn(II) and MnO4(-) byproducts to the reaction of a MnO2 film in the presence of cerium(IV) ammonium nitrate. Permanganate ion is involved in at least two key reactions: it may oxidize water to O2 or can combine with Mn(II) to remake MnO2 solid. We propose mechanisms for water oxidation and present a self-healing process for this reaction.

Nanostructured Manganese Oxides as Highly Active Water Oxidation Catalysts: A Boost from Manganese Precursor Chemistry

“…This corroborates with the results illustrated by Najafpour et al that it is indeed possible to convert some manganese oxides and calcium-manganese oxides structurally into their amorphous layered form by treatment with CAN but only at higher concentration (1.8 m) and after prolonged treatments (ranging from a few hours to 4 weeks). [50,88] The photocatalytic cycles of water oxidation for all mineral phases of the Mn 2 2 + ; at this site, water molecules are oxidized to form oxygen molecules at the surface. The dissolved-oxygen content can then by analyzed by using a Clark oxygen electrode system.…”

The effect of different metal ions between nanolayers of manganese oxide on water oxidation

“…However, the water oxidation by the compounds depends on some factors (Scheme 1) [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57].…”

“…Among Mn oxides, nanolayered Mn oxides with different organic or inorganic ions between layers are efficient and stable in water oxidation [41]. Inspired by the WOC, layered MnACa oxides were reported as efficient catalyst for water oxidation [42][43][44][45][46][47][48][49][50][51][52][53][54][55]. X-ray absorption spectroscopy (XAS) reveal similarities between layered oxide and MnACa cluster in PSII [42].…”

From manganese complexes to nano-sized manganese oxides as water-oxidizing catalysts for artificial photosynthetic systems: Insights from the Zanjan team

“…In high enough potential both water oxidation and MnO 4 À reactions take place. MnO 4 À ions and similar species cause a long-term stability problem, separate Mn ions from the catalysts and decrease the activity of these compounds toward water oxidation [41,52,68,69]. Our group reported a new self-healing process of Mn oxides in the presence of Ce(IV).…”

“…Our group also introduced a new mechanism for selfhealing of the Mn oxide phase in the presence of Ce (IV) (Fig. 7a) [41,52,68,69]. From the Pourbaix diagram (Fig.…”