Understanding the Role of Gold Nanoparticles in Enhancing the Catalytic Activity of Manganese Oxides in Water Oxidation Reactions

Abstract

The Earth‐abundant and inexpensive manganese oxides (MnOx) have emerged as an intriguing type of catalysts for the water oxidation reaction. However, the overall turnover frequencies of MnOx catalysts are still much lower than that of nanostructured IrO2 and RuO2 catalysts. Herein, we demonstrate that doping MnOx polymorphs with gold nanoparticles (AuNPs) can result in a strong enhancement of catalytic activity for the water oxidation reaction. It is observed that, for the first time, the catalytic activity of MnOx/AuNPs catalysts correlates strongly with the initial valence of the Mn centers. By promoting the formation of Mn3+ species, a small amount of AuNPs (<5 %) in α‐MnO2/AuNP catalysts significantly improved the catalytic activity up to 8.2 times in the photochemical and 6 times in the electrochemical system, compared with the activity of pure α‐MnO2.

Manganese oxides supported on gold nanoparticles: new findings and current controversies for the role of gold

“…-The role of redox-active supports combined with Mn oxides toward water oxidation is complex. For the catalyst reported here and in the presence of Ce(IV), gold shows a lower effect than in the previously reported gold-doped catalysts (Najafpour et al 2013e;Gorlin et al 2014;Kuo et al 2014). We propose that the true role of gold in these catalysts depends on the methods of synthesis and the effect should be studied more carefully.…”

“…Gold nanoparticles are more active toward KMnO 4 reduction than the bulk substance: Subbaraman et al reported that water oxidation of four first-row transition metal oxides did not vary with the nature of the metal support (Subbaraman et al 2012), other groups reported the importance of supports for the first-row transition metal oxides in water oxidation (El-Deab et al 2007;Mohammad et al 2008;Najafpour et al 2013e;Gorlin et al 2014;Kuo et al 2014;Bell 2011, 2012). In the Photosynth Res previous study (Najafpour et al 2013e), the gold nanoparticles deposited on layered Mn oxide were reported.…”

“…These groups proposed the increase of the Photosynth Res amount of Mn(III) ions as the important factor affecting the water-oxidizing activities. They indicated that gold nanoparticles improve the catalytic activity up to 8.2 times in the photochemical and 6 times in the electrochemical system, compared with the activity of pure a-MnO 2 (Kuo et al 2014).…”

“…Thus, a scalable catalyst production would be possible under these conditions (El-Deab et al 2007;Mohammad et al 2008;Najafpour et al 2013e;Gorlin et al 2014;Kuo et al 2014). …”

“…Recently, the Suib's and He's groups showed that doping of MnO x with gold nanoparticles can result in a strong enhancement of water oxidation catalyzed by MnO x (Kuo et al 2014). These groups proposed the increase of the Photosynth Res amount of Mn(III) ions as the important factor affecting the water-oxidizing activities.…”