Oxygen Evolution Reaction by Silicate-Stabilized Manganese Oxide

Abstract

Oxygen evolution reaction (OER) through water oxidation under acidic conditions catalyzed by first-row transitionmetal-based compounds remains a challenge in artificial photosynthesis. A critical issue for OER under acidic conditions is the solubility of first-row transition-metal compounds during the reaction. This study investigates the silicate-stabilized Mn oxide for OER under acidic conditions (H 2 SO 4 (0.10 M)). Compared to Mn oxide, the silicate-stabilized Mn oxide is significantly more stable under acidic conditions , with an overpotential of 457 mV for the onset of OER. The Mn oxides forming in the absence and presence of silicate groups are α-Mn 2 O 3 and α-MnO 2 , respectively. For the Mn oxides forming in the presence of silicate groups, the corresponding current densities of 1 and 10 mA/cm 2 are recorded at 527 and 640 mV, respectively. Silicate-stabilized Mn oxide was characterized by several methods before and after OER. The 29 Si NMR spectrum for silicate-stabilized Mn oxide shows that the Si− O groups chemically bonded to Mn ions. The scanning transmission electron microscopy shows small 2−10 nm particles of Si−O compound in silicate-stabilized Mn oxide, especially Si−O, to stabilize the higher-indices facets of the Mn oxide crystallites. X-ray absorption spectroscopy confirms that the predominant structure for silicate-stabilized manganese oxide is α-MnO 2 , with di-and mono-μ-oxo-bridged Mn atoms. After prolonged oxygen evolution, a certain fraction of the mono-μ-oxo bridges disappears for silicate-stabilized manganese oxide. Adding silicate to Mn oxide is a low-cost and environmentally friendly procedure to increase the stability of Mn oxide toward OER under acidic conditions. Thus, our procedure is a clear improvement on current methods to stabilize Mn oxide for OER under acidic conditions.

The current state of transition metal-based electrocatalysts (oxides, alloys, POMs, and MOFs) for oxygen reduction, oxygen evolution, and hydrogen evolution reactions

“…These metals are more affordable, which facilitates their use in industrial conditions. Still, one should also be aware of the stability of these transition-metal-based electrocatalysts, which, in acidic conditions, is generally low (Goberna-Ferrón et al, 2015;Sun et al, 2015;Lu et al, 2019;Zand et al, 2023), hence why there are fewer studies on this type of media.…”

“…The results showed that the catalytic activity was less than optimal since the overpotential needed to achieve 10 mA/cm 2 was 640 mV, and the OER onset potential was 1.757 V vs RHE. On the other hand, the stability was greatly improved because the modified Mn oxide showed higher current retention and virtually no structural changes after OER (Zand et al, 2023).…”

Oxygen-evolution reaction in the presence of cerium(iv) ammonium nitrate and iron (hydr)oxide: old system, new findings

“…For example, phase conversions were observed for metal (hydr)oxides during the OER while many Mn oxides (Mn 3 O 4 , α-Mn 2 O 3 , β-MnO 2 , CaMnO 3 , Ca 2 Mn 3 O 8 , CaMn 3 O 6 , and CaMn 4 O 8 ) convert to layered Mn oxide in the presence of CAN and during the OER, where layered Mn oxide is an efficient OER catalyst. 6…”

“…2,3 However, developing efficient and stable oxygen-evolution catalysts (OECs) is crucial to yield breakthroughs in water-splitting technology. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Mn, [4][5][6][7][8][9][10] Fe, [11][12][13][14][15] Co, [16][17][18] Ni, [19][20][21] and Cu 22,23 compounds are synthesized using different methods and applied as OECs. Among other conditions, the oxygen-evolution reaction (OER) in the presence of cerium(IV) ammonium nitrate (CAN) as a sacrificial oxidant has been extensively investigated.…”

“…For example, phase conversions were observed for metal (hydr)oxides during the OER while many Mn oxides (Mn 3 O 4 , α-Mn 2 O 3 , β-MnO 2 , CaMnO 3 , Ca 2 Mn 3 O 8 , CaMn 3 O 6 , and CaMn 4 O 8 ) convert to layered Mn oxide in the presence of CAN and during the OER, where layered Mn oxide is an efficient OER catalyst. 6 There are four crystalline polymorphs of Fe 2 O 3 : α-Fe 2 O 3 , β-Fe 2 O 3 , γ-Fe 2 O 3 , and ε-Fe 2 O 3 . β/ε-Fe 2 O 3 are generally synthesized in the laboratory.…”