One key objective in electrocatalysis is to design selective catalysts, particularly in cases where the desired products require thermodynamically unfavorable pathways. Electrochemical synthesis of hydrogen peroxide (H 2 O 2 ) via the two-electron water oxidation reaction (2e − WOR) requires a +0.54 V higher potential than four-electron O 2 evolution. So far, best-performing electrocatalysts require considerable overpotentials before reaching peak faradaic efficiency. We present Mn-alloyed TiO 2 coatings prepared by atomic layer deposition (ALD) and annealing as a stable and selective electrocatalyst for 2e − WOR. Faradaic efficiency of >90% at < 150 mV overpotentials was achieved for H 2 O 2 production, accumulating 2.97 mM H 2 O 2 after 8 hours. Nanoscale mixing of Mn 2 O 3 and TiO 2 resulted in a partially filled, highly conductive Mn 3+ intermediate band (IB) within the TiO 2 mid-gap to transport charge across the (Ti,Mn)O x coating. This IB energetically matched that of H 2 O 2 -producing surface intermediates, turning a wide bandgap oxide into a selective electrocatalyst capable of operating in the dark. However, the high selectivity is limited to the low overpotential regime, which limits the system to low current densities and requires further research into increasing turn-over frequency per active site.
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Effect of doping TiO 2 with Mn for electrocatalytic oxidation in acid and alkaline electrolytes
Electrochemical oxidation of water and electrolyte ions is a sustainable method for producing energy carriers and valuable chemicals. Among known materials for catalyzing oxidation reactions, titanium dioxide (TiO 2 ) offers excellent electrochemical stability but is less active than many other metal oxides. Herein, we used density functional theory calculations to predict an increase in catalytic activity by doping anatase TiO 2 with manganese atoms (Mn). We synthesized Mn-doped TiO 2 and then utilized X-ray absorption spectroscopy to study the chemical environment around the Mn site in the TiO 2 crystal structure. Our electrochemical experiments confirmed that TiO 2 , with the optimal amount of Mn, reduces the onset potential by 260 mV in a 2 M KHCO 3 (pH = ∼8) electrolyte and 370 mV in a 0.5 M H 2 SO 4 (pH = ∼0.5) electrolyte. Moreover, in 0.5 M H 2 SO 4 , we observed that the amount of Mn doping greatly impacts the selectivity towards oxygen production versus peroxysulfate formation. In 2 M KHCO 3 , the Mn doping of TiO 2 slightly decreases the selectivity towards oxygen production and increases the hydrogen peroxide formation. The Mn-doped TiO 2 shows good electrochemical stability for over 24 hours in both electrolytes.
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- Award ID(s):
- 2029425
- NSF-PAR ID:
- 10358670
- Date Published:
- Journal Name:
- Energy Advances
- Volume:
- 1
- Issue:
- 6
- ISSN:
- 2753-1457
- Page Range / eLocation ID:
- 357 to 366
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Electrochemical two-electron water oxidation reaction (2e-WOR) has drawn significant attention as a promising process to achieve the continuous on-site production of hydrogen peroxide (H2O2). However, compared to the cathodic H2O2generation, the anodic 2e-WOR is more challenging to establish catalysts due to the severe oxidizing environment. In this study, we combine density functional theory (DFT) calculations with experiments to discover a stable and efficient perovskite catalyst for the anodic 2e-WOR. Our theoretical screening efforts identify LaAlO3perovskite as a stable, active, and selective candidate for catalyzing 2e-WOR. Our experimental results verify that LaAlO3achieves an overpotential of 510 mV at 10 mA cm−2in 4 M K2CO3/KHCO3, lower than those of many reported metal oxide catalysts. In addition, LaAlO3maintains a stable H2O2Faradaic efficiency with only a 3% decrease after 3 h at 2.7 V vs. RHE. This computation-experiment synergistic approach introduces another effective direction to discover promising catalysts for the harsh anodic 2e-WOR towards H2O2.
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2YA00027J
