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Earth-abundant manganese-based oxides have emerged as promising alternatives to noble-metal-based catalysts for the oxygen evolution reaction (OER) in acidic conditions; however, their inferior activity and stability present critical challenges for the sustainable production of hydrogen via water electrolysis. Moving beyond oxides, heteroanionic materials, which incorporate anions with lower electronegativity than oxygen, have shown potential for improving the OER performance, but a detailed understanding of the underlying mechanisms is lacking. Here, we investigate manganese based oxychlorides (Mn8O10Cl3 and FeMn7O10Cl3) that exhibit excellent activity and stability for acidic OER to elucidate material property dynamics and correlate them with OER behaviors. Our rigorous electrochemical stability testing reveals that the high operating potential mitigates Mn dissolution over prolonged exposure to the OER conditions. Through a combination of ex situ and in situ surface and bulk-sensitive X-ray spectroscopy analyses, we observe a trade-off between increasing Mn valence and maintaining structural integrity, which results in dynamic bond length changes within the [MnCl6] octahedra during the activation and degradation processes of these oxychloride catalysts. This study provides insights into the fundamental relationships between the chemical, electronic, and geometric properties of the catalysts and their electrocatalytic outcomes.
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Ultrathin Silicon Oxide Overlayers Enable Selective Oxygen Evolution from Acidic and Unbuffered pH-Neutral Seawater
Seawater electrolysis is an attractive approach for producing clean hydrogen fuel in scenarios where freshwater is scarce and renewable electricity is abundant. However, chloride ions (Cl−) in seawater can accelerate electrode corrosion and participate in the undesirable chlorine evolution reaction (CER). This problem is especially acute in acidic conditions that naturally arise at the anode as a result of the desired oxygen evolution reaction (OER). Herein, we demonstrate that ultrathin silicon oxide (SiOx) overlayers on model platinum anodes are highly effective at suppressing the CER in the presence of 0.6 M Cl− in both acidic and unbuffered pH-neutral electrolytes by blocking the transport of Cl− to the catalytically active buried interface while allowing the desired oxygen evolution reaction (OER) to occur there. The permeability of Cl− in SiOx overlayers is 3 orders of magnitude less than that of Cl− in a conventional salt-selective membrane used in reverse osmosis desalination. The overlayers also exhibit robust stability over 12 h in chronoamperometry tests at moderate overpotentials. SiOx overlayers demonstrate a promising step toward achieving selective and stable seawater electrolysis without the need to adjust the pH of the electrolyte.
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- Award ID(s):
- 1752340
- PAR ID:
- 10210249
- Date Published:
- Journal Name:
- ACS Catalysis
- Volume:
- 11
- ISSN:
- 2155-5435
- Page Range / eLocation ID:
- 1316 to 1330
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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A mixed-metal ternary chalcogenide, cobalt molybdenum telluride (CMT), has been identified as an efficient tri-functional electrocatalyst for seawater splitting, leading to enhanced oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR). The CMT was synthesized by a single step hydrothermal technique. Detailed electrochemical studies of the CMT-modified electrodes showed that CMT has a promising performance for OER in the simulated seawater solutions, exhibiting a small overpotential of 385 mV at 20 mA cm−2, and superior catalyst durability for prolonged period of continuous oxygen evolution. Interestingly, while gas chromatography analysis confirmed the evolution of oxygen in an anodic chamber, it showed that there was no chlorine evolution from these electrodes in alkaline seawater, highlighting the novelty of this catalyst. CMT also displayed remarkable ORR activity in simulated seawater as indicated by its four-electron reduction pathway forming water as the dominant product. One of the primary challenges of seawater splitting is chlorine evolution from the oxidation of dissolved chloride salts. The CMT catalyst successfully and significantly lowers the water oxidation potential, thereby separating the chloride and water oxidation potentials by a larger margin. These results suggest that CMT can function as a highly active tri-functional electrocatalyst with significant stability, making it suitable for clean energy generation and environmental applications using seawater.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acscatal.0c04343
