Electrochemical hydrogenation of nitrate to ammonia using renewable electricity is a promising route for sustainability but lacks catalysts that can deliver balanced selectivity, activity, and durability. Here, a new family of noble metal‐free and high‐performing Chevrel phase Ni2Mo6T8(T = S, Se, and Te) catalysts that have similar structural and textural properties and differ presumably only in chalcogenide anion is systematically studied. The side‐by‐side comparisons allow the uncovering of the critical roles of chalcogenide anions in impacting kinetic activities and long‐term durability. The incorporation of anions with larger size and smaller electronegativity from sulfide to selenide and telluride invokes stronger inhibition of the otherwise competing hydrogen evolution reaction (HER) and steers the hydrogenation toward the selective formation of ammonia, thus improving both Faradic selectivity and the turnover frequency to high levels of 99.4% and 21.5 s−1, respectively, on the Ni2Mo6Te8catalyst. More significantly, the bulkier anion in the Ni2Mo6T8catalyst kinetically inhibited the intercalation of electrolyte cations, a major degradation mechanism in the catalyst family examined here and delivered several times improved durability. Therefore, this study introduces novel active motifs for selective nitrate reduction and provides insights into the catalyst degradation mechanism and practical ways to improve durability.
Electrocatalytic two‐electron reduction of oxygen is a promising method for producing sustainable H2O2but lacks low‐cost and selective electrocatalysts. Here, the Chevrel phase chalcogenide Ni2Mo6S8is presented as a novel active motif for reducing oxygen to H2O2in an aqueous electrolyte. Although it has a low surface area, the Ni2Mo6S8catalyst exhibits exceptional activity for H2O2synthesis with >90% H2O2molar selectivity across a wide potential range. Chemical titration verified successful generation of H2O2and confirmed rates as high as 90 mmol H2O2gcat−1h−1. The outstanding activities are attributed to the ligand and ensemble effects of Ni that promote H2O dissociation and proton‐coupled reduction of O2to HOO*, and the spatial effect of the Chevrel phase structure that isolates Ni active sites to inhibit OO cleavage. The synergy of these effects delivers fast and selective production of H2O2with high turn‐over frequencies of ≈30 s−1. In addition, the Ni2Mo6S8catalyst has a stable crystal structure that is resistive for oxidation and delivers good catalyst stability for continuous H2O2production. The described Ni‐Mo6S8active motif can unlock new opportunities for designing Earth‐abundant electrocatalysts to tune oxygen reduction for practical H2O2production.
more » « less- NSF-PAR ID:
- 10361730
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Functional Materials
- Volume:
- 31
- Issue:
- 47
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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