Vacancy-Rich SnO₂ Quantum Dot Stabilized by Polyoxomolybdate as Electrocatalyst for Selective NH₃ Production

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Tin dioxide (SnO2) nanoparticles exhibit excellent conductivity, making them promising electrode materials.
• Stabilizing SnO2 quantum dots (QDs) in aqueous environments is crucial for their application.
• Polyoxomolybdates (POMs) offer potential as inorganic ligands for nanomaterial stabilization.

Purpose of the Study:

• To stabilize ca. 6 nm SnO2 QDs using an Anderson-type polyoxomolybdate, (NH4)6[Mo7O24].
• To investigate the structural, chemical, and electrochemical properties of the resulting Mo@SnO2 material.
• To evaluate the performance of Mo@SnO2 as a catalyst for electrocatalytic nitrate reduction to ammonia.

Main Methods:

• Synthesis of Mo@SnO2 using polyoxomolybdate as a ligand.
• X-ray scattering and diffraction for structural analysis.
• Elemental analysis and mass spectrometry for composition verification.
• Surface zeta potential, Raman spectroscopy, and EXAFS for surface linkage confirmation.
• Electrochemical measurements including cyclic voltammetry and chronoamperometry for electrocatalytic activity.
• Electron paramagnetic resonance (EPR) for identifying oxygen vacancies.

Main Results:

• Successful stabilization of ~6 nm SnO2 QDs by (NH4)6[Mo7O24] via [Mo-O-Sn] covalent linkages, forming Mo@SnO2.
• Mo@SnO2 exhibits remarkable aqueous stability across a pH range of 3-9.
• Dominant oxygen vacancies in the SnO2 core facilitate electronic conduction.
• Mo@SnO2 demonstrates high efficiency (94% FE) for electrocatalytic nitrate reduction to ammonia at -0.2 V vs RHE.
• The catalyst shows good reusability over four cycles with a high ammonia production rate.

Conclusions:

• Polyoxomolybdate ligands are essential for stabilizing SnO2 QDs in aqueous media.
• The Mo@SnO2 material effectively harnesses the electrochemical properties of SnO2 for ammonia synthesis.
• This work presents a viable strategy for developing stable and efficient electrocatalysts for sustainable ammonia production.