Vacancy-Rich SnO 2 Quantum Dot Stabilized by Polyoxomolybdate as Electrocatalyst for Selective NH 3 Production

The pronounced conductivity of tin dioxide (SnO ) nanoparticles makes it an ideal multifunctional electrode material, while the challenge is to stabilize the quantum dot (QD) SnO nanocore in water. An Anderson-type polyoxomolybdate, (NH ) [Mo O ], is employed as an inorganic ligand to stabilize a ca. 6 nm SnO QD (Mo @SnO ). X-ray scattering and diffraction studies confirm the tetragonal SnO nanocore in Mo @SnO . Elemental analyses are in good agreement with the mass spectrometric detection of the [Mo O ] cluster present in Mo @SnO . The ionic POMs attached to the SnO surface through [Mo-O-Sn] covalent linkages have been established by surface zeta potential, shift of the [Mo = O] Raman vibration, and extended X-ray absorption fine structure (EXAFS) analyses. The presence of the [Mo O ] cluster in the Mo @SnO is responsible for the remarkable aqueous stability of Mo @SnO in the pH range of 3-9. Dominant oxygen vacancy in the SnO core, identified by EXAFS data and the anisotropic electron paramagnetic resonance (EPR) signals ( ∼ 2.4 and 1.9), results in facile electronic conduction in Mo @SnO while being deposited on the electrode surface. Mo @SnO acts as an active catalyst for the electrocatalytic nitrate reduction (eNOR) to ammonia with 94% faradaic efficiency (FE) at -0.2 V vs RHE and a yield rate of 28.9 mg h cm . The stability of Mo @SnO in acidic pH provides scope to reuse the Mo @SnO electrode at least four times with notable NH selectivity and a superior production rate (239.06 mmol g h ). This study demonstrates the essential role of POM in stabilizing SnO QD, harnessing its electrochemical activity toward electrocatalytic ammonia production.