Piezoelectricity regulated ohmic contact in M/BaTiO₃ (M = Ru, Pd, Pt) for charge collision and hydrogen free radical production in ammonia electrosynthesis

Electrochemical nitrate reduction reaction (NO₃RR) is a promising alternative technique for NH₃ generation toward the energy-consuming Haber-Bosch process. Nevertheless, it remains hindered by the competitive hydrogen evolution reaction (HER). Herein, the piezoelectric effect of electron-rich BaTiO₃ with oxygen vacancies is introduced to promote NO₃RR performance. Combining with metal particles (Ru, Pd and Pt), the catalyst achieves a maximal Faradaic efficiency of 95.3% and NH3 yield rate of 6.87 mg h⁻¹ mg_cat.⁻¹. Upon piezoelectricity, the interface between metal nanoparticles and BaTiO₃ is effectively modulated from Schottky contact to ohmic contact, which leads to unobstructed electron transfer. Abundant hydrogen radicals (·H) can be then produced from the collision between plentiful electrons and polar water molecules adsorbed on the polar surface. Such ·H can significantly facilitate the hydrogenation of reaction intermediates in NO₃RR. Meanwhile, this process suppresses the Volmer-Heyrovsky step, therefore inhibiting the HER within a wide range of external potential. This work suggests a new strategy for promoting the performance of multi-electron-involved catalytic reactions.