Oxygen vacancy engineering in spinel-structured nanosheet wrapped hollow polyhedra for electrochemical nitrogen fixation under ambient conditions

Abstract

Electrochemical nitrogen-to-ammonia conversion by the nitrogen reduction reaction (NRR) under ambient conditions is regarded as a potential approach to tackle the energy-intensive Haber–Bosch process with excessive CO₂ emission. However, the NRR is still restricted by low faradaic efficiency and NH₃ yield, which is due to the chemical inertness of N-related groups for efficient adsorption/activation on the electrocatalysts. Here, a series of spinel-structured nanosheet wrapped hollow nitrogen-doped carbon polyhedra with abundant oxygen vacancies are constructed successfully. From theoretical aspects, these materials show increased charge density on their surface for enhanced capture and activation of N₂ molecules. As a result, oxygen vacancy-rich NiCo₂O₄ on hollow N-carbon polyhedra (V_o-rich NiCo₂O₄@HNCP) shows outstanding electrocatalytic NRR performance with high production yield (NH₃: 4.1 μg h⁻¹ cm⁻²/17.8 μg h⁻¹ mg⁻¹; faradaic efficiency: 5.3%) and high stability under ambient conditions and is superior to the counterpart oxygen vacancy-poor electrocatalysts. Oxygen vacancy engineering introduces a new concept for rational design of advanced NRR catalysts for energy conversion systems.