Boosting charge-transfer in tuned Au nanoparticles on defect-rich TiO2 nanosheets for enhancing nitrogen electroreduction to ammonia production.

The electrocatalytic nitrogen reduction reaction (eNRR) to ammonia (NH3) has been recognized as an effective, carbon-neutral, and great-potential strategy for ammonia production. However, the conversion efficiency and selectivity of eNRR still face significant challenges due to the slow transfer kinetics and lack of effective N2 adsorption and activation sites in this process. Herein, we designed and fabricated defect-rich TiO2 nanosheets furnished with oxygen vacancies (OVs) and Au nanoparticles (Au/TiO2-x) as the electrocatalyst for efficient N2-fixing. The experimental results demonstrate that OVs act as active sites, which enable efficient chemisorption and activation of N2 molecules. The Au nanoparticles loaded on the OVs-rich TiO2 nanosheets not only accelerate charge transfer but also change the local electronic structure, thus enhancing N2 adsorption and activation. In this work, the optimal Au/TiO2-x electrocatalyst displays a considerable NH3 yield activity of 12.5 μg h-1 mgcat.-1 and a faradaic efficiency (FE) of 10.2 % at -0.40 V vs reversible hydrogen electrode (RHE). More importantly, the Au/TiO2-x exhibits a stable N2-fixing activity in cycling and it persists even after 80 h of consecutive electrolysis. Density functional theory (DFT) calculations reveal that the OVs serve as the active sites in TiO2, while Au nanoparticles are crucial for improving N2 chemisorption and lowering the reaction energy barrier by facilitating the charge transfer for eNRR with a distal hydrogenation pathway. This research offers a rational catalytic site design for modulating charge transfer of active sites on metal-supported defective catalysts to boost N2 electroreduction to NH3.