Incorporating Pd into Cu-Coordinated Metal-Organic Frameworks to Promote N2 Electrochemical Reduction into Ammonia

Abstract

Fixation nitrogen using renewable energy has attracted much attention recently. However, the performance is limited by the competing hydrogen evolution reaction (HER) and the difficulty in activating N2. Here, an attractive strategy was proposed to enhance the electrochemical nitrogen reduction reaction (NRR) activity by introducing Pd into the HKUST-1 framework. After thermal treatment, the obtained Pd/HKUST-1 (250 °C) catalyst exhibited an ammonia production rate of 42.0 mg/gcat ⋅ h at −0.4 V vs. RHE with Faradaic efficiency of 4.6 %. The ammonia production reached as high as 415 mg/gcat in a 10-hours stability test. With the assistance of density functional theory (DFT) calculations, the incorporated Pd was revealed to have the unique property to react with adsorbed H (Had) atom from HER and form α-PdH species. Compared with other metals such as Ag, Au, and Pt, the in situ formed α-PdH species could reduce the energy barrier of the rate-limiting *N2H step, resulting in an enhanced NRR activity.