Hierarchical Cobalt Phosphide Hollow Nanocages toward Electrocatalytic Ammonia Synthesis under Ambient Pressure and Room Temperature

Electrochemical nitrogen reduction reaction (NRR) under room temperature and ambient pressure is a promising energy- and environmental-friendly method for ammonia synthesis, which currently highly relies on the energy-consuming Haber-Bosch process with enormous CO2 emissions. This study reports the synthesis of a noble-metal-free CoP hollow nanocage (CoP HNC) catalyst from a metal-organic framework precursor through a layered-double-hydroxide intermediate, and the use as the cathode for electrochemical NRR. The 3D hierarchical nanoparticle-nanosheet-nanocage structure provides rich surface active sites for nitrogen adsorption and reduction. When applied for NRR, CoP HNC exhibits exciting performance with high Faraday efficiency at low overpotentials (7.36% at 0 V vs reversible hydrogen electrode [RHE]), and the ammonia yield rate increases exponentially at more negative potential, reaching 10.78 mu g h(-1) at -0.4 V (vs RHE) with good selectivity (no hydrazine produced) under ambient conditions. This noble-metal-free electrocatalyst with promising performance demonstrates the unique potential of transition metal and their compounds in the field of NRR, providing new perspectives to rational catalyst design and mechanism study.