Modulation of surface properties on cobalt phosphide for high-performance ambient ammonia electrosynthesis

Tuning surface properties of electrocatalysts for sustainable electrocatalytic nitrogen reduction reaction (NRR) with high selectivity and activity is highly demanded but still lacks fundamental understanding and modulation methods. Herein, we report the transformation of hydrogen evolution reaction (HER)-favorable cobalt phosphide (CoP) to NRR-favorable electrocatalyst via modulation of surface properties. The oxidized CoP particles encapsulated in carbon nanotubes (O-CoP/CNT) exhibits a high NH3 yield of 39.58 µg h−1 mg-1 cat as well as high Faradaic efficiency (FE) of 19.4% at −0.5 V vs. reversible hydrogen electrode (RHE), which is confirmed by 15N2 isotope-labeling tests. In-situ Raman spectra identify that N2 molecules are preferentially captured by Co ions, while the surface-adsorbed H+ are gradually eliminated. The hydrophobic surface of CNT can limit the contact of protons with the catalyst surface to inhibit HER, and the formation of hydrogen bond facilitates a more efficient NRR process. The surface modulation effects are confirmed by density functional theory calculations.