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 mu g 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 N-15(2) isotope-labeling tests. In-situ Raman spectra identify that N-2 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.

Automated summary

This study presents a method to transform cobalt phosphide, which favors the hydrogen evolution reaction, into an electrocatalyst favorable for the nitrogen reduction reaction by modulating surface properties. The oxidized CoP particles encapsulated in carbon nanotubes exhibit high NH3 yield and Faradaic efficiency, while inhibiting the hydrogen evolution reaction and facilitating the nitrogen reduction reaction. In-situ Raman spectra and density functional theory calculations confirm the surface modulation effects.