The Birth of Nickel Phosphide Catalysts: Monitoring Phosphorus Insertion into Nickel

Tri-n-octylphosphine (TOP) is used widely as a phosphorating agent to yield metal phosphide nanocatalysts, which are receiving intense attention because of their high performance in both electrochemical and hydrotreatment catalytic processes, such as the hydrogen evolution reaction and the hydrodesulfurization reaction. We used in situ ambient-pressure X-ray photoelectron spectroscopy to investigate the formation of nickel phosphide on the surface of a nickel foil at temperatures close to those employed to form nickel phosphide nanoparticles in the colloidal route. We showed that the onset of phosphorus insertion into nickel occurs at as low as 150 degrees C, which is much lower than that reported previously (> 210 degrees C). Moreover, the formation of sp(2) carbon was observed on the surface as the consequence of TOP alkyl chain decomposition. These findings provide new insights into the surface chemistry of metal phosphide nanoparticles, which are increasingly employed in several fields of catalysis. Our results demonstrate that even below 150 degrees C, significant phosphorus and carbon incorporation can occur during metal nanoparticle syntheses if TOP is employed as the stabilizing agent.