Temperature‐Driven Nickel Phosphide Phase Transformation and Its Impact on Furfural Hydrogenation Catalysis

This study investigates the hydrothermal synthesis of nickel phosphides (Ni x P y ) and the factors governing phase transformation between Ni 2 P and Ni 12 P 5 . We demonstrate that Ni 2 P forms as the dominant phase at 180 °C with a high phosphorus precursor ratio; however, this phase transforms into Ni 12 P 5 at 210 °C due to the hydrothermal instability of Ni 2 P at elevated temperatures. Density functional theory (DFT) calculations corroborate this observation, revealing that the higher thermodynamic stability of Ni 12 P 5 is driven by its larger entropy of formation, which renders the Gibbs free energy of Ni 12 P 5 more favorable at elevated temperatures. Catalytic performance was evaluated for both furfural hydrogenation and the hydrogen evolution reaction (HER). Ni 2 P and Ni 12 P 5 exhibited a similar selectivity‐conversion profile in furfural hydrogenation, where furfuryl alcohol (FA) selectivity decreases at higher conversions as over‐hydrogenation to tetrahydrofurfuryl alcohol (THFA) becomes dominant. Electrochemical surface area (ECSA) measurements revealed a higher electrochemically active surface area for Ni 12 P 5 , which accounts for differences in current density between the two phases. Both phases exhibited comparable Tafel slopes for the HER, indicating a similar reaction mechanism. These findings elucidate the thermal phase behavior of nickel phosphides and highlight their structure‐sensitive catalytic properties for both thermocatalytic upgrading and electrocatalytic hydrogen production.