Core Effect on the Performance of N/P Codoped Carbon Encapsulating Noble-Metal Phosphide Nanostructures for Hydrogen Evolution Reaction

The concept of core-shell nanostructured catalysts with a highly active yet insufficient stability in direct contact with electrolyte solution core and a chemically stable carbon shell has been proposed and turned out to be a new category of electrocatalysts for various electrochemical reactions. Such catalysts can take the mutual benefits of the core, i.e., high activity, and the shell, i.e., high stability. However, the understanding about how the core affects the electrocatalytic performance of the shell is still not clear. In this study, we performed a systematic study of hydrogen evolution reaction (HER) catalytic activities of different noble-metal phosphide-based core-shell nanostructured hybrids (noble-metal phosphides nanoparticles wrapped by ultrathin N, P codoped graphitic carbon (NPGC) shells, MP_x@NPGC, MP_x = RhP₂, RuP₂, PtP₂, IrP₂, and Pd₅P₂) in both acidic and alkaline aqueous solutions for the first time. Among them, RhP₂@NPGC core-shell nanostructure exhibited the highest HER activity in 0.5 M H₂SO₄, while the RuP₂@NPGC composite was the best one in 1 M KOH. Taking microstructure into account, it is obvious that the catalytic behavior of the MP_x@NPGC category was largely attributed to the different noble-metal phosphide cores. The ECSA normalized activity further revealed the RhP₂@NPGC and RuP₂@NPGC hybrids are the most active HER catalysts in acidic and alkaline electrolytes, respectively, along with fastest charge transfer and surface reaction rates during the HER process. This study provides useful guidelines in the further development of high-performance core-shell structured electrocatalysts for HER and other electrochemical reactions such as oxygen evolution reaction and oxygen reduction reaction.