Ru-doped cobalt-iron bimetallic phosphide nanoflowers: Electronic structure modulation for high-efficiency hydrogen evolution reaction

Transition metal phosphides are promising catalysts for the alkaline hydrogen evolution reaction (HER), yet further enhancing their performance remains a significant challenge due to the limited tunability of their electronic structures. In this study, we prepare Ru-doped transition metal phosphides with a three-dimensional "nanoflower" structure to further improve alkaline HER performance. This structure not only accelerates mass transfer and product release but also increases the number of active sites for the HER. More importantly, density functional theory calculation reveal that doping an appropriate amount of Ru can, on one hand, adjust the internal electronic structure of the catalyst, promote the adsorption and activation of water molecules, reduce the energy barrier for the dissociation of water into hydrogen adsorption intermediates H* and OH^-, and accelerate the alkaline Volmer step. On the other hand, the highly electronegative Ru can attract electrons around the metal Co and Fe, adjust the electron density of the active sites, optimize the hydrogen adsorption energy at the active sites, and speed up the HER catalytic reaction kinetics. As expected, the optimal Ru-doped cobalt iron bimetallic phosphide (Ru_0.2CoFeP/NF) exhibited excellent HER catalytic activity in 1 M KOH solution, requiring only 27 and 78 mV overpotentials to reach current densities of 10 and 100 mA cm^-2, respectively, with a Tafel slope of just 30.8 mV dec^-1. This study provides a perspective for the preparation of highly efficient noble metal doped alkaline hydrogen evolution catalysts.