Dynamic Evolution of Hydroxylated Layer in Ruthenium Phosphide Electrocatalysts for Alkaline Hydrogen Evolution Reaction
Alkaline water electrolysis represents one of the most promising technology in constructing environment-friendly energy cycles. Ruthenium phosphides are attractive candidates that have recently shown high electrocatalytic activity for hydrogen evolution reaction (HER) in alkaline condition and even higher performance than in acid, while the origin has not been addressed well up to date. Here, we demonstrate that outermost hydroxylated Ru layers reconstructed by HER in basic electrolyte are key active sites for alkaline HER, based on in-depth X-ray photoelectron spectroscopic study. The Ru phosphides with higher Ru/P ratio in bulk composition possess higher ratio of hydroxylated Ru at the surface region of several nanometers with less P sites exposed, which determines HER in alkaline condition. The Ru phosphide nanofiber electrocatalysts presented here enable almost zero overpotentials for alkaline HER with stable performance for 320 h. This work provides deeper understanding on the origin of high HER activity in alkaline condition.