Double Metal Diphosphide Pair Nanocages Coupled with P-Doped Carbon for Accelerated Oxygen and Hydrogen Evolution Kinetics.

Developing efficient and durable bifunctional transition metal phosphide (TMP) electrocatalysts is still a great challenge because of its relatively sluggish kinetics of oxygen evolution reaction (OER). Herein, we report a unique bimetallic diphosphide pair (FeP2-NiP2) forming spherical nanocages encapsulated in P-doped carbon layers (FeP2-NiP2@PC) as advanced bifunctional electrocatalyst synthesized by a very facile phosphorization approach. The obtained FeP2-NiP2@PC electrocatalyst exhibits an outstanding OER activity with an ultralow overpotential of 248 mV in 1 M KOH and a low overpotential of 117 mV for HER in 0.5 M H2SO4 (@10 mA·cm-2). Also it gives an exceptional long-term durability toward OER (60 h) and HER (20 h). Differently from the electrocatalysts as reported, after successive 3000 cycles CV acceleration, its overpotential decreases about 10 mV. Further investigation unveils that the electrochemical activation process boosts in situ phase transformation of oxides and phosphides to oxyhydroxides as the vital intermediates in FeP2-NiP2@PC during OER electrocatalysis. The direct observation of vital intermediates has been rarely reported on Fe/Ni-based phosphide electrocatalysts. Our exploration demonstrates an extraordinarily efficient and stable nonprecious TMP bifunctional electrocatalyst and provides a novel prospect to shed light on the intrinsic OER electrocatalytic behavior of Fe/Ni-based phosphide electrocatalysts.