Component regulation in flower-like FexCoNiP/C nanohybrids as bifunctional efficient electrocatalysts for overall water splitting

Abstract

Incorporating bi-metal transition metal phosphides (TMPs) with high-valent metal is a powerful method to obtain highly efficient and low-cost bifunctional electrocatalysts in alkaline media for overall water splitting. However, the composition-activity relationship of such incorporation has not been investigated yet due to the challenge in constructing tri-metal TMPs with continuously variable composition while maintaining a homogenous elemental distribution. In this study, we proposed a strategy using a trimetal oleta composite with a homogenous elemental distribution at the molecular scale as an ideal precursor. This precursor was then used to fabricate Fe-incorporated Ni-Co phosphide on a flower-like carbon substrate, resulting in a continuously changeable Fe content (Fe_xNiCoP/C). Benefiting from the fully exposed structure and the incorporation of Fe, the flower-like Fe_xNiCoP/C hybrids exhibited excellent electrocatalytic performance for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). By optimizing the Fe content, the flower-like Fe_0.4NiCoP/C hybrid achieved 10 mA/cm² at a low overpotential of 243 mV for the OER and 107 mV for the HER, respectively. When the optimal Fe_0.4NiCoP/C electrodes were employed as the anode and cathode for water electrolysis in an alkaline electrolyte, the electrolyzer achieved 10 mA/cm² at a low cell voltage of 1.59 V. This work provides an inexpensive, highly active, and durable electrocatalyst, while revealing the composition-activity relationship of Fe_xNiCoP/C for overall water splitting in alkaline media.