Nitrogen-Doped Carbon-Encased Bimetallic Selenide for High-Performance Water Electrolysis

Demand of highly efficient earth-abundant transition metal-based electrocatalysts to replace noble metal materials for boosting oxygen evolution reaction (OER) is rapidly growing. Herein, an electrochemically exfoliated graphite (EG) foil supported bimetallic selenide encased in N-doped carbon (EG/(Co, Ni)Se₂-NC) hybrid is developed and synthesized by a vapor-phase hydrothermal strategy and subsequent selenization process. The as-prepared EG/(Co, Ni)Se₂-NC hybrid exhibits a core-shell structure where the particle diameter of (Co, Ni)Se₂ core is about 70 nm and the thickness of N-doped carbon shell is approximately 5 nm. Benefitting from the synergistic effects between the combination of highly active Co species and improved electron transfer from Ni species, and N-doped carbon, the EG/(Co, Ni)Se₂-NC hybrid shows remarkable electrocatalytic activity toward OER with a comparatively low overpotential of 258 mV at an current density of 10 mA cm^-2 and a small Tafel slope of 73.3 mV dec^-1. The excellent OER catalysis performance of EG/(Co, Ni)Se₂-NC hybrid is much better than that of commercial Ir/C (343 mV at 10 mA cm^-2 and 98.1 mV dec^-1), and even almost the best among all previously reported binary CoNi selenide-based OER electrocatalysts. Furthermore, in situ electrochemical Raman spectroscopy combined with ex situ X-ray photoelectron spectroscopy analysis indicates that the superb OER catalysis activity can be attributed to the highly active Co-OOH species and modified electron transfer process from Ni element.