Tuning the Interface of Co 1- x S/Co(OH)F by Atomic Replacement Strategy toward High-Performance Electrocatalytic Oxygen Evolution.

The construction of heterostructures is one of the most promising strategies for engineering interfaces of catalysts to perform high-efficiency oxygen evolution reaction (OER). However, accurately tuning heterostructures' interface during operation remains a challenge. Herein, we fabricated the needled-like heterostructure Co 1- x S/Co(OH)F supported on flexible carbon fiber cloth via an atomic substitution strategy, in which sulfur atoms are simultaneously grafted into F vacancies after the partial removal of F atoms from Co(OH)F during the electrodeposition, thus achieving the growth of cobalt sulfide on the interface of Co(OH)F. This electrocatalyst with such design exhibits the following advantages: (1) The lattice distortion caused by atomic substitution leads to the increase of active sites; (2) Co 1- x S constructed on the surface of Co(OH)F by the atomic replacement strategy optimizes the adsorption (OH - ) and desorption (O 2 ) energy in the OER process; (3) the needle-like structure possesses the tip-enhanced local electric field effect. As a result, the Co 1- x S/Co(OH)F/CC catalyst exhibits very high OER catalytic performance with an overpotential of 269 mV at a current density of 10 mA cm -2 and a Tafel slope of 71 mV dec -1 . The asymmetric electrode shows superior catalytic activity and stability in overall water splitting. The catalytic mechanism of these highly efficient Co 1- x S/Co(OH)F/CC catalysts was investigated via DFT theoretical calculations and ex situ characterizations. This atomic substitution strategy displays universality for other transition metal sulfides (metal = Ni, Mn, Cu).