Strategic Atomic Layer Deposition and Electrospinning of Cobalt Sulfide/Nitride Composite as Efficient Bifunctional Electrocatalysts for Overall Water Splitting

Reported herein is comprehensive study of a highly active and stable cobalt catalyst for overall water splitting. This composite SFCNF/Co_{1- x} S@CoN, consisting of S-doped flexible carbon nanofiber (SFCNF) matrix, Co_{1- x} S nanoparticles, and CoN coatings, is prepared by integration of electrospinning and atomic layer deposition (ALD) technique. Representative results include the following: 1) ultrathin CoN layer is deposited by ALD on the surface of flexible substrate without any sacrifice of SFCNF and Co_{1- x} S; 2) the composite exhibits strong electrocatalytic activity in both acidic and basic solutions. The overpotentials of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are 20 and 180 mV, respectively, at a current density of 10 mA cm^-2 in basic medium. A small Tafel slope of 54.4 mV dec^-1 is observed in 0.5 m H₂ SO₄ electrolyte; 3) tested as overall water splitting electrode, the composite records a current density of 10 mA cm^-2 at a relative low cell voltage of 1.58 V and long-term stability for 20 h at a current density of up to 50 mA cm^-2 . The superior performance for overall water splitting is probably attributed to the synergistic effect of Co_{1- x} S and ALD CoN. Specifically, implementation of ALD can be extended to innovate nanostructured materials for overall water splitting and even other renewable energy aspects.