Synthesis Of Iron-based Sulfide Nanomaterials For Electrocatalytic Water Splitting

Hydrogen is recognized as a clean energy with the advantages of high calorific value and no generation of greenhouse gases,so it is an ideal alternative energy source for traditional fossil fuels.Electrolysis of water is one of the most promising hydrogen production strategies due to its no environmental pollution.It involves two half reactions:the cathodic hydrogen evolution reaction（HER）and the anodic oxygen evolution reaction（OER）.Due to the slow kinetics of HER and OER,catalysts are required to reduce the overpotential and increase the reaction rate in the actual electrolysis process.To date,Pt-based precious metal materials serve as the high efficient electrocatalysts for HER,and the precious metals Ru O₂ and Ir O₂ also show good catalytic performance toward OER.However,the high cost and low reserves of these precious metal materials limit their wide application.In view of this,it is urgent to develop and design inexpensive and efficient non-precious metal-based electrocatalysts.Iron-based sulfides are one of the more common transition metal sulfides in the crust of earth.Iron-based sulfides have poor catalytic activity toward HER and OER due to the poor electrical conductivity.In this paper,the surface structure of iron-based sulfides is modified by interfacial engineering,thereby tuning their electrocatalytic performance.The specific research contents include the following three aspects:（1）The surface structure and composition of catalysts are important factors for affecting their electrocatalytic activity.The carbon-layer-coated Co S₂-Fe S₂heterojunction nanosheets were obtained via a simple hydrothermal synthesis method.The carbon-layer-coated Co S₂-Fe S₂ heterojunction nanosheets required a voltage of1.47 V to drive the current density of 10 m A/cm~2 toward OER in 1.0 mol/L KOH electrolyte.Meanwhile,the current density of the carbon-layer-coated Co S₂-Fe S₂heterojunction nanosheets at an overpotential of 210 m V was 10 m A/cm~2 toward HER.Moreover,the carbon-layer-coated Co S₂-Fe S₂ heterojunction nanosheets needed a voltage of 1.66 V to drive the current density of 10 m A/cm~2 and maintained long-term stability in the i-t test toward overall water splitting in a two-electrode system.The prominent electrocatalytic activity of the carbon-layer-coated Co S₂-Fe S₂heterojunction nanosheets could be related to the carbon layer and the interface structures between Co S₂ and Fe S₂.（2）Fe₇S₈/FeS₂ heterojunction nanosheets with interface structures and defect sites were prepared via the hydrothermal synthesis method,and then Fe₇S₈/Fe S₂/C electrocatalysts were constructed through the addition of carbon powder.The Fe₇S₈/Fe S₂/C electrocatalysts showed the excellent electrochemical performance.Fe₇S₈/Fe S₂/C electrocatalysts required the overpotential of 262 m V and 198 m V to reach the current density of 10 m A/cm~2 toward OER and HER,respectively.Moreover,Fe₇S₈/Fe S₂/C electrocatalysts attained a voltage of 1.67 V at 10 m A/cm~2 and maintained long-term stability toward overall water splitting in a two-electrode system.The excellent electrocatalytic performance of Fe₇S₈/Fe S₂/C electrocatalysts could be associated with the surface defect sites,carbon powder and the interface structures between Fe₇S₈ and Fe S₂.（3）Fe₇S₈/CoS heterojunction microsheets were prepared via the hydrothermal synthesis method.Fe₇S₈/Co S heterojunction microsheets required the overpotential of241 m V and 216 m V to drive the current density of 10 m A/cm~2 via the addition of carbon powder toward OER and HER,respectively.Moreover,Fe₇S₈/Co S heterojunction microsheets achieved the voltage of 1.68 V at the current density of 10m A/cm~2 and exhibited excellent stability through the addition of carbon powder toward overall water splitting in a two-electrode system.The excellent activity of Fe₇S₈/Co S heterojunction microsheets could be related to the interface structures between Fe₇S₈ and CoS.