Interface To Enhance The Performance Of Noble Metal Catalysts Of Water Electrolysis

The fossil fuels cause serious environmental pollution and global warming,so it is increasingly urgent to develop a clean,efficient and renewable new energy sources to replace fossil fuels.Hydrogen energy has attracted extensive attention because of its high energy density and high combustion value.Among various hydrogen production technologies,electrolysis of water for hydrogen production is regarded as the most attractive hydrogen production method because of its simple process and no environmental pollution caused by the product of oxygen and hydrogen.Hydrogen production from electrolyzed water mainly includes two half reactions of cathodic reduction hydrogen evolution reaction?HER?and anodic oxygen evolution reaction?OER?.Among the HER catalysts,Pd is regarded as the most likely to replace the Pt-based catalyst because of its good catalytic ability and relatively abundant reserves.Ir has good catalytic activity and stability for the OER.Precious metal material has good catalytic activity in electrolytic water,but its large scale application is limited by its scarce reserves and high price.In order to reduce the amount of precious metal used,it can be carried out by designing a unique nanostructure of a precious metal,alloying with other metals,and compounding with non-precious metal compound.So Pd-based HER and Ir-based OER catalysts are currently the most studied catalyst materials.The nanosizing of precious metal and alloys with other metals can enhance the catalytic performance and durability of precious metals,but the proportion of precious metals is still high.Many non-precious metal compound materials are inexpensive and have a large surface area,which facilitates the dispersion of noble metal particles.The non-precious metal compound can also avoid the agglomeration of noble metals in the catalytic process.Therefore,the combination of noble metal and s non-precious metal compound is very advantageous in the precious metal-based composite catalyst.Although precious metal and non-precious metal compound composite catalysts have been reported and exhibit good electrolyzed water properties,for the composite catalyst of this type,the influence of the contact interface between noble metal and non-precious metal compound on the catalytic performance has not been explored..In response to the above problems,we constructed a NiCo₂S₄/precious metal interface and studied the enhancement of the catalytic performance of the noble metal by the interface between the two.The reasons for the enhancement of the catalytic performance of precious metals Pd and Ir at the interface were analyzed in detail.Specifically,the following three aspects of research have been carried out:1)NiCo₂compound nanowire arrays on carbon cloth?NiCo₂ NW/CC?was synthesized from nickel nitrate,cobalt nitrate and urea by hydrothermal reaction.And then NiCo₂S₄ nanotube arrays?NiCo₂S₄NT/CC?were prepared.The formation of NiCo₂S₄ nanotubes?NiCo₂S₄ NT/CC?arrays through a secondary hydrothermal reaction with sodium sulfide in aqueous solution was confirmed by SEM and XRD.Compared with NiCo₂ NW/CC,NiCo₂S₄ NT/CC has a rough surface with a larger specific surface area,providing more sites for subsequent loading of precious metals Pd or Ir.And it also provides a favorable channel for the rapid precipitation of gas molecules generated in the precious metal catalysis.2)Based on the synthesis of NiCo₂S₄ NT/CC,a composite Pd-NiCo₂S₄ NT/CC was prepared by hydrothermal reduction by showed SEM,TEM,XRD.The composite exhibited better catalytic HER ability in 1 M KOH electrolyte solution by LSV test.At 10 mA/cm² current density,the overpotential of Pd-NiCo₂S₄ NT/CC is much smaller than which of Pd?390 mV?.The test of XPS confirmed the improvement of composite performance attributed to the maximum transfer of Pd electrons to NiCo₂S₄NT/CC.The material conductivity is increased by two orders of magnitude,and the rate-limiting step of Pd in the catalysis moves from the Volmer reaction to the more favorable Heyrovsky reaction?electrochemical desorption rate?,which accelerates the rapid desorption of active hydrogen atoms and the formation of hydrogen molecules.3)Using the same preparation method and characterization method,a composite Ir-NiCo₂S₄ NT/CC was also prepared by hydrothermal reduction.This composite has highly efficient OER electrocatalytic ability in 1 M KOH electrolyte solution.The overpotential of Ir-NiCo₂S₄ NT/CC has reduced 23 mV compared with Ir?1.574 V?at 50 mA/cm² current density.The electron of Ir transfer to NiCo₂S₄ NT/CC can highly promote autocatalysis activity.While improving the catalytic activity and during the OER test,the composite material is oxidized to enrich the active species,so that the electrochemically active surface area is significantly increased,and the OER performance is further improved.