| As environmental pollution and energy depletion continue to increase,green,clean and sustainable energy has become an important topic of concern.While solar,wind and tidal energy are intermittent,hydrogen does not have this disadvantage and is considered one of the most promising clean energy sources due to its high combustion calorific value and the many forms of utilization.Hydrogen production by electrolysis of water,using water as the only raw material,is seen as the greenest and most sustainable method of hydrogen production.However,its anode oxygen evolution reaction(OER)has a slow kinetics due to the involvement of four electrons,which hinders the overall efficiency.Therefore,there is a very urgent need to explore a highly active electrocatalyst to improve the OER efficiency.Currently,noble metal-based catalysts(e.g.IrO2,RuO2,etc.)are considered as the most advanced electrocatalysts,while their scarcity and high cost limit their large-scale applications.Therefore,we need to explore highly active,earth-enriched and low-cost transition metalbased electrocatalysts for enhancing OER reaction rates.NiFe layered double hydroxides(LDH)is one of the most promising OER catalysts under alkaline conditions due to its excellent intrinsic catalytic activity.In this paper,we designed novel catalysts by doping and nitriding methods,deeply investigated the electron transfer and interaction mechanisms between elements,and explored the mechanism of oxygen evolution reaction and Faraday efficiency.The main studies are as follows:1.Preparation of NiFeHf LDH materials and study of the performance of oxygen evolution reactionA simple one-step hydrothermal method was used to dope Hf elements into NiFe LDH catalyst for the first time,and NiFeHf LDH was successfully prepared.The morphology,elemental valence and electron transfer of the NiFeHf LDH catalysts were investigated by physical characterization using XRD,TEM,SEM,XPS,ICP-OES and FT-IR.Among them,XPS confirms that the doping of Hf improves the chemical environment of Ni and Fe and accelerates the electron transfer efficiency through the synergistic effect between the three elements.The oxygen evolution reaction of the NiFeHf LDH@NF catalyst was studied in 1.0 M KOH using a series of electrochemical characterization tools,and its overpotential at 10 mA cm-2 was only 176 mV,which was lower than that of other non-precious metal catalysts.We also investigated its oxygen evolution reaction mechanism and Faraday efficiency.In addition,the effect law of Hf doping on the oxygen evolution reaction efficiency of NiFe LDH was investigated by DFT+U theoretical calculations,and the reason for the excellent OER catalytic performance of NiFeHf LDH was explained.2.Preparation and oxygen evolution reaction properties of Fe,Hf codoped Ni3N.A highly efficient OER catalyst Fe,Hf-Ni3N has been prepared for the first time using the chemical vapor deposition method.Its physical morphology and elemental valence were standardized and analyzed using XRD,TEM,XPS and other characterization methods.After electrochemical data analysis,it exhibited excellent OER activity with an overpotential of only 198 mV at a current density of 10 mA cm-2,a Tafel slope of 89 mV dec-1 and a Cdl of 26 mF cm-2.This may be due to the fact that the doping of Fe and Hf enhanced the electron interaction between the three elements and accelerated the electron transfer efficiency,thus enhancing the OER activity.We also investigated the kinetics of the oxygen evolution reaction of Fe,Hf-Ni3N using a rotating ring-disk electrode.In addition,Fe,Hf-Ni3N also exhibited outstanding stability after a 105 h long-stability test and is expected to be a promising commercial candidate. |
