The Synthesis Of Transition Metal Phosphides And The Regulation Of Phosphorus Vacancies For Electrocatalytic Water Splitting

Due to population and economic growth,the demand for fossil fuel energy has gradually increased.However,by the middle of this century,the cumulative emission of CO₂ in the atmosphere requires that the level of CO₂ in the atmosphere be kept twice their pre anthropogenic values,which requires the development and deployment of carbon-free energy clean production schemes.Hydrogen is clean energy with high heating value,non-toxic and pollution-free,and hydrogen could be effectively stored by electrochemical water splitting.This energy conversion technology has attracted widespread attention.However,current energy conversion technologies rely on noble metals or noble metal-containing electrocatalysts to drive their related redox reactions.Due to the high cost and scarcity of precious metals,their widespread use has been limited,so it is necessary to design and develop inexpensive and efficient non-noble metal electrocatalysts.Transition metal phosphide is the emerging electrocatalysts due to its excellent catalytic activity,high selectivity,low cost,and versatility.In this paper,cobalt-iron bimetallic phosphide was synthesized by phosphating method,and the cobalt-iron bimetallic phosphide was treated with Ar plasma technology to construct phosphorus vacancies,providing a new method for the development of highly active metal phosphide electrocatalysts.The main research contents are as follows:1.Cobalt-iron bimetallic phosphide was synthesized by simple phosphating method.First,cobalt-iron layered double hydroxide was synthesized by hydrothermal method as the precursor,and then the precursor was phosphated by regulating the amount of NaH₂PO₂ and the annealing temperature respectively.All samples were characterized by morphology and structure,as well as electrochemical OER and HER.The sample with a mass of 1.5 g of NaH₂PO₂ and an annealing temperature of 300°C has both optimal OER and HER performance.In the OER test,the sample has an overpotential of 303 mV at a current density of 10 mA cm^-2 and a Tafel slope value 59.5 mV dec^-1.In the HER test,the overpotential at a current density of 10 mA cm^-2 of the sample is116 mV,and the Tafel slope value is 63.2 mV dec^-1,which is an excellent bifunctional electrochemical water splitting catalyst.2.Phosphorus vacancy was constructed in Co_0.68Fe_0.32P by Ar plasma technology,and the number of phosphorous vacancy could be controlled by adjusting the treatment time.The generation of phosphorus vacancy leads to a unique surface state of Co_0.68Fe_0.32P.The increase of surface oxygen makes up for the deficiency of surface anions caused by phosphorus vacancy,resulting in abnormal electron loss of surface Co/Fe ions.All samples were tested by OER,Co_0.68Fe_0.32P treated with Ar plasma has the best OER performance.The high activity of Ar-plasma treated Co_0.68Fe_0.32P could originate from the electron loss of Co and Fe on the surface,which may reduce the overpotential of the intermediate conversion from OH^-to O₂.Besides,as the actual active site of the metal phosphides is an oxyhydroxide species,the addition of surface oxygen may also be beneficial to the OER reaction.