The Preparation And Study Of Ultrathin FeP Nanosheet Electrocatalyst For Electrocatalytic Oxygen Evolution Application

Electrochemical water-splitting is an attractive hydrogen production technology and of great potential in solving energy crisis and environment.Water-splitting devices usually operate at a much larger voltage of 1.8–2.0 V relative to the theoretical limit of1.23 V,and the most challenging step is oxygen evolution involving a four-electron transfer process.Hence,the developing and designing of electrocatalysts with promoted surface reaction kinetics are of great importance in this field.Up to now,the state-of-the-art OER electrocatalysts are the oxides of Ru or Ir,but the scarcity and high cost hinder their widespread deployment.Therefore,the development of low-cost and efficient catalysts as substitutes for precious metals is crucial to promote their wide application in H₂ production through electrochemical water-splitting.Transition metal-based electrocatalysts are the most widely studied oxygen evolution catalysts,and the transition metal phosphide has become a research hotspot because of its unique physical and chemical characteristics such as metalloid and electrical conductivity.It has been found in previous studies that deliberate introducing of the iron into nickel and cobalt based catalysts could remarkably enhance the OER performance.In some more in-depth study,it was demonstrated that Fe offered the most-active sites in these binary electrodes.However,unary Fe-based phosphides have much less been studied for oxygen evolution,and the activity is also far from satisfactory.Among them,one of the biggest obstacles to the poor activity of Fe-based catalysts is the weak adsorption of reaction intermediates.The emerging two-dimensional(2D)nanostructured materials are a kind of attractive materials.In addition to the maximum surface area,the ultrathin nature and confinement effect of 2D materials are prone to the formation of more defects and low coordinated surface atoms with numerous dangling bonds,which are promising in exploring efficient electrocatalysts.Herein,self-supported ultrathin FeP nanosheets were synthesized by a two-step method.Firstly,ultrathin Fe OOH nanosheets were synthesized on nickel foam,and then FeP nanosheets were obtained by phosphating treatment.The AFM characterization indicated that the thickness of the Fe OOH nanosheet is about 3.2 nm.SEM and TEM images showed that the treated FeP nanosheets still maintained 2D morphology without obvious aggregation.As a comparison,the bulk FeP was synthesized on nickel foam by a similar method.Electrochemical tests showed the overpotential of FeP-NS/NF are220 and 270 m V at the current density of 10 and 100 m A cm^-2,respectively.It's worth noting that the superior performance of FeP-NS/NF exceeds that of most unary Fe-based catalysts.The Tafel slope is 51 m V dec^-1,which is obviously smaller than its bulk counterpart.It can maintain more than 85 h at the current density of 10 m A cm^-2 with only 8%decrease.The XPS and ESR results showed that abundant Fe defect sites were formed on the surface of ultrathin nanosheets during phosphating treatment.The methanol competitive oxidation experiment shows that the ultrathin nanosheet can facilitate oxygenated intermediates adsorption.Our study here not only provides an efficient and low-cost Fe-based electrocatalyst for oxygen evoluation but also makes a beneficial attempt at exploring two-dimensional materials for electrochemical field.