Preparation And Performance Of Mesoporous Iron Phosphide Electrocatalysts For Hydrogen Evolution Reaction

With the rapidly depletion of fossil fuel,exploring efficient and sustainable clean energy has become the focus of current research.Hydrogen is an ideal clean energy with the advantages of high energy density,non-pollution and renewability.Among the various hydrogen production strategies,water electrolysis is a clean,efficient and sustainable way to produce hydrogen,and meets the requirements of energy regeneration and environmental conservation demands.During the process of water splitting,usage of efficient catalysts can decrease the overpotential required for the decomposition of water molecules,thereby reducing the consumption of energy.Nowadays,Pt-based materials are considered to be the most active catalysts towards hydrogen evolution reaction?HER?by virtue of its high catalytic activity and low overpotential.However,their large-scale application is limited by low abundance and high cost.Therefore,explorating cheap,efficient and stable catalyst is of great significance for the large-scale application of water electrolysis technique.Among various catalysts,transition metal phosphides with the advantages of high conductivity,high catalytic activity and low cost have become typical non-precious metal-based catalysts.The introduction of porous structure into transition metal phosphides enables the exposure of active sites and rapid mass transport during water splitting.Among various porous structures,mesoporous structure exhibits the advantages of large specific surface area and high porosity.Owing to the low-cost and abundant reserves of iron,we focused on the preparation and electrocatalytic performance of iron phosphide.In this work,we successfully fabricated two kinds of mesoporous iron phosphide self-supporting electrodes with different mesoporous structures and evaculated their HER performance.First,we successfully constructed a mesoporous iron phosphide self-supporting electrode on a carbon cloth substrate?meso-FeP/CC?by sol-gel method and a low-temperature phosphation reaction.The as-obtained meso-FeP/CC exhibits uniform mesoporous structure.The average pore size is about 5.5 nm,and the specific surface area is as high as 74.1 m^-22 g^-1.The high specific surface area of the mesoporous structure facilitates the exposure of active sites,and the electrochemically active surface area is as high as 183 mF cm^-1,thereby improving its electrocatalytic hydrogen evolution performance.In addition,the conductive carbon cloth structure facilitates electron transport during the electrocatalytic reaction.As a result,meso-FeP/CC shows excellent hydrogen evolution catalytic performance in acidic conditions:when the current density reaches 10 mA cm^-22 and 50 mA cm^-2,the required overpotential is only 88 mV and 159 mV,and the Tafel slope is as small as51 mV dec^-1.In order to further optimize the mesoporous structure of iron phosphide and improve its cytalytic activity and long-term stability,we fabricated ordered meso-FeP/CC through evaporation-induced self-assembly method and low-temperature phosphation reaction.The thickness of the as-prepared mesoporous FeP film is only 50 nm,leading to a strong interaction between FeP and carbon cloth fiber,which is effectively prevented the microstructure from collapsing.Compared with nanoparticle-stacked mesopores,the ordered mesoporous structure formed by the self-assembly method exposed more active sites.The number of active sites reaches2.32×10¹77 sites mg^-1,which is beneficial for the catalytic reaction and the mass transport.As a result,ordered meso-FeP/CC exhibits excellent HER performance:when the current density reaches 10 mA cm^-22 and 50 mA cm^-2,the required overpotential is only 65 mV and 107 mV,and the Tafel slope is as small as 44 mV dec^-1,which is comparable to the recently reported noble metal-free electrocatalysts.Moreover,it maintained 90.8%catalytic activity after 20 h long-term stability test.