Structural Design And Water Splitting Performance Of Highly Active Transition Metal-Based Electrocatalysts

As an important component in the water electrocatalysis system,electrocatalysts have a significant impact on the efficiency and cost of hydrogen production,and the development of green,efficient and low-cost catalysts is the key to realize the wide application of water electrocatalysis technology.In this work,a series of iron,cobalt and nickel-based electrocatalysts were constructed by using heterogeneous atom doping,heterostructure construction and surface modification,and the influence of the electronic structure of cations on the electrocatalytic performance and the existence form of cations after undergoing electrocatalytic reconstruction were investigated in depth to reveal the evolution of the active site phase in the electrocatalytic reaction.In addition,this work provides a new method for constructing highly stable electrocatalysts,which further accelerates the pace of industrial application of transition metal-based catalysts.The specific work is as follows:（1）Optimization of geometric site distribution of cobalt ion in spinel to enhance the performance of electrocatalytic oxygen evolution reaction（OER）.The intrinsic activity of spinel-based electrocatalysts was enhanced by introducing Ru into spinel oxides through ambient liquid-phase reaction and heat treatment to modulate the conversion of Co²⁺（O_h）and Co²⁺（T_d）sites to Co³⁺（O_h）sites in spinel oxides;using carbon in precursors and the reducing atmosphere of heat treatment to compound spinel oxides with alloy and carbon materials to enhance the electrical conductivity and structural stability of catalysts.The prepared catalyst was applied to OER with an overpotential of 237 m V at a current density of 10 m A cm^-2;in the stability test,it was able to cycle stably for 50 h at a current density of about40 m A cm^-2.（2）The ionic biosorption method was proposed to construct iron phosphide catalysts to enhance OER performance.Based on the small size of bacterial particles and the screening function of cell membrane,highly active iron phosphide nano-catalysts were constructed by ionic bacterial adsorption method and heat treatment.The preparation of this catalyst is more environmentally friendly compared to the general synthesis process of transition metal phosphides.The prepared catalyst was applied to OER with an overpotential of 266 m V at a current density of 10 m A cm^-2;in the stability test,it was able to cycle stably for 15 h at a current density of about40 m A cm^-2.（3）Construction of Ru/iron phosphate heterojunctions to enhance the OER performance of iron phosphate-based catalysts.Ru nanocrystal-modified iron-rich phosphate materials were prepared by a simple two-step of hydrothermal-thermal treatment using lecithin as the phosphorus source.The introduced Ru nanocrystals can not only form a Ru/iron phosphate heterojunction with the iron phosphate material,but also capture the phosphorus element in the metal phosphate,reduce the atomic ratio of phosphorus to iron in the phosphate,and drive the conversion of iron phosphate to iron-rich phosphate,thus enhancing the activity and conductivity of the catalyst.The prepared catalyst was applied to OER with an overpotential of 250 m V at a current density of 10 m A cm^-2;in the stability test,it was able to cycle stably for 45 h at a current density of about20 m A cm^-2.（4）Ni was introduced into iron phosphide to elucidate the fundamental reason for the synergistic enhancement of the performance of electrocatalytic OER and hydrogen precipitation reaction（HER）by the two.Ni₂P/Fe P-FF electrocatalysts were prepared using a simple double-chloride（Na Cl-Ni Cl₂）etching method and a conventional phosphating method.The introduced Ni element can improve the Fe-O bond energy on the catalyst surface and promote the catalyst to reconstruct into a highly active Fe OOH phase in OER to enhance the OER performance;Ni₂P can reconstruct into a highly active Ni₂P/Ni（OH）₂ heterojunction in HER to enhance the HER performance.The Ni₂P/Fe P-FF was applied to electrocatalytic OER and HER.When the current density was 10 m A cm^-2,the overpotentials were 217 and 42 m V,respectively;in the stability test of the symmetric two-electrode system,it was able to cycle stably for 50 h at a current density of 100 m A cm^-2.（5）The in situ corroding method was proposed to construct highly stable electrocatalysts and to elucidate the kinetic growth process of the catalysts as well as the active phase in the reaction.The iron-rich modified nickel-iron phosphide（o-Ni Fe P/NFF）electrocatalysts were constructed by a simple low-concentration acid corroding method and a conventional phosphating method.The surface acid corroding method not only enhances the tightness of the connection between the surface catalyst and the conductive substrate material,substantially improving the stability of the electrode material,but also increases the iron-nickel atomic ratio on the catalyst surface so that it can be directly reconstructed into the highly activeβ-Ni OOH/α-Fe OOH phase in alkaline solution.o-Ni Fe P/NFF was applied to the electrocatalytic OER.When the current densities were 100 and 400m A cm^-2,the overpotential was only 224 and 272 m V,respectively;in the stability test,it was able to cycle stably for more than 468 h at a current density of～320 m A cm^-2.This paper includes 82 figures,13 tables,and 231 references...