Complex-derived Hydrotalcite-like/Nanocarbon Composite As An Efficient Water Electrolysis Catalyst

Layered double hydroxide（LDH）-based catalysts have gradually become highlight due to the advantages in economy,adjustable structure and simple preparation process in water-splitting.However,the pristine LDH still has many shorts such as conductivity and catalytic performance.The combination of hydrotalcite-like and carbon-based catalysts can improve its conductivity.The composites formed by pre-synthesizing LDH and carbon-based catalyst（carbon nanotube,etc.）has the shorts that cannot combine tightly.MOF-derived carbon-based catalysts usually requires harsh conditions.In this work,by complexation of rust inhibitors for metal ions to synthesize hydrotalcite-like/nanocarbon composites for water electrolysis.By the one-step solvothermal,we synthesis the composites which realizing the close combination of hydrotalcite-like and nanocarbon and avoiding the harsh conditions of MOF-derived carbon-based materials.The main works are as follows:（1）The sulfur-modified cobalt-iron hydrotalcite/nanocarbon composite was synthesized by two-step solvothermal method using TAAT as the ligand.As a water-based rust inhibitor,TAAT can not only complex iron ions in the precursor solution so that iron ions can better embed the nanocarbon in the first solvothermal process,but also as a source for the formation of nanocarbon.The cobalt ion does not complex with TAAT in the precursor solution,but it catalyzes the process that TAAT converses into nanocarbon.The close combination of hydrotalcite-like and carbon-based materials is realized by a simple solvothermal process.The molecular identity of the iron complex in precursor solution can contribute to the uniform distribution of metal nanoparticles in the nanocarbon which can expose more active sites.The one-step in-situ synthesis can benefit the intimate contact between the metal active site and nanocarbon,accelerates the electron transfer.In the second step,cobalt sulfide which can benefit OER is made,valence state of cobalt ions can be adjusted to enhance the activity of OER and HER.Only 168 m V of overpotential is required to reach a current density of10 m A/cm²,and the Tafel slope is 128.3 m V·dec^-1 in the OER.Only 283 m V of overpotential is required to reach a current density of 10 m A/cm²and the Tafel slope is94.0 m V·dec^-1 in the HER.Using Co S_1.097/Co Fe-LDH/C as overall water splitting catalyst,the voltage at a current density of 10 m A/cm² is 1.50 V.In order to simulate the process of seawater electrolysis,the performance of OER and HER was tested in a mixed solution of Na Cl and KOH.Although the performance is not as ideal as before,it can still be used as a good electrocatalyst.（2）Using MBT as ligand,Ni foam as conductive substrate,we one-step synthesis Ni Fe Mo-LDH/C as bifunctional electrocatalyst in situ.MBT can not only complex mental ions in the precursor solution so that mental ions can better embed the nanocarbon in the solvothermal process,but also as a source for the formation of nanocarbon.The molybdate ion does not complex MBT in the precursor solution,but it can catalyze the process of MBT converse into nanocarbon.The close combination of hydrotalcite-like and carbon-based materials is realized by a simple solvothermal process.The molecular identity of the iron complex in precursor solution can contribute to the uniform distribution of metal nanoparticles in the nanocarbon which can expose more active sites.The in-situ synthesis can benefit the intimate contact between the metal active site and nanocarbon,accelerates the electron transfer.Maintaining the general structure of the nickel-iron hydrotalcite,the introduction of molybdenum greatly enhances the its HER activity.Only 124 m V of overpotential is required to reach a current density of 10 m A/cm²,and the Tafel slope is 44.3 m V·dec^-1 in the OER.Only60 m V of overpotential is required to reach a current density of 10 m A/cm²and the Tafel slope is 44.0 m V·dec^-1 in the HER.Using Ni Fe Mo-LDH/C/Ni Foam as overall water splitting catalyst,the voltage at a current density of 10 m A/cm² is 1.51 V.In order to simulate the process of seawater electrolysis,the performance of OER、HER and overall water splitting was tested in a mixed solution of Na Cl and KOH.Although the performance is not as ideal as before,it can still be used as a good electrocatalyst.