Synthesis Of Metal-organic Frameworks Resistant To Acid-alkali Based On N-containing Heterocyclic Ligands And Water Electrolysis Performance

As we all know,fossil fuels are limited resources which have been consumed at a rapid and visible rate since the industrial revolution.Some scientists have pointed out that the fossil fuels stored on the earth have been difficult to meet long-term human needs,the potential crisis of energy shortage and a series of environmental pollution issues such as global warming caused by burning fossil fuels need to be addressed urgently.Developing of renewable clean-energy to gradually replace the fossil energy used at present is an effective solution to solve those problems.Hydrogen produced by electrocatalytic water splitting is considered to be a promising clean-energy in contemporary times,which is called the future energy by researchers.At present,noble metal（Pt,Ru and Ir）-based electrocatalysts are the most efficient electrocatalysts for HER and OER.However,their large-scale applications have been greatly limited by scarcity and high price.Therefore,developing inexpensive,efficient and resourceful non-noble metal electrocatalysts are of great scientific significance and application value.Metal-organic frameworks（MOFs）possess characteristic advantages,such as diversified and designable structure,large surface areas and high porosity,abundant and uniform active sites,have become a kind of promising electrocatalysts.However,the majority of MOFs is unstable under strongly acidic or alkaline conditions.Herein,we successfully fabricated a series of MOFs which have excellent chemical stabilities,and further researched electrocatalytic performance by different measures of regulating the stability of MOFs.This thesis mainly carried out the following three aspects of work:1.Using 3,5-pyrazole dicarboxylic acid as organic ligand,Cu（Ⅱ）metal salts as metal center and regulating the types of free ions in the framework by solvothermal synthesis,two types of metal-organic framework materials were synthesized:Pdc-Cu-0:{[Cu（Pdc）]·（H₂O）Cl}_n,Pdc-Cu:{[Cu₂（Pdc）₂]·Ni（H₂O）₆}_n.Pdc-Cu-0 is stable in p H=2-12solutions.Pdc-Cu exists stably in p H=0-12 solutions showing the excellent acid-base stability.By Co²⁺doping of Pdc-Cu,a series of Co_x@Pdc-Cu electrocatalysts were prepared.In 0.5M H₂SO₄,Co_0.1@Pdc-Cu showed excellent HER catalytic activity,with overpotentials of 240 m V at 10 m A cm^-2,Tafel slopes of 102.1 m V dec^-1 and the maintenance of its catalytic activity for at least 12 hours.The results show that the chemical stability of this kind of material can be effectively improved by regulating the types of free ions in the framework.Co²⁺doping improves HER activity of catalysts,which provides a new idea for the application of such materials to HER in strong acidic electrolytes.2.Using 4,4-Oxybis（benzoic acid）and 1,10-Phenanthroline as organic ligands,Co（Ⅱ）metal salts as metal center,phen-Co-1:{[Co（phen）（oba）]·0.5H₂O}_n were synthesized by solvothermal synthesis.phen-Co-3:[Co（phen）（oba）（H₂O）₂]_n were synthesized by immersing phen-Co-1 in H₂O.Soaking phen-Co-1 in mother liquor to obtain phen-Co-2:[Co（phen）（oba）·H₂O]_n.Achieve single crystal to single crystal conversion.phen-Co-1 and phen-Co-3 are stable in p H=2-12 solutions.phen-Co-2 exists stably in p H=2-13 solutions showing the excellent acid-base stability.By Ni²⁺doping of phen-Co-2,a series of Ni_x@phen-Co-2 electrocatalysts were prepared.In 0.1M KOH,Ni_0.2@phen-Co-2 showed outstanding HER and OER catalytic activity,with overpotentials of 231 m V and 392 m V at 10 m A cm^-2.Consequently,MOFs with superior chemical stability can be obtained by conversion from single crystal to single crystal through external regulation.The catalytic activities of HER and OER can be effectively improved by Ni²⁺doping,and the optimal catalytic performance can be achieved by Ni²⁺doping at the appropriate concentration.3.A special Fe-doped hybrid zeolite imidazolate frameworks was synthesized in situ by solvothermal synthesis that is stable in p H=1-14 solutions exhibited outstanding acid-base stability.In 1M KOH,Fe@HZIFs showed excellent HER and OER catalytic activity,with overpotentials of 179 m V and 340 m V at 10 m A cm^-2.At 50 m A cm^-2,the Fe@HZIFs overpotential of OER is 438 m V,which is better than that of Ru O₂（516 m V）,in other words,the catalytic activity is far superior to Ru O₂ at large current density.The results showed that the introduction of Fe（Ⅲ）into the frameworks increased the active site and improved the electrocatalytic activity of the catalyst.It provides an effective way for this kind of catalyst to enhance the electrocatalytic activity.