Electrocatalytic Properties Of Porous Coordination/Organic Polymers And Their Derivatives

The development of clean energy conversion/storage systems such as water electrolyzers and Zn-air batteries（ZABs）is an effective way to achieve the energy transition.However,the hydrogen evolution（HER）,oxygen evolution（OER）,and oxygen reduction reactions（ORR）involved in these devices generally suffer from the sluggish kinetics.Thus,it is urgent to design and develop efficient and stable catalysts to improve the energy conversion efficiency of such energy systems.In this context,porous coordination/organic polymers（MOFs/POPs）have been regarded as hotpot materials to replace noble metal catalysts due to their high variability of inorganic nodes and organic ligands.However,the application of such materials in the field of catalysis is still plagued by issues such as low activity and poor stability.To solve this problem,in the thesis,various defect types and active components were introduced into MOFs by doping and recombination,and MOFs-derived materials with different structures and compositions were constructed by specific thermal induction methods.Besides,the active metal centers were introduced into POPs through molecular design,and the POPs/carbon compound catalysts were prepared by a non-pyrolysis method.Based on the above methods,a series of MOFs/POPs derived catalysts were synthesized.The effects of the structure and chemical composition of as-prepared catalysts on electrocatalytic performance were systematically investigated.The main research contents and conclusions of this paper are summarized as follows:（1）During the experiment,we selected microporous ZIF-67 as the structure inducers,agarose gel as the composite substrates,and melamine as the C and N sources.Based on this,we prepared carbon aerogel-supported nitrogen-doped carbon nanotube-encapsulated Co nanoparticles composites（Co/NCNT/CA-900）by an in-situ growth strategy.Then,the effects of composition and hierarchical structures on catalytic performance were systematically explored.The results showed that the ORR half-wave potential of Co/NCNT/CA-900 is 0.83 V,demonstrating excellent ORR activity.Moreover,HER/OER overpotentials of Co/NCNT/CA-900 were 230 m V and 410 m V at 10 m A cm^-2,respectively,showing the good HER/OER catalytic activity.The above good catalytic performance could be attributed to the following points:（i）the synergy between Co nanoparticles and nitrogen-doped carbon;（ii）the tightly encapsulated structure of NCNTs to Co nanoparticles;（iii）the high electron transport capacity of three-dimensional conductive network.（2）During the experiment,we selected microporous ZIF-67 as the structural framework,and phosphazene polymer shell as the P sources and heteroatom doping dopants.Based on this,we prepared the N,P,S co-doped carbon hollow polyhedron encapsulated Co2P nanoparticle composites（Co2P/NPSC-800）through the polymerization-pyrolysis.Then,the effects of multiple active components and hollow encapsulation structures on catalytic performance were systematically investigated.The results indicated that the Co2P/NPSC-800shows excellent catalytic performance for HER,OER and water splitting.The overpotentials of HER and OER are 173 m V and 315 m V at 10 m A cm^-2,respectively.And the driving voltage of the overall water splitting device could reach 1.67 V.The above excellent catalytic performance could be attributed to:（i）Co2P with unique geometry and suitable band structures;（ii）the synergy between Co2P nanoparticles and N,P,and S doped carbon;（iii）the hollow encapsulation structures which can effectively prevent the active materials from falling off.（3）During the experiment,we selected MIL-101 with high porosity as the structural substrates and iron tetraaminophthalocyanine（Fe TAPc）as the Fe metal site doping sources.Based on this,we synthesized Fe-Nx/mesoporous carbon composites（Fe TA-Nx/NC-900）by stepwise pyrolysis and systematically explored the effects of Fe-Nx sites and mesoporous rod-like structures on the catalytic performance.The results suggested that the half-wave potentials of Fe TA-Nx/NC-900 in alkaline/acidic media are 0.82 V and 0.65 V,respectively.When used as the cathode catalyst for ZABs,the Fe TA-Nx/NC-900 exhibits a peak power density of 74.3 m W cm^-2.The good catalytic performance of this material in alkaline/acidic media could be attributed to:（i）the Fe-Nx sites with high atom utilization;（ii）the stronger interactions between metal atoms and supports compared to metal nanoparticles;（iii）the rod-like structures with high porosity which can effectively stabilize the Fe-Nx sites.（4）The metal polyphthalocyanine（MPPc）were constructed by molecular design,and then the MPPc/multi-walled carbon nanotube composites（MPPc@MWCNT,M=Fe,Co,Ni）loaded with M-N4 sites were prepared by in-situ polymerization strategy under relatively mild conditions.The effect of metal sites of the composites on catalytic performance was systematically explored.The molecular orbital energies of Fe PPc,Co PPc and Ni PPc were calculated by density functional theory（DFT）calculations.The results showed that Fe PPc has the smallest energy level gap and the best electronic conductivity,and the identified Fe-N4 as the real active sites for the catalytic reaction.The experimental results showed that the half-wave potential of Fe PPc@MWCNT is 0.89 V,which indeed performed better ORR catalytic activity than that of Co PPc@MWCNT and Ni PPc@MWCNT,and even exceeds that of the commercial Pt/C.When used as the cathode catalyst for ZABs,the peak power density is 124.20 m W cm^-2.Besides,it also exhibits good battery performance as the all-solid-state ZABs catalysts.The superior catalytic performance could be attributed to:（i）Fe PPc with higher electronic conductivity;（ii）the well-defined Fe-N4 active sites dispersed uniformly on MWCNTs;（iii）the high conductivity and large specific surface area provided by MWCNTs.