Design,Synthesis And Properties Of Electrocatalysts Based On Tetrapyrrole Compounds And Their Derivatives

As energy consumption and climate warming are aggravating,many energy conversion techniques(such as water electrolyzers,fuel cells,metal-air batteries,and CO2 reduction)have been developed,which can mitigate the energy crisis and climate problems.Development of high-performance electrocatalysts is crucial to realize fast energy conversion.Although noble metal catalysts(such as Pt/C,IrO2,and RuO2)have exerted many advantages,they are restricted in large-scale practical applications due to scarcity and high cost.Excellent electrocatalysts generally have the following advantages:large specific surface area and fully exposed active sites;the high flexibility in the molecular design of components and the control of network structures;high atomic efficiency.Based on the above research background and ideas,a series of two-dimensional organic conjugated polymers(CPs)and high loaded single atom catalysts(SACs)based on MNx(M=Metal)single catalytic site were designed and synthesized.The main research contents are as follows:(1)Ethynyl-linked Fe/Co Heterometallic Phthalocyanine Conjugated Polymer for Oxygen Reduction ReactionAn ethynyl-linked Fe/Co heterometallic Pc-based 2D conjugated polymer Fe0.5Co0.5Pc-CP with alternate distribution of Fe and Co fragments was successfully prepared by rational design and artful synthesis.It was found that the heterometallic polymer exhibits superior oxygen reduction reaction(ORR)catalytic activity to the homometallic counterparts(CoPc-CP and FePc-CP),which is comparable to the commercially available Pt/C catalyst.Based on the experimental analysis and theoretical calculation,the excellent ORR catalytic activity of Fe0.5Co0.5Pc-CP is attributed to the synergetic effect between the proximate Fe and Co ions in the conjugated network,which results in a fast 2 ×2e-synergetic catalytic reaction pathway.This work is not only helpful for gaining insight into the origin of the ORR catalytic activity of FeCo double active center catalysts,but also offers a practical way to develop novel electrocatalysts with well-defined chemical composition and structure for various electrochemical reactions.(2)Exfoliation of Amorphous Phthalocyanine Conjugated Polymers into Ultrathin Nanosheets for Highly Efficient Oxygen ReductionWe prepared a series of phthalocyanine-conjugated polymer ultrathin nanosheets MPc-CP NSs(M=Fe,Co,Fe0.5Co0.5)by exfoliation method,owing to the introduction of the defects into the individual layers,which enable diminished interlayer overlapping and weakened interlayer π-π stacking.The ultrathin MPc-CP NSs possess a smooth surface with a uniform thickness and a lateral size of several hundred nanometers.In particular,the as-prepared bimetallic Fe0.5Co0.5PC-CP NSs can be used to fabricate heterostructure Fe0.5Co0.5Pc-CP NS@G with graphene NSs as high performance ORR catalysts,the half-wave potential of Fe0.5Co0.5Pc-CP NS@G reaches 927 mV in alkaline medium,outperforming most of the state-of-the-art ORR catalysts reported so far.Its excellent ORR activity has also been demonstrated by the good performance of the Zn-air battery device.This work is surely helpful for further design and synthesis of ultrathin two-dimensional organic polymer nanomaterials with tunable conjugated electronic and geometric structure,which might have various promising applications in electronics and energy-related fields.(3)An Ultrathin Phthalocyanine Conjugated Polymer Nanosheets-based Electrochemical Platform for Accurately Detecting H2O2 in Real TimeWe synthesized diyne-linked phthalocyanine-based conjugated polymer two-dimensional nanomaterials FePc-CP-2 NSs with a thickness of 4.0 nm using a top-down strategy.An efficient H2O2 electrochemical sensor has been fabricated based on the multilayer films of the FePc-CP-2 NSs prepared by QLS method.Owing to the highly exposed active centers on the surfaces,the sensor based on the FePc-CP-2 NSs films exhibited excellent H2O2 determination performance with a detection limit as low as 0.017 μM,which is comparable to the best results reported so far for electrochemical H2O2 sensing.Moreover,the fabricated FePc-CP-2 NSs sensor was able to be applied in the real-time monitoring of H2O2 in real-sample analysis.The present result is surely helpful for developing high-efficiency electrochemical H2O2 sensors with practical application value.(4)Cascade Surface Immobilization Strategy to Access High-density and Closely-distanced Atomic Pt Sites for Enhancing Alkaline Hydrogen Evolution ReactionA facile and scalable method has been developed for the successful fabrication of carbon-supported noble metal single atom catalysts with high loading density.This new synthetic strategy involves the initial physical adsorption and then chemical immobilization of the porphyrinato noble metal molecules onto the carbon surface followed by relocating the single metal atoms into the carbon matrix.The newly prepared Pt SACs exhibits outstanding catalytic performance for hydrogen evolution reaction(HER)under alkaline condition with excellent stability,small overpotentials and Tafel slopes,and high turnover frequencies and mass activities,much superior to the HER benchmark electrocatalyst of commercial Pt/C.Mechanism studies suggest the origination of the excellent electrocatalytic performance from the synergic effect between closely distanced PtC2N1 active centers.(5)Edge-located Fe-N4 Sites on Porous Graphene-like Nanosheets for Boosting CO2 ElectroreductionDuring pyrolysis,the porous structure of catalyst can be changed by changing the ratio of KCl to LiCl,and the content of edge Fe(Ⅱ)site[E-Nd-Fe(Ⅱ)]and center Fe(Ⅱ)site[C-Nd-Fe(Ⅱ)]can be regulated.A variety of Fe atomic catalysts A-Fe@NG-LixKy with Fe(Ⅱ)-N4 sites anchored on porous graphene were synthesized by pyrolysis of bimetallic Fe/Zn two-dimensional zeolite imidazolate framework in the presence of KCl and LiCl.Though varying the ratios of KCl and LiCl in the pyrolysis process,the porous architecture of A-Fe@NG-LixKy can be adjusted,and the content of edge Fe(Ⅱ)sites[e-ND-Fe(Ⅱ)]and center Fe(Ⅱ)sites[c-ND-Fe(Ⅱ)]can be regulated.Electrochemical measurements indicate the CO2 reduction reaction(CO2RR)activity has positively relation to the ratio of e-ND-Fe(Ⅱ)and c-ND-Fe(Ⅱ).Density functional theory calculations as well as the in situ attenuated total reflection-infrared spectroscopy experiments further demonstrate that the higher electron density around the Fe sites of e-ND-Fe(Ⅱ)diminishes the bonding of CO on the metal sites as compared to c-ND-Fe(Ⅱ).Particularly,the optimized sample A-Fe@NG-Li1K3 exhibits ultrahigh activity for CO2-to-CO conversion with a small overpotential of 340 mV to achieve a CO partial current density at industrial application level(97 mA cm-2),The present work provides an insight into the effect of coordination environment on the CO2RR activity of Fe-N4 active sites and offers a guidance for developing high-efficiency single atom electrocatalysts.