Study On The Electrochemical Sensing And Hydrogen Evolution Properties Of Metalloporphyrin Complexes

As one of the novel materials,metalloporphyrin complexes are of important research significance and have widespread application prospects in solar cells,photoelectric conversion,photoelectric catalysis and photoelectrochemical sensors,due to their unique conjugated structure,good chemical stability and excellent photoelectric properties.However,they have not been widely used in the field of electrochemical sensors and hydrogen evolution.The structure and function of metalloporphyrin complexes are very similar to natural enzymes.And they exhibit good electrocatalytic activity toward the reduction or oxidation of many small electroactive molecules.Therefore,the use of metalloporphyrin complexes as electrochemical sensing materials or catalysts for hydrogen evolution reaction is of great significance for improving their performance and exploring their new applications.In this paper,the applications of metalloporphyrin complexes in the construction of electrochemical sensors and electrocatalytic proton reduction to H₂ were reviewed.On this basis,a series of porphyrin molecules and porphyrin functional composites with different substituents were synthesized and modified on the surface of galss carbon electrode.The electrochemical sensors for dopamine and hydroquinone isomers were constructed.In addition,the electrocatalytic activities of a series of metallporphyrin complexes for proton reduction to H₂was systematically studied,and the possible catalytic mechanism was dicussed.Specific research contents are as follows:（1）A novel dopamine electrochemical sensor（RGO/CuTECP/GCE）was constructed by combining 5,10,15,20-tetrakis（ethoxycarbonyl）porphyrin copper（Ⅱ）complex（CuTECP）with graphene oxide（GO）throughπ-πinteraction.Under the optimized experimental conditions,the linear range of the dopamine sensor was 2²00μmol?L^-1 with the limit of detection（LOD）of 0.58±0.09μmol?L^-1（S/N=3）.Meanwhile,the proposed sensor also had good selectivity,stability and reproducibility.The synergistic effect of CuTECP and reduced graphene oxide（RGO）accelerated the electron transfer rate in the system and realized the sensitive detection of small biological molecule dopamine.（2）Palladium（Ⅱ）,copper（Ⅱ）,gallium（Ⅲ）,nickel（Ⅱ）,cobalt（Ⅱ）and iron（Ⅲ）complexes of 5,10,15,20-tetrakis（ethoxycarbonyl）porphyrin（MTECP）was successfully modified on the surface of graphene oxide（GO）byπ-πnon-covalent interactions,and GO/MTECP hybrids was obtained.Then,RGO/MTECP hybrids modified electrode were prepared by further electrochemical reduction of GO/MTECP.It was found that the RGO/PdTECP/GCE electrochemical sensor,which was prepared form PdTECP functionalized graphene hybrids,has the highest detection activity of catechol（CC）and hydroquinone（HQ）,as well as good stability and selectivity.The linear ranges for CC and HQ were 2²00μmol?L^-1 and2¹80μmol?L^-1,respectively.The detection limits for CC and HQ were 0.42±0.05μmol?L^-1and 0.48±0.07μmol?L^-1（S/N=3）.This method provides a simple and feasible way to control the electrocatalytic activity of porphyrin functionalized graphene composites,and broadens the application of metal porphyrin complexes in electrochemical sensors.（3）Poly（CoTFPP）film was synthesized on GO/GCE modified electrode by electropolymerization with 5,10,15,20-tetrakis（pentafluorophenyl）porphyrin cobalt（Ⅱ）complex（CoTFPP）as monomer.Then,the electrochemical sensors of catechol（CC）and hydroquinone（HQ）were constructed by poly（CoTFPP）/GO hybrids.The electrochemical response signal was amplified and the sensitivity of the sensors was improved because of the synergistic catalysis between GO and poly（CoTFPP）film.The response of the sensor to CC and HQ had a wide linear range and a low detection limit.The linear range for CC and HQ were 1²20μmol?L^-1 and 1²00μmol?L^-1,respectively.The detection limits for CC and HQ were 0.17±0.03μmol?L^-1 and 0.21±0.05μmol?L^-1（S/N=3）.CoTFPP and GO were compounded by electrochemical polymerization,which improved the electron transfer rate of GO and realized the simultaneous detection of CC and HQ.（4）The electrocatalytic proton reduction capacity of CoTECP was studied in N,N-dimethylformanmide（DMF）after addition of increasing amounts of acetic acid（HOAc）or trifluoroacetic acid（TFA）as the proton sources.The cyclic voltammetry curves showed that the reduction peak of CoTECP at-2.37 V（vs.Fc/Fc⁺）had electrocatalytic activity for proton reduction to hydrogen in the presence of acetic acid.In the presence of trifluoroacetic acid,CoTECP could electrocatalyze at-1.88 V（vs.Fc/Fc⁺）.The results showed that the types of proton sources had great influence on the electrochemical behavior of CoTECP electrocatalytic proton reduction,and the mechanism of CoTECP electrocatalytic proton reduction for hydrogen production was different with different proton sources.The catalytic activities of TECP ligand and their iron（Ⅲ）,palladium（Ⅱ）,copper（Ⅱ）,nickel（Ⅱ）and gallium（Ⅲ）metal complexes for electrocatalytic proton reduction to H₂ were investigated with acetic acid or trifluoroacetic acid as the proton sources.Compared with acetic acid,a strong electrocatalytic response was obtained when using trifluoroacetic acid（TFA）as proton source.The order of catalytic activity was FeTECP>PdTECP>CoTECP>NiTECP>GaTECP>TECP.The results indicate that the type of central metal ions and proton sources has great influence on the electrochemical behavior of proton catalyzed by metalloporphyrin complexes.