Electrocatalytic Hydrogen Evolution By A₂B-type Cobalt Corroles Appended Ester Or Carboxyl Group

With the continuous development of the modernization society,the exploration of high efficiency,and green new clean energy to partially replace fossil energy has become the research priorities in many fields.Hydrogen is one of the most potential new-energy because of its high energy density,environment friendly(water is the only product of combustion reaction),and the feasible conversion between electrical and chemical energy for energy storage and release.At present,it is common to produce hydrogen by water electrolysis.However,it is hard to break the H-O bond during the water-splitting process unless providing the extra energy to overcome the high energy barrier.Therefore,suitable electrocatalysts are necessary for a higher efficient and low-cost hydrogen evolution reaction(HER).Here,the main point of this research is as follow,based on the design of molecular structure,a corrole macrocyclic complex with transition metal cobalt as the centre is synthesized and used as HER electrocatalysts,and then investigating the possible different HER performance of corroles caused by the introduction of different types of functional groups on their macrocyclic periphery,the detailed description is as follows:1.Firstly,10?(4?Methoxycarbonylphenyl)?5,15-bis(pentafluorophenyl)corrole was synthesized via the“one-pot two-step method”.A low-cost method with high-yield was created to synthesize 10-(4-Carboxyphenyl)-5,15-bis(pentafluorophenyl)corrole.The corresponding metal cobalt corroles 1 and 2 were prepared.A series of characterization methods including ultraviolet-visible spectroscopy,nuclear magnetic resonance,high-resolution mass spectrometry,and X-ray photoelectron spectroscopy,were used to confirm the structure of the products.2.The study of electrochemical hydrogen evolution performance of metal corroles 1 and2 in the organic and the neutral aqueous media was carried out,respectively.In the organic solution(DMF was the solvent,TBAP was the supporting electrolyte,and acetic acid was the proton source),with the gradual increment of acidity,the peak current density increased proportionally.Meanwhile,the peak of Co^II/I couple has shifted from-1.54 to-1.41 V(vs.Ag/Ag NO₃)with the gradually irreversible change of relative CV curves,indicating that both corrole 1 and 2 have the possible electrocatalytic activity for HER.Combined with the CV results,there are two possible mechanisms for cobalt corrole 1 and 2 to catalyze HER under different acidity conditions:(1)EECC route(low acidity condition):[Co^III-PPh₃]disassociates the axial ligand and then combines with two electrons to form[Co^I]^2–,and then[Co^I]^2–reacts with a proton to give[Co^III-H]^–.With a further protonation,H₂ is released.[Co^III-PPh₃]is regenerated after the reconnection of the axial ligand and metal centre.(2)ECEC route(high acidity condition):similarly,after the generation of[Co^III-H]^–,[Co^III-H]^–goes through one-electron reduction to form[Co^II-H]^2–.After further combining with H⁺,H₂ is released with the species of[Co^II]^-continue to react in the catalytic cycle.In the neutral aqueous medium(acetonitrile-water,water as the proton source),the same electrocatalytic HER performance tests were carried out with cobalt corrole 1 and 2.In the 2-minute controlled potential electrolysis,when the overpotential is 838 m V(vs.Ag/Ag Cl),the conversion frequency(TOF)of 1 and 2 are 291.8 and 190.5 h^-1,respectively.After one hour of electrolysis,the amount of hydrogen catalyzed by 1 and 2 are 3.34 and 1.47 m L,with TOF of507.4 and 237.3 h^-1,respectively.After 8 hours of electrolysis,the TOF are 1758 and 1623 h^-1for 1 and 2,respectively,and the produced catalytic current maintain generally smooth with the time increasing,indicating that the corroles can perform stably.After the comparison of the catalytic performance of other A₂B cobalt corroles which have different or same types of substituents at the 10-meso position,the results suggest that corrole 1 and 2 can catalyze HER with high activity while performing stably during the long-time electrocatalysis in an aqueous medium.