Synthesis And Electro-catalyzed Hydrogen Evolution Performance Of Xanthene-bridged Bis-corrole And Its Metal-complexes

The continuous growth of the world economy and population has led to the rapid development of energy demand.Traditional fossil energy has the major defects of being non-renewable and serious pollution,and it will also deteriorate the greenhouse effect.Therefore,it no longer meets the requirements of sustainable development.The clean,high-energy-density hydrogen energy is expected to become an alternative energy source.New hydrogen production technologies,such as electrocatalytic decomposition,photocatalytic decomposition,biocatalytic photolysis,and solar pyrolysis of water have been proposed in recent years.Notably,the electrocatalytic hydrogen production technology is not restricted by seasons and weather,and the electric energy required can be obtained from renewable energy sources such as wind energy and hydropower.It has a promising application prospect,and thus received great attention from researchers.Hydrogen Evolution Reaction（HER）is an important step in electrocatalytic water splitting to produce hydrogen.A highly efficient and stable catalyst is the key to the hydrogen evolution reaction（HER）.The precious metals platinum,rhodium,and iridium have highly-efficient HER performance,but their high cost greatly limits their application in electrocatalytic hydrogen production technology.Therefore,it is very necessary to find a cheap,efficient and stable HER catalyst.In recent years,studies have showed that corroles and their metal complexes have good HER activity.In order to enhance the HER activity and stability of corrole and its metal complexes and inspired by the"Hangman group effect",the bis-corrole molecule bridged by xanthene at the 5-meso position（Xanthene-bridged bis-Corrole,CXC）was synthesized.It then reacted with cobalt salt and copper salt to give cobalt bis-corrole complex Co2（CXC）（PPh3）2 and copper bis-corrole complex Cu2（CXC）.The three compounds had been characterized by¹H-NMR,HR-MS and UV-Vis spectra.Cyclic voltammetry（CV）,controlled potential electrolysis（CPE）and controlled current（CC）methods were used to study its electrocatalytic hydrogen evolution performance.In addition,the actual rate of the electrocatalytic hydrogen production catalyzed by bis-corrole CXC was studied by gas chromatography（GC）and stability of the bis-corrole during electrolysis were investigated by controlled potential electrolysis test（CPE）combined with ultraviolet-visible spectroscopy.The experimental results show that two pairs of redox peaks appear in the CV spectrum of CXC under DMF system,and their half-wave potentials were-1.275 and 0.48 V,respectively.When the proton source（acetic acid）was continuously added to the system,the peak current of the reduction peak at the wave potential of-1.275 V increased sharply.In the organic phase,the result of controlled potential electrolysis test showed that TOF are 14.61,367.77,627.75 h^-1 under overpotential of 724,824 and 924 m V,respectively.In the acetonitrile-aqueous mixed phase,the results of controlled potential electrolysis showed that the TOF of bis-corrole CXC in acetonitrile-aqueous medium are 118.76,259.20,407.33 and 581.42 h^-1 under overpotential of 538,638,738 and 838 m V,respectively.Gas chromatography（GC）was applied to evaluate the actual H2 generating rate using bis-corrole as catalyst.The result showed that acetonitrile-aqueous solution consisting of 1.5 mg（1?μM）of bis-corrole as catalyst could generate 0.84 m L of H2 during 1-hour electrolysis under applied potential of 1.45V vs.Ag/Ag Cl.UV-Vis spectra of the catalyst bis-corrole CXC before and after 6 h of electrolysis were basically the same,and the current of the system remained basically constant during the electrolysis process,indicating that bis-corrole has good electrocatalytic hydrogen evolution stability.Cyclic voltammetry scans in DMF solvent were performed on the cobalt bis-corrole complex Co2（CXC）（PPh3）2 and the copper complex Cu2（CXC）.The results showed that the cyclic voltammetry curves of both complexes were unstable and both complexes need further investigation in HER.