| With the daily serious environmental pollution and rapid consumption of fossil fuels,the development and application of new generation energy conversion,transmission and storage device are more urgent for researchers both academic and industrial communities.Compared with other energy storage devices,supercapacitors are widely applied in new energy vehicles due to their high power density,stable cyclability and long service life favored by people.However,traditional electrode material doesn’t yield a high capacitance,gradually,it is difficult to meet the needs of miniaturization and mobility of portable energy storage devices,which restricts the development of supercapacitor to some extent.Therefore,new electrode materials need to be constructed.While ensuring high specific capacity and high stability,other characteristics such as non-toxic,environmentally-friendly should be taken into consideration.As the most abundant natural organic molecules,chlorophyll(Chl)organic materials widely exist in algae,photosynthetic bacteria and green plants.Besides,Chls are highly plastic with multiple active sites.If Chls and its derivatives could be widely applied into supercapacitor as electrode materials,it will not only solve the problem of insufficient performance of traditional materials,but also achieve the reuse of green,cheap,abundant and renewable materials.High efficiency,good performance,stable cyclability and at the same time environmrntally-friendly,this hypothetical supercapacitor yields great potential and will provides a new way on the construction of future clean energy system.As an attempt to apply Chl derivative to supercapacitors,J-aggregation Chl electrode is prepared using scrape coating method directly.In three-electrode system,Chl electrode exhibits a capacitance of 55 F g-1 at a scan rate of 10 m V s-1.And then an asymmetric solid-state capacitor with an increased potential window ranges from 0.6-1.7 V is assembled where Chl serves as a positive electrode and activated carbon(AC)plays the role of a negative electrode.The Chl-based hybrid capacitor exhibits a capacitance of 18.2 F g-1(24.3 C g-1)at a scan rate of 10 m V s-1.The energy density of hybrid capacitor reaches 5.81 Wh kg-1 at the lower power density of 1.067 k W kg-1,and1.22 Wh kg-1 when power density increases to 8.460 k W kg-1.To demonstrate practicality,this hybrid capacitor is connected to a Chl-based solar cell,constitute a Chl-based green energy capture,conversion and storage system.This research applyes Chl derivative into energy storage system,gets good electrochemical performance,provides a rich material source for developing low-cost and pollution-free supercapacitors.To improve the electrochemical performance of Chl derivative-based supercapacitor electrode,we should explore methods to modify its structure.To explore the method of improving electrochemical performance,we select protoporphyrins(protoporphyrin IX noted as Por and Mn(III)protoporphyrin IX chloride noted as Mn Por)as the pristine materials which shares similar structure to chlorophyll.Through the electrochemical coupling of the vinyl groups on the porphyrin macrocycles,we get the polymerized protoporphyrin films.Compared ultraviolet–visible spectra(UV-vis)and Fourier transform infrared(FTIR)spectrum of pristine porphyrin and film,obivious changes confirm the polymerization of porphyrin.The extension of the π-conjugated backbone lengthens the intramolecular channel of electrons and allows the electron transporting in higher speed,leading to an excellent electrochemical performance.For the fact of central metal element Mn,Poly Mn Por forms extra coordination bond and exhibits a layered structure,which allows a more sufficient contact with electrolyte ion and Poly Mn Por surface and thus achieve higher capacitance.In three-electrode system,Poly Por gives capacitance of 93 F g-1,whereas Poly Mn Por provides significantly higher capacitance of up to 135 F g-1.This research proves that using the electrochemical cationic coupling of unsaturated bonds on the porphyrin ring,we could synthesize polymeric porphyrin materials with better electrochemical properties.After the successful synthesis of polymerized porphyrin films,we continue our research work and further explored the electrochemical cationic vinyl polymerization of chlorophylls.In this part,we synthesize 6 Poly Chl films via electroinitiated cationic polymerization using Chl derivatives that feature vinyl group on the C3 position of the chlorin macrocycle with different central metal elements(Ni,Cu,Mg,Co,Zn and GaOH).In ultraviolet–visible spectra(UV–vis),evident expansion and slight redshifts of Soret band verify the formation of Poly Chl.The transformation of the sample from the disordered massive structure of chlorophyll to the uniform ordered nanospheres of polymeric chlorophyll was also observed under Scanning Electron Microscope.In three-electrode system,Poly Cu Chl film exhibits the highest capacitance of 344 F g-1 at a scan rate of 5 m V s-1.And 90% retention left after 10000 charging-discharging cycles.This study has identified a new bio-based organic polymer system and pointed out the great potential of polymeric chlorophyll in the field of energy storage.Finally,to further study the effects on types of unsaturated bonds in chlorophyll,we design chlorophyll derivatives with peripheral ethyl,vinyl and ethynyl groups at the C3-position of the tetrapyrrole ring,use the same electrochemical polymerization method and observe the curves changes during cyclic voltammetry(CV)process.No obvious growth or reduction is observed in the ethyl-based Chl curves or as a color change on the Indium Tin Oxide(ITO)glass.The results of vinyl and ethynyl based Chl exhibit substantial changes in the size of the CV curves after successive scans,and Chl films were deposited on the ITO glass with a steadily deepening color on working electrode.Therefore,it is clear that unsaturated vinyl or acetylene functional groups are the key factor that enable the polymerization of Chls.There is no significant difference between ethylene and acetylene polymerized chlorophyll films in subsequent absorption spectrum tests,indicating that the polymers have similar molecular structure,which are all chain molecules assembled by unsaturated bonds.In electrochemical performance,the polymer of ethynyl-based Ni Chl yields a capacitance of 466 F g-1,which is a high value even compared with traditional conductive polymer.After using polymerized ethynyl-based nickel Chl film to assemble solid symmetrical supercapacitor,we connected it with Chl-based organic solar cell by co-anodic method,forming a green and sustainable integrated solar energy conversion storage device based on chlorophyll.The Chl-based solar energy conversion and storage device can stably complete multiple charging-discharging cycles under different light intensity,and there is no performance attenuation of light energy conversion or energy storage in this process,which highlights the practical value.The integrated chlorophyll solar energy conversion and storage device simulates the process of photosynthesis and completes the conversion and storage of solar energy.Moreover,the composition material is cheap,easy to obtain and environmental,which provides a new idea for the construction of green and clean energy system in the future.Based on the above exploration and research of chlorophyll derivatives,we have gradually discovered a series of chlorophyll polymers with great development potential,which retaines the main structure of chlorophyll,but the extended π conjugation system improves its electrochemical performance effectively.Understanding and realizing its application potential in the field of energy storage will help realize the commercial application of cheap renewable energy storage devices... |
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