Fabrication And Performance Investigation Of Novel Glucose Fuel Cell

Enzymatic biofuel cells(EBFCs)are devices that utilize oxidoreductase as catalyst to convert the chemical energy within biomass fuels into electrical energy.Due to their mild operating environment,wide sources of available enzyme catalysts and biomass fuels,renewablity,and high specificity of enzyme catalysts,energy conversion based on EBFCs is becoming one of the research hotspots in the field of international bioelectrochemistry.At present,EBFCs are facing the main challenges in the aspects of low electron transfer efficiency,low fuel utilization and poor stability of the biological enzymatic catalysts.This paper focuses on the key issues in the research field of EBFCs,taking glucose as the representative biomass fuel,glucose oxidase(GOx)and glucose dehydrogenase(GDH)as the anodic enzymes,organic molecular electrocatalysts(TEMPO and its derivatives)as the anode catalysts,laccase(Lac)and bilirubin oxidase(BOD)as the cathodic enzymes.The study on fabrication and performance investigation of novel glucose fuel cell has been carried out by combining with material science,first principles,electrochemistry and spectral analysis.The specific research contents and main achievements can be summarized as follows:(1)We describe here a dual-capture strategy for immobilization of enzymatic catalysts in the fabrication of glucose/O2 EBFCs.N-CNTs@C3N4 composite with bamboo-like hollow structure is prepared by pyrolysis of cobalt nitrate and melamine at high temperature.The results of the physical and chemical characterizations reveal that the enzymatic catalysts can be dual-captured both inside and outside the carbon materials.The constructed glucose/O2 EBFCs exhibit an OCV of 0.93 V,a maximum power density of 0.57 mW cm-2 and a maximum current density of 1.93 mA cm-2.After loading with 100 kΩ electrical resistance for 120 h,the discharge voltage of the fabricated glucose/O2 EBFC can remain～81.8%of the initial value,showing superior operating stability.(2)To further improve the performance of glucose fuel cell,we describe here an enzyme-modified electrode based on graphitized N-doped graphene/CNTs threedimensional network structure.The graphitized N-doped graphene/CNTs threedimensional network structure is synthesized by electrostatic adsorption and followed by thermal treatment.Combining with the first principle calculation,the effects of different N configurations on the electronic structure of graphene are clarified.The prepared bioanode can realize direct electron transfer(DET)of GOx and maintain specificity for its substrate glucose.The constructed glucose/O2 EBFCs show an open circuit voltage(OCV)of 0.89 V and deliver a maximum power density of 0.9mW cm-2 and a maximum current density of 2.25 mA cm-2,with no OCV attenuation after resting for 120 h(3)To improve the utilization of glucose,we describe here an organic molecular electrocatalytic system for constructing glucose/O2 fuel cell,realizing the 6e-deep oxidation of glucose.Combining with electrochemical test and spectral analysis,the catalytic mechanism is revealed,that is,the oxidation depth of glucose is affected by the pH value of the electrolyte.At pH 7.0,glucose is oxidized to form glucuronic acid in a 4e-pathway.When the pH value increases to 12.0,glucose is oxidized to form gluconic acid in a 6e-pathway.The results offer ideas for improving the energy density of EBFCs,and provide a theoretical basis and reference for the synthesis of high value-added glucose derivatives.Combining with an air breathing Pt/C cathode,a glucose/O2 fuel cell based on the proposed organic molecular catalysis is constructed.In the electrolyte at pH=12.0,the cell shows an OCV of 0.72 V.Additionally,a maximum power density of 34 μW cm-2 and a maximum current density of 598 μA cm-2 are achieved.The maximum power density(100μW cm-2)and maximum current density(973.3 μA cm-2)of the cell can be significantly improved by introducing acetylene black with high electroactive area and excellent charge transfer kinetics.It is found that the penetration of organic molecular catalyst from anolyte to catholyte deteriorates the ORR performance of the Pt/C catalyst and reduces the stability of the cell.Subsequently,the organic molecular catalyst is fixed by covalent grafting method,which effectively solves the problem of permeation of the organic molecular catalyst.(4)To improve the catalytic efficiency of anode on glucose,we describe here a hybrid enzymatic-organic molecular electrocatalysis cascade system for the deep oxidation of glucose at room temperature under neutral condition.Combining with electrochemical test and spectral analysis,the catalytic mechanism of the hybrid anode for glucose oxidation is unravelled:TEMPO is used as both an electrocatalyst for glucose oxidation and a mediator for biological enzymatic catalyst.Combining with an air breathing Pt/C cathode,glucose/O2 EBFCs based on the hybrid enzymatic-organic molecular electrocatalytic cascade system are constructed.In neutral electrolyte,the cell shows a maximum power density of 38.1 μW cm-2 with a maximum curre1t density of 651.4 μA cm-2.(5)We describe here the fabrication of a membrane-free glucose/O2 EBFC.Using CNTs as supporting material,GDH-functionalized bioanode is constructed by co-immobilization of GDH and the mediator.The onset potential for glucose oxidation catalyzed by the as-fabricated bioanode is-0.2 V(vs.Ag/AgCl),and the glucose oxidation current of 1.63 tA cm-2 is realized.BOD-modified biocathode with high DET behavior is prepared by using protoporphyrin(PIX)as molecular orientation inducer.As an electronic communication bridge between BOD and electrode,PIX can reduce cathodic ORR overpotential,improve ORR catalytic current and the electrode operation stability.The co-immobilization of enzyme and mediator as well as the construction of DET catalytic electrode avoid the existence of free mediator.Finally,the OCV of the membrane-free glucose/O2 EBFCs assembled by the above bioelectrodes can reach 0.8 V with a maximum power density up to 1.17 mW cm-2 and a maximum current density of 2.61 mA cm-2.