Preparation And Performance Of Electrodes For Photoelectrochemical Biofuel Cells Based On A Water/Oxygen Circulation System

Photochemical biofuel cell（PBFCs）is a typical hybrid biofuel cell,which converts solar energy and biomass energy into electric energy by changing the single electrode of enzyme biofuel cell（EBFCs）into semiconductor material with light response.PBFCs further broadens the utilization of renewable energy（solar energy and biomass energy can be involved）in traditional biofuel cells,and avoids the influence of enzyme inactivity at both poles,thus improving the overall service time of the whole battery.In this work,photoanode and biological cathode were prepared and studied respectively,and the corresponding PBFCs were assembled.The holes generated by n-type semiconductor photoexcitation were used to drive water oxidation to oxygen,which can be diffused to the enzyme cathode and reduced to the fuel water needed for the anode,so as to realize the water/oxygen cycle battery system without supplementary fuel.The specific research contents are as follows:（1）WO_3-x nanorods with suitable oxygen vacancies were prepared by one-step thermal reduction of ethylene glycol.WO_3-x maintains an independent rod-like structure,which can be fully infiltrated by the electrolyte and has a high reactive area.The optimal photocurrent density of WO_3-x photocatalytic water oxidation is 1.89 m A cm^-2（0.6 V vs.Ag/Ag Cl）,and the applied bias solar energy conversion efficiency（ABPE）is up to 0.38%.The WO_3-x photocurrent density remained at 95%of the initial value after 10h photoswitching cycle test.It shows that photoanode is successfully prepared and stable.（2）A biocathode of BOD/PPIX/CNTs was prepared with CNTs as carrier material and protoporphyrin（PPIX）as directed inducer.The introduction of PPIX further reduced the oxygen reduction overpotential of the BOD modified cathode,which had an oxygen reduction current of 0.58 m A cm^-2 and excellent oxygen reduction activity and O₂ mass transfer characteristics.At the same time,the peroxide yield of the cathode is less than 1.5%,which is more favorable for the 4e^-oxygen reduction step.After 10 h of chronoamperometry,the cathode current retention rate was 93.75%,indicating that the BOD/PPIX/CNTs modified electrode had good stability.（3）Using WO_3-x/FTO as photoanode and BOD/PPIX/CNTs/CC as biological cathode,a full PBFCs battery based on water/oxygen cycle was assembled.The PBFCs full battery is capable of producing an open circuit voltage of 0.81 V and a maximum power density of up to283μW cm^-2.In an open system,the cell maintained 97%of its original power after a long-term stability test（36000 s）.The sealing test successfully verifies that the water/oxygen cycle can be completed spontaneously without external force.After 240 h of storage,the discharge current is still 0.24 m A cm^-2,and the current retention rate is as high as 55%,which proves that the system has the potential for practical use.