Study On The Performance Of Photocatalytic Fuel Cell With Organic-ZnIn₂S₄ Co-Modified TiO₂ Photoanode

Photocatalytic fuel cell（PFC）combines photocatalysis（PC）with fuel cell（FC）,which synergizes oxidative degradation of organic pollutants and electrical energy generation.In a PFC system,the photoanode acts as a strong oxidation electrode for photoexcited carrier generation and organic waste degradation.Therefore,the design of efficient and stable photoanodes is the key to improve the performance of PFC.TiO₂is used as a PFC photoanode material because of its good chemical stability and photocatalytic activity,but it can only absorb UV light and has a high electron-hole recombination rate.Although the modification of TiO₂with narrow band gap semiconductor ZnIn₂S₄broadens its optical response range to some extent,it still has the problem of low separation efficiency of photogenerated carriers.Therefore,in this paper,organic-ZnIn₂S₄co-modified TiO₂photoanode were prepared by introducing organic materials（Ui O-66,PANI and PPy）simultaneously.Among them,the organics act as co-photocatalysts to enhance the light collection and dye adsorption of the photoanode while providing additional photogenerated carrier transport paths to promote efficient electron-hole pair separation.The specific contents and conclusions of this study are as follows:1.ZnIn₂S₄/Ui O-66/TiO₂/Ti composite photoanode was successfully developed by the solvothermal and sol-gel methods.The optimum preparation conditions were obtained by optimization of the electrode preparation process:Ui O-66 doping ratio of 20%,calcination temperature was 140°C and calcination time was 2 h.The composition,morphology and optical properties of the prepared electrode were analyzed by various characterization methods such as XRD,FT-IR,SEM,XPS and DRS.PFC system was constructed by connecting ZnIn₂S₄/Ui O-66/TiO₂/Ti photoanode and Cu cathode,and the optimal treatment conditions for RhB were explored:initial concentration was 10 mg/L and initial p H was3.0.Under this condition,the RhB removal rate,open circuit voltage(V_oc),short circuit current density(J_sc),maximum power density(JV_max)and fill factor（FF）were 90.3%（1 h）,0.49 V,0.22 m A/cm²,16.97μW/cm²and 0.157,respectively.The improvement of PFC performance was mainly due to the excellent energy band matching and nanoscale interface contact between ZnIn₂S₄and Ui O-66.The existence of Ui O-66 could be used as an electron transmission bridge,which not only promoted the rapid transfer and utilization of photogenerated electrons,but also improved the adsorption capacity of photoanode to RhB molecules.2.ZnIn₂S₄/PANI/TiO₂/Ti composite photoanode were successfully prepared,and the optimum electrode preparation conditions were explored:the doping ratio of PANI was 1%,the calcination time was 100℃,and the calcination time was 1 h.The structural composition,microscopic morphology and optical properties of the prepared electrode were analyzed by XRD,FT-IR,SEM,HRTEM,XPS,DRS and elemental mapping.The results showed that the ZnIn₂S₄/PANI flower-like microspheres with interlaced structure were mosaicked on the surface of TiO₂layer and the materials were tightly bonded to each other.The composite photoanode showed significantly enhanced absorption in the visible region.PFC system was constructed by connecting ZnIn₂S₄/PANI/TiO₂/Ti photoanode and Cu cathode,and the optimal treatment conditions for RhB were explored:initial concentration was 10 mg/L and initial p H was 3.0.Under this condition,the RhB removal rate,open-circuit voltage(V_oc),short-circuit current density(J_sc),maximum power density(JV_max)and fill factor（FF）were 93.8%（1 h）,0.51 V,0.26 m A/cm²,18.83μW/cm²and0.142,respectively.The enhancement of the PFC performance was due to the outstanding photoelectric properties of ZnIn₂S₄/PANI composite,in which PANI,as a photosensitizer,promoted the absorption of visible-light by photoanode.The photoexcited electrons of ZnIn₂S₄and PANI tended to be directly transferred to the CB of TiO₂,while holes accumulated in the VB of PANI to participate in the oxidation reaction.The synergistic effect accelerated the separation of photogenerated electron-hole pair and improved the photoelectric conversion efficiency of PFC.3.ZnIn₂S₄/PPy/TiO₂/Ti composite photoanode was successfully prepared,and the optimum electrode preparation conditions were explored:the doping ratio of PPy was 3%,the calcination time was 120℃,and the calcination time was 2 h.The structural composition,microscopic morphology and optical properties of the prepared electrode were analyzed by XRD,FT-IR,SEM,XPS and DRS.The results showed that ZnIn₂S₄/PPy consisted of microspheres and amorphous particles with smaller sizes and widely bound in the surface and gaps of TiO₂layer,and the DRS results indicated that PPy could also be used as a photosensitive material to enhance the optical absorption of the composite photoanode in the visible region.By connecting the ZnIn₂S₄/PPy/TiO₂/Ti photoanode with Cu cathode to construct the PFC system,the optimum RhB treatment conditions were investigated:initial concentration was 10 mg/L,initial p H was 3.0.Under this condition,the RhB removal rate,open circuit voltage(V_oc),short circuit current density(J_sc),maximum power density(JV_max)and filling factor（FF）of the optimum PFC system were94.6%（1 h）,0.47 V,0.23 m A/cm²,21.10μW/cm²and 0.195,respectively.The results of the photocatalytic mechanism analysis showed that the improved performance of the PFC was attributed to the good visible-light response of ZnIn₂S₄/PPy and the presence of PPy can also acted as both electron donor and hole acceptor,providing an ideal path for the separation and transport of photogenerated carriers.4.In this thesis,the interfacial contacts between unequal energy band structures of photocatalytic semiconductor materials were used to fabricate organics-ZnIn₂S₄/TiO₂/Ti composite photoanode with heterogeneous structures,and three different PFC systems were constructed.The results show that organic materials had a positive contribution in enhancing the photocatalytic performance of PFC.Among them,the metal-organic framework（MOF）Ui O-66 provided additional reactive sites and fast electron transfer channels for the photocatalytic reaction due to its stable framework structure and large specific surface area,while the conducting polymers PANI and PPy mainly played the roles of light collector and synergistic promotion of efficient electron-hole pair separation in photocatalytic systems due to their high optical absorption coefficients in the UV-Vis region and narrow band gap characteristics.By comparison,ZnIn₂S₄/PPy/TiO₂/Ti-Cu PFC considered the best PFC system in this study.