Modification And Electrocatalytic Properties Of Oriented TiO₂ Nanostructires On Carbon Electrode

Microbial fuel cell?MFC?is a green energy device,which decomposes organic matter by metabolic activity of electrochemically active microorganism,and releases the electrons to the electrode by extracellular electron transfer?EET?process to realize the conversion of the chemical energy to electric energy.Anode material and its surface properties are the key factors affecting the overall performance of MFC.Surface modification is an effective technical method to optimize the power output of an anode by improving interface electron transfer ability between electrode and the microorganism.TiO₂ nanomaterials have been widely used for their excellent stability,environmental compatibility and various structural characteristics.In this paper,the performance of carbon paper electrodes with decorated TiO₂ nanostructures is improved by surface treatment technology.It is found that ammonia water treatment and ammonia gas treatment could effectively change the surface properties of rutile TiO₂ nanorods as well as anatase nanosheets that increase the current output of S.loihica PV-4,demonstrating ammonia water treatment is a simple and effective technology for surface modification of nano TiO₂ electrodes.1.Rutile TiO₂ nanorods were grown on the surface of carbon paper by hydrothermal method to give TiO₂ NRs/CP electrode and then treated by ammonia water with different concentrations to obtain NH₄OH-TiO₂ NRs/CP.It is found that without changing surface morphology of the electrode,ammonia water treatment induces larger current of Shewanella loihica PV-4.On the best electrode that treated in 4 M ammonia water,the PV-4 current increases by 2.5 times than that on untreated TiO₂ NRs/CP electrode.This attributes that electrode surface changes from hydrophobicity to superhydrophilic after the treatment.The alteration of surface chemical state is beneficial to the growth of bacteria,and also electrochemical active of riboflavin,thus improves flavin mediated indirect electron transfer.2.At 550?C,TiO₂ NRs/CP was heated in NH₃ atmosphere to obtain NTiO₂ NRs/CP electrode.This treatment also changes the surface chemical state of TiO₂ NRs,and the contact angle of NTiO₂ NRs/CP electrode?47.96??was reduced compared to TiO₂ NRs/CP electrode?127.5^°?.Correspondingly,the current density of NTiO₂ NRs/CP increases by 1.7 times relative to TiO₂ NRs/CP after inoculating PV-4.The NTiO₂ NRs/CP electrode is further treated by 4M ammonia water,and the obtained N-NH₄OH-TiO₂ NRs/CP electrodes become superhydrophilic.As a result,the interfacial electron transfer rate of riboflavin is faster and the current of PV-4on N-NH₄OH-TiO₂ NRs/CP is further enhanced.3.Up-standing anatase TiO₂ nanosheets were prepared on carbon paper to give TiO₂NSs/CP electrode.The electrode was then treated by 4M ammonia water to obtain NH₄OH-TiO₂ NSs/CP electrode.The process also introduces N-containing species on NH₄OH-TiO₂NSs/CP and changes local surface microenvironment of the electrode,thus is benefical to the EET via complex of outer membrane cytochrome c protein with riboflavin.After ammonia water treatment,the PV-4 current is increased by 20%on NH₄OH-TiO₂ NSs/CP electrode.