Selective Electro-oxidation Of Phenol To Prepare Electrode Materials With High Capacitance

Polyaniline?PANI?-based conductive polymers are promising capacitive electrode materials,but they suffer the common hurdle of poor cycling stability due to structural rupture during the doping and undoping process.Phenol,a highly toxic substance,widely exists in various industrial wastewaters.Electrochemical oxidative process for the degradation of phenol can result in the formation of benzoquinone?BQ?/hydroquinone?HQ?with reversible redox activity.However,the side reaction of phenol electrochemical oxidation leads to the generation of an insulating layer on the electrode,which can passivate the electrode and hinder the further degradation of phenol.In this study,we attempt to achieve selectively electrocatalytic oxidation of phenol to BQ/HQ using the PANI electrode?PANI-GB?,which can substantially enhance the the capacitance and cycling stability of PANI.PANI can effectively catalyze the electro-oxidization of phenol to BQ and HQ with high selectivity.Meanwhile,BQ/HQ deposited on PANI can significantly improve the electrode's specific capacitance and charge–discharge cycling stability.The first effort is made to prepare the PANI electrode and apply it to support the selectively electrocatalytic oxidation of phenol,resulting in the formation of the P/n-PANI-GB electrode?n represents the cycle number?.The results indicate that the peak current representing the redox behavior of BQ/HQ as a consequence of phenol electro-oxidization on the PANI electrode significantly increases with the cyclic voltammetry?CV?scans.The selectivity of BQ/HQ reaches an inflection point at cycle 40,showing a maximum value of 71.20%.The specific capacitance of the P/40-PANI-GB is 553 F?g^-1,with 88%capacitance retained after 2000 consecutive charge–discharge cycles,which are both higher than the PANI-GB electrodes(424 F g^-1 and 51%,respectively)without the decoration of BQ/HQ.The second attempt is made to clarify the reasons for the increased capacitance and cycle stability,by investigating the interaction between the phenol-oxidized products and the conductive polymer.It is found that the incorporation of phenol-oxidized products in the PANI matrix enlarges the surface area.BQ/HQ is a second redox system introduced in the electrode,which improves the capacitance and cycle due to the strong interactions??–?stacking,hydrogen bonding,and chemical doping?between PANI and BQ/HQ.The performance of a microbial fuel cell?MFC?using the resultant material as the anode was examined.The MFC equipped with the P/40-PANI-GB anode delivers higher power output as compared to that with the PANI-GB anode,because the presence of pseudocapacitive species?BQ/HQ?substantially increases extracellular electron transfer and enhances bacterial adhesion on the anode.On the whole,we have successfully demonstrate that the PANI-GB electrode is effective in selectively catalyzing phenol conversion to BQ/HQ with redox activity and significantly alleviating the passivation effect.Meanwhile,the strong interactions??–?stacking,hydrogen bonding,and chemical doping?between PANI and BQ/HQ can improve the electrode's specific capacitance and charge–discharge cycling stability,and boost the power output of the MFC.These findings might provide insights into the resource recovery from phenol in the wastewater and the improvement of cycling stability of conductive polymers using the electrochemical oxidation technology.