Photoelectrocatalytic Oxidation Of Glycerol By Bismuth Vanadate Photoanode

Glycerol is the main by-product of biodiesel production.Due to the increasing production of biodiesel,there is a significant surplus of glycerol in the global market.The transformation of glycerol to value-added oxidation products has attracted extensive attention.Traditional industrial glycerol oxidation is realized through microbial fermentation,which is limited by long production cycles and difficulties in product separation.Photoelectrocatalytic（PEC）glycerol oxidation has been attracting increasing attention due to its green,mild reaction conditions,and low catalyst cost.The key to PEC glycerol oxidation is to develop photoanodes with high activity and stability.BiVO₄ is widely investigated in PEC water splitting and alcohols oxidation due to its suitable valence band position and good electrical conductivity.However,it still suffers from low carrier separation efficiency,poor PEC stability,and poor selectivity towards valuable products.In this dissertation,BiVO₄ was modified by Mo,N-codoping to improve its PEC performance for glycerol oxidation.The mechanism behind the boosted activity and stability are systematically investigated through comprehensive characterization methods and theoretical calculations.The adsorption and reaction behavior of different alcohols on BiVO₄ were further explored to probe the reasons behind the low selectivity of BiVO₄ towards C3 products.The main research contents and innovative results are as follows:1)The unsual trend of increased PEC glycerol oxidation activity with decreasing electrolyte p H was investigated and the optimal p H condition for the reaction was established as the p H of the isoelectric point of BiVO₄（p H=2）.The activity and stability of BiVO₄ under this acidic condition were improved by Mo and N codoping.The reason for the improved performance was thoroughly investigated.The glycerol oxidation current density on N,Mo-BiVO₄ reaches 5.5 m A cm^-2 at 1.23 V_RHEand was stable for over 20 h of reaction,which is the best performance reported so far PEC for glycerol oxidation.2)To investigate the reasons behind the low selectivity of glycerol oxidation on BiVO₄,The adsorption and reactivity behavior of alcohol molecules with different numbers and position of hydroxyl groups were explored.It was found that monoalcohols and polyols without vicinal hydroxyl groups were adsorbed on the surface of BiVO₄ through the hydrogen bonding between the H atom of the alcohol molecule and the O atom of BiVO₄.In contrast,the alcohol molecules containing vicinal dihydroxyl groups are adsorbed on the surface of BiVO₄ through the coordination between the two O atoms of the adjacent hydroxyl group and the Bi atom of BiVO₄ as well as the hydrogen bond between the H atom of the hydroxyl group and the O atom of BiVO₄.This configuration is conducive to the adsorption and reaction of alcohol molecules on the surface of BiVO₄.However,the strong interaction of the alcoholwith BiVO₄ may weaken the carbon skeleton,leading to C–C bond cleavage and over-oxidation.