Layered Material-modified Semiconductor Photoelectrodes And Photoelectrochemical Water Oxidation Performance

Obtaining hydrogen from solar water splitting is one of the important way to develop clean energy.The overall water splitting includes two half reactions i.e.water reduction and oxidation,where water oxidation is regarded as the speed-limiting step.It is critical to design high-efficiency photoanodes for water splitting.The performance of the photo anodes is affected by three main factors i.e.the light harvesting,charge separation and charge transfer.It is of great importance to design the photoanodes capable of enhancing the efficiencies of these processes.Layered double hydroxides(LDHs)possess a unique two-dimensional layered structure with flexible chemical compositions.As a result,the catalytically active components can be incorporated LDHs to construct a variety of catalysts.Much attention has been paid to utilize LDHs as a water oxidation catalyst(WOC)when the first-row transitional metals are bonded in the layers of LDHs.This thesis focuses on the design of high-efficiency photoanodes using LDHs as a WOC.The light harvesting,charge separation and charge transfer efficiencies could be improved by the modification of semiconductor photoanodes.The major findings are below.1.A flower-like structured photoanode was constructed by the growth of a hybrid LDHs/graphene on the BiVO4 electrode(G@LDHs@BiVO4).The as-prepared photoanode achieved a photocurrent density of 2.13 mA·Cm-2(1.23 V vs.RHE),four times higher than the pristine BiVO4.The oxidation efficiency is beyond 80%even at a low potential(<0.8 V vs.RHE).The IPCE reached 52%at 400 nm.The enhancement was attributed to three folds.First,LDHs are excellent WOCs,expediting the oxidation kinetics.Second,the graphene has good charge transport properties,promoting photo-induced charge transfer.Third,the incorporation of graphene enhances the light absorption in the visible light regime.2.A new LDHs/Au@SiO2/BiVO4 photoanode was designed,where the localized surface plasmon resonance(LSPR)effect of Au@SiO2 was utilized.A control photoanode Au@SiO2/LDHs/BiVO4 was also prepared,where the LDHs were firstly grown on the BiVO4.The LDHs/Au@SiO2/BiV04 achieved a photocurrent density of 1.92 mA·cm-2(1.23 V vs.RHE),a 52%enhancement compared to the control(1.26 mA·cm-2).The oxidation efficiency of LDHs/Au@Si02/BiV04 was around 69%,1.3 times higher than that of Au@Si02/LDHs/BiV04.The findings verified that the BiV04 mainly contributes to charge separation and the LSPR is distance-dependent.LDHs acted as a WOC to accumulate photo-generated holes and accelerate water oxidation.Both LDHs and Au@SiO2 enhanced the water oxidation performance of the photoanode.