Synthesis Of Multi-layer Photocathodes For Photoelectrochemical Hydrogen Evolution

The fossil energy depletion and environmental pollution are two challenges that limiting the sustainable development of human society and economy in the 21st century.Hydrogen evolution has attracted great interest as an effective way of converting sunlight into chemical energy in the form of hydrogen,which is green,environmental friendly and sustainable.Photoelectrochemical?PEC?water splitting is an emerging hydrogen production technology by utilizing the solar light.This technology integrates in the same device both solar energy collection and water electrolysis.Both photo-active semiconductor and catalysts for hydrogen evolution reaction?HER?are necessary in this device.In order to promote the solar energy conversion efficiency,the essential way is to explore proper photocatalysts for the target photocatalytic reactions.On the basis of new trends of photoelectrocatalysis research,the object of the dissertation is to develop photoelectrocatalysts for capturing solar energy and investigate their photoelectrocatalytic activities for exploring the potential application value in new energy field.In the dissertation,we have synthesized several kinds of nanostructured Cu₂O?Ti O₂?g-C₃N₄?WS₂ via electrochemical deposition,drop-casting method,and systematically investigated their photoelectrocatalytic activities.It can be summarized as follows.?1?The Cu₂O film was first prepared on FTO by electro-deposition method.After optimization,electrodeposition process was the performed at 65?at a constant bias of-0.4V vs Ag/AgCl for 60 min.The pH of the solution need to be adjusted to 11.0.G-C₃N₄ was prepared by polycondensation.Then g-C₃N₄ then loaded on the surface of Cu₂O by dip-coating and WS₂ used as HER catalysts.This photocathode is effective for photoelectrochemical hydrogen evolution,and a photocurrent of-9.5 mA?cm^-2 at-0.55V versus RHE?pH 6.0?can be obtained under visible light(?>420 nm,100 mW?cm^-2)and its overpotencail is-0.23 V?vs RHE?at pH=6.0.?2?To compare semiconductor on photoelectrochemical hydrogen evolution,Au/Cu₂O/TiO₂/WS₂ was fabricated.By optimizing the different processing parameters,Au film were acquired.The optimal parameters were as follows:the concentrantion of HAuCl₄ is 1.25 mM;a constant bias of-1 V vs Ag/AgCl;depositing time is 300 s.After loading TiO₂ on Cu₂O by dip-coating,a photocurrent of Au/Cu₂O/TiO₂/WS₂photocathode is-9.1 mA?cm^-2 at-0.6 V versus RHE?pH 6.0?under visible light(?>420nm,100 mW?cm^-2).?3?Cu₂O/g-C₃N₄/WS₂ triple-layer photocathode was fabricated using a layer-by-layer assemble method for photoelectrochemical hydrogen evolution.Cu₂O was electrodeposited on the FTO as active layer for light harvesting.The chemical inert g-C₃N₄ or TiO₂ can protect the unstable Cu₂O layer and form p-n junction with Cu₂O to increase the light-to-electricity conversion efficiency.Mixed phase WS₂ nanosheets were obtained by lithium insertion method and used as effective hydrogen evolution catalyst for photocurrent-to-hydrogen conversion.The Au/Cu₂O/TiO₂/WS₂photocathode increase the light-to-electricity conversion efficiency and has a good stability.This photocathode is effective for photoelectrochemical hydrogen evolution.