Research On Construction And Photoelectrochemical Properties Of Co₃O₄-based Heterojunction Composite Structures

Clean and high-energy hydrogen is produced by using abundant solar energy and water via photoelectrochemical(PEC)water splitting,which can solve the both of environmental and energy problems,causing scientists extensive attentions.The semiconductor photoelectrode is critical in the PEC water splitting system,meanwhile the response and absorption of sunlight as well as the separation and transportion of photogenerated carriers are key to the semiconductor photoelectrode.This paper studied p-type Co3O4 as photocathode material applied in PEC water splitting.Co3O4 films with different morphologies were prepared on indium tin oxide(ITO)glass substrate via both hydrothermal method and annealing process.The reaction process and specific formation mechanism of Co3O4 nanowires(NWs),Co3O4 nanosheets(NSs),Co3O4 nanoparticles(NPs)and Co3O4 nanocubes(NCs)were studied by using different precursors,reaction time and additives.And the effects of specific morphologies of Co3O4 on the PEC properties were also have been analyzed and discussed in detail.Based on the one-dimensional(1D)structure with high carriers transport efficiency,the 1D Co3O4 NWs were ameliorated.1D Co3O4/Cu O heterojunction was fabricated by electrochemical deposition method and thermal oxidation method to broaden the photoresponse range and to improve the transport separation performance of carriers.The co-catalyst Ag nanoparticles were loaded on the surface of 1D Co3O4/Cu O heterojunction to further enhance the transport separation performance of carriers via chemical bath process.The morphology,structure and PEC properties of the as-prepared samples were characterized.The effect of morphology,the mechanisms of heterojunction and co-catalyst on the PEC performance of photoelectrode were investigated.The results show that Co3O4 with different morphologies can be obtained by controlling different precursors,reaction time and adding different additives during the hydrothermal process.The photocurrent densities of Co3O4 NWs,Co3O4 NSs,Co3O4 NPs and Co3O4 NCs photocathodes were-0.40 m A/cm2?-0.28 m A/cm2?-0.22 m A/cm2 and-0.69 m A/cm2 at-0.2 V vs.RHE,respectively.Based on the 1D Co3O4 NWs with high carriers transport efficiency,Cu O nanoparticles were loaded on 1D Co3O4 NWs to construct 1D Co3O4/Cu O heterojunction as a photocathode applied for the PEC water splitting to generate hydrogen and its photocurrent density achieved to-1.55 m A/cm2(-0.20 V vs.RHE),which was 3.9 times that of the 1D Co3O4 NWs.This should be attributed to the narrower band gap of Cu O,which broadened the light response range and enhanced light absorption.As well as,the constructed heterojunction facilitated the separation and transport of carriers.The co-catalyst Ag nanoparticles were further loaded on 1D Co3O4/Cu O heterojunction.The photocurrent density of the 1D Co3O4/Cu O/Ag composite photocathode achieved to-5.13 m A/cm2 at-0.2 V vs.RHE,which was roughly 12.8 times that of the 1D Co3O4 NWs.This was mainly due to that Ag nanoparticles can capture up photogenerated electrons and further enhance the separation of carriers as well as suppress carriers recombination effectively.