Preperation And Photoelectrochemical Properties Of Cu₂O Film Homoiunction And N-Cu₂O/p-Cu₂O Nanocomposite

In recent years, with the worsening energy crisis and the emergence of soot-black air, traditional energy is being increasingly questioned. In response to the energy crisis and environmental pollution problems of traditional fossil energy, the research and development of new clean and renewable energy technologies is much-needed. Solar and hydrogen are both new green pollution energy, which have received widespread concern. The photoelectrochemical water splitting technology combines the use of solar energy and the preparation of hydrogen, which is cheaper and more energy-saving than traditional electric decomposition of water to hydrogen. Cuprous oxide (Cu2O) is a p-type direct band gap semiconductor with band gap of about 2.0 eV, which is conducive to the absorption of visible light. The theory photoelectric conversion efficiency of Cu2O is about 18%. Furthermore, the position of conduction band in Cu2O materials is very beneficial to reduction H2O to H2. Therefore CU2O has great potential as the photoelectrochemical water splitting photocathode material. However, the minority carrier diffusion length of CU2O is only 20-100 nm, leading to the composite of light-generated carriers happen easily, which limits the photoelectrochemical performance of CU2O materials. To improve the carrier separation efficiency, an efficient way is to construct p-n composite structures with n-type semiconductors. Since means of growing n-Cu2O are very limited, there are few previous reports about CU2O homojunction, and most of the previous CU2O p-n composite based PEC electrodes were prepared by coupling p-Cu2O to an intrinsic n-type semiconductor. However, homojunction based devices are generally expected to present better performance than heterojunction based devices. In 2009, n-Cu2O film was successfully produced electrochemically using a slightly acidic medium by McShane and Choi, after which the elecrodeposition of CU2O homojunction has become a hotspot. The pairing of n-type CU2O material with p-Cu2O to form a p-n CU2O composite is thought to be a potential way to improve the photovoltaic and PEC performance of CU2O materials. Currently, the conversion efficiency of CU2O homojunction solar cell has reached 1.06%, while the research and application of CU2O homojunction in photoelectrochemical area has not yet received enough attention.In this paper, two kinds of p-n CU2O composite photoelectrodes were fabricaitoned: the CU2O thin film homojunction electrode and the Pt/n-Cu2O/p-Cu2O nanocomposite photoelectrode. And the morphology, band structure and photoelecchemical properties of them were analysised and studied. Photoelectrochemical properties of Cu2O photoelectrodes were characterized by photocurrent under potential of 0 V vs. NHE (Normal Hydrogen Electrode). The main contents are as follows:(1) P-Cu2O film was grown on FTO substrate by electrochemical deposition. The effects of deposition parameters on the morphology, carrier density, band structure, and photoelectrochemical properties of p-Cu2O film were explored. The p-Cu2O film with best photoelectrochemical performance was abtained by optimizing growth parameters, photocurrent density of which is -0.1 mA·cm-2 at 0 V vs. NHE.(2) N-Cu2O film was electrodeposited on FTO substrate, and the preparation parameters were explored. Cu2O film homojunction was prepared through electrodepositing n-Cu2O film on the top of optimized p-Cu2O film. The influence of deposition parameters of n-Cu2O film on the photoelectrochemical properties of Cu2O homojunction was studied. The photocurrent of Cu2O homojunction is -0.5 mA·cm-2, which is 4 times larger than the photocurrent of bare p-Cu2O film.(3) Cu2O nanostructure film was prepared by thermal decomposition of Cu(OH)2 precursor. N-Gu2O/p-Cu2O nanocomposite film was grown by electrodepositing n-Cu2O nanoparticels on the Cu2O nanostructure film. The effects of precursor preparation parameters, annealing conditions, and deposition time of n-type Gu2O on the photoelectrochemical properties of n-Cu2O/p-Cu2O nanocomposite photoelectrode were researched, and the preparation parameters were optimized. Furthermore, Pt particels were modified on the n-Cu2O/p-Cu2O nanocomposite to improve the photoelectrochemical properties and stability of n-Cu2O/p-Cu2O nanocomposite. Photocurrent density of optimized Pt/n-Cu2O/p-Cu2O composite photoelectrode reached-0.6 mA·cm-2 under the test potential of 0 V vs. NHE, better than the p-Cu2O film and Cu2O homojunction photoelectrodes.