SYNTHESIS AND PHOTOELECTROCHEMICAL PROPERTIES OF SU2O-CU3VO4 COMPOSITE FILMS

Abstract

Cu2O-Cu3VO4 films were obtained by elect­rochemical synthesis. The analysis of polarization curves and Pourbaix diagrams for copper and vanadium ions made it possible to analyze the possible reactions that occur during the deposition of films. At potentials from 0  to -0.2V, mainly monovalent copper oxide Cu2O with Cu3VO4 impurities precipitated in the working solution. At the same time, there are two competing processes of acidification of the near-electrode layer as a result Cu2O formation reaction and alkalinization as a result of the chemical interaction of Cu2O with HVO42-. The formation of an excess of OH- ions can inhibit the reaction rate of the formation of  Cu3VO4, accelerating the reaction of the formation of Cu2O. Thus, deposition of Cu3VO4 will take place to a lesser extent compared to Cu2O. Accordingly, to increase the yield of  Cu3VO4, an attempt was made to reduce the deposition current, which, according to literature, helps to reduce the effect of the pH change near the electrode layer. Where, as known the critical current limit at change pH starts from  5 or more mA/cm2. For the synthesis of the films, a current of up to 1 mA/cm2 selected, which contributed to the production of the Cu3VO4 - Cu2O composite, as was established further from the analysis of X-ray patterns. It is shown that their photoelectrochemical pro­perties depend on the heat treatment conditions. This is expressed by the difference in the spectral characteristics of the quantum yield and the value of the photocurrent in the samp­les annealed in air and argon. Using the X-ray phase analysis method, it was established that heat treatment in argon contributes to the formation of a Cu3VO4 and Cu2O composite, in contrast to heat treatment in air, where a mixture of CuO and V2O5 oxides is mainly formed. In the film annealed in air due to impact of wide-band oxide compounds, a smaller value of the quantum yield of the photoelectrochemical current and a narrower spectral dependence were observed. The stretching of the spectrum into the region of visible light on the spectral curves of the photocurrent quantum yield is caused by the contribution of copper vanadate with Eg = 1.5 eV. Analysis of photo­current quantum output spectra and X-ray patterns showed that an increase in monovalent copper in the film structure contributes to the growth of photocurrent in the wavelength range of 450-600nm at a potential of -0.2 relative. h.s.e in 2 times. This indicates a positive effect of heat treatment in argon on increasing the efficiency of photocathodes based on a composite of Cu3VO4 and Cu2O for photoelectrochemical cells.