Abstract
Abstract The performance of free-standing parallel-aligned nanowire arrays and interconnected networks of single-crystalline cuprous oxide (Cu2O) coated with titanium oxide (TiO2) as photocathodes for solar energy harvesting was analyzed. The nanostructures were synthesized by electrodeposition in polymer membranes prepared by ion-track technology. To enhance the photoelectrochemical stability of the nanowires in aqueous solution, they were conformally coated with a 10 nm thick TiO2 layer by atomic layer deposition. The diameter, size, geometry and number density of the parallel nanowires were systematically varied. The generated photocurrents show a clear increase as a function of wire diameter and wire number. In turn, the photocurrent does not get larger with increasing wire length. Highly interconnected networks of nanowires under 45° from various directions enabled further increase of wire density number and exhibited higher photocurrent densities compared to parallel arrays.
Highlights
The efficient photoelectrolysis of water to form molecular hydrogen and oxygen is being intensively investigated as a direct way to store solar energy as chemical fuel [1]
In this paper we focus on the synthesis and characterization of nanowirebased Cu2O/TiO2 photocathodes obtained by ion-track technology combined with electrodeposition
The electrodeposition process during the potentiostatic growth of the Cu2O nanowires is characterized by four different regimes: (1) nucleation and subsequent creation of a diffusion layer, indicated by the sharp initial current peak; (2) nanowire growth inside the nanochannels at nearly constant current; (3) start of cap growth identified by pronounced current increase when Cu2O reaches the top end of the channels and forms caps on the surface of the membrane; and (4) merging of neighboring caps resulting in a closed film if the process is continued [39]
Summary
The efficient photoelectrolysis of water to form molecular hydrogen and oxygen is being intensively investigated as a direct way to store solar energy as chemical fuel [1]. It is well known that the way to efficient solar water splitting is challenging and that, in spite of the intensive and productive research efforts in recent years, numerous aspects still need to be optimized This includes: (i) the synthesis of high quality semiconductor materials at moderate costs. Systematic photoelectrochemical measurements with controlled variation of the relevant wire dimensions have not been yet reported, they are essential to understand and optimize the physical processes accompanying the water splitting reaction. In most cases this is due to limited control and lack of flexibility of the applied synthesis techniques. The photocurrent generated during photoelectrochemical measurements is analyzed as a function of the geometrical wire parameters
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