Self-supported CdSe nanowire/nanosheet photoanodes on cadmium foil via in situ hydrothermal transformation of CdSe(en) _0.5 complex nanostructures

To solve energy crisis, the engineering of highly efficient and cost-effective photoanodes is urgently required for clean fuel generation. Herein, CdSe(en)_0.5 (en = ethylenediamine) hybrid photoanodes were synthesized by a solvothermal approach. It was revealed that a second in situ hydrothermal treatment successfully converts cadmium foil-based inorganic-organic CdSe(en)_0.5 (en = ethylenediamine) hybrid nanosheets to an oriented cadmium hydroxide crowned CdSe nanowire-decorated porous nanosheet (Cd(OH)₂/CdSe NW/NS) heterostructure by dissolution and regrowth mechanisms. The alteration in second hydrothermal reaction conditions could modify the morphology and optical properties of the Cd(OH)₂/CdSe NW/NS heterostructure photoanodes. The possible growth mechanism of the Cd(OH)₂/CdSe NW/NS porous structure is studied at various second hydrothermal times using the control experiments of the synthesis. The optimized 3D porous Cd(OH)₂/CdSe NW/NS photoanodes exhibited an outstanding photocurrent density of 6.1 mA cm^-2 at 0 V vs. Ag/AgCl, which is approximately 7.6 times higher than that of the inorganic-organic CdSe(en)_0.5 hybrid under light irradiation (>420 nm cut off filter). A mechanism is proposed to explain the enhanced charge separation at the Cd(OH)₂/CdSe NW/NS photoanode/electrolyte interface, which is supported by PL and photoelectrochemical analyses. These findings open an avenue of phase and morphology transmutation for efficient formation of other hierarchical structures of metal selenides and sulfides. Additionally, the Al₂O₃ co-catalyst can act as effective hole trapping sites and improves the stability of the photoelectrode through the timely consumption of photogenerated charges, particularly holes.