ZnO/CuO heterojunction branched nanowires for photoelectrochemical hydrogen generation.

We report a facile and large-scale fabrication of three-dimensional (3D) ZnO/CuO heterojunction branched nanowires (b-NWs) and their application as photocathodes for photoelectrochemical (PEC) solar hydrogen production in a neutral medium. Using simple, cost-effective thermal oxidation and hydrothermal growth methods, ZnO/CuO b-NWs are grown on copper film or mesh substrates with various ZnO and CuO NWs sizes and densities. The ZnO/CuO b-NWs are characterized in detail using high-resolution scanning and transmission electron microscopies exhibiting single-crystalline defect-free b-NWs with smooth and clean surfaces. The correlation between electrode currents and different NWs sizes and densities are studied in which b-NWs with longer and denser CuO NW cores show higher photocathodic current due to enhanced reaction surface area. The ZnO/CuO b-NW photoelectrodes exhibit broadband photoresponse from UV to near IR region, and higher photocathodic current than the ZnO-coated CuO (core/shell) NWs due to improved surface area and enhanced gas evolution. Significant improvement in the photocathodic current is observed when ZnO/CuO b-NWs are grown on copper mesh compared to copper film. The achieved results offer very useful guidelines in designing b-NWs mesh photoelectrodes for high-efficiency, low-cost, and flexible PEC cells using cheap, earth-abundant materials for clean solar hydrogen generation at large scales.

[1]  M Bonn,et al.  Local field effects on electron transport in nanostructured TiO2 revealed by terahertz spectroscopy. , 2006, Nano letters.

[2]  Yichuan Ling,et al.  Sn-doped hematite nanostructures for photoelectrochemical water splitting. , 2011, Nano letters.

[3]  M. Graetzel,et al.  New Benchmark for Water Photooxidation by Nanostructured α‐Fe2O3 Films. , 2007 .

[4]  Benjamin J. Hansen,et al.  Transport, Analyte Detection, and Opto-Electronic Response of p-Type CuO Nanowires , 2010 .

[5]  Vincent Laporte,et al.  Highly active oxide photocathode for photoelectrochemical water reduction. , 2011, Nature materials.

[6]  Shaohua Shen,et al.  A perspective on solar-driven water splitting with all-oxide hetero-nanostructures , 2011 .

[7]  Liejin Guo,et al.  Vertically aligned WO₃ nanowire arrays grown directly on transparent conducting oxide coated glass: synthesis and photoelectrochemical properties. , 2011, Nano letters.

[8]  J. A. Seabold,et al.  Effect of a Cobalt-Based Oxygen Evolution Catalyst on the Stability and the Selectivity of Photo-Oxidation Reactions of a WO3 Photoanode , 2011 .

[9]  Nripan Mathews,et al.  Ultrathin films on copper(I) oxide water splitting photocathodes: a study on performance and stability , 2012 .

[10]  Alireza Kargar,et al.  3D branched nanowire heterojunction photoelectrodes for high-efficiency solar water splitting and H2 generation. , 2012, Nanoscale.

[11]  Xiaobo Chen,et al.  Increasing Solar Absorption for Photocatalysis with Black Hydrogenated Titanium Dioxide Nanocrystals , 2011, Science.

[12]  Peng Wang,et al.  Highly stable copper oxide composite as an effective photocathode for water splitting via a facile electrochemical synthesis strategy , 2012 .

[13]  G. Gary Wang,et al.  Hydrogen-treated WO3 nanoflakes show enhanced photostability , 2012 .

[14]  Yichuan Ling,et al.  The influence of oxygen content on the thermal activation of hematite nanowires. , 2012, Angewandte Chemie.

[15]  E. Thimsen,et al.  Plasmonic solar water splitting , 2012 .

[16]  Kijung Yong,et al.  Fabrication of CuO-ZnO nanowires on a stainless steel mesh for highly efficient photocatalytic applications. , 2011, Chemical communications.

[17]  Leonardo C. Campos,et al.  On the growth and electrical characterization of CuO nanowires by thermal oxidation , 2009 .

[18]  Chia-Ying Chiang,et al.  Biological templates for antireflective current collectors for photoelectrochemical cell applications. , 2012, Nano letters.

[19]  H. Hng,et al.  Epitaxial Growth of Branched α‐Fe2O3/SnO2 Nano‐Heterostructures with Improved Lithium‐Ion Battery Performance , 2011 .

[20]  G. Jung,et al.  3D Branched nanowire photoelectrochemical electrodes for efficient solar water splitting. , 2013, ACS nano.

[21]  H. Fan,et al.  Branched nanowires: Synthesis and energy applications , 2012 .

[22]  P. Salvador,et al.  Hole diffusion length in n‐TiO2 single crystals and sintered electrodes: Photoelectrochemical determination and comparative analysis , 1984 .

[23]  Peng Wang,et al.  CuO/ZnO core/shell heterostructure nanowire arrays: synthesis, optical property, and energy application. , 2010, Chemical communications.

[24]  Peng Wang,et al.  ZnO-coated CuO nanowire arrays: fabrications, optoelectronic properties, and photovoltaic applications. , 2011, Optics express.

[25]  Yichuan Ling,et al.  Hydrogen-treated TiO2 nanowire arrays for photoelectrochemical water splitting. , 2011, Nano letters.

[26]  Anna N. Ivanovskaya,et al.  A Cu2O/TiO2 heterojunction thin film cathode for photoelectrocatalysis , 2003 .

[27]  Liejin Guo,et al.  Nanostructured WO₃/BiVO₄ heterojunction films for efficient photoelectrochemical water splitting. , 2011, Nano letters.

[28]  Z. Yin,et al.  Full Solution‐Processed Synthesis of All Metal Oxide‐Based Tree‐like Heterostructures on Fluorine‐Doped Tin Oxide for Water Splitting , 2012, Advanced materials.

[29]  S. Zaman,et al.  Optical and current transport properties of CuO/ZnO nanocoral p–n heterostructure hydrothermally synthesized at low temperature , 2012 .

[30]  Chun Xing Li,et al.  Solution synthesis of large-scale, high-sensitivity ZnO/Si hierarchical nanoheterostructure photodetectors. , 2010, Journal of the American Chemical Society.

[31]  Michael Grätzel,et al.  Light-induced water splitting with hematite: improved nanostructure and iridium oxide catalysis. , 2010, Angewandte Chemie.

[32]  J. Moon,et al.  Fabrication of 3D copper oxide structure by holographic lithography for photoelectrochemical electrodes. , 2010, ACS applied materials & interfaces.

[33]  Xingjiu Huang,et al.  ZnO/CuO hetero-hierarchical nanotrees array: hydrothermal preparation and self-cleaning properties. , 2011, Langmuir : the ACS journal of surfaces and colloids.

[34]  Xiaolin Zheng,et al.  Branched TiO₂ nanorods for photoelectrochemical hydrogen production. , 2011, Nano letters.

[35]  P. D. Jongh,et al.  Cu2O: Electrodeposition and Characterization , 1999 .

[36]  W. Li,et al.  Efficient photocatalytic hydrogen evolution over hydrogenated ZnO nanorod arrays. , 2012, Chemical communications.

[37]  G. Jung,et al.  Tailoring n-ZnO/p-Si branched nanowire heterostructures for selective photoelectrochemical water oxidation or reduction. , 2013, Nano letters.

[38]  Anke Weidenkaff,et al.  Photoelectrochemical water splitting with mesoporous hematite prepared by a solution-based colloidal approach. , 2010, Journal of the American Chemical Society.

[39]  Younan Xia,et al.  CuO Nanowires Can Be Synthesized by Heating Copper Substrates in Air , 2002 .

[40]  Peidong Yang,et al.  Nanowire dye-sensitized solar cells , 2005, Nature materials.

[41]  Ning Wang,et al.  Controllable Fabrication of Three-Dimensional Radial ZnO Nanowire/Silicon Microrod Hybrid Architectures , 2011 .

[42]  Fang Qian,et al.  Nitrogen-doped ZnO nanowire arrays for photoelectrochemical water splitting. , 2009, Nano letters.

[43]  Yongcai Qiu,et al.  Secondary branching and nitrogen doping of ZnO nanotetrapods: building a highly active network for photoelectrochemical water splitting. , 2012, Nano letters.

[44]  Hao Gong,et al.  Hierarchical assembly of ZnO nanostructures on SnO(2) backbone nanowires: low-temperature hydrothermal preparation and optical properties. , 2009, ACS nano.

[45]  Peidong Yang,et al.  Light trapping in silicon nanowire solar cells. , 2010, Nano letters.

[46]  K. Sun,et al.  Solution-grown 3D Cu2O networks for efficient solar water splitting , 2014, Nanotechnology.