Artificial photosynthesis for solar water-splitting

Journal name:
Nature Photonics
Volume:
6,
Pages:
511–518
Year published:
DOI:
doi:10.1038/nphoton.2012.175
Published online

Abstract

Hydrogen generated from solar-driven water-splitting has the potential to be a clean, sustainable and abundant energy source. Inspired by natural photosynthesis, artificial solar water-splitting devices are now being designed and tested. Recent developments based on molecular and/or nanostructure designs have led to advances in our understanding of light-induced charge separation and subsequent catalytic water oxidation and reduction reactions. Here we review some of the recent progress towards developing artificial photosynthetic devices, together with their analogies to biological photosynthesis, including technologies that focus on the development of visible-light active hetero-nanostructures and require an understanding of the underlying interfacial carrier dynamics. Finally, we propose a vision for a future sustainable hydrogen fuel community based on artificial photosynthesis.

At a glance

Figures

  1. Comparison between NPS and APS.
    Figure 1: Comparison between NPS and APS.

    a, NPS charge-separation processes, including type I and II reaction centres (simplified Z-scheme). P680: pigment (chlorophyll) that absorbs 680 nm light in photosystem II (PSII); P680*: the excited state of P680; P700: pigment (chlorophyll) that absorbs 700 nm light in photosystem I (PSI); P700*: the excited state of P700. Mn: manganese calcium oxide cluster; Tyr: tyrosine in PSII; Pheo: pheophytin, the primary electron acceptor of PSII; QA: primary plastoquinone electron acceptor; QB: secondary plastoquinone electron acceptor; PQ: plastoquinone; FeS: Rieske iron sulphur protein; Cyt. f: cytochrome f; PC: plastocyanin; A0: primary electron acceptor of PSI; A1: phylloquinone; FX, FA, FB: three separate iron sulphur centres; FD: ferredoxin; FNR: nicotinamide adenine dinucleotide phosphate (NADP) reductase. This Z-scheme process is driven by the absorption of two photons, one at PSII and the other at PSI. Light absorption at PSII creates P680*, which provides an electron to reduce pheophytin, and the step-wise electron transfer occurs from pheophytin to P700+ (the oxidizing species after the electron transfer from P700*). Following this initial electron transfer, P680+ can oxidize tyrosine and subsequently the manganese calcium oxide cluster. Light absorption at PSI creates P700*, which provides an electron to reduce A0 to FNR. A series of electron transfer pathways are indicated by black arrows. b,c, APS charge-separation processes: single-step reactions (b) and two-step (Z-scheme) reactions (c). P: chromophore of a single-step reaction system; P*: excited state of P; P1: the first chromophore of a two-step reaction system; P1*: excited state of P1; P2: second chromophore of a two-step reaction system; P2*: excited state of P2.

  2. Structural designs of APS reaction processes.
    Figure 2: Structural designs of APS reaction processes.

    a, Structure of the carotenoid–porphyrin–fullerene molecular dyad system. b, Single-step semiconductor particle with attached hydrogen- and oxygen-evolving co-catalysts. c, Two-step system: mixture of semiconductor particles with attached hydrogen- or oxygen-evolving co-catalyst and redox electrolyte couples. d, Single-excitation-step water-splitting cell, containing a semiconductor electrode with water oxidation co-catalysts and a counter-electrode to reduce water. e, Dye-sensitized transparent metal oxide water-splitting cell. f, Two-step tandem water-splitting cell. Inset of a reproduced with permission from ref. 24, © 2004 Wiley.

  3. New concepts of nanomaterial developments.
    Figure 3: New concepts of nanomaterial developments.

    a, Fabrication and characterization of a ZnOS nanowire array electrode on a fluorine-doped tin oxide (FTO) transparent conducting substrate. Top: the fabrication process. Bottom-left: scanning electron microscopy, transmission electron microscopy and selected area electron diffraction images of pristine ZnO nanowires. Bottom-centre: transmission electron microscopy images of ZnO nanowires covered in ZnS quantum dots. Bottom-right: elemental profiles extract from scanning transmission electron microscopy. b, High-resolution transmission electron microscopy images of black TiO2 nanocrystals with a disordered outer layer. Inset: Density of states of black TiO2 nanocrystals, as compared with that of unmodified TiO2 nanocrystals. Image courtesy of S. S. Mao, adapted from ref. 71. c, Combinatorial method to investigate the incorporation of titanium, silicon and aluminium on the performance of α-Fe2O3 photoanodes, including the template used for the printed pattern (left) and the corresponding photocurrent maps (right). Image courtesy of Bruce A. Parkinson. Figure reproduced with permission from: a, ref. 70, © 2011 Wiley; c, ref. 75, © 2011 ACS.

  4. Photo-induced charge separation and recombination of a semiconductor photoanode.
    Figure 4: Photo-induced charge separation and recombination of a semiconductor photoanode.

    a, Photoelectrochemical water-splitting cell employing a photoactive anodic electrode that induces a space-charge region at the semiconductor–solution interface. A photogenerated electron is separated from the interface and then consumed to generate hydrogen at the counter-electrode. A hole is generated at the interface and consumed for water oxidation reaction. b, Transient absorption data obtained for photogenerated holes in an α-Fe2O3 photoanode under a bias of −0.1 or +0.4 V relative to Ag/AgCl (ref. 91). Rapid decay under negative bias is due to electron–hole recombination. Under positive bias, the formation of a space-charge layer results in the generation of long-lived holes, which can oxidize water on a timescale of around 1 s.

  5. Vision of a sustainable hydrogen fuel community based on APS.
    Figure 5: Vision of a sustainable hydrogen fuel community based on APS.

    Hydrogen is produced from an APS solar water-splitting power plant using seawater on floating ports, tankers and seashore plants. Electricity needed to operate such an infrastructure is provided by renewable energy sources such as photovoltaic, wind and tidal power.

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Affiliations

  1. School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Bundoora, Victoria 3083, Australia

    • Yasuhiro Tachibana
  2. Japan Science and Technology Agency (JST), PRESTO, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan

    • Yasuhiro Tachibana
  3. Center for Advanced Science and Innovation (CASI), Osaka University, 2-1 Yamada-Oka, Suita, Osaka 565-0871, Japan

    • Yasuhiro Tachibana
  4. International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, School of Energy and Power Engineering, Xian Jiaotong University, Xi'an 710049, China

    • Lionel Vayssieres
  5. Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, UK

    • James R. Durrant

Contributions

Y.T. and L.V. contributed equally to this work. J.R.D. wrote the section on charge carrier dynamics and assisted in drafting other aspects of the manuscript. Y.T. organized the submission.

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The authors declare no competing financial interests.

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