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Identifying champion nanostructures for solar water-splitting

Abstract

Charge transport in nanoparticle-based materials underlies many emerging energy-conversion technologies, yet assessing the impact of nanometre-scale structure on charge transport across micrometre-scale distances remains a challenge. Here we develop an approach for correlating the spatial distribution of crystalline and current-carrying domains in entire nanoparticle aggregates. We apply this approach to nanoparticle-based α-Fe2O3 electrodes that are of interest in solar-to-hydrogen energy conversion. In correlating structure and charge transport with nanometre resolution across micrometre-scale distances, we have identified the existence of champion nanoparticle aggregates that are most responsible for the high photoelectrochemical activity of the present electrodes. Indeed, when electrodes are fabricated with a high proportion of these champion nanostructures, the electrodes achieve the highest photocurrent of any metal oxide photoanode for photoelectrochemical water-splitting under 100 mW cm−2 air mass 1.5 global sunlight.

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Figure 1: Photoelectrochemical response of nanostructured haematite electrodes.
Figure 2: Classical structure analysis by SEM and BF-TEM.
Figure 3: Identification of champion nanostructures.
Figure 4: Imaging the crystalline structure of nanoparticle aggregates.
Figure 5: Analysis of charge transport by C-AFM.
Figure 6: Modelling the water-splitting photocurrent for electrodes with grain boundaries.

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Acknowledgements

The authors acknowledge support of this research by the European Commission (Nanostructured Photoelectrodes for Energy Conversion, NanoPEC, contract number 227179) and the Swiss Federal Office for Energy (PECHouse Competence Center, contract number 152933). M.G. thanks the European Research Council (ERC) for funding part of this work under the advanced research grant (ARC) 247404 ‘Mesolight’. We thank E. Thimsen, C. Koch, T. Mason, U. Wiesner, D. Gamelin, M. Hersam and R. van de Krol for helpful discussions.

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Contributions

S.C.W. conceived most experiments and performed the electrochemical and electron microscopy measurements. K.V. performed the C-AFM measurements, performed statistical analyses and, with F.S., analysed these results. A.R. and H.D. conceived and developed the photocurrent model. S.C.W. and C.H. analysed the DF-TEM data. C.M.L. measured the macroscopic electrical properties of electrodes. M.C. prepared electrodes. S.C.W. and M.G. analysed the electrochemical data. S.C.W. wrote most of the manuscript; K.V. wrote sections on C-AFM. All authors contributed to revisions.

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Correspondence to Scott C. Warren.

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Warren, S., Voïtchovsky, K., Dotan, H. et al. Identifying champion nanostructures for solar water-splitting. Nature Mater 12, 842–849 (2013). https://doi.org/10.1038/nmat3684

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