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Long-term solar water and CO2 splitting with photoelectrochemical BiOI–BiVO4 tandems


Photoelectrochemical (PEC) devices have been developed for direct solar fuel production but the limited stability of submerged light absorbers can hamper their commercial prospects.1,2 Here, we demonstrate photocathodes with an operational H2 evolution activity over weeks, by integrating a BiOI light absorber into a robust, oxide-based architecture with a graphite paste conductive encapsulant. In this case, the activity towards proton and CO2 reduction is mainly limited by catalyst degradation. We also introduce multiple-pixel devices as an innovative design principle for PEC systems, displaying superior photocurrents, onset biases and stability over corresponding conventional single-pixel devices. Accordingly, PEC tandem devices comprising multiple-pixel BiOI photocathodes and BiVO4 photoanodes can sustain bias-free water splitting for 240 h, while devices with a Cu92In8 alloy catalyst demonstrate unassisted syngas production from CO2.

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Fig. 1: Performance of the individual PV and electrocatalytic components of the BiOI photocathodes.
Fig. 2: Photoelectrochemistry of the BiOI photocathodes.
Fig. 3: PEC performance of the BiOI–BiVO4 tandem devices.

Data availability

The raw data that support the findings of this study are available from the University of Cambridge data repository36:


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We acknowledge I. Aldawood and A. Althumali for TEM specimen preparation and Z. Sun for aid with BiOI deposition. This work was supported by: the OMV Group (V.A. and E.R.); the Cambridge Trusts (Vice-Chancellor’s Award), the Winton Programme for the Physics of Sustainability, Cambridge Philosophical Society, Trinity College, St John’s College (Title A Research Fellowship; V.A.); an EPSRC Department Training Partnership studentship (EP/N509620/1) and Bill Welland (R.A.J.); a Marie Sklodowska-Curie Individual European Fellowship (SolarFUEL, GAN 839763) and a SNSF EPM Fellowship (P2BEP2_184483; M.R.); the Royal Academy of Engineering under the Research Fellowships scheme (no. RF\201718\1701; R.L.Z.H.); and the Royal Academy of Engineering Chair in Emerging Technologies scheme (no. CIET1819_24; J.L.M.-D.).

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Authors and Affiliations



V.A., R.A.J., R.L.Z.H. and E.R. designed the project. R.A.J. and R.L.Z.H. developed and characterized the BiOI solar cells. V.A. developed the encapsulation, prepared the photoelectrodes and performed the photoelectrochemical characterization. M.R. designed, synthesized and characterized the CO2 reduction catalyst. L.L. and V.K.L. performed TEM characterization and data analysis. V.A. and R.A.J. drafted the manuscript. All authors contributed to the discussion and completion of the manuscript. J.L.M.-D. proposed the use of BiOI for optoelectronic applications. R.L.Z.H. and E.R. supervised the work.

Corresponding authors

Correspondence to Judith L. MacManus-Driscoll, Robert L. Z. Hoye or Erwin Reisner.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–41, Discussion and Refs. 1–5.

Supplementary Video 1

H2 and syngas production using BiOI photocathodes. Details are given in the embedded video subtitles and in the caption of Supplementary Fig. 41.

Supplementary Video 2

Degradation of unprotected BiOI photocathodes during CVs under chopped light irradiation. Details are given in the video subtitles and in the caption of Supplementary Fig. 15.

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Andrei, V., Jagt, R.A., Rahaman, M. et al. Long-term solar water and CO2 splitting with photoelectrochemical BiOI–BiVO4 tandems. Nat. Mater. 21, 864–868 (2022).

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