Decoupled hydrogen and oxygen evolution by a two-step electrochemical–chemical cycle for efficient overall water splitting

Abstract

Electrolytic hydrogen production faces technological challenges to improve its efficiency, economic value and potential for global integration. In conventional water electrolysis, the water oxidation and reduction reactions are coupled in both time and space, as they occur simultaneously at an anode and a cathode in the same cell. This introduces challenges, such as product separation, and sets strict constraints on material selection and process conditions. Here, we decouple these reactions by dividing the process into two steps: an electrochemical step that reduces water at the cathode and oxidizes the anode, followed by a spontaneous chemical step that is driven faster at higher temperature, which reduces the anode back to its initial state by oxidizing water. This enables overall water splitting at average cell voltages of 1.44–1.60 V with nominal current densities of 10–200 mA cm−2 in a membrane-free, two-electrode cell. This allows us to produce hydrogen at low voltages in a simple, cyclic process with high efficiency, robustness, safety and scale-up potential.

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Fig. 1: Schematic of alkaline water electrolysis and the E-TAC water-splitting process.
Fig. 2: Electrochemical properties of Ni0.9Co0.1(OH)2 and NiFe LDH anodes.
Fig. 3: E-TAC water splitting in alkaline solution.
Fig. 4: Schematic of the multi-cell E-TAC process.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

The research leading to these results has received funding from the Israeli Ministry of National Infrastructure, Energy and Water Resources, as well as the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement number 727606). The results were obtained using central facilities at Technion’s Hydrogen Technologies Research Laboratory, created and supported by the Nancy and Stephen Grand Technion Energy Program and the Adelis Foundation, and at the N2–H2 alternative fuel laboratory donated by Ed Satell. G.S.G. also acknowledges the support of the Arturo Gruenbaum Chair in Material Engineering. The authors thank Y. Ein-Eli for reading the manuscript and providing useful suggestions for improving it, and N. Haimovich for some of the heat balance calculations.

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Authors

Contributions

H.D. conceived the conceptual idea. H.D. and A.L. designed the experiments and analysed the data. A.L. performed the main experiment presented in Fig. 4 of the article, and most of the experiments presented in the Supplementary Information. S.W.S. designed and performed the experiments presented in Fig. 3 of the article, and tested alternative electrolyte solutions. K.D.M., A.L., M.H., N.Y. and C.C. prepared the electrodes. K.D.M., H.D. and D.A.G. performed the material characterizations. Z.A., N.Y., N.G. and N.H. performed the complementary experiments presented in the Supplementary Information. G.E.S. assisted in the experimental and system design. A.R., G.S.G., A.L., H.D., S.W.S. and D.A.G. wrote the manuscript. A.R. and G.S.G. supervised and guided the entire project.

Corresponding authors

Correspondence to Avner Rothschild or Gideon S. Grader.

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Competing interests

H.D., A.L., G.E.S., A.R. and G.S.G. hold the following patent applications in relation to the E-TAC process and systems: Patent Cooperation Treaty international applications EP3221493A1, WO2016079746A1, US20170306510A1 and JP2017526564A (2015), and Israeli Patent Application number 258252 (2018). The above authors hold shares in H2Pro—a start-up company that aims to develop hydrogen generators based on the E-TAC process.

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Supplementary information

Supplementary Information

Supplementary notes 1–7, Figs. 1–37, Tables 1–2 and refs. 1–27.

Supplementary Video 1

Hydrogen generation step.

Supplementary Video 2

Oxygen generation step.

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Dotan, H., Landman, A., Sheehan, S.W. et al. Decoupled hydrogen and oxygen evolution by a two-step electrochemical–chemical cycle for efficient overall water splitting. Nat Energy 4, 786–795 (2019). https://doi.org/10.1038/s41560-019-0462-7

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