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Hydrogen production via microwave-induced water splitting at low temperature


Supplying global energy demand with CO2-free technologies is becoming feasible thanks to the rising affordability of renewable resources. Hydrogen is a promising vector in the decarbonization of energy systems, but more efficient and scalable synthesis is required to enable its widespread deployment. Here we report contactless H2 production via water electrolysis mediated by the microwave-triggered redox activation of solid-state ionic materials at low temperatures (<250 °C). Water was reduced via reaction with non-equilibrium gadolinium-doped CeO2 that was previously in situ electrochemically deoxygenated by the sole application of microwaves. The microwave-driven reduction was identified by an instantaneous electrical conductivity rise and O2 release. This process was cyclable, whereas H2 yield and energy efficiency were material- and power-dependent. Deoxygenation of low-energy molecules (H2O or CO2) led to the formation of energy carriers and enabled CH4 production when integrated with a Sabatier reactor. This method could be extended to other reactions such as intensified hydrocarbons synthesis or oxidation.

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Fig. 1: Schematic illustration of the microwave-induced redox cycle.
Fig. 2: Microwave radiation process induces reduction of Ce4+ in CeO2.
Fig. 3: Application and time sequence in water deoxygenation.
Fig. 4: Hydrogen production flowchart based on microwave reduction.
Fig. 5: Energy balance and efficiency for hydrogen production.
Fig. 6: Microwave electrocatalysis in energy conversion reactions.

Data availability

The data used in this study are presented in the text, Supplementary Information and Source Data. Additional data and information are available from the corresponding author on request. Source data are provided with this paper.


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This work was supported by the Spanish Government (RTI2018-102161, SEV-2016-0683 and Juan de la Cierva grant IJCI-2017-34110). We thank the support of the Electronic Microscopy Service of the Universitat Politècnica de València.

Author information




J.F.B.-M, P.P.-G., L.N and B.G.-B. performed the experiments. J.M.S., J.M.C.-C., M.B. and B.G.-B. designed the experiments. J.M.C.-C. and P.P.-G designed and fabricated the microwave-cavity assembly. J.F.B.-M, P.P.-G., B.G.-B., J.S.-B., and J.M.C.-C. analysed electrochemical and physical data. M.B, L.N., J.F.B.-M. and J.M.S performed the gas analyses and evaluated catalytic data. D.C.-M. performed thermodynamic and process simulations. M.B. collected physicochemical characterization. J.M.S. and J.M.C.-C. initiated the project. J.M.S., J.M.C.-C., L.N., J.S.-B., D.C.-M. and M.B. wrote the manuscript, whereas all authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to J. M. Serra or J. M. Catalá-Civera.

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Competing interests

The Universitat Politècnica de València and Consejo Superior de Investigaciones Científicas have jointly applied for a patent based on the method for microwave-driven reduction of oxides and its uses. The inventors are J.M.S., J.F.B.-M., B.G.-B., J.M.C.-C. and L.N and the Spanish priority number is ES2726028-B2.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–23, Notes 1–14, Tables 1–8 and references.

Source data

Source Data Fig. 2

Source data for plots b–d in Fig. 2. Figure 2b displays the flow of oxygen released, in ml min−1, and the CGO material temperature, in °C, as a function of time, in min. Figure 2c compares the electric conductivity behaviour of the solid-state material, in S m−1, for microwave-assisted and conventional heating as a function of inverse temperature, in K−1. Figure 2d reflects an analogous comparison for microwave-assisted heating above and below the material power threshold.

Source Data Fig. 3

Source data for plots b–d in Fig. 3. Figure 3b represents the time sequence, in s, of the control parameters for the microwave-assisted redox process that follows: material absorbed power, in W; temperature, in °C; electric conductivity, in S m−1; and H2 and O2 flows, in ml min−1. Figure 3c compares the time evolution, in s, of the microwave-assisted redox process with H2O and D2O, attending to the following control parameters: temperature, in °C; electric conductivity, in S m−1; and H2 and O2 flows, in arbitrary units. Figure 3d shows the time sequence, in s, of H2 and O2 flows, in ml min−1, and temperature, in °C, for several redox cycles.

Source Data Fig. 6

Source data for plots b and d in Fig. 6. Figure 6b displays the time evolution, in s, of the gas flows involved in CH4 production integrated with a Sabatier reaction, in ml min−1, that is O2, H2, CH4 and CO2. Figure 6d reflects analogous time sequence for the conversion of CH4 into syngas, which involves the gas flows for O2, H2, CH4 and CO, in ml min−1.

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Serra, J.M., Borrás-Morell, J.F., García-Baños, B. et al. Hydrogen production via microwave-induced water splitting at low temperature. Nat Energy 5, 910–919 (2020).

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