A membrane-based seawater electrolyser for hydrogen generation | Nature

https://www.nature.com/articles/s41586-022-05379-5

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Abstract

Electrochemical saline water electrolysis using renewable energy as input is a highly desirable and sustainable method for the mass production of green hydrogen1234567; however, its practical viability is seriously challenged by insufficient durability because of the electrode side reactions and corrosion issues arising from the complex components of seawater. Although catalyst engineering using polyanion coatings to suppress corrosion by chloride ions or creating highly selective electrocatalysts has been extensively exploited with modest success, it is still far from satisfactory for practical applications891011121314. Indirect seawater splitting by using a pre-desalination process can avoid side-reaction and corrosion problems15161718192021, but it requires additional energy input, making it economically less attractive. In addition, the independent bulky desalination system makes seawater electrolysis systems less flexible in terms of size. Here we propose a direct seawater electrolysis method for hydrogen production that radically addresses the side-reaction and corrosion problems. A demonstration system was stably operated at a current density of 250 milliamperes per square centimetre for over 3,200 hours under practical application conditions without failure. This strategy realizes efficient, size-flexible and scalable direct seawater electrolysis in a way similar to freshwater splitting without a notable increase in operation cost, and has high potential for practical application. Importantly, this configuration and mechanism promises further applications in simultaneous water-based effluent treatment and resource recovery and hydrogen generation in one step.

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Data availability

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

This work is supported by the National Natural Science Foundation of China (grant numbers 52004166, 52104400 and 51827901) and the Science and Technology Department of Sichuan Province (grant number 2020YFH0012). We thank the Program for Guangdong Introducing Innovative and Entrepreneurial Teams (grant number 2019ZT08G315), and we thank the Institute of New Energy and Low-Carbon Technology, Sichuan University for support.

Author information

Authors and Affiliations

  1. Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization, Institute of Deep Earth Sciences and Green Energy, College of Civil and Transportation Engineering, Shenzhen University, Shenzhen, China

    2. Heping Xie

Contributions

H.X., T.L. and Z.S. conceived and designed the project. Z.Z., Y.W. and C.L. performed the characterizations and experiments. Z.Z., T.L., W.J. and Y.W. analysed the data. L.Z. and D.Y. designed the devices. H.X., Z.Z., T.L., Y.W. and Z.S. drafted the article and revised it critically. All authors reviewed the manuscript.

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Extended data figures and tables

a, A schematic diagram of the lab-scale SES. b, Photos of the lab-scale SES and operation process. c, Ion chromatography tests show that the gas path can prevent seawater penetration, so the ion content in SDE is still nearly four orders of magnitude lower than that in seawater after long-term electrolysis. d, The energy consumption analysis. From the whole period, assuming that the water source is seawater, it is necessary to desalination before use in industrial alkaline electrolysis, which needs to consume at least 9–14.4 kJ \({\rm{k}}{{\rm{g}}}_{{\rm{water}}}^{-1}\), while the phase transition of SES is a spontaneous process, which saves the energy of desalination. During electrolysis, the energy input of our strategy is equivalent to industrial alkaline water electrolysis when the system conditions are the same, which has been confirmed above. e, Electrolysis durability test of conventional direct seawater (Shenzhen Bay seawater) splitting with commercial electrocatalysts. The inset shows photos of clear seawater before electrolysis, precipitation in seawater during electrolysis, and catalyst electrode dissolving and shedding in seawater after electrolysis.

a, Photograph and SEM images of the PTFE membrane. b, Fourier transform infrared spectroscopy (FTIR) result shows different chemical vibration bonds of PTFE. The two bands located at 1147 and 1202 cm−1 are assigned to the -CF2 stretching vibrations of PTFE, and the 638 cm−1 peak is the -CF2 wagging vibrations of PTFE. Due to the large electronegativity and small radius of F atoms, the PTFE membrane has a lower surface energy, thus resulting in an excellent hydrophobic characteristic. The inset demonstrates the superhydrophobic property of the PTFE membrane, and the average droplet contact angle in air was measured as 156.3°. Each mean value was calculated from five measurements. c, The breakthrough pressure and corresponding theoretical hydrostatic depth of the PTFE membrane with different pore sizes. The curve of water migration mass over time at different membrane areas (d), gas path lengths (e) and pore sizes (f). In this process, the electrolysis reaction was not involved. Each mean value was calculated from three measurements.

a, The average migration rate curve of water showing a fast migration rate induced by KOH electrolyte (SDE) under a vapour pressure difference. b, Photograms of the phase transition migration of seawater. c, The relationship curve of the water migration rate and SDE concentration. The inset shows the amount of water migration in simulated seawater (under conditions of 1 μm pore size and 9.6 cm2 gas path area, KOH solid as initial SDE). d, LSV scans of commercial catalysts (MoNi/NF anode paired with a PtNi mesh cathode) taken in various concentrations of KOH solution (SDE) at room temperature.

a—d, Water migration rate from seawater to 30-wt% KOH electrolyte (SDE) in various seasons (the average temperature is considered to be 20 °C-spring, 30 °C-summer, 10 °C-autumn and 0 °C-winter). The inset demonstrates that at different seasonal temperatures the water vapour pressure of the SDE generally increases with water migration until it is equal to that of the seawater side. e, The curve shows the variation in water vapour pressure and water vapour pressure difference with depths.

a, The scaled-up SES consists of an electrolytic module composed by 11 cells in parallel. The structure of each cell from left to right: positioning frame, anode plate, MoNi/NF anode catalyst layer, diaphragm, and cathode. The PTFE membrane was lined on the five inner walls of the electrolyser box (except the top) to create a gas path in seawater and hold KOH solution (SDE) at the same time. b, LSV curves of the scaled-up SES compared with the lab-scale SES by measuring the voltage at 0, 10, 50, 100, 150, 200 and 250 mA cm−2 current densities.

SEM images of the PTFE membrane before (a) and after (b) 15 days of electrolysis in SES. SEM images for the MoNi/NF anode catalyst before (c) and after (d) 200 h electrolysis in a scaled-up SES.

a, Schematic of hydrogen production using a hygroscopic PEM based on a phase transition migration mechanism. b, Electrolyte durability test for PAMPS at a constant current of 30 mA cm−2. The inset is a diagram of the PAMPS hygroscopic hydrogel SDE. c, Schematic of hydrogen production using a hygroscopic AEM based on a phase transition migration mechanism. d, Electrolyte durability test for PVA/KOH at a constant current of 250 mA cm−2. The inset is the diagram of the PVA/KOH hygroscopic hydrogel SDE.

a, OER polarization of Mo-Ni3S2/NF and MoNi/NF electrocatalysts in 30-wt% KOH (SDE). b, LSV scans of PtNi//Mo-Ni3S2/NF and PtNi//MoNi/NF in 30-wt% KOH solution (SDE) (in H-type electrolytic cell). c, Seawater electrolysis durability test based on the Mo-Ni3S2/NF anode and PtNi mesh cathode at a constant current density of 250 mA cm−2 in SES.

a, Water migration behaviour under different concentrations of H2SO4 solution (50 wt% KOH solution as the initial SDE). Each mean value was calculated from three measurements. b, Electrolysis durability in 0.5 M H2SO4 solution. c, The water migration behaviour under different concentration of NaOH solution (50 wt% KOH solution as the initial SDE). Each mean value was calculated from three measurements. d, Electrolysis durability in 0.5 M NaOH solution. e, The water migration behaviour under different concentrations of NaCl solution (50 wt% KOH solution as the initial SDE). Each mean value was calculated from three measurements. f, Electrolysis durability in saturated NaCl solution.

a, Schematic illustration of continuously enriching lithium from the feed solution through water migration and hydrogen generation. b, Photos of LiCl solution without precipitation when adding K2CO3 solution before concentration, LiCl solution with precipitation when adding K2CO3 solution after concentration, and the final Li2CO3 production. c, Electrolytic durability test for hydrogen production while lithium enrichment at a constant current of 400 mA cm−2.

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Xie, H., Zhao, Z., Liu, T. et al. A membrane-based seawater electrolyser for hydrogen generation. Nature (2022). https://doi.org/10.1038/s41586-022-05379-5

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