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Water electrolysis

Abstract

Electrochemistry has the potential to sustainably transform molecules with electrons supplied by renewable electricity. It is one of many solutions towards a more circular, sustainable and equitable society. To achieve this, collaboration between industry and research laboratories is a must. Atomistic understanding from fundamental experiments and modelling can be used to engineer optimized systems whereas limitations set by the scaled-up technology can direct the systems studied in the research laboratory. In this Primer, best practices to run clean laboratory-scale electrochemical systems and tips for the analysis of electrochemical data to improve accuracy and reproducibility are introduced. How characterization and modelling are indispensable in providing routes to garner further insights into atomistic and mechanistic details is discussed. Finally, important considerations regarding material and cell design for scaling up water electrolysis are highlighted and the role of hydrogen in our society’s energy transition is discussed. The future of electrochemistry is bright and major breakthroughs will come with rigour and improvements in the collection, analysis, benchmarking and reporting of electrochemical water splitting data.

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Fig. 1: Schematic of a typical water electrolyser.
Fig. 2: Electrochemical cells.
Fig. 3: Factors impacting the electrode–electrolyte interface of a working catalyst.
Fig. 4: Overview of important complementary characterization techniques in electrocatalysis.
Fig. 5: Example of data work-up for the study of hydrogen evolution on a polycrystalline platinum electrode.
Fig. 6: Density functional theory modelling for water electrolysis.
Fig. 7: Overview of the hydrogen economy.

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Acknowledgements

F.D. and N.L. thank the Spanish Ministry of Science and Innovation (RTI2018-101394-B-I00, Severo Ochoa CEX2019-000925-S). R.M. acknowledges the Dutch Organization for Scientific Research (NWO) for funding under grant number ECCM.TT.ECCM.001. A.H.M.d.S. and R.E.V. acknowledge the Materials Innovation Institute (M2i) and thank Tata Steel Nederland Technology BV and the Dutch Research Council (NWO) (project number ENPPS.IPP.019.002) for financial support. S.P. acknowledges support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2021R1A6A3A14039678). This project was also supported by the Solar-to-Products programme and the Advanced Research Center for Chemical Building Blocks (ARC CBBC) consortium, both co-financed by the NWO and by Shell Global Solutions B.V., and by the European Commission under contract 722614 (Innovative training network ELCoREL). The authors thank the invaluable peer reviewers who provided constructive comments.

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All authors researched data for the article. All authors contributed substantially to discussion of the content. A.J.S., M.C.O.M., F.D., D.P., M.P., A.H.M.d.S., R.E.V., K.O., S.P., O.v.d.H., G.M., A.G., M.V., G.T.K.K.G., R.M., N.L. and M.T.M.K. wrote the article. All authors reviewed and/or edited the manuscript before submission.

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Correspondence to Arthur J. Shih, G. T. Kasun Kalhara Gunasooriya, Ian McCrum, Rik Mom, Núria López or Marc T. M. Koper.

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Glossary

Hydrogen evolution reaction

(HER). The reaction at the cathode where hydrogen is produced.

Oxygen evolution reaction

(OER). The reaction at the anode where oxygen is produced.

Alkaline electrolysis

Water splitting under high-pH alkaline conditions. Although water splitting rates are lower under alkaline conditions, cell components exhibit higher resistance against corrosion and catalysts can be prepared from more earth-abundant materials.

Proton exchange membrane

(PEM). A membrane selective towards protons (H+), but not selective towards electrons (insulator) and gases (hydrogen, oxygen).

Anion exchange membrane

A membrane selective towards anions, but not selective towards electrons (insulator), gases (hydrogen, oxygen) and large cations.

Dimensionally stable anodes

Conductive and stable electrodes made of mixed metal oxides (typically of titanium, ruthenium and iridium).

Reversible hydrogen electrode

(RHE). A reference electrode defined as the equilibrium potential of platinum when exposed to 1 atm hydrogen and the pH of the working electrolyte.

Thiele modulus

The ratio of the reaction rate to the diffusion rate.

Effectiveness factor

The ratio of the experimentally measured reaction rate to the kinetic reaction rate in the absence of diffusion limitations.

Tafel slopes

The required increase in potential to increase the reaction rate by ten times.

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Shih, A.J., Monteiro, M.C.O., Dattila, F. et al. Water electrolysis. Nat Rev Methods Primers 2, 84 (2022). https://doi.org/10.1038/s43586-022-00164-0

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