Water electrolysers with closed and open electrochemical systems


Green hydrogen production using renewables-powered, low-temperature water electrolysers is crucial for rapidly decarbonizing the industrial sector and with it many chemical transformation processes. However, despite decades of research, advances at laboratory scale in terms of catalyst design and insights into underlying processes have not resulted in urgently needed improvements in water electrolyser performance or higher deployment rates. In light of recent developments in water electrolyser devices with modified architectures and designs integrating concepts from Li-ion or redox flow batteries, we discuss practical challenges hampering the scaling-up and large-scale deployment of water electrolysers. We highlight the role of device architectures and designs, and how engineering concepts deserve to be integrated into fundamental research to accelerate synergies between materials science and engineering, and also to achieve industry-scale deployment. New devices require benchmarking and assessment in terms of not only their performance metrics, but also their scalability and deployment potential.

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Fig. 1: Schematic illustrating closed versus open electrochemical systems.
Fig. 2: Schematic of set-ups used for performance characterization at the lab-scale and the pilot-scale/industry-scale.
Fig. 3: Cost aspects of WE systems.
Fig. 4: Architecture and design approaches and their implementation for emerging WEs.


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The authors acknowledge financial support from the ANR MIDWAY project (project ID: ANR-17-CE05-0008), from the French national network ‘Réseau sur le Stockage Electrochimique de l’Energie’ (RS2E) FR CNRS 3459 and from the Laboratory of Excellence programme STORE-EX (ANR 10-LABX-0076). They thank N. Dubouis for his contribution to Fig. 2b; C. Ferchaud for useful discussions regarding hydrogen pressurization; and J.-M. Tarascon, N. Dubouis, R. Dugas and B. M. Gallant for critical examination of the manuscript in its early stage.

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M.F.L. and A.G. contributed equally to conceiving, developing and writing the manuscript.

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Correspondence to Marie Francine Lagadec or Alexis Grimaud.

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Extended data

Extended Data Fig. 1 Low-temperature water electrolyser architectures and designs.

a, Alkaline water electrolyser. b, Proton exchange membrane water electrolyser. c, Anion exchange membrane water electrolyser. The components and commonly used materials or commercial products of each electrolyser design are listed at the top and at the bottom of the schematics, respectively.

Extended Data Fig. 2

Physical properties of proton exchange membrane and anion exchange membrane water electrolyser components which impact water electrolyser performance and stack cost.

Extended Data Fig. 3

Design and performance parameters of state-of-the-art alkaline, proton exchange membrane and anion exchange membrane water electrolysers.45,68,86,87,88,89,90.

Extended Data Fig. 4 Key information and assumptions for cost calculations used in ref. 37.

Mayyas et al. classify catalyst coated membranes (CCMs) and porous transport layers (PTLs) as membrane electrode assemblies (MEAs), which are held in place by a frame. In our definition, MEAs consist of a membrane and the electrodes.

Extended Data Fig. 5

Data extracted from ref. 37 using WebPlotDigitizer as plotted in Fig. 3a-c.

Extended Data Fig. 6 Data for Li-ion battery packs (ref. 74) and proton exchange membrane water electrolyser (ref. 37) and fuel cell (ref. 73) stacks and systems as plotted in Fig. 3d.

The data of references74 and37 were extracted using WebPlotDigitizer. For PEM fuel cell (PEMFC) and water electrolyser (PEMWE) systems, the balance of plant (BOP) cost includes cost associated with power supply, water circulation and gas processing parts as well as other parts (see Fig. 3a and Extended Data Fig. 5 for PEMWE systems). As shown in this table, the BOP cost of PEMWEs makes up a larger fraction of the system cost compared to the one of PEMFCs; at current production rates (10 units per year for PEMWEs and several thousand units per year for PEMFCs), the BOP cost fraction is about 50-60% for PEMWEs and 35-50% for PEMFCs. This is in part due to the different power supply requirements for large-scale, on-site PEMWE applications and for specific mobile PEMFC applications. For the highest projected production rates (50k units per year for PEMWEs and 500k units per year for PEMFCs), the BOP cost is fairly constant for PEMWEs (60-75% of system cost depending on system size) and PEMFCs (reaching up to 60% of system cost). Li-ion batteries deviated from portable electronics applications require a battery management system (BMS). The BMS can be seen as the equivalent of balance of stack equipment and its cost amounts to ~10% of reported LIB pack cost. For large-scale applications, balance of system (BOS) equipment is required (for example, comprising climate control, containerisation, inverter, controller and controls)91. This BOS cost is not comprised in the pack cost as reported in this table, and would lead to an additional ~10% on top of pack cost.92 At a production rate of 100k units per year, Li-ion battery pack cost is projected to be 210 $/kWh; thus, we estimate a BOS cost of ~21 $/kWh and a total Li-ion system cost (including battery pack, BOS, power conversion systems, and construction and commissioning cost) to be in the order of up to twice the battery pack cost (that is, ~400 $/kWh) based on the values given in ref. 92.

Extended Data Fig. 7 Design parameters and performance characteristics for emerging water electrolysers14,53,55,56,57,58,59,60,61,62,63,64,65,66,67.

The listed values are recorded at room temperature (except for ref. 60: 30-40 °C, refs. 65,66: 70-80 °C and ref. 67: 25-95 °C). The studies marked in blue are shown in greater detail in Fig. 4b-c. Efficiency values are given for system efficiency (SE), Faradaic efficiency (FE), voltage efficiency (VE) and higher heating value efficiency (HHVE) of hydrogen.

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Lagadec, M.F., Grimaud, A. Water electrolysers with closed and open electrochemical systems. Nat. Mater. 19, 1140–1150 (2020). https://doi.org/10.1038/s41563-020-0788-3

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