Protocol for assembling and operating bipolar membrane water electrolyzers

Abstract

Renewable energy-driven bipolar membrane water electrolyzers (BPMWEs) are a promising technology for sustainable production of hydrogen from seawater and other impure water sources. Here, we present a protocol for assembling BPMWEs and operating them in a range of water feedstocks, including ultra-pure deionized water and seawater. We describe steps for membrane electrode assembly preparation, electrolyzer assembly, and electrochemical evaluation. For complete details on the use and execution of this protocol, please refer to Marin et al. (2023).¹.

Keywords: Chemistry; Energy; Material Sciences.

Graphical abstract

Figure 1

Electrolyzer test station and components (A) An electrolyzer test station with labeled components. The labeled components include the stand, electrolyzer, secondary container, thermocouple, glass container, temperature probes, power supply, and on/off valves. The image highlights the arrangement and positioning of these components. (B) Labeled electrolyzer hardware. The labeled components include the flow fields, current collectors, gaskets, and electrolyzer body.

Figure 2

Gasket design and dimensions Gasket design to be cut out of polyester sheets with varying thicknesses. The design includes circular cutouts with a diameter of 0.3 cm, along with other dimensions labeled in the diagram. Scale bars defined in image.

Figure 3

Schematic of catalyst ink preparation Schematic representation of catalyst ink preparation. The diagram highlights the need for sonication to achieve a homogeneous catalyst ink with minimal nanoparticle agglomerates.

Figure 5

Airbrush handling Photograph of proper airbrush handling for catalyst spraying coating. The figure emphasizes the grip, hand position, and location of airbrush straw.

Figure 6

Stainless steel PTL preparation Back (left) and front (right) image of stainless steel PTL (25 cm²) before catalyst ink spraying. The left photograph showcases pencil markings on the backside indicating twenty-five 1 cm² squares. These markings serve as a reference for the subsequent catalyst ink spraying process, ensuring accurate placement of the catalyst material on the front surface of the PTL. Scale bars defined in image.

Figure 7

Electrode spray coating setup (A) Photograph illustrating the PTL securely taped onto a foil-covered hot plate prepared for the spraying procedure. (B) Schematic representation of the serpentine spray coating pattern applied to the PTL surface, followed by a 90° rotation of the hot plate. The diagram demonstrates the sequential actions involved in achieving an even and uniform distribution of the catalyst ink across the PTL surface (Methods video S2). Scale bars defined in image, 5 cm.

Figure 8

Spray coated PTL Image of sprayed PTL coated with anode catalyst, IrO_x. (A) Low quality PTL, showcasing an irregular and poorly adhered coating of IrO_x. (B) High quality PTL, exhibiting uniform coating. The image highlights a successful deposition of the catalyst material onto the PTL surface. Color enhanced images of (A) and (B) are included in panels (C) and (D), respectively, to highlight the differences in deposition quality. Scale bars defined in image, 2.5 cm.

Figure 9

Spray coated membranes Photographs of prepared membranes for comparison. (A) Successfully prepared membrane, exhibiting a uniform and smooth surface. (B) Unusable membrane with commonly observed defect from presence of air bubbles (marked with a black arrow). Scale bars defined in image, 1 cm.

Figure 4

Membrane spray coating process The image highlights the key components involved in the membrane spraycoating process, including the catalyst ink, airbrush, membrane or PTL, hot plate, and nitrogen regulator. The airbrush, controlled by the nitrogen regulator, then sprays a fine mist of catalyst ink onto the PTL/membrane surface.

Figure 11

Prepared cathode Photograph of a 1 cm² cathode, precisely cut to the required size, and prepared for insertion into an electrolyzer. Scale bar defined in image, 1 cm.

Figure 12

Schematic BPMWE architecture Depiction of the architecture of an assembled BPMWE, with a zoomed-in view of a cross-sectional graphic illustrating a zero-gap BPMWE configuration. The diagram showcases the overall architecture of the MEA setup, highlighting key components such as the anode, cathode, and membranes.

Figure 10

Diagram of BPMWE with additional hardware components Cross-sectional schematic of the catalyst/ionomer-coated porous transport layers (PTL) with their corresponding ion-exchange membranes and the water circulation scheme. The cation exchange membrane (CEL) refers to the Nafion membrane and ionomer overlayer, while the anion exchange layer (AEL) refers to the PiperION membrane and ionomer overlayer.

Figure 13

Schematic representation of the BPMWE setup coupled with a potentiostat The diagram illustrates the assembled electrolyzer horizontally oriented with the anode on the lower portion and the cathode on top, both connected to the potentiostat via two electrical leads. The diagram illustrated on the computer captures the first step in the break-in process (CP1). Note that the electrical connection to the electrolyzer should be made carefully—4 point connections to the anode and cathode are recommended to minimize undesired resistive losses. Stable, low resistance connections are also important to minimize resistive losses under high-current operation.

Figure 14

Flowchart for BPMWE assembly and testing The chart illustrates the decision points and key actions required at each stage. The chart outlines the process, starting from the electrolyzer assembly and preparation to electrochemical testing, with key troubleshooting points highlighted.

Figure 15

Comparison of voltage profiles during break-in of a BPMWE (A) Current density and (B) voltage of an acceptable and unacceptable BPMWE break-in. We used E_cell < 2.5 V at 500 mA as an additional performance metric to indicate successful BPMWE fabrication.