NREL High-Pressure LTE PEM Cell (4cm2 Surface Area) with internally pressure-balanced REs

NREL High-Pressure LTE PEM Cell (4 cm2 Surface Area) with internally pressure-balanced REs

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Introduction

This electrolyzer is a research-grade electrochemical setup designed for advanced electrocatalysis studies under controlled pressure, inspired by the NREL High-Pressure Liquid Testing (HPLT) electrolyzer concept and extended to enable true three-electrode measurements on both the anode and cathode sides. The detailed specification of the electrolyzer developed by National Renewable Energy Laboratory (NREL, now National Laboratory of the Rockies) can be found on its product page. On the present page, however, there is a description of the extension of functionality to internally pressure-balanced reference electrodes.
Unlike conventional two-electrode electrolyzer test cells, this system integrates two independent reference electrodes (REs), one dedicated to the anode and one to the cathode, allowing accurate, potential-resolved analysis of electrode kinetics, overpotentials, and degradation mechanisms. Each reference electrode is a classical glass-bodied electrode with a ceramic frit, mounted in a pressure-rated PEEK cup. The reference electrodes are equipped with a pressure vent, ensuring that the internal pressure of the reference electrode equilibrates with the operating pressure of the electrolyzer. This design eliminates pressure-induced drift and mechanical stress on the reference electrode junction.

Key Features 

• Dedicated PEEK Chambers
  Reference electrodes are installed in precision-drilled PEEK ports within the flow fields, ensuring robust chemical and mechanical stability.
• Double-Junction Configuration
  Utilizes a polyethylene (PE) frit to create a two-step ionic connection, minimizing contamination and enhancing long-term stability in aggressive electrolytes.
• Enhanced Contamination Resistance
  The dual junction design separates the reference electrode from the main flow field, significantly reducing degradation and drift over time.
• High-Pressure Compatibility
  Electrical contacts are implemented without compromising the pressure integrity of the PEEK chamber, enabling safe operation in high-pressure electrolysis experiments.
• Stable Electrochemical Measurements
  The system maintains reliable reference potentials even under aggressive chemical and electrochemical conditions, improving experimental reproducibility.

Application note
The pressure vent is made by installing a thin steel tube (such as those used in medical needles) into one of the openings intended for filling the electrode. This requires the electrode to be a refillable version. Depending on the membrane chemistry and electrolyte environment, different reference electrodes can be used. Our product range includes 30 mm-long Ag/AgCl electrodes for PEM and 30 mm-long mercury-based electrodes (Hg/HgO and Hg/Hg₂Cl₂) for AEM, which, after modification, can be used in this setup. The modification consists of drilling a hole at the top of the glass body. Before shipping the order, we will ask you which reference electrodes are optimal for your experiment.
The PEEK RE adaper (bottom compartment must be filled to two-thirds of its height with an appropriate electrolyte to: a) establish a stable ionic connection between the reference electrode and the working electrode (anode or cathode), b) protect the reference electrode from direct exposure to the bulk electrolyte, and c) enable operation with lower electrolyte concentrations, which is particularly critical for AEM systems. If a reference electrode is not used in the experiment, the bottom electrolyte compartment of the adapter must be fully filled.
The PEEK reference electrode adapters are fully modular and easily disassembled, allowing rapid replacement of reference electrodes without disturbing the main electrolyzer assembly. This design supports routine maintenance, electrolyte exchange, and experimental flexibility. The main applications of the electrolyzer with internally pressure-balanced REs are: a) electrocatalyst activity and stability studies, b) accurate separation of anode and cathode overpotentials, c) high-pressure water electrolysis research, d) PEM and AEM electrolyzer development and e) mechanistic studies requiring true three-electrode control. 

Specifications

Cell

Temperature Sensor

Adhesive-Backed Pad Heater

Fittings

Component Material

Cell

RE Adapter

Setup includes

1 x anode flow field
1 x cathode flow field
1 x threaded end plate 
1 x unthreaded end plate 
2 x current collector
4 x Swagelok® part #: SS-400-5-4ST fitting
8 x bolt
10 x FKM gasket
10 x skived PTFE gasket 
16 x washer
64 x Belleville washer
2 x insulating PEEK tape
4 x alignment pin 11 mm long, 3 mm OD
2 x alignment pin 8 mm long, 3 mm OD
2 x dual Pt100 temperature sensor
2 x adhesive backed pad heater
2 x bottom RE compartment
2 x top RE compartment
2 x RE electrical plug with 4 mm female banana socket
2 x set of FKM O-rings for RE adapter
2 x capillary with PE frit
2 x selected reference electrode

MSE offers a range of electrochemical cells. Please contact us for more information.