Development of a Hydrogen Contaminant Detector
Authors: Mukundan Rangachary , Romero Christopher J. , Brosha Eric L. , Rockward Tommy 
Published: May 2020

Hydrogen Refueling Stations (HRSs) are being deployed at scale in California, Japan, Europe and South Korea to support the introduction of Fuel Cell Vehicles.1 The hydrogen dispensed to the fuel cell should meet SAE J2719 standards for the maximum allowable concentration of various impurities.2 While HRSs can have their fuel analyzed periodically to verify that they meet the strict fuel quality standards, it would be greatly advantageous to have an in-linemonitor that can alert the user to any potential fuel quality problems. Los Alamos National Laboratory has been developing a low-cost hydrogen contaminant detector (HCD) that can be deployed at the HRS and is capable of detecting CO and H2S impurities in the hydrogen fuel.
The LANL HCD technology is based on a hydrogen pumping cell that utilizes a high loaded counter/pseudo-reference electrode and a low loaded working/sensing electrode.3 This hydrogen pumping cell, illustrated in Figure 1, consists of a Nafion® 117 membrane that is in contact with a water reservoir and two gas diffusion electrodes with wicking tabs that extend into the water reservoir. The active electrode area (≈ 1cm2) is exposed to dry hydrogen gas that first flows over the sensing electrode and then over the pseudo-reference electrode. The HCD is operated in a constant potential mode (0.1V) where the pumping current can be related to the purity of hydrogen. A voltage pulse (1.5V for 30s) is applied periodically (e.g. every 15mins) to clean up any contaminants that are adsorbed on the working electrode and reset the HCD current to the baseline.
The LANL HCD technology was installed at the H2Frontier HRS in Burbank, California and operated under real-world conditions. Calibration was performed on this HCD with certified CO/H2 gas, and its sensitivity to low concentrations of CO was demonstrated (Figure 2). The data shown in Figure 2 plots the current at 0.1V at the end of each 15-minute interval, just before the application of the 1.5V pulse. The HCD baseline and response were tracked intermittently for a period of over a year and demonstrated exceptional baseline stability and sensitivity to the SAE J2719 allowable limit of 100ppb CO. An analysis of the field-testing data will be presented along with the response to low concentrations (4 - 100 ppb) of H2S in H2.
The current LANL HCD operates at slightly above ambient temperature (30 °C) and at ambient pressures. Any change in the flow rate of H2 (usually 100sccm) over the HCD, or a drying of the water reservoir can result in a baseline drift. LANL is currently working on a HCD technology that can function without a humidification system and thus is immune to flow rate changes. Moreover, this system could be operated under pressure and at varying temperatures and has the potential to be deployed in-line just before the fueling nozzle. The development of membranes with sufficient protonic conductivity to operate in dry hydrogen and their sensitivity to CO in the H2 will also be presented in this talk.

Acknowledgements

This research is supported by the U.S. Department of Energy Fuel Cell Technologies Office, through the Safety, Codes & Standards (SCS) sub-program (Project Manager: Laura Hill).
REFERENCES:
1. Hardman, G. Tall, Int. J. Hydrogen Energy, 43, 17857-17866 (2018).
2. San Marchi, E. S. Hecht, I. W. Ekoto, K. M. Groth, C. LaFleur, B. P. Somerday, R. Mukundan, T. Rockward, T; J. Keller, C. W. James, Int. J. Hydrogen Energy, 42(11), 7263-7274 (2017)
3. Brosha, T. Rockward, C. J. Romero, M. S. Wilson, C. Kreller and R. Mukundan, U.S Patent # 10,490,833 (2019).

Figure 1