Optimization and application of characterization methods for acidic impurities in hydrogen for proton exchange membrane fuel cells.

BACKGROUND: To ensure the long-term efficient operation of proton exchange membrane fuel cells (PEMFC), the quality of hydrogen and trace impurities must be strictly controlled. Halides and formic acid, as acidic impurities, can have a negative impact on the performance and service life of fuel cells. However, the standard methods recommended by ISO, SAE and the National Energy Administration of China for detection of trace acidic impurities in hydrogen are still not mature. Poor selectivity and low sensitivity are exhibited in other methods. The manual absorption process is complex, and multiple acidic impurity components cannot be absorbed using conventional absorbents.

RESULTS: An analytical method was established for the simultaneous determination of trace acidic impurities including halides and formic acid in hydrogen for fuel cell vehicles using absorption combined with ion chromatography. The hydrogen absorption equipment for automatic modes were independently designed. After optimizing the types of absorption bottles, sampling flow rates, absorbent types, and absorbent concentrations, a new absorbent could be formed by adding thiosulfate ions to alkaline solutions. The measurement range was 0.025 μmol mol-1∼10 μmol mol-1, relative standard deviations (RSDs) for hydrogen chloride, chlorine gas, formic acid were 1.13%-5.34%, 2.13%-5.96%, 1.68%-5.28%, and the absorption efficiencies were all above 80%. The detection limits for hydrogen chloride, chlorine gas, and formic acid were 0.014 μmol mol-1, 0.007 μmol mol-1, and 0.001 μmol mol-1 respectively. The determination method can satisfy the measurement requirements of hydrogen energy in ISO 14687-2019 and GB/T 37244-2018.

SIGNIFICANCE: A specific method for detecting acidic impurities in hydrogen for PEMFC has been established, overcoming the difficulties in trace detection. The established method exhibited strong practicality, good accuracy, high sensitivity and high automation, and could fill the gap in the mature detection schemes for halides and formic acid in hydrogen for PEMFC. Hydrogen from different sources could be determined, providing strong guarantees for impurity control in hydrogen production enterprises and the safety of hydrogen fuel cell vehicles.