EIS equivalent circuit modeling of direct ammoniafuel cell (DAFC) and mass transfer characteristics for anode diffusion layers with different hydrophobicity

Clarifying the mass transfer mechanism of direct ammonia fuel cell (DAFC) can provide theoretical support for solving its complex water and heat management problems. Electrochemical impedance spectroscopy (EIS) as an electrochemical measurement technique that can characterize the losses in various parts of an electrochemical system, but it’s rarely used in DAFC experimental research. Therefore, this study proposes an EIS equivalent circuit model for low-temperature DAFC, which is used to quantitatively characterize the Faradaic impedance, Ohmic impedance, and mass transfer impedance of cells, meanwhile, the model takes into account the influence of solution aggregation in the anode diffusion layer (ADL). This study prepares 3 ADLs with different water contact angles and explores the influence of ADL hydrophobicity on DAFC performance through fitting between equivalent circuit model and experimental results. We find that DAFC with moderately hydrophobicity ADL which water contact angle of 126.5° exhibits better electrochemical performance, with peak power density of 10.07 mW cm −2 . As hydrophobicity decreases, water contact angle reduces to 100.9°, the solution aggregation phenomenon occurring at ADL becomes severe, which in turn increases the Ohmic impedance of 160 mΩ cm 2 and reduces cell performance. The cell with ADL water contact angle of 142.7° doesn’t exhibit solution aggregation in diffusion layer, its Ohmic impedance reduces by 270 mΩ cm 2 compare to the cell with ADL water contact angle of 126.5°, but its performance decrease to 9.23 mW cm −2 due to insufficient reactant supply. This study also explores the influence of ADL hydrophobicity on DAFC output stability. This achievement can enrich the theory of DAFC testing and to some extent fill the gap in the study of DAFC mass transfer mechanism.