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A novel method for replenishing platinum catalysts on an electrolyte membrane of polymer electrolyte membrane fuel cell (PEMFC) is studied. The method injects electrocatalyst‐supplementing ink into a pre‐assembled fuel cell in a simple and non‐destructive manner. For replenishing, straightforward catalyst‐replenishment equipment and corresponding protocol are proposed. The protocol consists of injection, penetration, and purge processes. As a feasibility study, the method is performed on fuel cells with pristine membranes. Target fuel cells for this study include a membrane‐assembled cell without catalyst layers (CLs) (Cell 1) and a cell assembled with a membrane‐coated cathodic CL (Cell 2). An open‐circuit voltage of 0.804 V in Cell 1 and a current of 77 mA in Cell 2 are measured, as supported through electrochemical impedance spectroscopy. Results of energy‐dispersive X‐ray spectroscopy and X‐ray photoelectron spectroscopy also support the presence of platinum catalysts. [ABSTRACT FROM AUTHOR]

Polymer electrolyte membrane fuel cells were analyzed to investigate changes in the structure of the flow field and operating conditions. The cell performance, which was controlled by adjusting the width of the cathodic channel, improved as the backpressure increases. With the anodic and cathodic flow channels mismatched, the maximum power densities at 3.0 bar for a narrow cathodic channel were 1115 and 1024 mW/cm2, and those for a wide cathodic channel were 959 and 868 mW/cm2, respectively. The diffusion characteristics were investigated using the non-dimensional numbers Re (Reynolds), Sc (Schmidt), and Sh (Sherwood) to confirm the improvement of mass transport. The narrower the channel or the higher the operating pressure, the larger Re was and the smaller Sc and Sh became. In particular, the wider the anodic channel, the larger the value of Sh. [ABSTRACT FROM AUTHOR]

Water management is essential to achieve guaranteed performance and durability of polymer electrolyte membrane fuel cells (PEMFCs), and to this end, accurate prognostics and health monitoring should be performed. In this study, we introduce high-frequency resistance (HFR) fluctuations as a parameter to accurately detect the flooding of PEMFCs. Low-frequency resistance (LFR), which is used for diagnosing flooding, is compared with HFR. Under the state of gradual flooding, severe flooding, and flooding mitigation, HFR shows a dynamic response of gradual increase, sharp rise, and decrease, respectively. Conversely, LFR does not respond to gradual flooding and flooding mitigation but only increases rapidly under severe flooding. According to current fluctuations, the reliability of the LFR and HFR fluctuations is evaluated and found to be 77.2 and 100%, respectively. In addition, the LFR and HFR fluctuations precede the current variations by an average of 0.927 s and 3.01 s, respectively. Experimental results demonstrate that HFR is more effective than LFR and current variations for real-time flooding diagnosis because of its high accuracy and fast response. In future work, dynamic HFR fluctuations can be used to simultaneously diagnose flooding and membrane dehydration. [Display omitted] • High-frequency resistance for analyzing real-time flooding diagnosis in fuel cell. • Dynamic HFR response was observed in various stages of flooding. • Detection accuracy of HFR was 100%. • HFR fluctuations caused by flooding preceded the current change on average by 3.01 s. • Flooding can be diagnosed by HFR even when condensation occurs in fuel cell. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNT) based nanoporous layer contacting the catalyst layer in polymer electrolyte membrane fuel cells (PEMFCs) is investigated. Nanoporous CNT-5, CNT-15, and CNT-40 sheets are prepared via direct spinning method with thicknesses is 5, 15, and 40 μm, respectively. The ethanol-derived CNT-5 possess sparse pore networks, whereas CNT-15 and CNT-40 derived from acetone exhibit fine networks, and CNT-15 and CNT-40 differ only in thickness. The CNTs are employed as either standalone nanoporous layer or as an additional layer with carbon-black microporous layer (MPL). Scanning electron microscopy and sessile drop method are utilized for CNT characterization. Current-voltage polarization curve and electrochemical impedance spectroscopy are recorded for the PEMFC characterization. The best performance is obtained when CNT-15 is adopted as an additional nanoporous layer with MPL in the dry operation. The current densities at a cell voltage of 0.6 V are 0.454 and 0.743 A cm−2 in dry and wet operations, respectively, corresponding to an increase of 28.5% and 57.1%, respectively, compared to carbon-black MPL. Enhancements in water management and reaction kinetics lead to this performance increase. In particular, the enhanced water storage and expulsion are benefits differentiated from employing CNT as the single nanoporous layer. [Display omitted] ∙ CNT-based nanoporous layers were employed to GDL of PEMFC. ∙CNTs were fabricated via cost-effective direct spinning method. ∙Additional nanoporous layer (w/ MPL) increased current density by 57% (at 0.6 V). ∙Mitigated charge transfer and ohmic resistances led to performance enhancements. ∙The correlation between the quality of CNT and fuel cell performance was subpar. [ABSTRACT FROM AUTHOR]