STUDY AND DEVELOPMENT OF CYLINDRICALLY STRUCTURED POLYMER ELECTROLYTE MEMBRANE FUEL CELLS

Abstract

The rapid increase in energy demand and fossil fuel consumption are the major challenges in terms of environmental stability and climate change, necessitating the use of alternative energy sources. Hydrogen energy, among such sources, has emerged as an environmentally friendly alternate energy source that changes the renewable energy scenario due to its ability to lower carbon footprint and reduce dependence on fossil fuels. Polymer electrolyte membrane fuel cells (PEMFC) are one such source with a high-power density (600-2000 kW/L) and efficiency (40-50%, in CHP >90%), lower operating temperature (~70oC), ultralow operational noise, and pollution that are preferred in transportation, stationary, aviation, and other applications. Furthermore, cylindrical PEMFCs (Cy-PEMFCs) are the most effective than that of planar cells in terms of gravimetric and volumetric power density for lower-power applications. In the cell construction, the membrane electrode assembly (MEA) was wrapped between anode and cathode current collectors (CC) and further clamped together appropriately. The absence of typical bipolar plates (BPPs) makes the cell compact and lightweight, thereby outperforming the planar cells, particularly in lower-power applications (<500 W). The advantages of cylindrical design over other designs that make it a promising candidate for both low and high-power portable applications are, • Cylindrical fuel cells are cost-effective because of the absence of graphite bipolar plates. • Weight and size are less than that of the planar cell, which leads to better gravimetric and volumetric power density. • The thinner cathode current collector used in the cylindrical design facilitates easier water management. • It can operate the stack in the air-breathing mode without the shell enclosure and with the oxidant supply from the compressed storage, as in the case of conventional PEMFCs, by employing a shell enclosure. This study focused on the development of Cy-PEMFC with optimized operating parameters and improved performance. The cell was first modelled numerically for both structural and CFD modelling and validated with an ICR of 0.40 Ω-cm2, with clamping pressure of ~1.5 MPa to determine the contact pressure and cell performance, respectively. Further, considering contact resistance identified as one of the key influencing parameters, a spring clamping system was developed using spring and rotating discs. The existing strap clamping system was ii compared with the spring mechanism on the basis of species transport, contact pressure distribution, contact resistance, and cell performance. The contact pressure distribution of the spring mechanism was found to be more uniform, resulting in a performance enhancement of 15 mW/cm² owing to a 33% rise in contact pressure. Additionally, the spring system availed better breathing space for the fuel and oxidant on the anodic (~6%) as well as cathodic sides (~12%). Subsequently, the cell performance was analyzed for energy and exergy efficiency, followed by sustainability indices. The energy and exergy efficiencies increased from 16.39 % to 36.67 % and 10.93% to 30.35 % for 91.21 mA/cm2 to 400 mA/cm2, respectively. The maximum exergy efficiency was obtained as 30.35% at 2.4 A and 0.3 V. Furthermore, the environmental sustainability index for the Cy-PEMFC was increased with exergy efficiency (10.93 to 30.35 %) from 0.04 to 0.25 at optimized operating conditions (at 1 bar, 323 K). Finally, the cell underwent degradation analysis through accelerated degradation tests under different operating temperatures and RH. The potential decay rate was found to be 0.35 mV/h for the 120-h test. However, the optimized operating condition was found to be at ~35oC and RH ~60%. The future scope of the study includes extended degradation studies to support the viability of practical applications. Keywords: PEMFC, Modelling, Stack design, Performance, Contact resistance, Degradation, Exergy analysis.