Manojkumar Balakrishnan,Pranay Shrestha,Nan Ge,ChungHyuk Lee,Kieran F. Fahy,Roswitha Zeis,Volker P. Schulz,Benjamin D. Hatton,Aimy Bazylak
We present electrospinning as a versatile technique to design and fabricate tailored polymer electrolyte membrane (PEM) fuel cell gas diffusion layers (GDLs) with a pore-size gradient (increasing from catalyst layer to flow field) to enhance the high current density performance and water management behavior of a PEM fuel cell. The novel graded electrospun GDL exhibits highly robust performance over a range of inlet gas relative humidities (RH). At relatively dry (50% RH) inlet conditions that exacerbate ohmic losses, the graded GDL lowers ohmic resistance and improves high current density performance compared to a uniform GDL with larger pores and fiber diameters. Specifically, the graded GDL facilitates a beneficial degree of liquid water retention at the catalyst layer/GDL interface due to the high capillary pressure inherent in its microstructure, thereby improving membrane hydration. Additionally, enhanced graphitization and connectivity of the graded electrospun fibers improves heat dissipation from the catalyst layer interface compared to the GDL with larger fiber diameters, thereby reducing membrane dehydration. When the inlet RH is raised to fully humid (100% RH) conditions, the graded GDL mitigates liquid water accumulation and lowers mass transport resistance. Specifically, the pore size gradient directs the removal of liquid water from the GDL, resulting in superior performance at high current densities.
Application of traditional electrospun scaffolds in tissue engineering is limited due to the sheet-like nanofiber layers hindered cell infiltration. In this study, a three-dimensional (3D) thick nanofiber stack with pore size gradient was fabricated via a novel electrospinning setup. Instead of a traditional flat-plate collector, a small copper plate which covered a hole of PMMA sheet was connected to negative voltage, resulting in focused collection of nanofibers and quickly enhanced scaffold thickness due to insulating PMMA preventing fibers from spreading elsewhere. The average pore size can reach more than 25 μm which benefit for cell infiltration. In the process of electrospinning, the mat with increased thickness may influence the electric field and has effect on fiber diameter and pore size.
A three-layer small-diameter vascular graft (SDVG) of polycaprolactone (PCL) and l -polylactic acid (PLLA) with pore diameter gradient was prepared through combining variable-extrusion speed iterative electrospinning and ultrasonic reaming. The SEM results showed that the three-layer PCL/PLLA SDVG has distinct pore diameter gradient. The Young’s modulus, ultimate tensile strength (UTS), burst pressure (BP) and compliance of the vascular graft were high as 20.116 ± 0.465 MPa, 2.259 ± 0.141 MPa, 2050 ± 249 mmHg and 4.203 ± 0.330 %/100 mmHg, respectively. The UTS of the graft is similar to human coronary arteries. The BP meets the basic requirements to prevent aneurysmal dilation, and the compliance is higher than that of sheep carotid artery. The fluid–solid coupling simulation results showed that the graft had high mechanical properties to withstand the same blood flow velocity as human coronary arteries, and there was no stress concentration in the wall. Besides, it had good biocompatibility, promoting the adhesion and proliferation of rat vascular endothelial cells (ECs). The successful preparation of the small-diameter vascular graft with high mechanical properties for preventing itself from rupturing and ensuring the overall function, provides more possibilities for the clinical transplantation of small-diameter vascular grafts.
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