Membrane electrode assembly based on buckypaper with gradient distribution of platinum, proton conductor and electrode porosity

A three-dimensional catalyst layer (CL) with gradient distribution of key components based on double-layered buckypaper (BPCL) as cathode for proton exchange membrane fuel cells (PEMFCs) was fabricated. This novel structured BPCL was prepared by using multi-walled carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) as main framework structure and Pt/C catalyst as active sites. The gradient distribution of platinum (Pt) nanoparticles, proton conductor (Nafion ionomer) and electrode porosity along the thickness of CL were established to reduce Pt loading and facilitate the transportation of protons, reactants and products. Two critical parameters for fabricating membrane electrode assembly (MEA), Nafion content which influences the proton transfer process in CL and hot-pressing temperature which affects the combination situation of CL with electrolyte membrane, were further optimized to promote proton transfer efficiency and decrease the contact resistance between CL and membrane. By using this unique structure, a maximum power density of 536.8 mW cm⁻² was achieved at cell temperature of 80 °C, inlet gas pressure of 100 kPa and relative humidity of 80% with an ultra-low Pt loading of 0.09 mg_Pt cm⁻² in cathode. The generated cathodic Pt utilization is 0.168 g_Pt kW⁻¹, reducing by 20.1% compared with the MEA based on traditional catalyst coated on membrane (CCM) process (0.21 g_Pt kW⁻¹).