Effect of glycerol on micro/nano structures of catalyst layers in polymer electrolyte membrane fuel cells

Effect of glycerol in catalyst ink on the micro/nano structures of polymer electrolyte membrane fuel cells (PEMFCs) catalyst layers was investigated. Catalyst layers were fabricated by the decal method for various mass ratios of glycerol to carbon in the catalyst ink r_gc (=m_g/m_c) from 0 to 20, and thus change the micro/nano structures of catalyst layer. The structures were evaluated by measuring the pore size with a mercury porosimeter and by observing the surface with a field emission scanning electron microscope (FE-SEM). At r_gc < 5, although the residual glycerol was almost zero, the cell performance decreased with decreasing r_gc, suggesting that the structure of the catalyst layers significantly depended on r_gc. At r_gc > 5, the remaining glycerol was proportional to r_gc. Because remaining glycerol blocks the pores and reduces the reaction sites, the cell performance decreased with increasing r_gc. If the remaining glycerol is removed by steam water, the performance is improved to the same level of the maximum performance for not steamed MEAs.