A Contrastive Study of the Prominence View and the Figure-Ground Theory

Because of the high cost and scarcity of Pt, the commercialization of fuel cell technology is still facing a great challenge. Compared with the proton exchange membrane fuel cell, one advantage of the anion exchange membrane fuel cell (AEMFC) is the possibility of partially replacing or completely removing Pt catalyst in the cathode. Recently, the oxygen reduction reaction (ORR) of transition metals (such as Fe, Co, Ni as well as their compounds) in alkaline environments has been greatly improved, with substantial efforts devoted to controlling the nanostructure and adjusting the active sites (including the density and chemical structure). Based on rotating disk electrode (RDE) tests, these transition metal compounds show attractive ORR performance as compared with state-of-art Pt/C catalysts. However, when fabricated into films for membrane electrode assembly, these highly active transition metal compounds (such as Co-based materials) do not show satisfactory fuel cell performance, hindering their further development for application in fuel cells. This is because of an insufficient understanding of structure-activity relationships of transition metal catalyst layers for fuel cells. Compared with conventional powder catalysts, nanostructured catalysts directly grown onto a conductive substrate, for example by electrodeposition, are anticipated to construct an electron conductive framework, optimizing the triple-phase-boundary within the catalyst layer. Furthermore, catalyst structures and their arrays can be easily and quickly obtained by the electrodeposition method.