Low and non-platinum electrocatalysts for PEMFCs: Current status, challenges and prospects

Abstract

Platinum-based nanomaterials are the most commonly adopted electrocatalysts for both anode and cathode reactions in polymer electrolyte membrane fuel cells (PEMFCs) fed with hydrogen or low molecular alcohols. However, the scarce world reserves of Pt and its high price increases the total cost of the system and thus limits the feasibility of PEMFCs. Based on this problem, for PEMFCs to have wide practical applications and become commercially viable, the challenging issue of the high catalyst cost resulting from the exclusive adoption of Pt or Pt-based catalysts should be addressed. One of the targets of the scientific community is to reduce the Pt loading in membrane electrode assemblies (MEAs) to ca. $150\mu \text{g}\text{c}{\text{m}}_{\text{MEA}}^{-2}$, simultaneously maintaining high PEMFCs performances. The present paper aims at providing the state-of-the-art of low Pt and non-Pt electrocatalysts for: (a) H₂-O₂ PEMFCs, (b) Direct Methanol Fuel Cells (DMFCs) and (c) Direct Ethanol Fuel Cells (DEFCs). The detailed analysis of a big number of recent investigations has shown that the highest mass specific power density (MSPD) value obtained for H₂-O₂ PEMFCs has far exceeded the 2015 target ($5\text{mW}\mu {\text{g}}_{{\text{Pt}}_{\text{total}}}^{-1}$) set by the USA department of energy, while a several number of investigations reported values between 1 and 5 mW μg_Pt⁻¹. However, the highest values measured under DMFCs and DEFCs working conditions are still relatively low and close to 0.15 and 0.05 mW μg_Pt⁻¹ respectively. Moreover, the last years, promising results have been reported concerning the design, fabrication, characterization, and testing of novel non-Pt (Pt-free) anodes and cathodes for PEMFCs applications.