Impact of Transition Metals and Electrocatalyst Layer Thickness on the Pt-Based Cathodes of Proton Exchange Membrane Fuel Cells – Do Multimetallic Electrocatalysts Necessarily Yield an Improved Performance?

The interplay between i) cathodic electrocatalytic layer (EC layer) features of proton exchange membrane fuel cell (PEMFC), focusing on the oxygen reduction reaction (ORR) electrocatalyst (EC) and the Pt loading; and ii) the PEMFC performance and durability is evaluated. An innovative hierarchical “core–shell” carbon nitride multimetallic ORR electrocatalyst (“PtCuNi/C” H-EC) is compared with a conventional Pt/C benchmark. The various contributions to PEMFC performance at beginning of test (BOT) are isolated and correlated to the physicochemical features of the ORR EC and the cathodic EC layer. The PEMFC durability is investigated extensively via accelerated stress tests (ASTs) mimicking long-term operation. Particular attention is dedicated to determine how ageing affects: i) PEMFC cell voltage; and ii) the cathode electrochemically active surface area (ECSA). “Post-mortem” studies are carried out to probe how ageing influences the cathodic EC layer features, including: i) chemical composition; ii) elements distribution; iii) EC morphology; and iv) structure and crystal size of the Pt-based metal nanoparticles bearing the active sites. Integrating the experimental results allows to identify both the positive and the detrimental effects triggered by the introduction of transition metals (TMs) in the ORR EC on the factors modulating PEMFC performance and long-term operation.