In Situ Construction of a Nanostructured Ultrathin Catalyst Layer on Both Sides of a Membrane toward Fuel Cell Application

As the core component, high-performance catalyst-coated membranes (CCMs) are of critical importance for proton exchange membrane (PEM) fuel cells. Composition and microstructure modulations of CCMs are feasible strategies to improve their performance. Herein, an integrated ultrathin ultralow-Pt CCM with a similar to 197-nm-thick catalyst layer (CL) and a Pt loading of similar to 16 mu g cm(-2) on each side is directly prepared with a wet-chemical method. The synergistic effect of the precursor and reductant is responsible for the regioselective nucleation and growth of a peony-like Pd nanoflower at the interface of a membrane and reaction solution, followed by the deposition of 4-5 layers of dense Pt nanoparticles on Pd (i.e., Pt/Pd nanoflower CCM). A single cell of the Pt/Pd nanoflower CCM demonstrates a significantly improved mass activity (4.38 A mg(Pt)(-1) at 0.9 V) compared with that of the conventional Pt/C CCM (0.22 A mg(Pt)(-1)). The enhanced performance originates from a high electrochemical active surface area (50.3 and 36.1 m(2) g(Pt)(-1) for the Pt/C CCM), an increased Pt utilization efficiency (50.4%, 38.7% for the Pt/C CCM), and remarkable oxygen reduction reaction activity (specific activity at 0.9 V: 86.98, 6.09 A m(-2) for the Pt/C CCM) closely related to the electronic effect at the Pt and Pd interface. An accelerated degradation test manifests that the prepared Pt/Pd nanoflower CCM is more stable than the conventional CCM. This study opens up a unique avenue to directly engineer nanostructured ultrathin CLs on both sides of a membrane with potential applications in electrochemical energy conversion and storage systems.