Controlling the deposition of Pt nanoparticles within the surface region of Nafion

The chemical reduction of Pt-complexes to generate Pt nanoparticles within the surface region of a Nafion membrane may provide an alternative route to producing more efficient and robust membrane electrode assemblies for fuel cells. Controlling the deposition to enable manipulation of the Pt loading and distribution is a necessary first step to allow full exploration of a Nafion–noble metal composite. We find that the hydration state of the Nafion has the most significant impact on constraining where Pt deposition happens in the Nafion membrane. When coupled with variations in the pH of the working solutions, the depth of the Pt deposition zone can be varied from a sharply defined 200 nm on up to a 15 μm. A suggested mechanism to explain these findings is provided, based on the use of NaBH4 as reductant and Pt(NH3)4(NO3)2 as the source of Pt. We also present electrochemical and spatially resolved conductivity measurements that suggested the deposted Pt nanoparticles form an interconnected network with the Nafion.

► A simplified method for the fabrication/manufacture of catalyst coated membranes (CCMs) has been developed for electrochemical applications. ► Parameters controlling the electroless deposition of Pt in the surface region of a Nafion membrane were determined. ► Pt nanoparticles are located in the near-surface region of the Nafion membrane. ► Fully hydrated Nafion membranes result in a dispersed Pt deposition region tens of microns below the Nafion surface. ► Low hydration levels create a Pt deposition zone that extends ∼200 nm below the membrane surface. ► Simultaneous deposition of Pt on both sides of the membrane is demonstrated. ► Electrical connectivity between Pt particles determined using absorbed current imaging and electrochemical surface area measurements.