Improvement of platinum adhesion to carbon surfaces using PVD coatings

The adhesion of Pt to carbon surfaces is an important technological consideration in proton exchange membrane fuel cells (PEMFCs). Thin films of Au, Ti and Cr were deposited on graphite, non-hydrogenated diamond-like carbon (NH-DLC) and hydrogenated DLC (H-DLC) coatingsʹ surfaces using a physical vapour deposition (PVD) process. The friction force curves obtained from sliding a Pt pin against these surfaces were used to evaluate the adhesion of Pt to the coated carbon surfaces. Interface strength calculations for graphite and diamond surfaces were carried out using first principles simulations. The incorporation of the interfacial PVD films enhanced the adhesion between Pt and graphite; rather than interfacial separation taking place, the bonds in graphite were broken (graphite decohesion) as confirmed by the first principles calculations. The bond between Pt and NH-DLC was stronger than that between Pt and graphite, and the transfer of Pt to the uncoated NH-DLC, as well as the Ti- and Cr-coated NH-DLC surfaces occurred as a result of the breaking of Pt–Pt bonds (Pt decohesion). Au film was peeled off the NH-DLC surface by the Pt pin contact, consistent with the calculated work of separation for the Au/carbon interface, which was weaker than works of decohesion for both NH-DLC and Pt. In case of the H-DLC, the low adhesion of Pt to this surface was improved by the PVD coatings, but the improvement was less compared to the coated graphite surfaces, as all PVD films were peeled off the H-DLC surfaces by the sliding action of the Pt pin.