Effect of boron-doping levels in Pt-B-graphene on the electrochemical properties and cell performance of high temperature proton exchange membrane fuel cells

Different levels of B were doped into graphene (Gr), and Pt nanoparticles were subsequently deposited to form Pt-xB-Gr (x = 0.0, 1.0, 3.0, and 5.0). B-doping led to a narrower Pt nanoparticle size distribution with a more uniform dispersion. The amount of Pt deposited onto Gr increased significantly by at least 13% upon B-doping, in comparison to Pt-Gr, and was proportional to the B-doping level. However, X-ray photoelectron spectroscopy and Raman analyses revealed an upper limit to B-doping in the form of BC3 within the graphene structure for x > 3.0 in Pt-xB-Gr. Rotating disk electrode experiments demonstrated an enhancement in the oxygen reduction reaction (ORR) upon B-doping, yielding a maximum ORR activity with Pt-3.0B-Gr. Koutechy-Levich plots estimated an electron transfer number (n) of 2.5, 3.2, 3.6, and 3.0 for Pt-xB-Gr, where x = 0.0, 1.0, 3.0, and 5.0, respectively, based on the diffusion limiting current density. The enhancement in the ORR and cell performance of high temperature proton exchange membrane fuel cells (HT-PEMFCs) upon B-doping was attributed to the transfer of pi electrons that were activated through the conjugation of electron deficient B with the inactive pi electron system within graphene, to Pt nanoparticles. (C) 2016 Elsevier Ltd. All rights reserved.