Fuel Cell Materials: Peptide-directed Strategies for One-Pot Growth, Immobilization and Dispersion of Platinum Nanoparticles on Graphene Electrodes

T.R. Walsh
Deakin University,
Australia

Keywords: graphene, platinum nanoparticle, peptides, immobilization

Summary:

The commercial viability of Pt/C catalysts for fuel cells remains uncompetitive with fossil-fuel solutions for several reasons, including Pt agglomeration and consequent loss of catalytic activity, and the fact that Pt is very expensive. Non-Pt-based solutions are currently the subject of intense scrutiny, however, Pt/C electrodes remain the top performers for both the hydrogen evolution (HER) and oxygen reduction (ORR) reactions, relevant to fuel cells. One way to minimize cost is to decrease the Pt loading by using Pt nanoparticles (NPs) adsorbed on the carbon electrode surface. Graphene, with its high surface-area-to-mass ratio, superior charge-carrier mobility, high tensile strength and excellent thermal conductivity, is an ideal electrode material. Unfortunately, the adhesion between Pt NPs and graphene is relatively weak, which is thought to result in the agglomeration of the Pt NPs. Pt NP immobilzation on the graphene surface is a key strategy to inhibiting agglomeration, for example by using surface-adsorbed ligands. Optimal ligand coverage is critical to successfully realizing this strategy; too much ligand will obscure the NP surface and reduce Pt accessibility needed to catalyze the HER/ORR reactions, too little coverage will not be sufficient to prevent agglomeration. Previously, we have shown, via integrated experimental and modeling research, that non-covalent adsorption of peptides can act as excellent ligands that can both stabilize dispersion of Au NPs in solution AND accelerate catalytic reactions on the AuNP surface in aqueous media. Key to the success of this approach was the use of gold-binding peptides that were specifically selected to recognize Au surfaces Here, we adapt this strategy, by using bi-functional peptides, comprising a graphene-recognizing domain at one end, and a Pt-recognizing domain at the other.These peptides are shown, via molecular simulations, to effectively assemble the Pt nanoparticles on the graphene substrate under aqueous conditions and prevent agglomeration, even at high operating temperatures. Our findings suggest a transformative low-cost and effective peptide-based strategy to realize the in-situ growth, organization, dispersion and activation of Pt NPs on carbon electrodes for fuel cells.