Over-Potential Deposited Hydrogen (Hopd) as Terminating Agent for Platinum and Gold Electro(co)Deposition

An approximate Pt monolayer is a desirable morphology for oxygen reduction reaction (ORR) catalysts with high mass activity. Such structures can, reliably, be synthesized on gold by monolayer-limited CO- or over-potential deposited hydrogen (H-opd)-terminated Pt electrodeposition. On a more appropriate catalyst support for proton-exchange membrane fuel cells (PEMFCs), namely, the native oxide on metallic titanium (TiOx/Ti), the synthesis is disrupted by preadsorption of the monolayer-limiting agent. The role of auxiliary NaCl during H-opd-terminated Pt electrodeposition (chloride-assisted H-opd termination) on TiOx/Ti is investigated and discloses effects similar to CO observed previously. Graphical Chloride-assisted, chloride-disrupted: NaCl and over-potential deposited hydrogen (H-opd) create an approximate Pt submonolayer with high specific ORR activity on gold while on TiOx/Ti, the same combination creates Pt particles with low specific ORR activity.