Palladium Nanoparticles Hardwired in Carbon Nanoreactors Enable Continually Increasing Electrocatalytic Activity During the Hydrogen Evolution Reaction

Catalysts typically lose effectiveness during operation, with much effort invested in stabilising active metal centres to prolong their functional lifetime for as long as possible. In this study palladium nanoparticles (PdNP) supported inside hollow graphitised carbon nanofibers (GNF), designated as PdNP@GNF, buck this trend. PdNP@GNF exhibits continuously increasing activity over 30000 reaction cycles when used as an electrocatalyst in the hydrogen-evolution-reaction (HER). The activity of PdNP@GNF, expressed as the exchange current density, is always higher than activated carbon (Pd/C), and after 10000 cycles PdNP@GNF surpasses the activity of platinum on carbon (Pt/C). The extraordinary durability and self-improving behaviour of PdNP@GNF is solely related the unique nature of the location of the palladium nanoparticles, i.e. at the graphitic step-edges within GNF. Transmission electron microscopy imaging combined with spectroscopic analysis reveals an orchestrated series of reactions occurring at the graphitic step-edges during electrocatalytic cycling, in which some of the curved graphitic surfaces open up to form a stack of graphene layers bonding directly with Pd atoms through Pd-C bonds. This results in the active metal centres become effectively hardwired into the electrically conducting nanoreactors (GNF), enabling facile charge transport to/from the catalytic centres resulting in the dramatic self-improving characteristics of the electrocatalyst.