Modifying electrodes with nickel-based molecular electrocatalysts for hydrogen production

The complex [Ni(P ₂ ^PhN ₂ ^Ph) ₂] ⁺² { P ₂ ^PhN ₂ ^Ph = 1,3,5,7-tetraphenyl-1,5-diaza-3,7-diphosphacyclooctane} catalyzes the electrochemical reduction of protons to form hydrogen useful for energy storage with a reported rate of 720 s ^-1. While this is a fast catalyst in a homogeneous solution, to be more useful in an integrated system, it would be useful to immobilize the catalyst at the interface between the electrode and bulk solution. A central issue with such modified electrodes is the transport of electrons and protons to the surface-confined catalyst. This work describes efforts in our laboratory to use functionalized versions of [Ni(P ₂ ^PhN ₂ ^Ph) ₂] ⁺² to modify electrode surfaces in ways that maintain catalytic activity and long term stability. Efforts include using covalent attachment, electropolymerization, thin films of ionic liquid, thin films of ionic liquid combined with Nafion, and adsorption. The more successful methods will be discussed.