Application of Electrochemically Deposited Cobalt Films in a Hydrogen Evolution Reaction

Abstract

Hydrogen gas production is a rapidly growing field of research due to its desirable properties from a sustainability viewpoint. The burning of hydrogen gas provides an environmental incentive as well, due to the lack of carbon-based byproducts [1-2]. Hydrogen gas is often evolved from water but is an energy intensive process. Solid chemical storage has been implemented through the use of metal hydrides, such as sodium borohydride. The oxidation reaction of sodium borohydride in water slowly evolves 4 moles of hydrogen gas. While a slow reaction is favorable for reduction, the use of NaBH4to produce hydrogen gas necessitates the use of catalysis to accelerate the reaction to an appreciable rate. A great deal of research has been conducted searching for catalysts of such reactions, often finding noble metals to be the most efficient. While less efficient than noble metals, cobalt materials have also demonstrated catalytic properties in a variety of hydrogen evolution reactions. Cobalt is more abundant in the earth’s crust than the noble metals, which makes it an arguably more attractive catalytic material due to a relatively lower cost and easier scalability [3-5]. Cobalt films deposited from aqueous (H2O/CoCl) and non-aqueous precursor (Ch:Ch/EG/CoCl) solutions were tested for catalytic activity in the hydrogen evolution reaction of aqueous NaBH4. The evolved gas was measured through the use of a water-displacement system, Ohaus microbalance, and mass logging software. The non-aqueously deposited films initially showed a higher reaction rate, but voids in the surface could prevent disassociation of the hydrogen, reducing the catalytic surface. The aqueously deposited films were largely amorphous, providing better active sites for the reaction than its non-aqueous counterpart. Both Co films outperformed the copper substrate (Cu). Catalytic Surface Rate Constant (10-3 min-1) Aqueous Co Deposition 4.9 Non-aqueous Co Deposition 4.6 Original Copper Substrate 3.3