Platinum-Modified Cobalt Oxide/Cobalt Nanotubes as Multifunctional Electrocatalysts in Alkaline and Acidic Conditions

Nanostructure platinum is an effective catalyst that is active toward a broad range of electrochemical processes over a wide range of pH values. However, its high cost and low abundance prevent its widespread use in practical devices. A promising strategy to overcome the limitations of platinum is to combine platinum with less expensive and more abundant transition metals. In this report, we employ an ambient, template-based approach to prepare monodisperse Co nanotubes (NTs) and modify them with platinum via an electroless deposition process. The composition of the resulting Pt modified Co NTs (Pt-Co NTs) can be varied by controlling the Pt ion concentration in the electroless deposition step. The resulting Pt-Co NTs have a hierarchical structure consisting of Pt-Co NTs coated with an amorphous Co-oxide film. The amorphous Co-oxide coating activates the Pt-Co NTs to the oxygen evolution reaction (OER) leading to a 9-fold enhancement in the OER activity in an 80% (by mass) Pt-Co NT relative to pure Pt nanowires. The surface oxide coating can be selectively removed by cycling the Pt-Co NTs in an acidic solution. Removing the oxide film activates the Pt-Co NTs toward methanol oxidation (MOR) and oxygen reduction (ORR) reactions. In both cases, the trends in MOR and ORR activity follow a volcano-type dependence as a function of composition. The catalyst with the optimum composition of 60% Pt has a 4-fold increase in the specific activity for MOR and maintains a +20 mV shift in the half-wave potential for ORR relative to that of pure Pt nanowires.