Catalysis of Au nano-pyramids formed across the surfaces of ordered Au nano-ring arrays

Gold (Au) is a noble metal that has been widely researched due to its high catalytic performance-to-cost ratio. The catalysis could be improved by fabrication of nanostructured arrays on Au thin film with a large area. In the present paper, a facile NSL-RIE approach comprising of nanosphere lithography followed by oxygen plasma reactive ion etching has been developed to fabricate ordered Au nano-ring arrays with almost 100% substrate coverage. The preferential etching of {1 1 1} lattice planes of Au gives rise to the formation of a number of Au nano-pyramids across the entire surface of the nano-ring arrays. The sharp tips along with the Au atoms around the edges of these nano-pyramids provide active sites that perform strong catalysis. Meanwhile, Moiré fringes are observed over the etched Au surface which is caused by the rotation of the partial Au lattice with respect to the original Au lattice. This lattice distortion provides high surface energy allowing the significant improvement of the catalysis of Au nano-ring arrays. The direct evidence is proven by the enhanced electrochemical properties of the as-produced Au nano-ring array, which has high efficiency in ethanol oxidation reactions (EORs) with low energy input requirement. Electrochemical testing with varying physical parameters shows that the detecting limit of ethanol is ∼5.0 mM and strong signals come with high concentrations of mobile charge carriers at extreme pH values. Long continuous CV scans reveal that in alkaline medium, C1 pathway could become increasingly preferential over C2 pathway, and thus making the Au nano-ring array structure useful in the field of direct ethanol fuel cell.