Nicotinamide adenine dinucleotide assisted shape-controlled synthesis of catalytically active raspberry-like gold nanostructures

We describe the shape-controlled growth of raspberry-like gold (Au) nanostructures and their application in the electrochemical oxidation of methanol and reduction of oxygen. Nicotinamide adenine dinucleotide (NAD⁺) plays a vital role in the growth of raspberry-like Au nanostructures. The preferential adsorption of NAD⁺ onto the (011) facets of Au favors the growth of raspberry-like morphology. In the absence of NAD⁺, icosahedral Au nanostructures were obtained. The raspberry-like Au nanostructures have been characterized by UV-visible spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and electrochemical measurements. The FESEM image shows that the raspberry-like morphology has an average size of 170 nm. The spectral profile shows a broad band between 650 and 795 nm. Compared to Au nanoseeds and icosahedral Au nanostructures that were grown in the absence of NAD⁺, the raspberry-like morphology has excellent catalytic activity towards the electrochemical oxidation of methanol and reduction of oxygen. On the raspberry-like nanoparticle-based electrode, the oxidation of methanol was observed at 0.35 V in alkaline pH, and the reduction of oxygen was observed at -0.06 and -0.4 V in 0.1 M PBS. The electrochemical reduction of oxygen occurs in two steps: (i) reduction of oxygen to H₂O₂ and (ii) further reduction of electrogenerated H₂O₂ to water. The electrochemical performance of the raspberry-like nanostructure-based electrode is highly stable.