Gram-scale synthesis of multipod Pd nanocrystals by a simple solid-liquid phase reaction and their remarkable electrocatalytic properties

In this paper, we describe how multipod Pd nanocrystals (NCs) have been synthesized on the gram scale by means of a simple solid-liquid phase reaction route (i.e., thermal reduction of solid Pd(CH₃COO)₂ in the liquid mixture of dodecylamine, oleic acid, and 1-octadecene under a temperature-programmed mode). The nanostructure evolves from the initially generated larger polyhedral NCs into smaller ones and then into the final multipods. The dodecylamine acts as both a mild reductant and a promoter, which affects the reduction rate and decreases the size of the initially formed polyhedral PdNCs. The morphology of the final NCs, such as tri- and tetrapods, may be determined by the number of growing points on each polyhedral NC. According to the temperature- and time-dependent experiments, a multistep growth mechanism including digestive ripening, oriented attachment, and fusion process is proposed. This simple solid-liquid phase reaction route can be extended to prepare other multipod metal nanostructures. The multipod PdNCs are found to have a high electrochemically active surface area and possess excellent electrocatalytic performance toward the oxidation of formic acid. Relative to that of polyhedral Pd and commercial Pd black catalysts, the multipod PdNCs exhibit much higher catalytic activity and long-term stability, which may make them a good candidate catalyst for direct formic acid fuel cells. This developed synthetic strategy together with the provided fundamental understanding of heterogeneous nucleation and growth has great potential for contriving a rational route to the preparation of advanced nanomaterials with specific morphology for catalytic and other functional applications. Multipod Pd nanocrystals were synthesized on the gram scale by means of a simple solid-liquid phase reaction route. A multistep formation mechanism that includes digestive ripening, oriented attachment, and a fusion process is proposed. This Pd nanostructure exhibits excellent electrocatalytic activity and long-term stability toward the oxidation of formic acid.