Highly-effective palladium nanoclusters supported on para-sulfonated calix[8]arene-functionalized carbon nanohorns for ethylene glycol and glycerol oxidation reactions

Non-Pt noble metal clusters like Pd clusters are considered as promising electrocatalysts for fuel cells, but they suffer from problems such as easy aggregation during the catalysis reactions. To solve these problems, we demonstrate a water-based method for the synthesis of ultrasmall Pd clusters with an average size of 2.5 nm uniformly dispersed on single-walled carbon nanohorns functionalized by para-sulfonated calix[8]arene (SCX8–SWCNHs) at room temperature without organic solvents. The high dispersibility of the 2.5 nm Pd clusters is caused by the large amount of SCX8 (with many negative charges of –SO3−) on SWCNHs. The large amount of negative charges from –SO3− enhances the interactions between the supports and metal precursors, resulting in the in situ growth of the highly dispersed Pd clusters. The Pd@SCX8–SWCNHs nanocatalyst exhibits increased catalytic activity for the electrooxidation of ethylene glycol and glycerol when compared with that of the Pd/C catalyst in alkaline media, which is ascribed to the high dispersity and ultrafine properties of the Pd clusters. This simple and facile approach has major importance for the preparation of electrocatalysts with high electrocatalytic activity on suitable supports.