Highly dispersed 1 nm PtPd bimetallic clusters for formic acid electrooxidation through a CO-free mechanism
Direct formic acid fuel cell (DFAFC) is an important research project in clean energy field. However, commercialization of DFAFC is still largely limited by the available catalysts with unsatisfied activity, durability and cost for formic acid electrooxidation (FAEO). Using Pt- and Pd-based nanoclusters as electrocatalysts is a particularly promising strategy to solve the above problem, but two attendant problems need to be solved firstly. (I) The controllable synthesis of practicable and stable sub-2 nm clusters remains challenging. (II) The catalyzing mechanism of sub-2 nm metal clusters for FAEO has not yet completely understood. Herein, different from traditional solution synthesis, by designing a novel supporting material containing electron-rich and electron-deficient functional groups, size- and dispersion-controllable synthesis of ∼1 nm PtPd nanoclusters is realized by an electrochemical process. The electrocatalytic properties and reaction mechanism of the PtPd nanoclusters for the FAEO were studied by different electrochemical techniques, in-situ fourier transform infrared (FTIR) spectra and density functional theory (DFT) calculations. The tiny PtPd nanoclusters have much higher catalytic activity and durability than commercial Pt/C, Pd/C and 3.5 nm PtPd nanoparticles. The present study shows that the metal-reactant interaction plays a decisive role in determining the catalytic activity and cluster-support interaction plays a decisive role in enhancing the durability of electrocatalyst. The ratio and arrangement of Pt and Pd atoms on the surface of 1 nm PtPd cluster as well as the overall valence state, d-band center and specific surface area make them exhibit different catalytic performance and reaction mechanism from nanoparticle catalysts. In addition, in situ FTIR and DFT calculations showed that on the surface of PtPd clusters, the generation of CO 2 through trans-COOH intermediate is the most optimal reaction pathway for the FAEO.
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