PtNi colloidal nanoparticle clusters: Tuning electronic structure and boundary density of nanocrystal subunits for enhanced electrocatalytic properties

Abstract

Colloidal nanocrystal clusters constructed of abundant nanocrystal subunits possess immense potential for catalysis in fuel cells due to their collective properties and novel functionalities deriving from the ensemble. Nevertheless, the effects of electronic structure and boundary density of subunits on their electrocatalytic properties are rarely reported. Herein, we report a facile synthesis of PtNi colloidal nanocrystal clusters with tunable electronic structure and boundary density through a one-step solvothermal approach. With the increase of Ni/Pt molar ratio, more grain boundary and interspace are generated in PtNi colloidal nanocrystal clusters, which result in more active sites and high electrochemical surface area for the electrooxidation reactions of methanol and formic acid. Specifically, the PtNi3 exhibit approximately 11.5 (9.6) times higher specific activity and 1.8 (1.5) times higher mass activity than those of benchmark Pt/C for methanol (formic acid) oxidation. The PtNi3 CNCs also possess more excellent diffusion ability for MOR (0.038) and FAOR (0.0082) compared with other PtNi CNCs and Pt/C. Combination of experiments and density functional theory calculation reveals the enhanced activity derives from the optimization of boundary density, d-band center and further OH adsorption ability. This approach provides a strategy to design other colloidal nanocrystal clusters with excellent electronic and surface structure for direct fuel cell applications.