Controllable synthesis of concave nanocubes, right bipyramids, and 5-fold twinned nanorods of palladium and their enhanced electrocatalytic performance

Concave palladium nanocrystals are attractive for their superior catalytic ability arising from high densities of atomic steps and kinks. However, it is still a challenge to generate the concave surface, which is not favored by thermodynamics owing to its higher surface energy. In this study, concave palladium nanocubes have been synthesized kinetically in high yield via a facile one-step wet chemical method using sodium ascorbate (NaA) as the reductant in an aqueous solution. This process allows independent control of the average edge length and the surface curvature of the nanocubes, respectively. The particle morphology can be tuned by changing the reducing rate during the reaction. Right bipyramids and 5-fold twinned nanorods with concave surfaces have also been synthesized with two reductants at the different stages or an appropriate amount of ascorbic acid only. Remarkable enhancements in both electrocatalytic activity and stability are observed on concave Pd nanocubes and twinned nanocrystals over conventional Pd nanocrystals with flat surfaces and commercial Pd/C.