Abstract
We report a facile bottom-up synthetic approach to preparing ultrathin two-dimensional (2D) palladium nanosheets (PdNSs) with selectively exposed surface facets. Our synthetic strategy is based on the utilization of the nanoconfined lamellar mesophases of amphiphilic functional surfactants to template the growth of PdNSs in aqueous solution. Preferential adsorption of functional groups (e.g., COOH, pyridyl and quaternary ammonium) and halide counter ions (e.g., Br(-) and Cl(-)) in the long-chain surfactants onto different Pd planes results in the epitaxial growth of {100}, {110} and {111}-exposed surface facets of ultrathin PdNSs. Our synthetic approach is a general, powerful and scalable method to precisely control the surface facets of ultrathin 2D PdNSs, thus providing an opportunity to evaluate facet-dependent catalytic performance of Pd nanocrystals. Ultrathin PdNSs have been examined as the electrocatalysts for hydrogen evolution reactions (HERs). We show that {100}-exposed PdNSs display superior catalytic activity and stability for HERs, compared to that of {110} and {111}-exposed ones as well as their bulk counterparts. Conceivably, our findings will offer a general guideline in rational design of surfactant templates for other 2D metal nanosheets.