We report selective electrocatalytic reduction of carbon dioxide to carbon monoxide on gold nanoparticles (NPs) in 0.5 M KHCO3 at 25 °C. Among monodisperse 4, 6, 8, and 10 nm NPs tested, the 8 nm Au NPs show the maximum Faradaic efficiency (FE) (up to 90% at -0.67 V vs reversible hydrogen electrode, RHE). Density functional theory calculations suggest that more edge sites (active for CO evolution) than corner sites (active for the competitive H2 evolution reaction) on the Au NP surface facilitates the stabilization of the reduction intermediates, such as COOH*, and the formation of CO. This mechanism is further supported by the fact that Au NPs embedded in a matrix of butyl-3-methylimidazolium hexafluorophosphate for more efficient COOH* stabilization exhibit even higher reaction activity (3 A/g mass activity) and selectivity (97% FE) at -0.52 V (vs RHE). The work demonstrates the great potentials of using monodisperse Au NPs to optimize the available reaction intermediate binding sites for efficient and selective electrocatalytic reduction of CO2 to CO.

Monodisperse nickel nanoparticles are prepared from the reduction of Ni(acac)(2) with borane tributylamine in the presence of oleylamine and oleic acid. Without any special treatment to remove the surfactants, the as-synthesized Ni nanoparticles supported on the Ketjen carbon support exhibit high catalytic activity in hydrogen generation from the hydrolysis of the ammonia-borane (H(3)NBH(3)) complex with a total turnover frequency value of 8.8 mol of H(2) x (mol of Ni)(-1) x min(-1). Such catalysis based on Ni nanoparticles represents a promising step toward the practical development of the H(3)NBH(3) complex as a feasible hydrogen storage medium for fuel cell applications.

Formic acid (FA, HCOOH) is a common small organic acid with a melting point of 8.4 8C and boiling point of 100.8 8C. It can undergo a dehydrogenation reaction, HCOOH!H 2 + CO 2 , releasing H 2 that will be important for hydrogen-based energy applications. [1] Traditionally, the dehydrogenation of FA is catalyzed by metal complexes dissolved in an organic solvent and the catalysis is enhanced by adding an additive, such as sodium formate or amine adducts. [2] To make more practical catalyst for the dehydrogenation reaction of FA, heterogeneous catalysts based on metal nanoparticles (NPs) have been developed. These catalysts are generally more stable but much less active than the homogeneous ones. [3] Recently, bimetallic NP catalysts were found to be more active than their single component counterparts for the dehydrogenation of FA. [4] For example, AgPd NPs supported on cerium oxide or AuPd NPs immobilized in a metal-organic framework showed an enhanced FA dehydrogenation catalysis with the initial turnover frequency (TOF) reaching 210 h À1 or 192 h À1 at 90 8C, respectively. [5] However, the high rate of hydrogen generation observed from these heterogeneous catalysts could only be achieved when an additive was present and the reaction was maintained at temperatures close to 100 8C. [6] Under these "harsh" conditions, HCOOH was also subject to an undesired dehydration reaction, HCOOH!H 2 O + CO. [7] Interestingly, Ag/Pd core/shell NPs were found to be promising in catalyzing the dehydrogenation of FA in an aqueous FA solution at lower temperatures (up to 50 8C) without any additive. [8] But their initial TOFs were in the range of 125-252 h À1 at temperatures between 25-50 8C.Considering the limitation seen from the previous syntheses in controlling the NP size and composition, we decided to re-evaluate the binary alloy NPs on their catalysis for the dehydrogenation of FA. Our very recent report showed that monodisperse 4 nm AuPd NPs were more active in catalyzing the dehydrogenation of FA in water at 50 8C without using any additive and their initial TOF reached 230 h À1 . [9] Encouraged by this result, we further improved our solution phase synthesis and produced monodisperse 2.2 nm AgPd NPs with the desired composition controls. We found that these monodisperse 2.2 nm AgPd alloy NPs were a highly active heterogeneous catalyst for the dehydrogenation of FA. In water without any additive, the Ag 42 Pd 58 NPs showed the highest catalytic activity among all AgPd NPs tested with their initial TOF reaching 382 h À1 at 50 8C and apparent activation energy at 22 AE 1 kJ mol À1 . These are the best values ever reported by a heterogeneous catalyst for the dehydrogenation of FA in aqueous solution. It demonstrates the great potential of binary alloy NPs as a more practical catalyst for the dehydrogenation of FA and hydrogen generation.The 2.2 nm AgPd alloy NPs were synthesized by coreduction of silver(I) acetate, Ag(Ac), and palladium(II) acetylacetonate, Pd(acac) 2 , in oleylamine (OAm), oleic acid (OA) and 1-octadecen...