Electrochemical conversion of CO holds promise for utilization of CO as a carbon feedstock and for storage of intermittent renewable energy. Presently Cu is the only metallic electrocatalyst known to reduce CO to appreciable amounts of hydrocarbons, but often a wide range of products such as CO, HCOO, and H are formed as well. Better catalysts that exhibit high activity and especially high selectivity for specific products are needed. Here a range of bimetallic Cu-Pd catalysts with ordered, disordered, and phase-separated atomic arrangements (Cu:Pd = 1:1), as well as two additional disordered arrangements (Cu3Pd and CuPd3 with Cu:Pd = 3:1 and 1:3), are studied to determine key factors needed to achieve high selectivity for C1 or C2 chemicals in CO reduction. When compared with the disordered and phase-separated CuPd catalysts, the ordered CuPd catalyst exhibits the highest selectivity for C1 products (>80%). The phase-separated CuPd and Cu3Pd achieve higher selectivity (>60%) for C2 chemicals than CuPd3 and ordered CuPd, which suggests that the probability of dimerization of C1 intermediates is higher on surfaces with neighboring Cu atoms. Based on surface valence band spectra, geometric effects rather than electronic effects seem to be key in determining the selectivity of bimetallic Cu-Pd catalysts. These results imply that selectivities to different products can be tuned by geometric arrangements. This insight may benefit the design of catalytic surfaces that further improve activity and selectivity for CO reduction.

Electroreduction of CO 2 has potential for storing otherwise wasted intermittent renewable energy, while reducing emission of CO 2 into the atmosphere. Identifying robust and efficient electrocatalysts and associated optimum operating conditions to produce hydrocarbons at high energetic efficiency (low overpotential) remains a challenge. In this study, four Cu nanoparticle catalysts of different morphology and composition (amount of surface oxide) are synthesized and their activities towards CO 2 reduction are characterized in an alkaline electrolyzer. Use of catalysts with large surface roughness results in a combined Faradaic efficiency (46%) for the electroreduction of CO 2 to ethylene and ethanol in combination with current densities of ~200 mA cm -2 , a 10-fold increase in performance achieved at much lower overpotential (only < 0.7 V) compared to prior work. Compared to prior work, the high production levels of ethylene and ethanol can be attributed mainly to the use of alkaline electrolyte to improve kinetics and the suppressed evolution of H 2 , as well as the application of gas diffusion electrodes covered with active and rough Cu nanoparticles in the electrolyzer. These high performance levels and the gained fundamental understanding on Cu-based catalysts bring electrochemical reduction processes such as presented here closer to practical application.-3-

The size dependencies of the hydrogen-storage properties in polymer-coated Pd nanoparticles with diameters of 2.6 ( 0.4 and 7.0 ( 0.9 nm were investigated by a measurement of hydrogen pressure-composition isotherms. Their storage capacities per constituent Pd atom in the particles decreased with decreasing particle size, whereas the hydrogen concentrations in the two kinds of nanoparticles were almost the same and 1.2 times as much, respectively, as that in bulk palladium after counting zero hydrogen occupancy on the atoms in the first surface layer of the particles. Furthermore, apparent changes in hydrogen absorption behavior with decreasing particle size were observed, that is, a narrowing of the two-phase regions of solid-solution and hydride phases, the lowering of the equilibrium hydrogen pressure, and a decrease in the critical temperature of the twophase state. By analyzing the isotherms, we quantitatively determined the heat of formation (∆H Rfβ ) and the entropy change (∆S Rfβ ) in the hydride formation of the nanoparticle. ∆H Rfβ and ∆S Rfβ for the 2.6 ( 0.4 nm diameter Pd nanoparticle were -34.6 ( 0.61 kJ(H 2 mol) -1 and -83.1 ( 1.8 J(H 2 mol) -1 K -1 , whereas for the 7.0 ( 0.9 nm diameter Pd nanoparticles the values were -31.0 ( 1.8 kJ(H 2 mol) -1 and -67.3 ( 5.1 J(H 2 mol) -1 K -1 , respectively. These quantities gave us a prospective picture of hydrogen absorption in Pd nanoparticles and the peculiarities in the formation of a single nanometer-sized hydride.

Bare metal clusters with fewer than ∼100 atoms exhibit intrinsically unique and size-specific properties, making them promising functional units or building blocks for novel materials. To utilize such clusters in functional materials, they need to be stabilized against coalescence by employing organic ligands, polymers, and solid materials. To realize rational development of cluster-based materials, it is essential to clarify how the stability and nature of clusters are modified by interactions with stabilizers by characterizing isolated clusters. The next stage is to design on-demand function by intentionally controlling the structural parameters of cluster-based materials; such parameters include the size, composition, and atomic arrangement of clusters and the interfacial structure between clusters and stabilizers. This review summarizes the current state of the art of isolation of gold clusters stabilized in various environments and surveys ongoing efforts to precisely control the structural parameters with atomic level accuracy.