A flow cell based, bench-scale electrochemical system for generation of synthesis-gas (syn-gas) is reported. Sensitivity to operating conditions such as CO 2 flow, current density, and elevated temperature are described. By increasing the temperature of the cell the kinetic overpotential for the reduction of CO 2 was lowered with the cathode voltage at 70 mA cm -2 decreased by 0.32 V and the overall cell voltage dropping by 1.57 V. This equates to an 18% increase in cell efficiency. By closely monitoring the products it was found that at room temperature and 70°C the primary products are CO and H 2 . By controlling the current density and the flow of CO 2 it was possible to control the H 2 :CO product ratio between 1:4 and 9:1. The reproducibility of performing experiments at elevated temperature and the ability to generate syn-gas for extended periods of time is also discussed.

A pressurized electrochemical system equipped for continuous reduction of CO 2 is presented. At elevated pressures, using a Ag-based cathode, the quantity of CO which can be generated is 5 times that observed at ambient pressure with faradaic efficiencies as high as 92% observed at 350 mA cm −2 . For operation at 225 mA cm −2 and 60 • C the cell voltage at 18.5 atm was 0.4 V below that observed at ambient pressure. Increasing the temperature further to 90 • C led to a cell voltage below 3 V (18.5 atm and 90 • C), which equates to an electrical efficiency of 50%.

Wavelength-selective infrared multiple photon photo-dissociation (IRMPD) was used to generate spectra of anionic nitrate complexes of UO(2)(2+) and Eu(3+) in the mid-infrared region. Similar spectral patterns were observed for both species, including splitting of the antisymmetric O-N-O stretch into high and low frequency components with the magnitude of the splitting consistent with attachment of nitrate to a strong Lewis acid center. The frequencies measured for [UO(2)(NO(3))(3)](-) were within a few cm(-1) of those measured in the condensed phase, the best agreement yet achieved for a comparison of IRMPD with condensed phase absorption spectra. In addition, experimentally-determined values were in good general agreement with those predicted by DFT calculations, especially for the antisymmetric UO(2) stretch. The spectrum from the [UO(2)(NO(3))(3)](-) was compared with that of [Eu(NO(3))(4)](-), which showed that nitrate was bound more strongly to the Eu(3+) metal center, consistent with its higher charge. The spectrum of a unique uranyl-oxo species having an elemental composition [UO(9)N(2)](-) was also acquired, that contained nitrate absorptions suggestive of a [UO(2)(NO(3))(2)(O)](-) structure; the spectrum lacked bands indicative of nitrite and superoxide that would be indicative of an alternative [UO(2)(NO(3))(NO(2))(O(2))](-) structure.

The Free-Electron Laser for Infrared Experiments (FELIX) was used to study the wavelength-resolved multiple photon photodissociation of discrete, gas-phase uranyl (UO22+) complexes containing a single anionic ligand (A), with or without ligated solvent molecules (S). The uranyl antisymmetric and symmetric stretching frequencies were measured for complexes with general formula [UO2A(S)n]+, where A was hydroxide, methoxide, or acetate; S was water, ammonia, acetone, or acetonitrile; and n = 0-3. The values for the antisymmetric stretching frequency for uranyl ligated with only an anion ([UO2A]+) were as low or lower than measurements for [UO2]2+ ligated with as many as five strong neutral donor ligands and are comparable to solution-phase values. This result was surprising because initial DFT calculations predicted values that were 30-40 cm(-1) higher, consistent with intuition but not with the data. Modification of the basis sets and use of alternative functionals improved computational accuracy for the methoxide and acetate complexes, but calculated values for the hydroxide were greater than the measurement regardless of the computational method used. Attachment of a neutral donor ligand S to [UO2A]+ produced [UO2AS]+, which produced only very modest changes to the uranyl antisymmetric stretch frequency, and did not universally shift the frequency to lower values. DFT calculations for [UO2AS]+ were in accord with trends in the data and showed that attachment of the solvent was accommodated by weakening of the U-anion bond as well as the uranyl. When uranyl frequencies were compared for [UO2AS]+ species having different solvent neutrals, values decreased with increasing neutral nucleophilicity.

The impact of membrane type and electrolyte composition for the electrochemical generation of synthesis gas (CO + H 2 ) using an electrolysis cell containing a Ag gas diffusion cathode is presented. Changing from a cation exchange membrane to an anion exchange membrane extended the cell operational time at low cell voltages (E cell ) without impacting product composition. The use of KOH as the catholyte decreased the E cell and resulted in a minimum electrolyte cost reduction of 34%. The prime factor in determining operational time at low E cell was the ability to maintain a sufficiently high anolyte pH.The co-reduction of CO 2 and water for the production of CO and H 2 (syn-gas) has seen renewed interest. 1-9 The optimism for this process is the possibility of generating syn-gas without fossil energy (Equations 12, E 0 vs. NHE). If performed using sustainable energy, carbon neutral liquid fuels or chemicals products (such as plastics) which sequester carbon can be produced from the syn-gas. In performing CO 2 reduction Ag and Au have almost exclusive selectivity for CO. 1-4, 10, 11 While a variety of cell configurations have been proposed for the reduction of CO 2 , 1, 3, 6, 9, 12-14 filter press cells which incorporate Ag gas diffusion electrodes (GDE) have shown promising early results. 1, 6 GDEs allow generation of CO to occur at levels above what would be possible at planar electrodes due to the lack of reliance on CO 2 solubility which is low in aqueous systems. GDEs enable the cell temperature to be elevated above ambient decreasing overpotentials and electrolyte impedance and increasing cell efficiency without significantly impacting syn-gas production. 1T otal r xn :Transitioning CO 2 reduction from the research arena to an industrial electrolysis process will require complete system optimization in terms of electrical input, syn-gas composition, and the rate of electrolyte consumption. Studies to date have utilized OH − oxidation to O 2 as the anode reaction as shown in Equation 3. 1, 6 At a 1:1 balance of CO and H 2 production, a complete reaction can be written as shown in Equation 4. Such a process consumes only CO 2 and H 2 O while generating syn-gas and O 2 .The acid/base chemistry of CO 2 (Equations 5-7) can dramatically alter solution chemistry during extended cell operation and leads to eventual precipitation of carbonates in the catholyte. 1 The consumption of OH − in the anolyte (Eqn. 3) also limits electrolyte lifetime. One means to address the issues of carbonate formation and OH − consumption is to use an anion exchange membrane (AEM). This letter provides results from initial investigations which show the impact CO 2 acid/base chemistry has on cell operation and how electrolyte and membrane type can be used to mitigate the impact.