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Electrochemical reduction of carbon dioxide (CO2) to formate (HCOO–) in aqueous solution is studied using tin–lead (Sn–Pb) alloys as new electrocatalysts. In electrochemical impedance spectroscopy (EIS) measurements, lower charge-transfer resistance is observed for the alloy electrodes when compared to the single metal electrodes such as Sn and Pb. The results of X-ray photoelectron spectroscopy (XPS) and cyclic voltammetric (CV) analysis show that the Sn in the Sn–Pb alloys facilitates the formation of oxidized tin (SnO x ) and metallic lead (Pb0) on the alloy surface by inhibiting the formation of low-conductive lead oxide (PbO) film. The CV analysis confirms that the Sn–Pb alloys exhibit higher reduction current than the single metal electrodes under CO2 atmosphere. The Faradaic efficiency (FE) and the partial current density (PCD) of HCOO– production on the alloy electrodes is investigated by electroreduction experiments at −2.0 V (vs Ag/AgCl) in an H-type cell. As results, respectively more than 16% and 25% higher FE and PCD of HCOO– are obtained from the Sn–Pb alloys compared to the single metal electrodes. A Sn–Pb alloy including surface composition of Sn56.3Pb43.7 exhibits the highest FE of 79.8% with the highest PCD of 45.7 mA cm–2.

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Isostructural [M 2 (DOBDC)(EG) 2 ] (M = Mg, Co, Ni) frameworks are first synthesized by controlling the pH* in the reaction medium. Coordinated ethylene glycols form a hexagonal OH cluster, which works as a template to grow single crystals with high crystallinity. After the liberation of solvated molecules, [M 2 (DOBDC)] shows notably higher surface areas than the reported values and completely different CO 2 and CO separation properties depending on the kinds of unsaturated metal. Therefore, breakthrough experiments using a CO 2 /CO mixed gas show that Mg-MOF has a longer breakthrough time for CO 2 than for CO, whereas Co/Ni-MOFs have longer breakthrough times for CO than for CO 2 . Apart from CO 2 and CO, other gases such as CH 4 , H 2 , and N 2 were almost not adsorbed at all in these materials at 298 K. To reveal the role of unsaturated metal sites, CO 2 and CO adsorption sites are unequivocally determined by single-crystal X-ray diffraction analysis. One of very interesting discoveries is that there are two CO 2 and CO adsorption positions (sites A and B) in the hexagonal channels. Site A is the unsaturated metal center working as Lewis acidic sites, and site B is the secondary adsorption site located between two A sites. A close inspection of crystal structures reveals that unsaturated Co(II) and Ni(II) sites adsorb both CO 2 and CO, whereas the unsaturated Mg(II) sites strongly capture only CO 2 , not CO. Density functional theory calculations elucidate the discrepancy in CO affinity: Co(II) and Ni(II) form strong π-backdonating bonds with CO via electron transfer from the d orbitals of the transition metals to the antibonding molecular orbitals of CO, whereas Mg(II) does not participate in electron transfer or orbital overlap with CO. This observation provides new insight into the synthesis of novel functional materials with high CO 2 /CO separation performance.