Cu electrode-based electrochemical CO 2 reduction using renewable energy is a promising method for conversion of CO 2 to useful compounds such as methane, ethylene, and ethanol. Heteroatom-doped and/or -derived Cu as oxide-derived Cu has been investigated in context of development of a stable catalyst with high selectivity, whereas the role of heteroatoms is not yet well understood. It is not known whether heteroatoms act as a moiety of the catalyst or simply induce reconstruction of the catalyst. This work is an investigation of the role of the heteroatom in electrocatalytic CO 2 reduction with a Cu electrode modified with methanethiol monolayers (MT−Cu), which is able to distinguish the presence of heteroatom contamination originating from electrolyte or air. Controlled potential electrolysis of CO 2 using an MT−Cu electrode at −1.8 V at Ag/AgCl exhibits greater selectivity for C 2 products than an unmodified polycrystalline Cu electrode (bare Cu). On the other hand, a sulfur-modified Cu (S−Cu) electrode predominantly generates formate as a CO 2 reduction product. In an investigation of the mechanism, an in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy instrument is used as a powerful surface analyzer. Scanning electron microscopy, grazing-incidence wideangle X-ray scattering (GIWAXS), and X-ray spectroscopy (XPS) are also employed in the investigation. The spectroscopic data show that reconstruction and formation of Cu + on the Cu surface occur at negative potential greater than −1.4 V vs Ag/AgCl by electrochemical reduction of methanethiol monolayers. DFT calculations are also performed under conditions close to the experimental conditions of electrical bias and aqueous electrolyte. The results indicate that a roughened surface is favorable for generating C 2 products. In addition, the Cu + moiety promotes generation of C 2 products, demonstrating that the doped heteroatom plays a crucial role in electrochemical CO 2 reduction.

Pt-based catalysts are commonly employed as NO x -trapping catalysts for automobiles, while perovskite oxides have received attention as Pt-free NO x -trapping catalysts. However, the NO x storage performance of perovskite catalysts is significantly inferior at low temperatures and with coexisting gases such as H2O, CO2, and SO2. This study demonstrates that NO x storage reactions proceed over redox site (Mn, Fe, and Co)-doped SrTiO3 perovskites. Among the examined catalysts, Mn-doped SrTiO3 exhibited the highest NO x storage capacity (NSC) and showed a high NSC even at a low temperature of 323 K. Moreover, the high NO x storage performance of Mn-doped SrTiO3 was retained in the presence of poisoning gases (H2O, CO2, and SO2). NO oxidation experiments revealed that the NSC of Co-doped SrTiO3 was dependent on the NO oxidation activity from NO to NO2 via lattice oxygen, which resulted in an inferior NSC at low temperatures. On the other hand, Mn-doped SrTiO3 successfully adsorbed NO molecules onto its surface at 323 K without the NO oxidation process using lattice oxygens. This unique adsorption behavior of Mn-doped SrTiO3 was concluded to be responsible for the high NSC in the presence of poisoning gases.

The mechanism of faradaic electro-swing for CO2 capture/release on a redox-active organic electrode is studied from the point of view of realizing a reversible process for CO2 separation. First, the cyclic voltammograms (CVs) of two redox-active organic monomers, anthraquinone (AQ) and 2,1,3-benzothiadiazole (BTZ), were measured under a CO2 atmosphere. The waveforms of CVs of the two redox-active organic monomers are altered under a CO2 atmosphere relative to a N2 atmosphere. There is a change in the number of redox waves from two to one for AQ and a change from reversible to irreversible waves for BTZ. To further understand the mechanisms of CO2 capture/release on redox-active organic compounds, redox-active polymer electrodes coated with polyanthraquinone (PAQ) and polybenzothiadiazole (PBTZ) were investigated using a spectroscopic analysis known as in situ attenuated total reflectance–surface-enhanced infrared absorption spectroscopy (ATR–SEIRAS) as well as density functional theory (DFT) calculations. The CVs measured with two redox-active polymer electrodes have more positive shifts of reduction potentials for PAQ and PBTZ under a CO2 atmosphere than under an N2 atmosphere, as measured versus Ag/AgNO3: −1.8 and −1.4 V → −1.4 and −0.9 V for PAQ and −2.5 V → −2.1 and −1.9 V for PBTZ. In addition, the oxidation current on the PBTZ electrode disappears only under a CO2 atmosphere. DFT calculations indicate that the positive shifts of reduction potentials in the two electrodes under CO2 conditions are due to an exergonic adsorption reaction of CO2 onto the redox-active organic compounds. To clarify the reaction behavior between CO2 and the redox-active organic electrode, an ATR–SEIRAS spectroscopic analysis was performed. Infrared peaks are observed at 2200 and 2100 cm–1 for PAQ and PBTZ electrodes, respectively, under a CO2 atmosphere, which have been confirmed by measurements under a 13CO2 atmosphere to have adsorbed CO2. The wavenumbers corresponding to the CO2 molecules adsorbed on the two electrodes are different. These findings indicate that one electron reduction and CO2 adsorption for each redox-active organic compound are occurring simultaneously. The calculated adsorption energy of CO2 for two redox-active organic electrodes indicates that the adsorption energies of two CO2 molecules for AQ and BTZ are −7.3 and −36.3 kJ/mol. The larger adsorption energy in BTZ than that in AQ is clearly related to the disappearance of the oxidation current. However, both adsorption energies indicating adsorption of CO2 onto organic units are less than the covalent bond energies of common organic compounds, indicating that such weak adsorptions are suitable for the faradaic electro-swing of CO2 capture/release on the redox-active organic units.

Insights into NO x storage materials have emerged as key components in NO x abatement technologies. Recently, the pursuit of promising materials has been conducted mostly among perovskite- and its derived-structured transition metal oxides involving metal-oxygen octahedral units. There is, however, little information on the outcomes of consideration among other oxide families having different polyhedral units as potential candidates for NO x storage materials. Here, we report that a Swedenborgite-structured oxide, YBaCo4O7+δ, can be a prominent candidate to be used without any platinum group metal loadings. Superior NO x storage capabilities at rather a lower temperature of 100 °C are demonstrated. The present oxide achieves a higher catalytic oxidation of NO to NO2 than a conventional platinum- and barium-impregnated catalyst (Pt/Ba/Al2O3) below 400 °C. It is anticipated that the oxide can be easily modified by taking advantage of chemical flexibilities, e.g., in terms of iso- and/or aliovalent substitutions, toward more efficient catalytic materials in NO x abatement industries.