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Direct conversion of dilute CO2 contained in power plant or industrial exhaust gas and the atmosphere into high-concentration hydrocarbons without a need of separate CO2 capture and purification processes is one of the awaited technologies in envisioned low-carbon societies. In this study, we investigated the performance of integrated CO2 capture and reduction to CH4 over Nibased dual functional catalysts promoted with Na, K and Ca. Ni/Na-γ-Al2O3 exhibited the highest activity for integrated CO2 (5% CO2) capture and reduction, achieving high CO2 conversion (>96%) and CH4 selectivity (>93%). In addition, very low concentration CO2 (100 ppm CO2) was successfully converted to 11.5% CH4 at the peak point (>1000 times higher concentration than that of the supplied CO2) over Ni/Na-γ-Al2O3. The Ni-based dual functional catalyst exhibited a high CO2 conversion exceeding 90%, even when 20%O2 was present during CO2 capture. Furthermore, an increased operation pressure had positive impacts on both CO2 capture and CH4 formation, and these advantageous effects were also observed when CO2 concentration was at the level of atmospheric CO2 (100-400 ppm). As pressure increased from 0.1 to 0.9 MPa, CH4 production capacity with 400 ppm CO2 was enhanced from 111 to 160 µmol gcat -1 . The approach in combination with the efficient catalyst shows encouraging promises for CO2 utilization, enabling direct air capture-conversion to value-added chemicals.CH4 productivity increased from 188 to 266 μmol gcat −1 . In addition, the effect of pressure on catalyst performance was also investigated at very low CO2 levels of 100 and 400 ppm, and high pressure was found to positively affect both CO2 capture and CH4 formation. These results suggest that high pressure enhances the CO2 absorption and CH4 formation capacities of dual-functional catalysts and allows for efficient integrated CO2 capture and reduction into CH4 even at atmospheric levels of CO2. The approach, in combination with the efficient catalyst, is promising for CO2 utilization, thus enabling direct air capture-conversion to value-added chemicals.

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To accelerate ammonia synthesis, the effect of the electrode potential on the kinetics of ammonia synthesis was investigated with a proton-conducting solid electrolyte, BaCe 0.9 Y 0.1 O 3 (BCY), at temperatures between 500−650 °C. Ammonia synthesis was conducted using a double chamber electrochemical setup with an electrolyte-supported Pt|BCY| K,Al-modified Fe-BCY cell. Although slow ammonia formation kinetics by cathodic polarization was observed when pure N 2 was supplied to the cathode side, obvious acceleration of the ammonia formation rate by cathodic polarization was observed following addition of 15% H 2 to the cathode side. The ammonia formation rate increased more than 20 times at −1.5 V relative to that at the open circuit voltage, which was not observed by anodic polarization. Notably, the acceleration at the cathodic potential was observed over 610 °C. These results indicate that the enhancement of ammonia formation occurs because of promotion of nitrogen dissociation by cathodic polarization and a change in the transport properties of the BCY electrolyte. The acceleration mechanism was discussed based on kinetic measurements and the dependence of the reaction kinetics on temperature and partial pressure.

Electrochemical synthesis of ammonia was performed at 500 • C using a mixed protonic-electronic conducting cathode, Ru-doped BaCe 0.9 Y 0.1 O 3 (BCYR) in a proton-conducting electrolysis cell (PCEC) using a BaCe 0.9 Y 0.1 O 3 (BCY) electrolyte. Ru nanoparticles were formed in situ on the surface of the BCYR particles after a heat-treatment in a reducing atmosphere, as determined by TEM and XPS measurements. The BCYR cathode exhibited activity toward electrochemical ammonia formation, which indicates that the Ru nanoparticles were active sites for the electrochemical synthesis of ammonia. We found that altering the reduction temperature could be used to control the exsolved Ru-nanoparticle size; decreasing the Ru particle size contributes to an improvement in electrochemical ammonia formation due to an increased triple-phase-boundary active length. The ammonia formation rate per amount of exsolved Ru nanoparticles achieved with BCYR was higher than that achieved with a previously reported Ru-doped La 1-x Sr x TiO 3 (LSTR) cathode. Our results suggest that the mixed protonic-electronic conduction in the BCYR cathode may contribute to the increased Ru-nanoparticles activity toward electrochemical ammonia synthesis. The dependence of the ammonia formation rate on the applied voltage and the reaction mechanism were discussed based on kinetic analysis.