Hidetomo Noda

Electrochemical Reduction Of Carbon Dioxide Using Gas Diffusion Electrodes Loaded With Fine Catalysts

Gas diffusion electrodes (GDEs) promising to use electrochemical reaction of gases at higher rates such as in fuel cells were used for CO2 electro‐reduction. Cu powder, Cu and ZnO mixed powder, and CuO/ZnO mixed oxides were examined as the catalysts. The reduction products with Cu‐GDEs in K2SO4 aq. soln. were CH4, C2H4, C2H5OH, CO, HCOO−, etc. The purer and the smaller particle size of the Cu powder, it shows the higher activity and efficiency for CO and hydrocarbons formation. CO2 reduction can be carried out ca. 100 times greater rate using a GDE than that with a Cu‐foil electrode. With GDEs of CuO/ZnO = 3/7, the main product was C2H5OH with an efficiency of 17% with selectivity of 88% at −1.32 V. With GDEs of Cu/ZnO = 3/7 reduced by H2, the selectivity became poorer due to additional production of n‐C3H7OH and C2H4, although the total efficiencies for CO2 reduction became 41% at −1.30 V.

Electroreduction of CO2 using Cu/Zn oxides loaded gas diffusion electrodes

Gas diffusion electrodes (GDEs) consist of a gas layer (mixture of hydrophobic carbon black (CB phob ) and PTFE dispersion) and a reaction layer (mixture of catalyst powder, CB phob , hydrophilic CB (CB phil ), and PTFE) laminated on a Cu mesh as a current collector. As the catalyst, CuO/ZnO (3:7 by mole ratio) mixed oxides and a mixture of a Cu powder (4N, -325 mesh) and a ZnO powder were examined. Electroreduction was performed potentiostatically passing in general 200 C using a W -shaped Pyrex cell having one gas and two liquid chambers, with two lines of gas circulating systems. When using a GDE of (CuO / ZnO = 3 / 7 : CB = 6 : 5 [by weight], the reduction products were mainly C 2 H 5 OH with slight amounts of CO and HCOO - , and a comparable amount of H 2 . Faradaic efficiency maximum of 16.7% for C 2 H 5 OH formation with maximum selectivity of 88% was observed at -1.32 V vs. Ag-AgCl, at a partial current density of 4.23 mA/cm 2 , which is about 50 times greater than that obtained on a sintered oxide electrode. In the case of the GDE of (Cu / ZnO = 3 : 7) : CB = 3 : 1 reduced by H 2 , the selectivity of the reduction products became poorer, like in the case of a Cu foil electrode, with lower current density, although the total faradaic efficiencies for CO 2 reduction was 40.5% with additional formation of n-C 3 H 7 OH and C 2 H 4 at -1.30 V.

Analysis of Consolidation Method of CO2 Clathrate for CO2 Disposal in Deep Ocean.

大気中の二酸化炭素濃度の上昇に伴う地球温暖化対策を目的としてCO2をクラスレート形態で海洋に貯留するシステムが提案されている.海洋中をより速く沈降するクラスレートを生成し, 海域に与える環境影響を抑制するプロセスとして, クラスレート生成部と圧密部で構成されるものを発案し, 上述のシステムへの適用を実験的に検討した。反応槽で生成されたクラスレート粉体は圧密槽内で圧縮されることで, 成形されることが確かめられた.また, この成形体が人工海水中を安定して沈降することが確認でき, 海洋貯留法には生成一圧密プロセスが有効な方法の一つであることが明らかとなった.さらに, CO2クラスレートの圧密過程の解析から, 圧密は, 低圧での圧縮によるクラスレート凝集粒子群間の空隙が減少する過程と高圧での凝集粒子が崩壊する過程の2段階で進行することが明らかとされた。その2段の境界となる圧力は約2.3MPaであった.また, そのクラスレート成形体の溶解速度はCO2が溶解していない人工海水中で測定され, その速度は最大で約1.9m/sであった.