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To overcome the drawbacks of high solubility and instability of polyoxometalates (POMs) in aqueous solution and to expand their application in the electrocatalytic reduction of CO2 (ECR), we assemble sandwich-type POMs, K10[(PW9O34)2M4(H2O)2] (M = Mn, Ni, Zn, shortened as P2W18M4), into the hexagonal channel of a porphyrin-based metal–organic framework (MOF) PCN-222 to form P2W18M4@PCN-222 composites. Their ECR behavior displays polyoxoanion-dependent activity. P2W18Mn4@PCN-222 demonstrates a faradaic efficiency of 72.6% for the CO product (FECO), more than four times that of PCN-222 (FECO = 18.1%), and exhibits exceptional electrochemical stability over 36 h. P2W18Ni4@PCN-222 and P2W18Zn4@PCN-222 slightly increase (26.9%) and decrease (3.2%) in FECO, respectively. We combine the results with density functional theory (DFT) calculations to help understand the intrinsic reasons which reveals that the rate-determining step (RDS) reaction energy of P2W18Mn4@PCN-222 and P2W18Ni4@PCN-222 is significantly reduced compared to that of PCN-222. It is different in P2W18Zn4@PCN-222. Frontier molecular orbitals electron distribution results hint at directional electron transfer from P2W18Mn4/P2W18Ni4 to the porphyrin ring active center in PCN-222, promoting the electro-reduction of CO2 activity. By contrast, P2W18Zn4 may accumulate electrons from PCN-222, thus facilitating the hydrogen evolution reaction (HER). This work reveals the critical role of sandwich-type POMs in manipulating the electron transfer pathway during the electrocatalytic process. Our findings would broaden the scope of POM applications in electrochemical carbon dioxide reduction. [ABSTRACT FROM AUTHOR]

To avoid the agglomeration of iron NPs and improve the dispersion of Fe SAs, we employed a mixed-ligand strategy to regulate the iron content in PCN-224(ZnxFey) and PCN-222(ZnxFey). Thanks to the sublimation of Zn and the Kirkendall effect, uniform dispersions of Fe SAs with 1.04–1.06 wt% were obtained in the pyrolysis products Zn0.5Fe0.5–N–C-224 and Zn0.5Fe0.5–N–C-222 with excellent CO2 → CO activity, super-stability, and recyclability. [ABSTRACT FROM AUTHOR]

In this study, we investigated the reduction of CO2 using magnesium and calcium hydride (AeH2, Ae = Mg or Ca), in the process of which clean H2‐mixed CH4 fuel is produced. The result of this investigation shows that the particle size of AeH2 and AeH2/CO2 molar ratio can greatly affect the molar percentage value and reaction yield of methane. In general, the magnesium or calcium hydride as‐milled for 2 hr is enough active for reduction of CO2 to CH4. When the molar ratio of AeH2/CO2 is set to 2:1, the methanation effect is optimal for both reaction systems. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

To overcome the drawbacks of high solubility and instability of polyoxometalates (POMs) in aqueous solution and to expand their application in the electrocatalytic reduction of CO 2 (ECR), we assemble sandwich-type POMs, K 10 [(PW 9 O 34 ) 2 M 4 (H 2 O) 2 ] (M = Mn, Ni, Zn, shortened as P 2 W 18 M 4 ), into the hexagonal channel of a porphyrin-based metal-organic framework (MOF) PCN-222 to form P 2 W 18 M 4 @PCN-222 composites. Their ECR behavior displays polyoxoanion-dependent activity. P 2 W 18 Mn 4 @PCN-222 demonstrates a faradaic efficiency of 72.6% for the CO product (FE CO ), more than four times that of PCN-222 (FE CO = 18.1%), and exhibits exceptional electrochemical stability over 36 h. P 2 W 18 Ni 4 @PCN-222 and P 2 W 18 Zn 4 @PCN-222 slightly increase (26.9%) and decrease (3.2%) in FE CO , respectively. We combine the results with density functional theory (DFT) calculations to help understand the intrinsic reasons which reveals that the rate-determining step (RDS) reaction energy of P 2 W 18 Mn 4 @PCN-222 and P 2 W 18 Ni 4 @PCN-222 is significantly reduced compared to that of PCN-222. It is different in P 2 W 18 Zn 4 @PCN-222. Frontier molecular orbitals electron distribution results hint at directional electron transfer from P 2 W 18 Mn 4 /P 2 W 18 Ni 4 to the porphyrin ring active center in PCN-222, promoting the electro-reduction of CO 2 activity. By contrast, P 2 W 18 Zn 4 may accumulate electrons from PCN-222, thus facilitating the hydrogen evolution reaction (HER). This work reveals the critical role of sandwich-type POMs in manipulating the electron transfer pathway during the electrocatalytic process. Our findings would broaden the scope of POM applications in electrochemical carbon dioxide reduction.

To avoid the agglomeration of iron NPs and improve the dispersion of Fe SAs, we employed a mixed-ligand strategy to regulate the iron content in PCN-224(Zn x Fe y ) and PCN-222(Zn x Fe y ). Thanks to the sublimation of Zn and the Kirkendall effect, uniform dispersions of Fe SAs with 1.04-1.06 wt% were obtained in the pyrolysis products Zn 0.5 Fe 0.5 -N-C-224 and Zn 0.5 Fe 0.5 -N-C-222 with excellent CO 2 → CO activity, super-stability, and recyclability.