Efficient Electroreduction of CO 2 to CO on Porous ZnO Nanosheets with Hydroxyl Groups in Ionic Liquid‐based Electrolytes

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Recent insights on the use of modified Zn-based catalysts in eCO2RR

Converting CO2 into valuable chemicals can provide a new path to mitigate the greenhouse effect, achieving the aim of "carbon neutrality" and "carbon peaking". Among numerous electrocatalysts, Zn-based materials are widely distributed and cheap, making them one of the most promising electrocatalyst materials to replace noble metal catalysts. Moreover, the Zn metal itself has a certain selectivity for CO. After appropriate modification, such as oxide derivatization, structural reorganization, reconstruction of the surfaces, heteroatom doping, and so on, the Zn-based electrocatalysts can expose more active sites and adjust the d-band center or electronic structure, and the FE and stability of them can be effectively improved, and they can even convert CO2 to multi-carbon products. This review aims to systematically describe the latest progresses of modified Zn-based electrocatalyst materials (including organic and inorganic materials) in the electrocatalytic carbon dioxide reduction reaction (eCO2RR). The applications of modified Zn-based catalysts in improving product selectivity, increasing current density and reducing the overpotential of the eCO2RR are reviewed. Moreover, this review describes the reasonable selection and good structural design of Zn-based catalysts, presents the characteristics of various modified zinc-based catalysts, and reveals the related catalytic mechanisms for the first time. Finally, the current status and development prospects of modified Zn-based catalysts in eCO2RR are summarized and discussed.

Interface Engineered V-Zn Hybrids: Electrocatalytic and Photocatalytic CO2 Reductions

V-Zn hybrids have widely been used as catalyst materials in the environment and as energy. Herein, V-Zn hybrid electrodes were prepared by the hydrothermal and sputter-deposition methods using a Zn foil support. Their electrocatalytic CO₂ reduction (EC CO₂ RR) performances were tested under various applied potentials, different electrolytes, and concentrations before and after thermal treatment of the demonstrated electrode. Gas and liquid products were confirmed by gas chromatography and nuclear magnetic resonance spectroscopy, respectively. For V-Zn electrode by hydrothermal method produced mainly syngas (CO and H₂) with tunable ratio by varying applied potential. Minor products include CH₄, C₂H₄, and C₂H₆. A liquid product of formate showed a Faradaic efficiency (FE) of 2%. EC CO₂ RR efficiency for CO, CH₄, and formate was best in 0.2 M KHCO₃ electrolyte condition. CO and formate were further increased by photoirradiation and Nafion-treated electrode. Formate and CH₄ productions were significantly increased by thermal treatment of the V-Zn electrode. CO production was diminished for the V-Zn electrode by sputter deposition but was recovered by thermal treatment. Photocatalytic CO₂ RR was tested to find that RR products include CH₃OH, CO, CH₄, C₂H₄, and C₂H₆. Interestingly long-chain hydrocarbons (C_nH_2n and C_nH_2n+2, where n = 3-6) were first observed under mild conditions. The long-chain formation was understood by Fisher-Tropsch (F-T) synthesis. Alkenes were observed to be more produced than alkanes unlike in the conventional F-T synthesis. The present new findings provide useful clues for the development of hybrid electro-and photo-catalysts tested under various experimental conditions in energy and environment.

Photoelectrochemical CO2 Reduction Products Over Sandwiched Hybrid Ga2O3:ZnO/Indium/ZnO Nanorods

Recycled valuable energy production by the electrochemical CO₂ reduction method has explosively researched using countless amounts of developed electrocatalysts. Herein, we have developed hybrid sandwiched Ga₂O₃:ZnO/indium/ZnO nanorods (GZO/In/ZnO_NR) and tested their photoelectrocatalytic CO₂ reduction performances. Gas chromatography and nuclear magnetic spectroscopy were employed to examine gas and liquid CO₂ reduction products, respectively. Major products were observed to be CO, H₂, and formate whose Faradaic efficiencies were highly dependent on the relative amounts of overlayer GZO and In spacer, as well as applied potential and light irradiation. Overall, the present study provides a new strategy of controlling CO₂ reduction products by developing a sandwiched hybrid catalyst system for energy and environment.