CO2 electroreduction reaction (CO2RR) to fuels and feedstocks is an attractive route to close the anthropogenic carbon cycle and store renewable energy. The generation of more reduced chemicals, especially multicarbon oxygenate and hydrocarbon products (C2+) with higher energy density is highly desirable for industrial applications. However, selective conversion of CO2 to C2+ suffers from high overpotential, low reaction rate and low selectivity, and the process is extremely sensitive to the catalyst structure and electrolyte. Here we discuss strategies to achieve high C2+ selectivity through rational design of the catalyst and electrolyte. Current state-of-the-art catalysts, including Cu and Cu-bimetallic catalysts as well as alternative materials are considered. The importance of taking into consideration the dynamic evolution of the catalyst structure and composition are highlighted, focusing on findings extracted from in situ and operando characterizations. Additional theoretical insight into the reaction mechanisms underlying the improved C2+ selectivity of specific catalyst geometries/compositions in synergy with a well-chosen electrolyte are also provided.

Rational Catalyst and Electrolyte Design for Co2 Electroreduction Towards Multicarbon Products

Metal-organic framework-based heterogeneous catalysts for the conversion of C1 chemistry: CO, CO2 and CH4

Layered two-dimensional (2D) conjugated metal-organic frameworks (MOFs) represent a family of rising electrocatalysts for the oxygen reduction reaction (ORR), due to the controllable architectures, excellent electrical conductivity, and highly exposed well-defined molecular active sites. Herein, we report a copper phthalocyanine based 2D conjugated MOF with square-planar cobalt bis(dihydroxy) complexes (Co-O4 ) as linkages (PcCu-O8 -Co) and layer-stacked structures prepared via solvothermal synthesis. PcCu-O8 -Co 2D MOF mixed with carbon nanotubes exhibits excellent electrocatalytic ORR activity (E1/2 =0.83 V vs. RHE, n=3.93, and jL =5.3 mA cm-2 ) in alkaline media, which is the record value among the reported intrinsic MOF electrocatalysts. Supported by in situ Raman spectro-electrochemistry and theoretical modeling as well as contrast catalytic tests, we identified the cobalt nodes as ORR active sites. Furthermore, when employed as a cathode electrocatalyst for zinc-air batteries, PcCu-O8 -Co delivers a maximum power density of 94 mW cm-2 , outperforming the state-of-the-art Pt/C electrocatalysts (78.3 mW cm-2 ).

A Phthalocyanine-Based Layered Two-Dimensional Conjugated Metal-Organic Framework as a Highly Efficient Electrocatalyst for the Oxygen Reduction Reaction.

Electrochemical reduction of CO2 is promising to utilize the intermittent renewable electricity and transform CO2 into value-added products, simultaneously. Herein, we designed a cobalt phthalocyanine-based catalyst supported on pyridine-functionalized carbon nanotubes (CoPc-py-CNT). This novel hybrid catalyst exhibited a high activity (TOFCO: 34.5 s−1 at −0.63 V vs. RHE) and selectivity (FECO > 98%) for electrochemical CO2 reduction. To the best of our knowledge, it is the best one among all reported molecular based electrocatalysts for CO2-to-CO conversion. Furthermore, structure characterizations (such as Raman and X-rays photoelectron spectroscopy), loading-dependent electrochemical analysis and mechanistic studies revealed that pyridine groups, through axial coordination with Co, not only functioned as physical promoters to improve the dispersion of cobalt phthalocyanine but also tuned the electronic structure of Co sites to increase the intrinsic turnover frequency.

Cobalt phthalocyanine coordinated to pyridine-functionalized carbon nanotubes with enhanced CO2 electroreduction

Mn and Na additives have been widely studied to improve the efficiency of CO2 hydrogenation to valuable olefins on Fe catalysts, but their effects on the catalytic properties and mechanism are still under vigorous debate. This study shows that Fe-based catalysts with moderate Mn and Na contents are highly selective for CO2 hydrogenation to olefins, together with low selectivities for both CO and CH4 and much improved space-time olefin yields compared to state-of-the-art catalysts. Combined kinetic assessment and quasi in situ characterizations further unveil that the sole presence of Mn suppresses the activity of Fe catalysts because of the close contact between Fe and Mn, whereas the introduction of Na mediates the Fe-Mn interaction and provides strong basic sites. This subtle synergy between Na and Mn sheds light on the importance of the interplay of multiple additives that could bring an enabling strategy to improve catalytic activity and selectivity.

Highly Selective Olefin Production from CO 2 Hydrogenation on Iron Catalysts: A Subtle Synergy between Manganese and Sodium Additives

Induced activation of the commercial Cu/ZnO/Al2O3 catalyst for the steam reforming of methanol

CeO2 nanorods supported Co–CoOx catalysts showed high selectivity for higher alcohol synthesis (HAS) from syngas. The selectivity has found to increase with lowering the Co loadings, and the value over Co1/CeO2 (19.86%) is twice higher than that over Co5/CeO2 (8.67%). The active sites at the interfaces between Co0 and CoOx, or to say, Co–CoOx pairs, have evidenced to be responsible for HAS. The strong metal–support interactions between Co and CeO2 retard the reduction of CoOx and stabilize the intermediates such as CO–Coδ+. Likely, CO favors dissociating on the metallic Co surface to form CHx species, while CO is associatively activated on Coδ+ sites. Moreover, the structure evolution of the Co–CoOx interface was revealed during calcination, reduction, and reaction using in situ X-ray diffraction (XRD), in situ Raman spectroscopy, X-ray absorption spectroscopy (XAS), and in situ diffuse reflectance infrared fourier transform spectroscopy (CO-DRIFTS). The structure–performance relationship of HAS over Co/C...

Structure Evolution of Co–CoOx Interface for Higher Alcohol Synthesis from Syngas over Co/CeO2 Catalysts

Understanding of dynamic structure of active sites is of paramount importance for rational design of industrial catalysts. This work revealed the structure evolution of iron active phases for CO2 hydrogenation over iron‐based catalysts. With a combination of operando Raman spectroscopy and X‐ray Diffraction coupled with online gas chromatography, the panoramic structure evolution of iron oxides (α‐Fe2O3 and γ‐Fe2O3) during activation and CO2 hydrogenation were elaborated, that is, α‐Fe2O3 (γ‐Fe2O3)→α‐Fe3O4 (γ‐Fe3O4)→α‐Fe (γ‐Fe)→χ‐Fe5C2 (θ‐Fe3C). Both iron carbides showed high catalytic activities while χ‐Fe5C2 exhibited higher selectivity to lower olefins but weaker chain growth probability than θ‐Fe3C.

Operando Spectroscopic Study of Dynamic Structure of Iron Oxide Catalysts during CO2 Hydrogenation

The study of structure-performance relationship of iron catalyst during a full life cycle for CO2 hydrogenation

In this work, Fe–Zn catalysts were prepared, characterized, and examined for the synthesis of linear high carbon α-olefins (LAOs; C ≥ 4) directly from CO2 hydrogenation The relationship of perform

Xianglin Liu

Papers

Induced activation of the commercial Cu/ZnO/Al2O3 catalyst for the steam reforming of methanol

Structure Evolution of Co–CoOx Interface for Higher Alcohol Synthesis from Syngas over Co/CeO2 Catalysts

Operando Spectroscopic Study of Dynamic Structure of Iron Oxide Catalysts during CO2 Hydrogenation

The study of structure-performance relationship of iron catalyst during a full life cycle for CO2 hydrogenation

Unraveling the Role of Zinc on Bimetallic Fe5C2–ZnO Catalysts for Highly Selective Carbon Dioxide Hydrogenation to High Carbon α-Olefins