HKUST-1-derived highly ordered Cu nanosheets with enriched edge sites, stepped (211) surfaces and (200) facets for effective electrochemical CO2 reduction

Copper foam supported g-C3N4-metal-organic framework bacteria biohybrid cathode catalyst for CO2 reduction in microbial electrosynthesis

Microbial electrosynthesis (MES) presents a versatile approach for efficiently converting carbon dioxide (CO2) into valuable products. However, poor electron uptake by the microorganisms from the cathode severely limits the performance of MES. In this study, a graphitic carbon nitride (g-C3N4)-metal-organic framework (MOF) i.e. HKUST-1 composite was newly designed and synthesized as the cathode catalyst for MES operations. The physiochemical analysis such as X-ray diffraction, scanning electron microscopy (SEM), and X-ray fluorescence spectroscopy showed the successful synthesis of g-C3N4-HKUST-1, whereas electrochemical assessments revealed its enhanced kinetics for redox reactions. The g-C3N4-HKUST-1 composite displayed excellent biocompatibility to develop electroactive biohybrid catalyst for CO2 reduction. The MES with g-C3N4-HKUST-1 biohybrid demonstrated an excellent current uptake of 1.7 mA/cm2, which was noted higher as compared to the MES using g-C3N4 biohybrid (1.1 mA/cm2). Both the MESs could convert CO2 into acetic and isobutyric acid with a significantly higher yield of 0.46 g/L.d and 0.14 g/L.d respectively in MES with g-C3N4-HKUST-1 biohybrid and 0.27 g/L.d and 0.06 g/L.d, respectively in MES with g-C3N4 biohybrid. The findings of this study suggest that g-C3N4-HKUST-1 is a highly efficient catalytic material for biocathodes in MESs to significantly enhance the CO2 conversion.

Single-Site Metal-Organic Framework and Copper Foil Tandem Catalyst for Highly Selective CO2 Electroreduction to C2 H4

Tandem catalysis is a promising way to break the limitation of linear scaling relationship for enhancing efficiency, and the desired tandem catalysts for electrochemical CO₂ reduction reaction (CO₂ RR) are urgent to be developed. Here, a tandem electrocatalyst created by combining Cu foil (CF) with a single-site Cu(II) metal-organic framework (MOF), named as Cu-MOF-CF, to realize improved electrochemical CO₂ RR performance, is reported. The Cu-MOF-CF shows suppression of CH₄ , great increase in C₂ H₄ selectivity (48.6%), and partial current density of C₂ H₄ at -1.11 V versus reversible hydrogen electrode. The outstanding performance of Cu-MOF-CF for CO₂ RR results from the improved microenvironment of the Cu active sites that inhibits CH₄ production, more CO intermediate produced by single-site Cu-MOF in situ for CF, and the enlarged active surface area by porous Cu-MOF. This work provides a strategy to combine MOFs with copper-based electrocatalysts to establish high-efficiency electrocatalytic CO₂ RR.

Two-Dimensional Metal Nanostructures: From Theoretical Understanding to Experiment

This paper reviews recent studies on the preparation of two-dimensional (2D) metal nanostructures, particularly nanosheets. As metal often exists in the high-symmetry crystal phase, such as face centered cubic structures, reducing the symmetry is often needed for the formation of low-dimensional nanostructures. Recent advances in characterization and theory allow for a deeper understanding of the formation of 2D nanostructures. This Review firstly describes the relevant theoretical framework to help the experimentalists understand chemical driving forces for the synthesis of 2D metal nanostructures, followed by examples on the shape control of different metals. Recent applications of 2D metal nanostructures, including catalysis, bioimaging, plasmonics, and sensing, are discussed. We end the Review with a summary and outlook of the challenges and opportunities in the design, synthesis, and application of 2D metal nanostructures.

Emerging 2D Copper-Based Materials for Energy Storage and Conversion: A Review and Perspective

2D materials have shown great potential as electrode materials that determine the performance of a range of electrochemical energy technologies. Among these, 2D copper-based materials, such as Cu-O, Cu-S, Cu-Se, Cu-N, and Cu-P, have attracted tremendous research interest, because of the combination of remarkable properties, such as low cost, excellent chemical stability, facile fabrication, and significant electrochemical properties. Herein, the recent advances in the emerging 2D copper-based materials are summarized. A brief summary of the crystal structures and synthetic methods is started, and innovative strategies for improving electrochemical performances of 2D copper-based materials are described in detail through defect engineering, heterostructure construction, and surface functionalization. Furthermore, their state-of-the-art applications in electrochemical energy storage including supercapacitors (SCs), alkali (Li, Na, and K)-ion batteries, multivalent metal (Mg and Al)-ion batteries, and hybrid Mg/Li-ion batteries are described. In addition, the electrocatalysis applications of 2D copper-based materials in metal-air batteries, water-splitting, and CO₂ reduction reaction (CO₂ RR) are also discussed. This review also discusses the charge storage mechanisms of 2D copper-based materials by various advanced characterization techniques. The review with a perspective of the current challenges and research outlook of such 2D copper-based materials for high-performance energy storage and conversion applications is concluded.

Integrated carbon capture and conversion: A review on C2+ product mechanisms and mechanism-guided strategies

The need to reduce atmospheric CO₂ concentrations necessitates CO₂ capture technologies for conversion into stable products or long-term storage. A single pot solution that simultaneously captures and converts CO₂ could minimize additional costs and energy demands associated with CO₂ transport, compression, and transient storage. While a variety of reduction products exist, currently, only conversion to C₂₊ products including ethanol and ethylene are economically advantageous. Cu-based catalysts have the best-known performance for CO₂ electroreduction to C₂₊ products. Metal Organic Frameworks (MOFs) are touted for their carbon capture capacity. Thus, integrated Cu-based MOFs could be an ideal candidate for the one-pot capture and conversion. In this paper, we review Cu-based MOFs and MOF derivatives that have been used to synthesize C₂₊ products with the objective of understanding the mechanisms that enable synergistic capture and conversion. Furthermore, we discuss strategies based on the mechanistic insights that can be used to further enhance production. Finally, we discuss some of the challenges hindering widespread use of Cu-based MOFs and MOF derivatives along with possible solutions to overcome the challenges.

Highly selective electrocatalytic reduction of CO2 to HCOOH over an in situ derived hydrocerussite thin film on a Pb substrate

A metal oxide electrode has been developed for the electrochemical CO₂ reduction reaction (eCO₂RR). It exhibits superior activity and product selectivity towards eCO₂RR by circumventing the previously encountered problem of self-reduction with high-valence metals. Specifically, a hydrocerussite [Pb₃(CO₃)₂(OH)₂] thin film has been synthesized in situ on a Pb substrate (denoted as ER-HC) by an electroreduction method using a lead-based metal-organic framework (Pb-MOF) as a precursor. The ER-HC electrode exhibits a high selectivity of 96.8% towards HCOOH production with a partial current density of 1.9 mA cm^-2 at -0.88 V vs. the reversible hydrogen electrode (RHE). A higher HCOOH partial current density of 7.3 mA cm^-2 has been achieved at -0.98 V vs. RHE. Physicochemical and electrochemical characterization results demonstrate that the defective hydrocerussite surface exhibits appropriate adsorption free energy of formate (HCOO^-) and a lower reaction free energy for HCOOH production from CO₂, which greatly boosts the eCO₂RR activity and HCOOH production selectivity. The structure and eCO₂RR performance of the hydrocerussite thin film remain stable in 0.1 M KHCO₃ as electrolyte, ensuring its durability. Overall, this work not only provides a metal oxide electrode (metal hydroxide, to be more precise) with excellent eCO₂RR performance, but also expands the in situ electrochemical derivatization strategy for the fabrication of metal oxide electrodes.

High Yield of CO and Synchronous S Recovery from the Conversion of CO2 and H2S in Natural Gas Based on a Novel Electrochemical Reactor

H₂S and CO₂ are the main impurities in raw natural gas, which needs to be purified before use. However, the comprehensive utilization of H₂S and CO₂ has been ignored. Herein, we proposed a fully resource-based method to convert toxic gas H₂S and greenhouse gas CO₂ synchronously into CO and elemental S by using a novel electrochemical reactor. The special designs include that, in the anodic chamber, H₂S was oxidized rapidly to S based on the I^-/I₃^- cyclic redox system to avoid anode passivation. On the other hand, in the cathodic chamber, CO₂ was rapidly and selectively reduced to CO based on a porous carbon gas diffusion electrode (GDE) modified with polytetrafluoroethylene and cobalt phthalocyanine (CoPc). A high Faraday efficiency (>95%) toward CO was achieved due to the enhanced mass transfer of CO₂ on the GDE and the presence of the selective CoPc catalyst. The maximum energy efficiency of the system was more than 72.41% with a current density of over 50 mA/cm², which was 12.5 times higher than what was previously reported on the H₂S treatment system. The yields of S and CO were 24.94 mg·cm^-2·h^-1 and 19.93 mL·cm^-2·h^-1, respectively. A model analysis determined that the operation cost of the synchronous utilization of H₂S and CO₂ method was slightly lower than that of the single utilization of H₂S in the existing natural gas purification technology. Overall, this paper provides efficient and simultaneous conversion of H₂S and CO₂ into S and CO.