Opportunity
The substantial emission of carbon dioxide (CO₂) is a primary driver of global environmental crises, including the greenhouse effect, ocean acidification, and rising sea levels. Electrochemically reducing this abundant atmospheric CO₂ into valuable chemical feedstocks and fuels using renewable electricity presents a highly promising strategy for carbon capture and utilization. However, the electrocatalytic CO₂ reduction reaction (ECO₂RR) faces significant technical hurdles. A major challenge is the competition from the hydrogen evolution reaction (HER), which consumes protons and electrons, reducing the overall efficiency for CO₂ conversion. Furthermore, the reaction pathway is complex, involving multiple proton-coupled electron transfer steps that can lead to a wide range of products, from single-carbon (C₁) compounds like carbon monoxide and methane to more valuable multi-carbon (C₂₊) products such as ethylene and ethanol. Copper (Cu) is a unique catalyst capable of producing C₂₊ products, but its selectivity, particularly for ethylene (C₂H₄), remains relatively low compared to C₁ products. This low selectivity is often attributed to suboptimal catalyst surface properties and local environments that do not sufficiently promote the critical carbon-carbon (C–C) coupling step. While metal-organic frameworks (MOFs) offer advantages like high surface area and tunable active sites, many pristine Cu-based MOFs suffer from excessive distances between active sites, hindering C–C coupling, and possess structural instability under electrochemical conditions. Therefore, there is a pressing and unmet need to develop a stable, efficient, and highly selective Cu-based electrocatalyst specifically designed to favor the production of high-value C₂₊ products from CO₂.
Technology
The present invention addresses this need by disclosing a novel copper-based metal-organic framework (MOF) electrocatalyst. The core innovation is a three-dimensional interconnected structure composed of Cu-5-mercapto-1-methyltetrazole (Cu-MMT) nanostructured monomers. These monomers are polymerized in an orthorhombic Pbca space group, with each monomer consisting of six Cu ions and six MMT ligands forming a cylindrical structure. A key feature is the intentional creation of single-atom Cu point defects within this framework. These defects arise from unsaturated Cu atoms, each coordinated by two sulfur (S) atoms and one nitrogen (N) atom from the MMT ligands, forming a unique and highly reactive Cu-1S-2N coordination structure. This configuration results in the formation of multiple, closely spaced bi-copper sites. The strong Cu–S and Cu–N bonds provide exceptional structural stability under the reducing potentials required for ECO₂RR. Crucially, the engineered interlayer spacing (approximately 7 Å) and pore diameter (approximately 5.5 Å) within the 3D network are optimized for efficient CO₂ capture and diffusion. The closely spaced bi-copper sites and the electron-donating methyl group on the ligand work synergistically to enhance the coverage of key CO intermediates and dramatically lower the energy barrier for C–C coupling. This targeted design shifts the product selectivity overwhelmingly towards multi-carbon (C₂₊) formation.
Advantages
- Achieves exceptionally high Faradaic efficiency (FE) for C₂₊ products, reaching 70-75% at -1.15V vs. RHE.
- Delivers high selectivity for the valuable product ethylene (C₂H₄), with an FE of 50-55% at the same potential.
- Exhibits superior structural stability during prolonged electrolysis, maintaining performance for over 12 hours due to robust Cu–S and Cu–N bonds.
- Features a tunable synthesis process that allows for the fabrication of catalysts with different morphologies (diamond, paddle, broom-shaped) by adjusting parameters like temperature, concentration, and time.
- Provides a high density of unsaturated, low-valence Cu(I) active sites and closely spaced bi-copper sites, which are ideal for promoting C–C coupling.
- Offers an optimized porous structure that facilitates efficient CO₂ mass transport and exposure of active sites.
Applications
- Integration into electrochemical reactors for the direct conversion of CO₂ from industrial flue gas or ambient air into high-value chemicals like ethylene.
- Use as a key component in energy conversion devices that store renewable electricity in the form of chemical bonds in C₂₊ fuels and feedstocks.
- Serving as a foundational catalyst material for further research and development in the field of carbon capture and utilization (CCU) technologies.
- Potential application in modular or distributed systems for on-site production of chemicals from CO₂.
