Carbon dioxide (CO₂) electroreduction is a promising strategy to mitigate climate change by converting CO₂ into value-added chemicals and fuels using renewable electricity. The success of this process hinges on the development of efficient catalysts that can drive the reaction with high selectivity, activity, and stability. Over the years, significant progress has been made in designing advanced materials that optimize CO₂ electroreduction performance, making it a viable alternative to fossil fuel-based production methods. Recent breakthroughs in catalyst materials, including transition metal-based catalysts, single-atom catalysts, and nanostructured materials, have demonstrated remarkable improvements in CO₂ conversion efficiency.
Transition metal-based catalysts have been widely explored due to their excellent electrochemical properties. Copper (Cu) has emerged as a particularly promising catalyst due to its unique ability to produce multi-carbon (C₂+) products, such as ethylene and ethanol, with reasonable efficiency. Unlike other metals that predominantly generate carbon monoxide (CO) or formate, Cu facilitates C-C coupling, a crucial step in producing higher-order hydrocarbons. Advances in copper-based catalysts, such as oxide-derived Cu, bimetallic Cu alloys, and nanostructured Cu surfaces, have significantly enhanced CO₂ electroreduction performance. For instance, oxide-derived Cu, formed through pre-reduction of Cu oxides, exhibits enhanced selectivity toward ethylene and alcohols due to the presence of grain boundaries and undercoordinated sites that favor CO dimerization. Additionally, alloying Cu with other metals, such as silver (Ag), gold (Au), or palladium (Pd), modulates electronic structures and enhances selectivity for specific products.
Single-atom catalysts (SACs) have recently gained attention as a novel class of materials with exceptional catalytic properties. SACs consist of isolated metal atoms embedded in a host material, often a carbon-based substrate or metal oxide, providing unique active sites for CO₂ electroreduction. These materials offer the advantage of maximizing atom efficiency while minimizing the use of expensive metals. Studies have shown that single-atom catalysts based on nickel (Ni), cobalt (Co), and iron (Fe) effectively catalyze CO₂ reduction to CO with high selectivity and stability. The strong metal-support interactions in SACs tune electronic properties and enhance catalytic activity by optimizing charge transfer and adsorption properties. Moreover, the ability to engineer SACs at the atomic level allows for precise control over reaction pathways, potentially leading to the selective production of high-value hydrocarbons and oxygenates.
Nanostructured materials represent another frontier in CO₂ electroreduction catalyst design. By controlling the morphology, size, and surface structure of catalysts, researchers have improved both activity and selectivity. Nanostructured catalysts exhibit enhanced catalytic performance due to increased surface area, the presence of high-index facets, and quantum confinement effects. For example, dendritic Cu nanostructures and Cu nanocubes have been shown to promote selective CO₂ reduction to ethylene and ethanol. Similarly, plasmonic nanomaterials, such as Au and Ag nanoparticles, harness localized surface plasmon resonance to enhance light absorption and charge transfer, thereby boosting CO₂ conversion efficiency. Furthermore, hybrid nanostructures combining metal catalysts with carbon-based supports, such as graphene or carbon nanotubes, improve charge transport and stability, offering a sustainable approach for practical CO₂ electroreduction applications.
The integration of electrocatalysts with tailored reaction environments has also emerged as a crucial factor in enhancing CO₂ electroreduction performance. For example, the development of gas-diffusion electrodes (GDEs) has enabled high-current-density electrolysis by improving mass transport and facilitating the availability of CO₂ at active sites. Electrolyte engineering is another key strategy, as the choice of electrolyte influences reaction selectivity and efficiency. Alkaline and neutral electrolytes suppress hydrogen evolution, a competing reaction that reduces CO₂ reduction efficiency, thereby enhancing the yield of desired products. Ionic liquids and solid-state electrolytes have also been explored to modulate CO₂ solubility and optimize reaction kinetics. Additionally, applying external fields, such as electric or magnetic fields, has been investigated to further improve catalytic activity by tuning adsorption energies and reaction pathways.
Despite these significant advances, several challenges remain in developing commercially viable CO₂ electroreduction catalysts. One major issue is catalyst stability, as prolonged operation often leads to degradation, surface reconstruction, and deactivation. Understanding and mitigating these degradation mechanisms through rational catalyst design and in situ characterization techniques is essential for long-term operation. Additionally, improving product selectivity and energy efficiency remains a key challenge. While Cu-based catalysts show promise for C₂+ products, their Faradaic efficiency and reaction rates need further enhancement to achieve industrially relevant performance. The development of new catalyst materials with optimized binding energies for key intermediates is crucial for overcoming these limitations. Moreover, integrating CO₂ electroreduction with renewable energy sources and optimizing process conditions will be necessary for practical deployment at a large scale.
In conclusion, the field of CO₂ electroreduction has witnessed remarkable progress due to breakthroughs in catalyst materials, including transition metal-based catalysts, single-atom catalysts, and nanostructured materials. These advancements have significantly improved reaction efficiency, selectivity, and stability, making CO₂ electroreduction a promising pathway for sustainable chemical production. However, challenges such as catalyst durability, energy efficiency, and process scalability must be addressed to enable widespread adoption. Future research should focus on designing next-generation catalysts with tailored electronic structures, leveraging machine learning for catalyst discovery, and integrating CO₂ electroreduction with renewable energy technologies. By overcoming these challenges, CO₂ electroreduction can play a pivotal role in carbon-neutral energy and chemical production, contributing to global efforts in combating climate change.