The escalating global warming crisis, driven by high CO₂ emissions, necessitates the development of sustainable technologies for CO₂ conversion into valuable products. Electrocatalytic CO₂ reduction, particularly the generation of CO, offers a promising avenue for clean energy. However, conventional electrocatalytic methods suffer from high energy consumption and reliance on expensive catalysts. This research explores an alternative approach: contact-electro-catalysis, a technique that leverages triboelectric nanogenerators (TENGs) to convert mechanical energy into electrical energy for driving the catalytic process. TENGs offer a sustainable and potentially cost-effective energy source for CO₂ reduction. While previous studies have demonstrated the use of contact-electro-catalysis for other reactions, such as hydrogen peroxide synthesis and organic dye degradation, applying this approach to CO₂ reduction faces considerable challenges. The main hurdles include the chemically inert nature of CO₂, the requirement for efficient CO₂ capture and activation sites, and the need for a suitable electron transfer mechanism under ambient conditions. This work aims to address these challenges by developing a novel contact-electro-catalytic system capable of efficiently reducing CO₂ from ambient air with high selectivity towards CO. The study hypothesizes that by combining a suitable CO₂ adsorption material with a highly efficient electron transfer catalyst within a TENG framework, it is possible to achieve high-performance, energy-efficient CO₂ reduction even at low CO₂ concentrations.

Extensive research has been conducted on electrocatalytic CO₂ reduction, focusing on improving efficiency and selectivity using various catalysts and reaction conditions. Studies have explored various materials, including metal nanoparticles (Cu, Ag, Au), metal oxides, and metal-organic frameworks (MOFs), to enhance catalytic activity. Significant advances have been made in achieving high Faradaic efficiencies for CO production. However, these methods often require high energy input, specific reaction environments, or expensive catalysts. The development of TENGs as sustainable energy sources has also gained significant traction, with applications ranging from self-powered sensors to energy harvesting. The use of TENGs in catalysis has emerged as a novel area of research, showing promise for driving chemical reactions using ambient mechanical energy. However, the application of TENG-based contact-electro-catalysis to CO₂ reduction remains largely unexplored, with limited research demonstrating the potential of this approach.

This research utilizes a TENG device consisting of two triboelectric layers: an electropositive layer of quaternized cellulose nanofibers (CNFs) and an electronegative layer of electrospun polyvinylidene fluoride (PVDF) loaded with single Cu atoms-anchored polymeric carbon nitride (Cu-PCN) catalysts. The quaternized CNFs provide strong CO₂ adsorption capabilities due to their abundance of hydroxyl groups and the positively charged quaternary ammonium salts. The Cu-PCN catalyst is designed to efficiently accumulate and transfer electrons. The preparation of quaternized CNF involved treating CNF with glycidyl trimethylammonium chloride (GTMAC). The Cu-PCN catalyst was synthesized through a solvothermal method involving urea, copper chloride, and dicyandiamide, followed by calcination. Electrospinning was used to create PVDF fibers loaded with the Cu-PCN catalyst. The optimal Cu-PCN to PVDF mass ratio of 1:100 was determined to prevent catalyst agglomeration. The TENG device was assembled by attaching the quaternized CNF film and the Cu-PCN@PVDF film with double-sided tape, with copper wires providing electrical connections. The contact-electro-catalytic CO₂ reduction was conducted in a sealed chamber with controlled humidity (99% RH). Experiments were conducted with varying CO₂ concentrations, Cu-PCN content, and reaction durations. The produced CO was analyzed using gas chromatography (GC), and the transferred charge was determined via current integration. Isotope labeling experiments were performed using ¹³CO₂ to confirm that the CO generated was derived from the CO₂ reduction. Characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculations, were employed to investigate the structure, morphology, electronic properties, and reaction mechanism of the materials and the process. The Faradaic efficiency (FE) was calculated using standard electrochemical equations. Additional experiments were carried out to test the performance of the device under ambient air conditions, with the CO₂ adsorption capacity evaluated using a breakthrough curve approach.

The study demonstrated the successful implementation of a novel contact-electro-catalytic CO₂ reduction system using a TENG device. Several key findings emerged: 1. **High CO Faradaic Efficiency:** The TENG achieved a remarkably high CO Faradaic efficiency of 96.24%, indicating highly efficient conversion of CO₂ to CO. 2. **Superior CO Yield:** The system produced a CO yield of 33 µmol g⁻¹ h⁻¹, significantly outperforming state-of-the-art air-based CO₂ reduction technologies. 3. **Ambient Air Operation:** The TENG-based catalyst effectively reduced CO₂ even in ambient air (low CO₂ concentration), highlighting its potential for real-world applications. 4. **Mechanism Elucidation:** Detailed mechanistic studies revealed that the high efficiency is due to the synergistic effects of the quaternized CNF's strong CO₂ adsorption capacity and the Cu-PCN's electron-enrichment ability. The quaternized CNF acts as the primary CO₂ adsorption site, while the single Cu atoms in Cu-PCN facilitate efficient electron transfer during contact electrification. DFT calculations confirmed the strong CO₂ adsorption on quaternized CNF and the electron enrichment effect of the single Cu atoms. 5. **Catalyst Optimization:** Experiments revealed an optimal Cu-PCN catalyst loading (1%) that balances high catalytic activity and material properties. 6. **Long-Term Stability:** The TENG demonstrated remarkable stability over multiple cycles (35 h), with consistent CO production and current output, indicating the robustness of the system. 7. **Isotope Tracing:** Isotope labeling studies confirmed that the generated CO originated from the CO₂ reduction reaction. 8. **Air-Based CO₂ Reduction:** The researchers successfully demonstrated CO₂ reduction directly from ambient air using the TENG device, with a CO yield of 33 μmol g⁻¹ h⁻¹. This result surpasses the performance of many existing air-based CO₂ reduction methods. These findings strongly support the viability and superior performance of the proposed contact-electro-catalytic approach for CO₂ reduction.

The results of this study significantly advance the field of sustainable CO₂ reduction. The demonstrated high Faradaic efficiency, superior CO yield, and successful operation in ambient air address critical limitations of traditional electrocatalytic methods. The synergistic combination of quaternized CNF for CO₂ capture and Cu-PCN for efficient electron transfer provides a novel and effective approach to CO₂ reduction. The use of TENGs as a sustainable energy source eliminates the need for high energy inputs, further enhancing the sustainability of the process. The findings demonstrate the potential for this technology to play a significant role in mitigating CO₂ emissions. This work provides a strong foundation for future research exploring the optimization of the catalyst and TENG design, as well as the potential to extend the method to other valuable chemicals beyond CO. The discovery opens up possibilities for scaling up the technology for practical applications, potentially creating localized carbon capture and utilization systems. The unique combination of materials and energy harvesting offers a promising avenue for developing more efficient and environmentally friendly solutions for addressing the climate change challenge.

This research successfully demonstrated a highly efficient and sustainable method for CO₂ reduction using contact-electro-catalysis powered by a TENG. The exceptional CO Faradaic efficiency (96.24%) and CO yield (33 µmol g⁻¹ h⁻¹) achieved even under ambient air conditions represent a significant advancement in the field. The underlying mechanism, involving synergistic CO₂ adsorption and electron transfer, was elucidated through experimental and computational studies. Future research directions could focus on exploring different single-atom catalysts and optimizing the TENG design for enhanced performance. The scalability and integration of this technology into practical carbon capture and utilization systems warrant further investigation.

While this study demonstrates the high potential of contact-electro-catalysis for CO₂ reduction, some limitations exist. The current setup operates under controlled humidity conditions (99% RH), which may not be easily replicable in all real-world scenarios. Further research is needed to explore the performance under varying humidity levels and environmental conditions. The long-term durability and stability of the device in practical applications also require further evaluation. Additionally, the current study primarily focuses on CO production. Future research should investigate the possibility of producing other higher-value products through catalyst optimization and reaction condition tuning.