What if turning captured carbon dioxide into useful chemicals could be made simpler, cheaper, and easier to scale up? Researchers may have found a way.
Study: Large-Scale Synthesis (75 g/Batch) of Single-Atom Catalysts for Selective Electrochemical CO2 Reduction to CO and Commercialization Potential Analysis. Image Credit: chayanuphol/Shutterstock.com
In a recent study, researchers developed a straightforward, single-step method for producing nickel/iron–nitrogen–carbon (Ni/Fe–N–C) catalysts using readily available melamine and multiwalled carbon nanotubes (MWCNTs). The process produced batches as large as 75 grams without the complicated pre- and post-treatment steps typically required.
Better still, the catalysts converted CO2 to carbon monoxide (CO) with more than 98% selectivity at industrially relevant current densities. The researchers’ economic and environmental analyses also suggest the approach could make CO production cheaper and less carbon-intensive than using conventional silver-based catalysts, bringing commercial CO2 conversion a step closer.
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Importance of Scaling Catalyst Production
eCO2R, a promising approach within carbon capture and utilization (CCU), uses renewable electricity to decarbonize sectors that are hard to electrify, like maritime transport and chemicals.
Scalable synthesis of electrocatalysts that durably and consistently deliver high product selectivity at >300 mA cm-² and industrially relevant current densities is crucial for eCO2R commercialization.
While noble metal (gold (Au) or silver (Ag))-based nanoparticles have been the most extensively studied catalysts for eCO2R to CO, producing them at scale is unviable owing to their high cost.
M–N–C-based Catalysts
Single-atom catalysts (SACs) based on M–N–C have received significant attention as a potential alternative to Ag nanoparticles. M–N–C catalysts with dominant single-atom sites are most effective for producing CO. These catalysts primarily use transition metals like Ni, Fe, zinc, and copper, which are abundant on Earth and cheaper than conventional Ag- and Au-based materials.
Among transition metals, Fe and Ni are commonly studied for synthesizing M–N–C SACs for CO production. Fe and Ni showed the highest thermodynamic favorability for eCO2R to CO.
However, conventional M–N–C-based SAC synthesis techniques depend on complex post- and pre-treatment processes and energy-intensive steps, which hinder scalability and adversely impact the environment.
Previous research efforts to produce commercially viable large batches of M–N–Cs often resulted in wasted precursors, electrical energy, and solvents, which limits their commercial viability.
The Proposed Scalable Synthesis Approach
In this work, researchers proposed a single-step scalable synthesis of M–N–C catalysts using commercially available melamine and MWCNTs as the feedstock for selective eCO2R to CO.
They also performed life cycle assessment (LCA) and technoeconomic analysis (TEA) on large-batch synthesis and the overall eCO2R process.
The starting materials were industrial-grade MWCNTs with more than 90 wt % purity (Raw indCNT), standard-grade MWCNTs with more than 95 wt % purity (Raw CNT), and melamine (Mel) as the nitrogen precursor during catalyst synthesis. Raw indCNT contained higher levels of Fe and Ni/residual metallic impurities.
Preparation of CNT-Mel and Derivatives
Researchers prepared four catalyst samples for this study: one using Raw IndCNT (designated as indCNT-Mel-75g) and three using Raw CNT as the carbon precursor (designated as CNT-Mel-x, with x representing the batch size). The batch sizes of the three samples were CNT-Mel-75g, CNT-Mel-50g, and CNT-Mel-25g.
Initially, a standard kitchen-top blender was used to mix 25 g of Raw CNT with 25 g of Mel, ensuring a 1:1 CNT/Mel mass ratio. Then, the resultant mixture was packed without a crucible or boat into an 8 cm diameter quartz tube. Thermal blocks and quartz wool were placed at both ends of the quartz tube to hold the mixture in position.
Subsequently, the tube was placed within a tubular furnace and treated at a constant 50 mL min-¹ flow rate under an argon atmosphere. The reactor temperature was increased to 650 °C at 5 °C min ¹ and held for three hours before cooling naturally to room temperature.
Researchers used the same synthesis method to prepare all four samples, regardless of CNT source or batch size. They assessed the electrochemical performance of the samples to evaluate the uniformity of catalyst quality and performed material characterization.
Feasibility of the Approach
Researchers successfully synthesized up to 75 g per batch of a Ni/Fe-based M–N–C catalyst (CNT-Mel) through a moderate-temperature, scalable, and repeatable pyrolysis process using commercial MWCNTs.
Batch sizes of up to 75 g were successfully produced using both cheaper industrial-grade MWCNTs (>90% carbon content) and regular-grade MWCNTs (>95% carbon content). The synthesis leveraged inherent Ni/Fe impurities in the MWCNTs and required only moderate-temperature pyrolysis at 650 °C, without pre- or post-treatments.
Material characterization validated the scalability and repeatability of the process, as all batch sizes showed almost identical properties. The catalysts consistently achieved >98% CO selectivity at commercially relevant 500 mA cm-² current densities, outperforming benchmark Ag nanoparticle catalysts.
TEA estimated a CO minimum selling price (MSP) of $145 per ton, lower than the $174 per ton price obtained using Ag catalysts and the current CO market price of $400, indicating commercialization potential. LCA also showed 21% lower CO2-equivalent emissions than Ag catalysts.
The findings of this study demonstrated the feasibility of the approach for synthesizing high-performance M–N–C catalysts while delivering economic and environmental advantages.
Journal Reference
Racine, C. et al. (2026). Large-Scale Synthesis (75 g/Batch) of Single-Atom Catalysts for Selective Electrochemical CO2 Reduction to CO and Commercialization Potential Analysis. ACS Omega, 11 (23), 34554–34567. DOI: 10.1021/acsomega.6c02693, https://pubs.acs.org/acsodf/article/11/23/34554/5157414/Large-Scale-Synthesis-75-g-Batch-of-Single-Atom
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