Key Takeaways & Executive Findings
- •• CoPc supported on hollow carbon nanospheres (HCNs) achieves a maximum CO2-to-CH4 selectivity of 15.1%, breaking the conventional CO-selective behavior of CoPc. • The Janus carbon shell architecture creates inner–outer functional asymmetry, where the inner surface promotes HER to enrich protons near the outer CoPc active sites. • Local proton enrichment is identified as the key mechanism enabling deep CO2 reduction to methane on a non-copper molecular catalyst. • This work demonstrates that catalyst structure can overcome intrinsic selectivity limits of molecular catalysts, offering a new design strategy for non-copper CO2 methanation.
Abstract
Exploring non-copper electrocatalysts for CO2-to-CH4 electrosynthesis is important for reducing overreliance on copper and broadening the catalyst landscape. We report a strategy that enables CH4 formation on cobalt phthalocyanine (CoPc) by regulating the local reaction microenvironment through the catalyst structure. Ultrathin hollow carbon nanospheres (HCNs) with a uniform size were synthesized and used as supports for CoPc, forming “Janus carbon shells” with inner–outer functional asymmetry. The resulting CoPc-HCN hybrid had a maximum CO2-to-CH4 selectivity of 15.1%, overcoming the conventional CO-selective behavior of CoPc. Mechanistic studies show that the hollow carbon structure induces a proton enrichment outside the shell through an inner–outer surface interaction. The inner carbon surface promotes the hydrogen evolution reaction (HER) and produces a proton-enriched environment near the CoPc-active outer surface, thereby enabling CO2 methanation. This work highlights the critical role of catalyst structure in overcoming intrinsic selectivity limits of molecular catalysts.
1. Introduction
The continued reliance on fossil fuels has led to a rapid increase in atmospheric carbon dioxide (CO2) concentration, posing severe risks to the environment and climate[1–3]. Electrochemical CO2 reduction (ECR), when powered by renewable electricity, provides a promising pathway to convert CO2 into value-added fuels and chemicals under mild conditions, thereby contributing to carbon neutrality and sustainable energy storage[4–10].
Among the products of ECR, deeply reduced carbon products are particularly attractive due to their high energy density and practical relevance[11–15]. Copper-based catalysts are currently the main systems capable of efficiently producing multi-carbon (C2+) products, owing to their unique ability to promote C―C coupling[16–18]. However, the development of non-copper catalysts for deep CO2 reduction remains highly desirable, especially for single-carbon (C1) products such as methane (CH4), which represent important synthetic fuels[12,13,19–22].
Molecular catalysts based on metal phthalocyanines (M-Pcs) and porphyrins, featuring well-defined metal-nitrogen (M-N4) active sites, have emerged as highly selective catalysts for CO2-to-CO conversion[23–25]. In particular, cobalt phthalocyanine (CoPc) is widely reported as an efficient and robust CO-selective catalyst[23–24]. However, CH4 formation on CoPc is generally considered unfavorable. The strong tendency for CO desorption, together with the lack of a proton-rich reaction environment hinders further hydrogenation steps beyond CO[11–13,26–27]. As a result, CH4 production has been almost exclusively achieved on copper-based catalysts or specially designed copper phthalocyanines[28–30], leaving a critical gap in non-copper systems for CH4 electrosynthesis.
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LIU Tengyi, HOU Xiaofan, Wijak Yospanya, YE Songbo, Yasutaka Matsuo, Shimpei Ono, Reiko Oda, LI Hao, Hiroshi Yabu (2025). Janus carbon shells with inner–outer functional asymmetry enable local proton enrichment for promoting CO2 methanation. SinoTechIntel Verified Research. https://doi.org/10.1016/S1872-5805(NCM2026-41-03-06)
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Frequently Asked Questions
What is the maximum CO2-to-CH4 selectivity achieved in this study?
The CoPc/HCNs hybrid exhibits a maximum CO2-to-CH4 selectivity of 15.1%, which is a significant improvement over conventional CoPc catalysts that typically produce CO.
How does the Janus carbon shell structure promote CO2 methanation?
The Janus carbon shell has inner and outer surfaces with distinct functions. The inner surface promotes the hydrogen evolution reaction (HER), creating a proton-enriched environment near the outer surface where CoPc is active, thereby facilitating the hydrogenation of CO2 to CH4.
What is the significance of this work for non-copper electrocatalysts?
This work demonstrates that by engineering the catalyst structure, it is possible to overcome the intrinsic selectivity limits of molecular catalysts like CoPc, enabling deep CO2 reduction to CH4 without relying on copper-based materials.
What are the key mechanistic insights from this study?
Mechanistic studies reveal that the hollow carbon structure induces proton enrichment outside the shell through an inner–outer surface interaction. The inner carbon surface promotes HER, producing a proton-rich environment near the CoPc-active outer surface, which is crucial for CO2 methanation.
What are the potential applications of this catalyst design?
This catalyst design offers a new strategy for developing non-copper electrocatalysts for CO2 reduction to valuable fuels like methane, which could contribute to sustainable energy storage and carbon neutrality.
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