In the relentless pursuit of sustainable solutions to climate change, the electrochemical reduction of carbon dioxide (CO₂) into valuable multi-carbon (C₂+) products stands as a beacon of promise. This process, which transforms a greenhouse gas into useful hydrocarbons like ethylene, offers a dual benefit: mitigating atmospheric CO₂ levels while generating important chemical feedstocks. Yet, despite its potential, the journey to efficient and durable CO₂ conversion faces formidable challenges, chiefly arising from the electrolytic environment. A groundbreaking study by Ding, Pan, Fan, and colleagues, recently published in Nature Energy, unveils a novel approach to overcoming these obstacles by leveraging surface-adsorbed iodide ions on copper electrodes to unlock remarkable enhancements in CO₂ reduction within strongly acidic media.
Traditionally, CO₂ electroreduction research has favored highly alkaline cathodic environments due to their ability to suppress the competing hydrogen evolution reaction (HER) and promote desirable multi-carbon product formation. However, alkaline conditions are a double-edged sword. CO₂ readily reacts with hydroxide ions to yield carbonate and bicarbonate species, leading to significant inefficiencies in CO₂ utilization and causing carbonate buildup that shortens device lifespan. This carbonate formation issue has constrained the scalability of alkaline CO₂ reduction systems, prompting researchers to explore alternative conditions, including acidic media, where carbonate formation is mitigated.
Acidic electrolytes, by their nature, reduce the propensity of CO₂ to transform into carbonate, thus preserving the feedstock and improving operational longevity. Yet, acidic environments introduce their own complications, most notably a pronounced competition from the HER. The high proton concentration in acid renders the hydrogen evolution reaction kinetically favored over CO₂ reduction, diminishing activity toward carbon-based products and drastically lowering selectivity for complex C–C coupled molecules like ethylene or ethanol. Thus, acidic CO₂ electroreduction has historically underperformed, creating a compelling need for innovative strategies that can selectively enhance C₂+ formation while suppressing HER in acid.
Addressing this challenge, the team led by Ding and colleagues has identified that the introduction of iodide ions (I⁻) via the acidic electrolyte fundamentally alters the copper electrode surface dynamics in a way that favors CO₂ reduction to multi-carbon products. The researchers demonstrated that these iodide ions strongly adsorb onto the copper surface during electrolysis, remaining stably anchored under operational potentials. This modification dramatically changes the reaction landscape: ethylene selectivity approximately doubles, CO production concomitantly decreases, and overpotentials—key measures of the energy efficiency of the reaction—are significantly reduced.
Delving into the mechanistic underpinnings, the study reveals that surface-adsorbed iodide induces an unusual asymmetrical coupling pathway between reaction intermediates—specifically an OC–COOH coupling mechanism. This pathway contrasts with the traditional symmetric coupling routes and is postulated to lower the energy barrier for C–C bond formation, a known bottleneck in CO₂ electroreduction. Consequently, the process more favorably leads to the generation of complex multi-carbon molecules, a hallmark of advanced CO₂ valorization technologies.
Central to the efficacy of iodide ions is their robust interaction with the copper electrode. Under acidic and reductive conditions—the very environment where conventional approaches stumble—iodide remains persistently adsorbed. This key feature ensures continuous modulation of the catalyst surface, stabilizing intermediates involved in multi-carbon product formation while simultaneously suppressing less desirable side reactions like CO production or hydrogen evolution. The persistence of iodide during operation is a remarkable finding, carrying significant implications for the design of future electrochemical CO₂ conversion devices.
Building upon this foundational insight, the research team further demonstrates that alloying copper with silver (Ag) and optimizing the electrolyte composition can synergistically enhance performance. With these modifications, their system attains an exceptional C₂+ partial current density of 940 milliamperes per square centimeter (mA cm⁻²) at a relatively modest potential of −1.08 volts versus the reversible hydrogen electrode. This performance metric not only underscores the high activity but also highlights the energy-efficient operation of the system. Equally impressive is the reported operational stability, a critical factor when considering the commercial viability of electrochemical CO₂ reduction technologies.
The implications of this work extend far beyond immediate laboratory achievements. By surmounting the dual challenges of low CO₂ utilization and competitive hydrogen evolution in acidic media, Ding et al. open a pathway toward scalable, efficient CO₂ electroreduction platforms. The ability to harness an acidic electrolyte environment while achieving high selectivity and activity for valuable multi-carbon products could revolutionize carbon capture and utilization strategies.
Furthermore, the discovery that halide ions—particularly iodide—can act as surface modifiers to steer reaction pathways invites a reassessment of electrolyte and catalyst design principles. Surface engineering via electrolyte composition, often overshadowed by catalyst material optimization, emerges here as a powerful lever to control reaction mechanisms. Such insights could inspire the tailoring of electrolytes with targeted adsorbates for a broad range of electrochemical transformations.
The methodology employed in this study encompasses a meticulous combination of electrochemical measurements, surface-sensitive spectroscopic analyses, and theoretical modeling. This integrative approach enabled the team to not only confirm the presence and stability of iodide adsorption but also to construct detailed mechanistic scenarios that illuminate the subtle interplay between surface chemistry and electrochemical reactivity. By anchoring their experimental observations in a solid mechanistic framework, the researchers provide a roadmap to further refine catalyst-electrolyte systems for CO₂ reduction.
From an industrial perspective, the robust performance metrics—high current density at low overpotential and stability—hold promise for implementation in commercial electrolysis devices. The employment of copper, an earth-abundant metal, combined with the utilization of iodide ions and modest silver alloying, balances activity and cost considerations. Moreover, operation in acidic media alleviates long-standing issues related to carbonate management, simplifying system design and operation.
It is worth emphasizing that the ethylene selectivity achieved in this work represents a significant leap compared to prior systems operating under similar acidic conditions. Ethylene is one of the most valuable multi-carbon products, widely used in polymer production and other chemical industries. Enhancing ethylene formation efficiency directly impacts the economic feasibility of CO₂-to-chemical conversion technologies. This selective boost, combined with the mechanistic insights, positions iodide-modified copper electrodes as frontrunners in the quest for viable CO₂ reduction catalysts.
The suppression of CO formation concomitant with enhanced C₂+ production also reflects an improved reaction pathway control, minimizing undesired product formation. Such selectivity tuning is critical for downstream processing, reducing separation costs and increasing overall process efficiency. The asymmetrical OC–COOH coupling pathway unveiled by the team may be applicable as a design principle across different catalyst systems, fostering new avenues for multicarbon product manipulation.
In the broader context of carbon utilization and electrochemical energy conversion, this study exemplifies a trend toward nuanced interface engineering. Rather than relying solely on the bulk properties of catalysts, directing efforts towards the atomic-scale environment at the electrolyte-catalyst interface offers transformative potential. Electrolyte additives, surface adsorbates, and co-catalysts can orchestrate reaction pathways, a concept that this work elegantly validates through the case of iodide enhanced CO₂ reduction.
Looking ahead, future research may exploit this halide ion adsorption strategy to explore other halogens or combinations thereof to further refine selectivity and efficiency. Coupling such chemical insights with advanced reactor engineering and renewable electricity integration could accelerate the deployment of CO₂ electroreduction technologies, contributing meaningfully to global carbon management goals.
In conclusion, the pioneering work by Ding, Pan, Fan, and colleagues sets a new benchmark in CO₂ electroreduction science, demonstrating that surface-adsorbed iodide ions can dramatically reshape electrochemical environments in strongly acidic media to favor multi-carbon product generation. The resulting improvements in selectivity, activity, and device stability mark a substantial advance in the field, with profound implications for sustainable chemical manufacturing and greenhouse gas mitigation.
Subject of Research: Electrochemical reduction of carbon dioxide to multi-carbon products in strongly acidic media enhanced by iodide ion adsorption on copper electrodes.
Article Title: Enhanced CO₂ electroreduction to multi-carbon products in strong acid induced by surface-adsorbed iodide ions.
Article References:
Ding, X., Pan, B., Fan, B. et al. Enhanced CO₂ electroreduction to multi-carbon products in strong acid induced by surface-adsorbed iodide ions. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01924-4
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