Key Takeaways & Executive Findings
- •• • AuAgCuPdPt HEAs achieve a peak Faradaic efficiency (FE) of 96.5% for CO at −0.3 V vs. RHE, with FE >90% across −0.2 to −0.7 V, demonstrating superior selectivity for CO2-to-CO conversion. • • In situ ATR-FTIR reveals that Pt addition promotes water dissociation to generate protonic hydrogen and facilitates *CO desorption, directly addressing the rate-limiting steps in CO2RR. • • Kinetic isotope effect (H-D) experiments confirm water dissociation as the key proton donor, providing mechanistic evidence for the reaction pathway. • • In a Zn-CO2 battery, the AuAgCuPdPt cathode delivers 90.23% FE for CO and a power density of 3.474 mW cm−2, showcasing practical energy storage and CO2 conversion integration.
Abstract
High-entropy alloys (HEAs) have shown great promise in the CO2 reduction reaction (CO2RR) due to their tunable composition and unique physical and chemical properties. However, the role of HEAs in CO2RR and the underlying reaction mechanism remain underexplored, particularly through in situ techniques. In this work, we investigate the mechanism of CO2 reduction on AuAgCuPdPt HEAs using in situ Raman spectroscopy and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy to reveal key intermediates and reaction pathways. Our results demonstrate that within the potential window of −0.2 to −0.7 V vs. reversible hydrogen electrode (RHE), the AuAgCuPdPt HEAs efficiently reduce CO2 to CO, achieving a Faradaic efficiency (FE) for CO greater than 90%, with a peak FE of 96.5% at −0.3 V vs. RHE. The CO2− intermediate was observed at low potentials, revealing the reaction pathway in the CO2 reduction process. Additionally, in situ ATR-FTIR results suggest that the introduction of an appropriate amount of Pt metal not only promotes water dissociation to generate protonic hydrogen, but also facilitates the desorption of *CO intermediates. The kinetic isotope effect of hydrogen-deuterium (H-D) confirms that water dissociation acts as a key proton donor in CO2RR. Furthermore, the catalyst of AuAgCuPdPt HEAs was applied as cathodes in a Zn-CO2 battery, achieving 90.23% FE for CO and a power density of 3.474 mW cm−2. This study provides new insights into the mechanistic understanding of CO2 reduction and underscores the importance of in situ spectroscopic techniques for advancing the design of efficient electrocatalysts for CO2 conversion.
1. Introduction
Global energy demand remains heavily reliant on fossil fuels, with 85% of supply derived from non-renewable sources, leading to escalating CO2 emissions and environmental degradation. Electrocatalytic CO2 reduction (CO2RR) offers a sustainable route to convert CO2 into valuable chemicals and fuels using renewable electricity. Among products, carbon monoxide (CO) is economically attractive due to its high energy efficiency per electron and its role as a precursor for industrial chemicals. However, the efficient activation of CO2 to reactive intermediates such as *CO2− radicals typically requires high overpotentials, limiting catalytic activity and selectivity. Coupling CO2RR with a Zn anode in a Zn-CO2 battery presents a dual-function system for both CO2 conversion and energy storage, yet its practical viability hinges on developing cathodes with high selectivity and stability.
High-entropy alloys (HEAs) have emerged as promising catalysts owing to their tunable compositions and unique properties like lattice distortion and cocktail effects. Prior work on AuAgCuPdPt HEAs demonstrated enhanced CO2RR activity, but mechanistic understanding remained superficial. This study addresses that gap by employing in situ Raman and ATR-FTIR spectroscopies to identify key intermediates and reaction pathways. The findings reveal that Pt content critically modulates water dissociation and *CO desorption, enabling >90% FE for CO. This mechanistic insight not only advances HEA catalyst design but also demonstrates a practical Zn-CO2 battery with high power density, offering a pathway toward integrated energy storage and CO2 utilization.
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LI Li, GAO Zengqiang, KANG Wenjing, FENG Yi, HOU Man, YIN Pengfei, LIU Hui, ZHANG Zhicheng (2026). Pt-optimized AuAgCuPdPt high-entropy alloys for selective CO2 reduction and high-performance Zn-CO2 battery. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3596-2
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Frequently Asked Questions
What is the specific role of Pt in the AuAgCuPdPt HEA for CO2 reduction, and how does it affect the reaction mechanism?
In situ ATR-FTIR and kinetic isotope effect studies indicate that Pt promotes water dissociation to generate protonic hydrogen, which acts as a key proton donor for CO2RR. Additionally, Pt facilitates the desorption of *CO intermediates, preventing catalyst poisoning and enhancing CO selectivity. This dual role is critical for achieving high FE (>90%) and is confirmed by the observed H-D kinetic isotope effect.
How does the AuAgCuPdPt HEA perform in a practical Zn-CO2 battery, and what are the key performance metrics?
When employed as a cathode in a Zn-CO2 battery, the AuAgCuPdPt HEA achieves a Faradaic efficiency of 90.23% for CO and a power density of 3.474 mW cm−2. These metrics demonstrate the catalyst's viability for integrated CO2 conversion and energy storage, though further optimization of the battery configuration may be needed to enhance power output.
What are the main challenges in scaling up the synthesis of AuAgCuPdPt HEAs for industrial CO2RR applications?
The synthesis method (top-down) may face scalability issues due to the need for precise control over multi-element composition and nanoparticle size. Additionally, the cost of Pt and other noble metals could be prohibitive. However, the high FE and stability observed suggest that with optimized synthesis and reduced Pt loading, industrial application could be feasible. Further studies on long-term stability and cost analysis are required.
How does the performance of AuAgCuPdPt HEAs compare to traditional Cu-based catalysts for CO2-to-CO conversion?
Traditional Cu catalysts often suffer from low selectivity for CO, producing a mixture of products. In contrast, AuAgCuPdPt HEAs achieve >90% FE for CO, with a peak of 96.5% at −0.3 V vs. RHE, significantly outperforming monometallic Cu. The synergistic effects among the five elements, particularly Pt's role in water dissociation and *CO desorption, contribute to this enhanced selectivity.
What is the significance of the CO2− intermediate observed at low potentials in the CO2RR mechanism?
The observation of CO2− intermediate at low potentials provides direct evidence for the initial electron transfer step in CO2RR. This intermediate is crucial for the formation of *CO, and its detection via in situ Raman spectroscopy confirms the reaction pathway. Understanding this step is essential for designing catalysts that stabilize this intermediate and lower the activation barrier, thereby improving overall efficiency.
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