Triple-Phase Interface Engineering in Electrocatalytic CO2 Reduction

Lanze Li; Jiexin Wen; Shengbo Zhang; Chenxi Ma; Jun Yin; Qiong Lei

doi:10.7536/PC20250633

Progress in Chemistry ›› 2026, Vol. 38 ›› Issue (1) : 130-140 DOI: 10.7536/PC20250633

review-article

Scan to read & Share

Triple-Phase Interface Engineering in Electrocatalytic CO₂ Reduction

Author information +

History +

PDF

Abstract

Catalytic materials offer multidimensional tunability for catalytic reactions， owing to their multi-level structural features in the condensed state， such as defect types， surface and interface configurations， and wettability. Aimed at maximizing reactive interfaces and enhancing catalytic efficiency， modulating hierarchical phase structures has emerged as a pivotal strategy for performance optimization in catalytic systems. The electrocatalytic CO₂ reduction reaction （eCO₂RR） system， as a typical solid-liquid-gas triple-phase interface reaction， inherently exhibits reaction kinetics and catalytic performance governed by the spatial distribution and dynamic characteristics of the triple-phase interface on catalyst surfaces. Therefore， the regulation of the triple-phase interface to maximize the reaction interface is a potent pathway to enhance the catalytic performance of eCO₂RR. This perspective systematically reviews the evolution from traditional liquid-solid biphasic interfaces to advanced solid-liquid-gas triple-phase interfaces delves into the primary challenges of constructing stable triple-phase interfaces on gas diffusion electrodes within the eCO₂RR system and summarizes the latest advancements in regulating the triple-phase interface by enhancing hydrophobicity. Achieving a fine balance between hydrophobicity and hydrophilicity （i.e.， optimal wettability） is crucial for constructing an efficient triple-phase interface. On one hand， sufficient hydrophobicity is required to prevent excessive electrolyte infiltration: on the other hand， moderate hydrophilicity must be maintained to ensure the supply of reactants/ions from the electrolyte. Their dynamic equilibrium can significantly optimize the triple-phase interface structure， enhance mass transfer of reactants， and improve the effective utilization of catalytic active sites. These insights provide valuable guidelines for designing high-performance triple-phase interfaces in eCO₂RR and other gas-involving electrochemical processes， thereby promoting the development of sustainable energy technologies.

Contents

1 Introduction

2 Condensed matter chemistry and eCO₂RR

3 Evolution of solid-liquid-gas interfaces and their challenges in catalysis

4 Condensed-matter-based strategies for triple-phase interface regulation in eCO₂RR

4.1 Triple-phase interface construction

4.2 Wettability regulation

4.3 Micro⁃nano structure design

5 Conclusion and outlook

Graphical abstract

Keywords

condensed matter chemistry / electrocatalytic CO₂ reduction / triple-phase interface

Cite this article

Download citation ▾

Lanze Li, Jiexin Wen, Shengbo Zhang, Chenxi Ma, Jun Yin, Qiong Lei. Triple-Phase Interface Engineering in Electrocatalytic CO₂ Reduction. Progress in Chemistry, 2026, 38(1): 130-140 DOI:10.7536/PC20250633

登录浏览全文

4963

注册一个新账户忘记密码

1 Introduction

As fossil fuels are extensively consumed and carbon dioxide (CO₂) emissions continue to rise, the world is facing increasingly severe environmental challenges, such as climate change, sea-level rise, and ocean acidification. This situation has compelled global efforts to actively explore decarbonization pathways, among which the capture, storage, and conversion of CO₂ have emerged as one of the key strategies^［1］. By leveraging low-carbon energy sources to transform CO₂ into chemicals and fuels, it not only helps mitigate the threats posed by extreme climate conditions but also provides a new avenue for meeting the growing energy demand, thereby attracting widespread attention^［2］. Among the various conversion technologies, the electrocatalytic CO₂ reduction reaction (eCO₂RR) has gradually become a research hotspot in both academic and industrial circles due to its mild operating conditions, minimal environmental impact, and particularly its broad development potential when integrated with renewable energy sources such as solar and wind power^［3］.

eCO₂ RR involves a multi-step proton–electron transfer and coupling process of reaction intermediates, capable of generating various reduction products, including one-carbon products (i.e., C₁, such as methane, carbon monoxide, and formic acid) and multi-carbon products (i.e., C₂₊, such as ethylene, ethanol, and propanol)^［4］. At present, highly efficient conversion processes for two-electron-transfer products (such as carbon monoxide and formic acid) have become relatively mature; however, achieving high selectivity toward multi-carbon products via multi-electron transfer pathways remains one of the core scientific challenges urgently needing to be addressed in this field^［5］. Furthermore, during prolonged operation, catalyst active sites tend to undergo deactivation, leading to insufficient stability. These issues severely constrain the further industrial-scale development of eCO₂ RR technology^［6］. To tackle these challenges, researchers have conducted multiscale and systematic manipulations targeting the composition, structure, and surface chemistry of catalysts, with the primary objective of enhancing the intrinsic activity of active sites. Typical strategies include modulating the electronic structure of catalysts^［7］, exposing more favorable crystal facets^［8］, or constructing defect sites^［9］, all of which can significantly improve the catalyst’s reactivity, selectivity, and stability. Meanwhile, it has gradually been recognized that the condensed-phase environment in which the catalyst resides—such as phase/interface configurations, surface wettability, and micro/nanoscale structural features—also exerts a critical influence on eCO₂ RR^［10］. Unlike conventional physicochemical processes, these factors not only affect the mass transport and supply of reactants such as CO₂, but also, by precisely tuning parameters like the local CO₂/H₂O ratio^［11-12］, pH value^［13］, and ion concentrations^［14］, can regulate the adsorption–desorption behavior of reaction intermediates at the catalyst surface, substantially alter the reaction pathway, and thereby exert a decisive impact on catalytic performance. As research has deepened, the concept of “condensed-phase chemistry” has been progressively introduced into the field of catalysis to describe the intrinsic interrelationships among “composition–multilevel structure–properties–functionality” within condensed-phase materials, as well as their profound influence on catalytic reaction processes. It should be noted that the “condensed-phase chemistry” concept discussed herein differs from traditional “materials chemistry.” The latter primarily focuses on material composition, preparation methods, and macroscopic properties, whereas the former centers on the synergistic interactions between multilevel structures and reaction microenvironments in solid, liquid, and other condensed phases, exploring how these factors affect reaction kinetics and product selectivity. For example, the introduction of defect structures, the regulation of interfacial environments, and the dynamic evolution of the system can all significantly alter the adsorption and transformation behaviors of reaction intermediates, thereby influencing the distribution of final products and the stability of the catalytic process^［15］. Collectively, these microenvironmental parameters constitute key dimensions that can be engineered and controlled during catalytic reactions^［16］. Among them, the fine-tuning of the triple-phase interface plays an indispensable role in expanding the effective reaction interface, optimizing mass transport and the local reaction environment, and ultimately enhancing catalytic efficiency; however, this area remains underexplored^［17］.

In the eCO₂RR system, the reaction predominantly occurs at the solid–liquid–gas three-phase interface formed by the contact among gaseous CO₂, liquid electrolyte, and solid catalyst. Compared with the conventional solid–liquid two-phase interface, in the three-phase interface CO₂participates directly in the reaction in its gaseous form without prior dissolution in the electrolyte, thereby significantly enhancing both the supply rate of CO₂and the interfacial mass transport efficiency^［18］. This configuration facilitates the optimization of the spatial distribution and coupling pathways of reaction intermediates, serving as a crucial physical foundation for achieving high selectivity toward multi-carbon products. Meanwhile, the introduction of the three-phase interface not only broadens the operational window regarding electrolyte pH and conductivity but also effectively boosts the local CO₂concentration and electron transfer kinetics at the interface, providing essential support for advancing eCO₂RR toward high current densities and industrial-scale reaction conditions^［19］.

To construct and precisely regulate an efficient three-phase interfacial microenvironment, recent research has conducted extensive explorations focusing on phase interface construction, wettability control, and micro/nanostructure design. For example, by constructing hydrophilic–hydrophobic regions, mass transfer between the gas and liquid phases can be simultaneously optimized, thereby effectively stabilizing and expanding the three-phase interface^［20］; whereas hydrophobic polymer modification^［21］and micro/nanostructure design^［22］can significantly enhance the CO₂flux across the interface and its resistance to flooding. Therefore, regarding the three-phase interface as the core space for catalytic performance regulation and precisely controlling it through structural design strategies constitute a key pathway toward achieving efficient and stable conversion in eCO₂RR.

This paper, from the perspective of condensed-phase structure regulation, systematically reviews the evolution of the interfacial structure in eCO₂ RR—from the conventional liquid–solid two-phase configuration to advanced three-phase configurations. It focuses on analyzing the construction methods and failure mechanisms of the three-phase interface in typical configurations such as the gas diffusion electrode (GDE). Furthermore, it summarizes representative research advances in regulating the three-phase interface across dimensions including phase-interface construction, wettability control, and micro/nanostructure design, aiming to provide theoretical support and practical insights for developing high-performance eCO₂ RR systems.

2 Condensed Matter Chemistry and eCO₂RR

Condensed matter chemistry is an emerging discipline that focuses on investigating the interrelationships between structural features and chemical functions in condensed matter^［23］. At its core, it seeks to transcend the traditional research paradigms of “ideal crystals” and “single-molecule reactions,” shifting attention to the pervasive role of structural defects, interfacial characteristics, intermolecular interactions, and multi-scale structural hierarchies in dictating chemical behavior within real materials. This perspective underscores the intimate connection between a material’s structure and its properties, with particular emphasis on the complex chemical processes occurring under specific environmental conditions, such as in liquid, solid, or gas–liquid–solid interfaces.

From the perspective of condensed-state chemistry, catalytic materials in eCO₂RR are no longer regarded as ideal crystals or aggregates of single components; instead, they are understood as complex systems with multi-level structures. Their catalytic performance is synergistically influenced by microenvironmental factors such as phase-interface configurations, hierarchical micro- and nanostructures, and phase distributions. This research perspective provides novel insights and methodologies for a deeper understanding and optimization of the three-phase interfaces in eCO₂RR.

3 Solid–Liquid–Gas Three-Phase Interface: Configuration Evolution and Reaction Bottlenecks

The concept of a three-phase interface was not established at the very beginning of eCO₂RR research. Early studies generally employed solid–liquid two-phase reaction systems (such as H-type electrolyzers), in which the catalyst was completely immersed in the liquid electrolyte. Gaseous CO₂had to first dissolve into the electrolyte and then diffuse to the electrode surface to participate in the reaction (Figure 1a). Although this solid–liquid two-phase interface laid a preliminary foundation for the development of eCO₂RR, its CO₂mass-transfer efficiency was constrained by multiple factors, including the extremely low solubility of CO₂in water (approximately 33 mmol/L at 25 ℃ and 1 atm [1 atm = 101325 Pa]), the rapid local consumption of CO₂during the reaction, and the local concentration decline caused by the carbonate buffering mechanism^［18］. These limiting factors collectively resulted in insufficient reaction activity and favored the formation of two-electron reduction products (such as carbon monoxide and formic acid), making it difficult to efficiently produce multi-carbon products.

From the perspective of condensed-phase chemistry, researchers have proposed a novel strategy for constructing solid–liquid–gas three-phase interfaces to overcome gas supply bottlenecks and enhance the selectivity toward multi-carbon products in reaction systems. The “condensed-phase perspective” referred to herein involves a holistic examination of catalytic reaction systems within their actual condensed-phase environments. This approach not only focuses on the intrinsic chemical reaction kinetics at the catalyst’s active sites but also takes into account the composition, structural defects, surface wettability, and multi-scale mass-transfer behaviors within the surrounding condensed-phase system—comprising the solid support, liquid electrolyte, or the solid–liquid–gas three-phase interface. By integrating the synergistic effects of these factors, a comprehensive understanding of the overall catalytic reaction process can be achieved. At the core of the three-phase interface is the direct transport of gaseous CO₂ to the vicinity of the catalyst, thereby establishing a stable interface where a gas phase channel, a liquid electrolyte, and a solid catalyst coexist (Figure 1b). This concept has led to the development of advanced reactor configurations such as gas-diffusion electrodes (GDEs), which significantly elevate the local CO₂ concentration and the fluxes of electrons and mass transfer. These advancements provide a crucial physical foundation for achieving highly selective synthesis of multi-carbon products under high current densities^[24].

The effectiveness of the three-phase interfacial configuration stems from its construction of a dynamic, multi-scale coupled mass transfer and reaction system: gaseous CO₂ rapidly diffuses to the catalytic sites through the back-channel of the GDE and the hydrophobic layer; the liquid electrolyte provides ionic conductivity and a proton source; and the solid-state catalyst offers active sites. This synergistic interaction significantly enhances the coupled transport efficiency of electrons, protons, gaseous reactants, and intermediates^［19］. Therefore, the evolution from a two-phase interface to a three-phase interface represents not only a change in the physical interfacial configuration but also an enhancement of interfacial functionality and multiphase coupling capability. This paves the way for achieving high activity, high selectivity, and high stability in industrial applications. However, despite the advantages of the three-phase interface in eCO₂RR, its industrialization still faces challenges^［5］.

First, the stable construction of the three-phase interface relies on the connectivity of the internal pores and interfaces within the electrode material. This connectivity ensures that the gas, liquid, and solid phases can achieve sufficient contact within the same reaction zone, thereby enabling efficient mass transfer and interfacial reactions. However, during the initial stage of the reaction, the three-phase interface is highly susceptible to uncontrollable factors such as gas entraining liquid and gas occupying the liquid pathways, which can lead to the collapse of the interfacial structure and deviation of the reaction pathway (Figure 2a). Therefore, establishing a robust initial phase interface through condensed-phase structural design is the primary prerequisite for ensuring the stable operation of the three-phase interface.

Secondly, the stable operation of the three-phase interface hinges on maintaining the synergistic interaction among gas, liquid, and solid phases at the interface. However, in practical operation, this synergistic relationship is highly susceptible to disruption, thereby compromising reaction efficiency and product selectivity. Among the various destabilizing factors, insufficient hydrophobicity of the electrode surface stands out as one of the most common causes^［25］. During the reaction, the electrolyte may gradually infiltrate the hydrophobic layer and even penetrate into the gas diffusion layer (GDL), disrupting the original gas channel structure. This leads to hindered CO₂ transport and a marked reduction in the three-phase interface (Figure 2b). Concurrently, liquid-phase retention exacerbates localized pH variations and the accumulation of by-products, further interfering with the primary reaction pathway. In severe cases, the electrolyte can inundate the pores of the GDE, resulting in the destruction of the three-phase interface structure (Figure 2c). Such phenomena constitute a key factor underlying the performance degradation of eCO₂RR electrolyzers under high current densities. Consequently, optimizing interfacial wettability (i.e., balancing hydrophilicity and hydrophobicity) has emerged as a core requirement for ensuring the stable operation of multiphase coupling mechanisms.

More complexly, eCO₂RR itself is a process that simultaneously consumes and generates gases (e.g., carbon monoxide and ethylene are both gaseous products). This implies that the three-phase interface remains in a dynamic state throughout the reaction, with the gas–liquid pressure distribution and flux at the interface continuously being disturbed. Once the three-phase interface is compromised due to wettability imbalance, the catalytic sites will experience CO₂mass transfer limitation, causing the operating condition to degrade into a solid–liquid two-phase interface. At this point, the hydrogen evolution reaction, which is kinetically favored, will rapidly dominate, significantly diminishing the activity and selectivity of eCO₂RR, particularly under high current densities (Figure 2d). Even if the electrode hydrophobicity is enhanced through surface engineering prior to the reaction, the applied electric field during operation may still drive the electrolyte to penetrate and exacerbate wetting, leading to gradual degradation of hydrophobicity and ultimately resulting in instability of the three-phase interface or even “flooding”^［26］. Therefore, it is essential to rely on more sophisticated interfacial micro- and nanostructural designs together with dynamically responsive control strategies in order to maintain the integrity and stability of the three-phase interface over long-term operation under complex conditions.

In summary, the challenges faced by three-phase interfaces fundamentally stem from the multidimensional coordination of condensed matter systems in interface construction, wettability regulation, micro- and nanostructure optimization, and dynamic responsiveness.

4 eCO₂RR Strategies for Controlling the Condensed-Phase Structure at the Three-Phase Interface

To address the challenges faced by the three-phase interface in eCO₂RR regarding product selectivity and system stability, researchers have developed multi-dimensional strategies based on the condensed-phase chemistry paradigm of "structure–function–reaction" synergistic regulation to precisely optimize the microenvironment of the three-phase interface. Unlike traditional regulation approaches that primarily focus on localized optimization within a single dimension—for example, increasing the number of active sites solely through facet exposure or improving a specific reaction step only via factors such as potential and electrolyte composition—this study proposes a condensed-phase chemistry paradigm of "structure–function–reaction" synergistic regulation. This paradigm emphasizes starting from the holistic nature of condensed-phase systems, integrating the three key dimensions involved in catalytic processes—material structure design, interfacial function modulation, and reaction pathway selection—into a unified regulatory framework to achieve coupled synergy. Specifically, material structure design focuses on lattice defect control, pore connectivity optimization, and surface micro- and nano-scale construction; interfacial function modulation centers on spatial distribution of wettability and regulation of interfacial electric field strength; while reaction pathway selection targets critical steps such as intermediate adsorption energy barrier modulation and C–C coupling pathway optimization. Through the synergistic regulation of these three aspects, comprehensive improvements in activity, selectivity, and stability can be achieved. This section will systematically review representative advances in the following key strategies:

4.1 Interface Construction

A stable initial three-phase interface is the prerequisite for the sustained operation of the three-phase interface. By introducing a structure within the catalyst layer that coexists with both hydrophilic and hydrophobic regions, it is possible to effectively coordinate the supply channels for the gas and liquid phases, thereby significantly enhancing the mass transfer efficiency of reactants and the stability of the interface. For example, Ge Lei’s research group designed a hollow fiber GDE that continuously delivers convective gas to the active sites, which not only enhances the mass transfer capability but also markedly improves the accessibility of gas near the catalytic sites^［27］. This strategy has been proven to be an effective approach for constructing high-performance three-phase interfaces.

Yuan Zhiguo’s research group^［20］developed a through-type hollow-fiber GDE, in which a unique hydrophilic–hydrophobic synergistic region was constructed within the bismuth catalyst layer, successfully achieving the formation of a phase interface (Figure 3a). This interfacial structure significantly facilitated the simultaneous transport of gases and liquids, enhanced the stability of the three-phase interface, and improved the accessibility of catalytic active sites. Compared with conventional all-hydrophilic electrodes, this strategy markedly increased the catalyst utilization efficiency (>80%) and achieved a formate faradaic current density of approximately 150 mA/cm²under neutral conditions, with a Faraday efficiency exceeding 90%. The performance substantially outperformed that of the untreated control sample (Figure 3b).

Apfel’s research group^［28］fabricated a well-defined four-layer GDE structure using a hot-pressing method, which comprises: i) a perfluorosulfonic acid ionomer surface coating; ii) a catalyst layer bonded with polytetrafluoroethylene (PTFE); iii) a microporous layer (MPL); and iv) a gas diffusion layer (GDL). This architecture achieves a stepwise wettability gradient from the electrolyte to the catalytic interface, effectively facilitating the construction of a synergistic gas–liquid phase interface (Figure 3c, d). In a 1 mol/L KOH electrolyte, this electrode operates stably at a high current density of 200 mA/cm², predominantly producing ethylene and ethanol, with n-propanol also observed. The Faraday efficiency reaches 7% (Figure 3e).

Furthermore, this strategy has also been successfully extended to other multiphase reaction systems. The research group of Zhang Tierui^［29］developed a “sandwich”-type “organic–solid–water” three-phase reaction system (Figure 3f) in their study on the conversion of benzyl alcohol (BA) to benzaldehyde. By inserting a Janus-like porous electrode at the organic–aqueous phase boundary, they achieved efficient construction of a three-phase interface. This electrode consists of superhydrophobic β-Ni(OH)₂nanosheets supported on a superhydrophilic carbon-based substrate and exhibits remarkable capability for regulating three-phase distribution. Ultimately, this system attained a Faraday efficiency for benzaldehyde as high as 97.0%, while maintaining excellent structural and catalytic stability even after 800 hours of continuous operation (Figure 3g).

Based on the synergistic construction of hydrophilic and hydrophobic regions, the interfacial regulation strategy has demonstrated broad applicability and efficient interfacial mass transfer performance in various solid–liquid–gas three-phase reaction systems, becoming one of the important directions for achieving stable construction and functional expansion of three-phase interfaces. This strategy aims to enhance the contact efficiency in the phase interface reaction zone and can maintain a stable gas supply and ion conduction during catalytic processes; however, it poses high requirements for structural complexity and manufacturing consistency.

4.2 Wetting Regulation Strategies

The successful construction of the two-phase interface provides the necessary physical foundation for the three-phase interface, while precise control of interfacial wettability is the core component for maintaining the dynamic equilibrium of the three-phase system. At high current densities, insufficient hydrophobicity leading to electrolyte infiltration and pore flooding becomes the primary factor causing instability of the three-phase interface^［30］. Therefore, achieving control over the wettability of the three-phase interface through condensed-phase structural design has become a key breakthrough for suppressing side reactions, enhancing product selectivity, and improving system stability.

Currently, methods such as electrochemical deposition, chemical grafting, and ligand attachment are commonly employed to introduce hydrophobic organic molecules onto the catalyst surface, thereby regulating its surface wettability. These molecules possess a low surface free energy and can effectively enhance the hydrophobicity of the catalytic interface, making them one of the key approaches for wettability engineering^［10］.

Among numerous strategies, introducing a hydrophobic coating on the catalyst surface or the gas diffusion layer has become the most widely adopted interface optimization method due to its straightforward approach and general applicability. The research group led by Peng Yang^［31］employed electrospinning technology to fabricate a polycationic sheath layer on the copper-based GDE surface and proposed a "metal–organic bilayer" model to describe the three-phase interfacial structure (Figure 4a). This electrode exhibited excellent performance in an alkaline flow cell: at a current density of 300 mA/cm²,the Faraday efficiency for multi-carbon products reached 91.2% ± 3.8%, and it could operate continuously and stably for more than 300 hours (Figure 4b, c).

However, although the surface coating strategy can significantly enhance hydrophobicity and to some extent suppress the hydrogen evolution reaction, it neither increases the total number of active sites nor eliminates potential risks such as masking existing catalytic sites and reducing the effective surface area. To inhibit the hydrogen evolution side reaction while expanding the three-phase interface area and enhancing intrinsic catalytic activity, the synergistic doping strategy involving polymers/molecules with catalysts has gradually attracted attention in recent years. Feng Xiaofeng’s research group^［32］achieved precise regulation of the GDE microenvironment by introducing hydrophobic PTFE nanoparticles into the Bi-based catalyst layer (Figure 4d). Under a potential of −0.7 V (vs. RHE) and a CO₂gas flow rate of 15 sccm (1 sccm = 1 cm³/min), this structure achieved a formate conversion efficiency as high as 86% (Figure 4e). Studies have shown that moderate hydrophobicity of the catalyst layer helps establish a dynamic equilibrium microenvironment for gas and liquid supply within the catalytic layer, thereby effectively reducing the diffusion layer thickness, accelerating the mass transfer of CO₂,and forming a highly catalytically active reaction zone near the solid–liquid–gas three-phase interface, which significantly enhances both the reaction rate and selectivity. Similarly, Wang Tianfu’s research group^［33］constructed a highly hydrophobic GDE by loading copper catalysts onto a PTFE substrate, providing a highly stable approach for efficient carbon dioxide conversion under high current densities. The purpose of wettability control is to strike a balance between electrolyte wetting and gas diffusion, thereby preventing electrode flooding or insufficient electrolyte supply. This strategy can rapidly and effectively regulate reactant supply, improve product selectivity, and facilitate integration with existing electrode/membrane assemblies; however, wettability may change over long-term operation, necessitating monitoring and timely correction.

4.3 Micro- and Nanostructure Engineering Strategies

The aforementioned chemical modification methods for wettability control (such as coating or doping with hydrophobic polymers or molecules) have significant limitations, including: potentially masking the active sites of catalysts; reducing electrode conductivity; and being easily washed away during the reaction. In contrast, nature provides an ingenious strategy to achieve hydrophobicity—simultaneously capturing gas while repelling water—thereby forming an ideal solid–liquid–gas three-phase interface to sustain biological functions. From lotus leaves to water spiders, these natural hydrophobic surfaces all rely on hierarchical micro–nano structures that significantly enhance surface roughness. Inspired by these natural phenomena, researchers have developed micro–nano structural engineering to precisely regulate the three-phase interface in GDEs, enabling dynamic and stable wettability control and substantially improving the performance of eCO₂RR.

The research group led by Professor Gao Min^［34］prepared a biomimetic copper catalyst whose gas diffusion layer structure mimics the unique hierarchical architecture of the hydrophobic leaves of foxtail grass (Figure 5a). This hierarchical copper structure endows the CO₂reduction electrode with sufficient hydrophobicity, successfully establishing a stable solid–liquid–gas three-phase interface. Such an interface not only directs more CO₂molecules to the vicinity of the copper active surface but also effectively resists flooding under high-current operating conditions. Based on this, in a flow cell, a C₂₊product selectivity with a Faraday efficiency of 64% ± 1.4% was achieved at a current density of (255 ± 5.7) mA/cm²(Figure 5b, c), and continuous stable operation for over 45 hours was demonstrated at a current density of 300 mA/cm²(Figure 5d). The overall performance significantly outperformed that of conventional wettable copper-based electrodes.

Han Buxing’s research group^［35］fabricated a metal/polymer–carbon paper GDE (M/polymer-CP) with a three-dimensional hierarchical micro–nano structure using in situ electrochemical synthesis. This structure simultaneously enables efficient electron transport and rapid CO₂ diffusion (Figure 6a). As shown in Figure 6b, the GDE prepared via three-dimensional micro–nano structural engineering (Method I) exhibits superior catalytic efficiency and operational stability compared with other morphologically distinct polymer-composite electrodes fabricated by alternative methods, including metal nanoparticles drop-casted onto the polymer surface (Method II), hydrothermal synthesis of polymer–metal composites (Method III), and electrodeposition of metal nanoparticles (Method IV). Specifically, it achieves a Faraday efficiency for ethylene as high as 59.4% (Figure 6c, d). In-depth mechanistic studies reveal that its performance advantages arise from the synergistic effects of the three-dimensional hierarchical metallic structure and the in situ construction feature: the hierarchical architecture provides a high specific surface area and abundant defect sites, substantially enhancing catalytic activity; the hydrophobicity of the polymer ensures a stable gas supply and improves product selectivity; and the in situ deposition significantly reduces the charge-transfer resistance at the metal/polymer and polymer/carbon paper interfaces. Moreover, the three-dimensional micro–nano structure facilitates uniform dispersion of the metal phase, effectively suppressing particle agglomeration and thereby further enhancing electrode stability. In summary, micro–nano structural engineering offers dual functional benefits: on one hand, it imparts appropriate hydrophobicity to the interface to maintain a stable three-phase boundary, and on the other hand, it creates a wealth of active sites on the electrode surface, thereby markedly improving the overall catalytic performance of eCO₂RR. This approach can optimize the adsorption and coupling of reaction intermediates and establish rapid transport pathways to shorten diffusion distances without altering the catalyst composition or compromising electrical conductivity. However, achieving reproducible morphology and defects, along with long-term stability, remains a significant challenge.

5 Conclusion and Future Work

eCO₂As a typical multiphase interfacial reaction system, the reaction kinetics and catalytic performance of RR are fundamentally governed by the spatial configuration and dynamic evolution characteristics of the three-phase interface on the catalyst surface. From a condensed-phase chemistry perspective, this paper systematically reviews the configuration evolution and failure mechanisms of the three-phase interface, and delves into the synergistic effects of condensed-phase structure regulation on interfacial configuration, wettability control, and micro- and nanostructure design. On one hand, the establishment of a stable three-phase interface is the primary prerequisite for its sustained operation, providing the necessary space for solid–liquid–gas contact and reaction. On the other hand, precise control of interfacial wettability is the core element in maintaining the dynamic equilibrium among the three phases. This dynamic evolutionary behavior is typically achieved through chemical means to balance hydrophilicity and hydrophobicity, thereby realizing a dynamic equilibrium among the three phases. To further enhance product selectivity and system stability, it is also necessary to employ more sophisticated hierarchical micro- and nanostructural designs to ensure interfacial stability and continuous reaction progress.

Based on the above analysis, the following insights can be drawn: From phase interface construction and wettability regulation to micro- and nanostructure design, these condensed-phase structure control strategies can significantly improve interfacial wettability through direct or indirect pathways. Their common mechanism of action lies in effectively enhancing the hydrophobicity of the system and stabilizing the three-phase interface. Based on this, the present paper proposes the following outlook.

(1) During the construction and operation of three-phase interfacial systems, interface structure collapse and reaction pathway deviation (such as gas entraining liquid or gas invading liquid flow channels) remain critical challenges that urgently need to be addressed. To this end, this study proposes dynamic equilibrium control of the gas–liquid two-phase system as a core design principle. By constructing a three-phase interfacial structure with precisely regulated hydrophobic/hydrophilic microdomain distribution, it aims to achieve synergistic optimization of mass transfer efficiency and system operational stability. It is particularly worth noting that precise regulation of the intrinsic wettability of catalysts is a decisive factor in realizing efficient solid–liquid–gas three-phase contact, thereby providing new theoretical guidance for the design of high-performance three-phase interfacial systems.

(2) Currently, research on the regulation of tri-phase interface wettability primarily focuses on enhancing interfacial hydrophobicity, even to the point of superhydrophobic design. Although such strategies have significantly improved the catalytic performance of eCO₂ RR by increasing CO₂ mass transfer efficiency and suppressing the hydrogen evolution side reaction, an overemphasis on hydrophobicity may lead to: i) hindered liquid-phase transport and an imbalance in the construction of the tri-phase interface; ii) a reduction in the tri-phase contact area, resulting in decreased utilization of active sites. More importantly, existing studies often use the doping amount of polymers or hydrophobic molecules as the regulating parameter, rather than directly employing wettability indicators (such as the contact angle) as independent variables. This indirect regulation approach results in: i) a limited wettability control window, which is predominantly confined to a highly hydrophobic range (contact angle 140°–155°); ii) the resulting “optimal wettability” often deviates from practical requirements (with contact angles generally exceeding 150°)^［36］. In response to this situation, Tie-rui Zhang’s research group^［37］, by directly controlling the contact angle of the Au/C GDE, established for the first time a quantitative structure–activity relationship between wettability and catalytic performance (with the contact angle varied within the range of 15°–175°), thereby providing a more instructive reference for optimizing the tri-phase interface structure. It is thus evident that the precise balance between hydrophilicity and hydrophobicity to achieve optimal interfacial wettability is crucial for optimizing the construction of the tri-phase interface and enhancing electrocatalytic performance.

(3) Precise micro/nanostructural design not only enhances the flexibility of three-phase interfacial wettability regulation, but also effectively preserves and even expands the exposure of catalytic active sites, thereby fully leveraging the intrinsic catalytic advantages. However, during electrochemical processes, the electrowetting effect induces dynamic changes in interfacial wettability, which in turn weakens the structural robustness of the three-phase interface. A large body of research has demonstrated that although a superhydrophobic surface can be initially achieved, its hydrophobicity often decreases as the reaction proceeds, reflecting the continuous erosion of the interfacial structure by electrowetting. To address this issue, introducing dielectric-hydrophobic materials (or constructing a dielectric-type hydrophobic layer) is considered an effective strategy that can significantly inhibit electrowetting-induced wettability degradation, enhance the anti-instability capability of the three-phase interface, and extend its service life.

(4) Optimization of the three-phase interface is not only crucial for enhancing electrocatalytic performance at the laboratory scale, but also provides important insights for the design of industrial electrolyzers. On one hand, rational regulation of the three-phase interface can effectively alleviate mass-transfer limitations of CO₂ and electrolyte wetting issues, thereby enabling long-term stable operation at high current densities. On the other hand, by introducing a hydrophobic–hydrophilic synergistic regionalized design in gas-diffusion electrodes, the utilization efficiency of the solid–liquid–gas three-phase reaction zone can be improved, offering a reference for structural optimization of large-area electrodes and stack-type electrolyzers. Furthermore, three-phase interface control strategies possess good engineering scalability, laying both theoretical and practical foundations for the modularization and industrial-scale application of eCO₂ RR.

Overall, the eCO₂ RR regulation based on condensed-phase structures has yet to establish a systematic research framework. The key lies in conducting synergistic optimization of the structure and wettability around the three-phase interface. Future research should focus on advancing the fine-tuning of hydrophilicity/hydrophobicity and determining the "optimal wetting window" of the interface under practical operating conditions. This will enable the high-quality construction and long-term stable maintenance of the three-phase interface, thereby simultaneously enhancing reaction efficiency and system stability under high current densities.

References

Publishing order | Descend order by publishing year | Descend order by cited within

[1]	Asadi M， Kim K， Liu C， Addepalli A V， Abbasi P， Yasaei P， Phillips P， Behranginia A， Cerrato J M， Haasch R， Zapol P， Kumar B， Klie R F， Abiade J， Curtiss L A， Salehi-Khojin A. Science， 2016， 353（6298）: 467.

[2]	Xu H P， Rebollar D， He H Y， Chong L N， Liu Y Z， Liu C， Sun C J， Li T， Muntean J V， Winans R E， Liu D J， Xu T. Nat. Energy， 2020， 5（8）: 623.

[3]	Zhang W， Hu Y， Ma L， Zhu G， Wang Y， Xue X， Chen R， Yang S， Jin Z. Adv. Sci.， 2018， 5（1）: 1700275.

[4]	Zhao Y， Hao L， Ozden A， Liu S， Miao R K， Ou P， Alkayyali T， Zhang S， Ning J， Liang Y. Nat. Synth.， 2023， 2: 403.

[5]	Xu D Z， Li K K， Jia B H， Sun W P， Zhang W， Liu X， Ma T Y. Carbon Energy， 2023， 5: e230.

[6]	Lai W， Qiao Y， Wang Y， Huang H. Adv. Mater.， 2023， 35（51）: 2306288.

[7]	Guo L， Zhou J W， Liu F， Meng X， Ma Y B， Hao F K， Xiong Y C， Fan Z X，. ACS Nano， 2024， 18（14）: 9823.

[8]	Hong S， Abbas H G， Jang K， Patra K K， Kim B， Choi B U， Song H， Lee K S， Choi P P， Ringe S， Oh J. Adv. Mater.， 2023， 35（8）: 220899.

[9]	Wang Y F， Han P， Lv X M， Zhang L J， Zheng G F. Joule， 2018， 2（12）: 2551.

[10]	Chen X L， Chen C H， Wang Y Y， Pan Z Y， Chen J J， Xu Y Y， Zhu L N， Song T Y， Li R R， Chen L， Lu J Q. Chem. Eng. J.， 2024， 482: 148944.

[11]	Kang Z Y， Zhang M， Wang Y， Yue P T， Li J， Zhu X， Fu Q， Liao Q. Catal. Today， 2025， 450: 115208.

[12]	Gao W， Wang C， Yang H， Ran C， Xu S， Ren D. Adv. Funct. Mater.， 2025， 35（50）: e09314.

[13]	Li Y J， Han S G， Wei W， Ma D D， Zhu Q L. Adv. Funct. Mater.， 2025， 35（34）: 2501936.

[14]	Tan M L， Hua Q F， Zhang C H， Zhang H N， Huang B， Feng F K， Gao Y X， Zhang X Y， Zhang F Y， Yang N L， Huang Q L， Ling C Y， Huang Z Q， Ge Y Y. Adv. Funct. Mater.， 2025: 2510570.

[15]	Ashebir M E， Sabhapathy P， Nasr O， Modak V， Moradlou O， Sabbah A， Huang C Y， Nachimuthu S， Jiang J C， Hu Y-L， Hung C H， Chen L C， Chen K H. Chem. Eng. J.， 2025， 509: 161319.

[16]	Xu R R， Wang K， Chen G， Yan W F. Natl. Sci. Rev.， 2019， 6（2）: 191.

[17]	He Y Z， Liu S S， Wang M F， Cheng Q Y， Qian T， Yan C L. J. Energy Chem.， 2023， 80: 302.

[18]	Xing Z， Hu L， Ripatti D S， Hu X， Feng X F. Nat. Commun.， 2021， 12: 136.

[19]	Tian X P， Xu G L， Chen S， Li Q， Duan J J. J. Mater. Chem. A， 2025， 13（28）: 22295.

[20]	Rabiee H， Ge L， Zhao J， Zhang X Q， Li M R， Hu S H， Smart S， Rufford T E， Zhu Z H， Wang H， Yuan Z G. Appl. Catal. B Environ.， 2022， 310: 121362.

[21]	Dinh C T， Burdyny T， Kibria M G， Seifitokaldani A， Gabardo C M， García de Arquer F P， Kiani A， Edwards J P， De Luna P， Bushuyev O S， Zou C Q， Quintero-Bermudez R， Pang Y J， Sinton D， Sargent E H. Science， 2018， 360（6390）: 783.

[22]	Liang H-Q， Zhao S Q， Hu X-M， Ceccato M， Skrydstrup T， Daasbjerg K. ACS Catal.， 2021， 11（2）: 958.

[23]	Xu R. Natl. Sci. Rev.， 2018， 5（1）: 1.

[24]	Zhang W， Yu A， Mao H， Feng G， Li C， Wang G， Chang J， Halat D， Li Z， Yu W. J. Am. Chem. Soc.， 2024， 146（31）: 21335.

[25]	Zhang L， Wei Z C， Thanneeru S， Meng M， Kruzyk M， Ung G， Liu B， He J. Angew. Chem. Int. Ed.， 2019， 58（44）: 15981.

[26]	Rabiee H， Ge L， Zhang X Q， Hu S H， Li M R， Yuan Z G. Energy Environ. Sci.， 2021， 14（4）: 1959.

[27]	Chen G L， Rabiee H， Li M R， Ma B B， Kuang Y Z， Dorosti F， Zhu Z H， Wang H， Ge L. Adv. Mater.， 2025， 37（28）: 2420391.

[28]	Junge Puring K， Siegmund D， Timm J， Möllenbruck F， Schemme S， Marschall R， Apfel U P. Adv. Sustain. Syst.， 2021， 5: 2000088.

[29]	Shi R， Zhang X R， Li C Y， Zhao Y X， Li R， Waterhouse G I N， Zhang T R. Sci. Adv.， 2024， 10（17）: eadn0947.

[30]	Nwabara U O， Hernandez A D， Henckel D A， Chen X Y， Cofell E R， de-Heer M P， Verma S， Gewirth A A， Kenis P J A. ACS Appl. Energy Mater.， 2021， 4（5）: 5175.

[31]	Cheng J， Chen L， Zhang Y Z， Wang M， Zheng Z Y， Jiang L， Deng Z， Wei Z H， Ma M T， Xiong L K， Hua W， Song D Q， Huo W X， Lian Y B， Yang W J， Lyu F L， Jiao Y， Peng Y. Nat. Commun.， 2025， 16: 3743.

[32]	Xing Z， Hu X， Feng X F. ACS Energy Lett.， 2021， 6（5）: 1694.

[33]	Lu C B， Shi P F， Huang S H， Yang C Q， Zhu J H， Zhang J C， Ke C C， Su Y Z， Zhuang X D， Wang T F. Angew. Chem. Int. Ed.， 2025， 64（13）: e202423263.

[34]	Niu Z Z， Gao F Y， Zhang X L， Yang P P， Liu R， Chi L P， Wu Z Z， Qin S， Yu X X， Gao M R. J. Am. Chem. Soc.， 2021， 143（21）: 8011.

[35]	Jia S Q， Zhu Q G， Chu M G， Han S T， Feng R T， Zhai J X， Xia W， He M Y， Wu H H， Han B X. Angew. Chem. Int. Ed.， 2021， 60（19）: 10977.

[36]	Li L Z， Wen J X， Lo T W B， Yin J， Lei Q. Chemistry–Methods， 2025， 5（8）: e202400080.

[37]	Shi R， Guo J H， Zhang X R， Waterhouse G I N， Han Z J， Zhao Y X， Shang L， Zhou C， Jiang L， Zhang T R. Nat. Commun.， 2020， 11: 3028.