Microenvironment engineering by targeted delivery of activated Ag NPs for boosting electrocatalytic CO2 reduction reaction

Microenvironment engineering by targeted delivery of activated Ag NPs for boosting electrocatalytic CO2 reduction reaction | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Microenvironment engineering by targeted delivery of activated Ag NPs for boosting electrocatalytic CO 2 reduction reaction Shun Wang, Ting Xu, Hao Yang, Tianrui Lu, Rui Zhong, Jing-Jing Lv, and 10 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4692796/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 24 Jan, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract To boost the performance of electrocatalytic CO 2 reduction reaction (eCO 2 RR), a unique synthetic method that deploys the in situ reduction of precoated precursors was developed to produce activated Ag nanoparticles (NPs) within the gas diffusion layer (GDL), where the thus-obtained Ag NPs-Skeleton could block direct contact between the active Ag sites and electrolyte. Specifically, compared to the conventional surface loading mode in the acidic media, our freestanding and binder free electrode could achieve obvious higher CO selectivity of 94%, CO production rate of 23.3 mol g -1 h -1 , single-pass CO 2 conversion of 58.6%, and enhanced long-term stability of 8 hours. Our study shows that delivering catalysts within the GDL does not only gain the desired physical protection from GDL skeleton to achieve a superior local microenvironment for more efficient pH-universal eCO 2 RR, but also manifests the pore structures to effectively address gas accumulation and flood issues, thereby stabilizing the catalysts. Physical sciences/Chemistry/Catalysis/Electrocatalysis Earth and environmental sciences/Environmental sciences/Environmental chemistry/Atmospheric chemistry Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction The electrocatalytic CO 2 reduction reaction (eCO 2 RR), when powered by renewable electricity, provides a sustainable and appealing pathway to convert the greenhouse gas CO 2 into value-added chemicals 1 , 2 , 3 , 4 . To date, significant efforts have been directed towards the conversion of CO 2 to carbon monoxide (CO) due to its economic viability and extensive industrial applications 5 , 6 , 7 , 8 . Silver (Ag)-based catalysts have emerged as superior candidates for CO production, showing promising prospects for market feasibility based on techno-economic assessments. 9 , 10 , 11 High CO Faradaic efficiencies (FE) of up to 90% has been achieved over various Ag-based catalysts in neutral or alkali media 12 , 13 . However, in acidic media, the hydrogen evolution reaction (HER) is normally predominant, resulting in poor catalytic activity. Considering that acidic media have been proved useful with high carbon utilization 14 , 15 , 16 , developing catalysts that work well over a wide pH range is therefore important not only for understanding the different eCO 2 RR mechanisms occurring in acidic to alkaline media but also for determining their use under different pH conditions based on special requirements. From a technical point of view, constructing a gas/solid/liquid interface in a flow cell, where a powdery Ag-based catalyst deposited on a gas diffusion layer (GDL) has generally served as the cathode, is crucial for achieving industrial-level reaction rates 17 , 18 . To improve the eCO 2 RR performance of Ag-based catalysts at high current densities, extensive attention has been given to strategies for modulating the microenvironment around the electrocatalytic center 19 , 20 , 21 . For examples, the surface modification of Ag catalyst with functional molecules 22 , 23 , 24 or polymer binders 25 , could increase the CO 2 /H 2 O ratio, effectively inhibiting the HER and driving the eCO 2 RR. However, these additives may reduce conductivity and impede mass transport within active sites. Moreover, the thus-coated catalysts are prone to detach from the GDL under the impact of gas and electrolyte flush during electrocatalysis because of weak interfacial adhesion 26 . Previous successful examples have demonstrated that the construction of metal sandwich electrodes 27 and self-supported metal species-decorated carbon membranes 28 can greatly enhance eCO 2 RR activity and stability in alkaline and neutral media. However, such three-dimensional (3D) skeleton-type electrodes have rarely been employed to optimize electrocatalytic eCO 2 RR behavior in acidic media, primarily due to the high concentration of protons and indispensable cations. In addition, the in-depth understanding of electrocatalytic mechanism involving the active sites and microenvironment of those electrodes remains elusive, challenged by the encapsulated state of the active sites within the 3D skeleton 29 , 30 , 31 . Therefore, achieving targeted delivery of activated Ag NPs to a superior microenvironment that offers a safe shelter to prevent direct contact with the electrolyte and buffer gas flush, while preserving accessibility to the Ag active sites, is highly desirable for practical eCO 2 RR applications. In this work, activated Ag NPs catalysts were in situ generated within GDL skeleton, resulting in a binder free, self-supported electrode. Referred to as Ag NPs-Skeleton, this electrode utilizes a layer of carbon nanoparticles within the GDL to prevent direct contact between the Ag NPs and electrolyte, and buffer gas flush. Therefore, the Ag NPs-Skeleton exhibit a high local CO 2 /H 2 O ratio and a high concentration of K + , favoring the formation of a highly active and stable solid-liquid-gas interfacial microenvironment. The Ag NPs-Skeleton exhibit a high CO FE of over 94% for the eCO 2 RR at a current density of 400 mA cm − 2 in pH-universal (acidic, neutral and alkaline) electrolytes over a wide potential range. Impressively, high durability was also achieved for this binder-free electrode, with a remarkably high current density of 100 mA cm − 2 for nearly 8 h in acidic media. In situ bubble observation by an optical microscope and COMSOL Multiphysics simulation revealed that the Ag NPs-Skeleton exposed more mass transporting pores and thus equalized the interfacial gas pressure and decreased the gas flow rate of each pore, which can efficiently address gas accumulation and flood issues, and stabilize the catalyst surface. Furthermore, density functional theory (DFT) calculations demonstrated that defect-rich Ag NPs with a high local CO 2 /H 2 O ratio promoted H 2 suppression and CO production. 2. Results and discussion 2.1 Preparation of the Ag NPs-Skeleton The Ag NPs-Skeleton were prepared by a simple in situ electrodeposition method. The silver nitrate (AgNO 3 ) precursor (6 mg mL − 1 ) was sonicated in ethanol for dispersion and drop-casting in the GDL and then in situ electro-reduced at a constant current density of 25 mA cm − 2 in a flow cell ( Figure S1 ). The cross-sectional field emission scanning electron microscopy (FESEM) image and corresponding X-ray energy-dispersive (EDS) mapping images in Fig. 1 a-c show that the bright Ag NPs are uniformly distributed within the three-dimensional GDL skeleton, heavily overlapping with the microporous layer (MPL) of carbon nanoparticles with traces in the carbon fiber substrate (CFS) of the GDL. Negligible amount of Ag NPs was located on the surface of the GDL, as shown in Figure S2a-b , which shows no difference from the surface of the bare GDL in Figure S2c . Transmission electron microscopy image (TEM, Fig. 1 d) and size distribution plot ( Figure S3 ) of the Ag NPs-Skeleton illustrate the distribution of Ag NPs with an average diameter of 60 nm. Importantly, high-resolution TEM (HRTEM) images of the Ag NPs (Fig. 1 e, Figure S4 ) show the presence of a high density of structural defects along the Ag(111) plane 32 , as evidenced by the periodic stacking sequence in Fig. 1 f and Fig. 1 g. The formation of structural defects in Ag NPs-Skeleton could be caused by the disruption of the surface atomic assembly under electroreduction conditions, which is beneficial for improving the adsorption energy and catalytic activity of the intermediates for the eCO 2 RR 33 , 34 , 35 . The crystal structures of the Ag NPs-Skeleton in the GDL, including the MPL surface, MPL skeleton, MPL back, and CFS surface, were identified by powder X-ray diffraction (XRD) (Fig. 1 h). All samples show diffraction peaks consistent with the face-centered cubic structure of Ag (JCPDs#04-0783) 12 , 36 , with the intensity of the Ag signal following the order of MPL skeleton > MPL surface > MPL back > CFS surface, indicating that the Ag NPs are mainly distributed and seamlessly loaded within the MPL of the GDL. Ag NPs-Skeleton also exhibit a characteristic peak with the typical (002) plane feature of graphitic carbon (JCPDSs#41-1487) at 26.6° 37 , 38 , 39 , 40 . This intense and sharp peak indicates the highly crystalline nature of graphene in the GDL, which provides decent conductivity for electron transfer during electrolysis. In addition, the chemical state of the Ag NPs-Skeleton was examined by X-ray photoelectron spectroscopy (XPS), where the peaks at 374.3 and 368.3 eV (Fig. 1 i) could be assigned to the Ag 3d 5/2 and Ag3d 3/2 peaks, respectively, suggesting the metallic Ag phase 36 . In addition, the Ag signal intensity also follows sequence of MPL skeleton > MPL surface > MPL back > CFS surface ( Figure S5 ), which is consistent with the XRD results. Thus, these results underscore the effectiveness of a simple method involving drop coating silver precursors and in situ electroreduction to obtain evenly distributed Ag NPs-Skeleton with abundant structural defects located in the porous carbon nanoparticle layer of the GDL, enabling direct utilization as an electrode without any extra use of organic binder. 2.2 eCO 2 RR performance in a flow cell The electrochemical performance for the eCO 2 RR was firstly studied in acidic media by performing bulk electrolysis in 1 M KCl with the pH adjusted to 1.4 by 20 mM H 2 SO 4 . A high concentration of K + cations can make the electrode-electrolyte interface alkaline when the current density increases, effectively suppressing the HER in acidic electrolytes 6 , 17 , 41 . The only products of the Ag NPs-Skeleton produced were CO and H 2 , as evidenced by nuclear magnetic resonance (NMR) spectroscopy results with no signal from liquid products (Fig. 2 a, Figure S6 ). The CO and H 2 Faradaic efficiencies (FEs) reach close to 100%. Previous work from Fan et al. 6 reported that the FE for CO of commercial gold nanoparticles that were sprayed onto the surface of a GDL at pH = 2 was 40% at current densities below 50 mA cm − 2 . Similar results were also obtained for a Ag-PTFE GDL with 53% FE CO 30 . The low FEs for CO production can be understood because the corresponding production of OH − is not sufficient to neutralize the protons diffusing from the bulk acidic media toward the catalyst surface, thus favors the HER. In our case, the in situ formed OH − during the eCO 2 RR process can rapidly neutralize the local acidic environment because they are far away from the bulk electrolyte. As a result, the Ag NPs-Skeleton displayed superior selectivity for CO over a wide range of current densities from 25 mA cm − 2 to 400 mA cm − 2 (Fig. 2 a). The Ag NPs-Skeleton electrode can maintain nearly 85% of the FE CO during the 8 h stability test (Fig. 2 b). Both the morphology and composition of the Ag NPs-Skeleton electrode remained stable, as indicated by the post-reaction XRD and TEM measurements ( Figure S7 ). However, over the extended time, due to the gradual variation in hydrophobicity and the presence of too many cracks on the GDL surface ( Figure S2) , the electrolyte gradually permeates into the gas layer as electrolysis proceeds, eventually leading to flooding. Future systematic research can focus on optimizing the GDL properties to further improve the eCO 2 RR stability. Subsequently, we investigated the loading effect of the Ag NPs-Skeleton under the same conditions by conducting the eCO 2 RR under a constant current density of 100 mA cm − 2 with different catalyst loadings, and the results were summarized in Figure S8a. No significant changes in CO selectivity were observed, but at a loading of 0.3 mg cm − 2 , the electrode exhibits the lowest overpotential. Therefore, we chose a catalyst loading of 0.3 mg cm − 2 for the subsequent investigations, which led us to achieve high CO yield rates of 6.3 mol g − 1 h − 1 at 100 m A cm − 2 and 22.9 mol g − 1 h − 1 at 400 m A cm − 2 ( Figure S8b ). Moreover, we examined the eCO 2 RR product distribution of Ag NPs-Skeleton in 20 mM H 2 SO 4 with different concentrations of K + at a current density of 100 mA cm − 2 , which was expected to shed light on the key role of K + in suppressing the HER. 42 Figure S8c shows that CO 2 can be converted with a high selectivity even at a low concentration of K + (0.01 mol L − 1 ), and a higher concentration of K + in the electrolyte results in a lower resistance and cell potential 17 , 30 , 43 . These results illustrate that the presence of K + is truly important for the selective eCO 2 RR in acidic media, and the local cation concentration of the Ag NPs-Skeleton is sufficient even at a low concentration of K + in the bulk electrolyte for the Ag NPs-Skeleton, possibly resulting from their skeleton configuration. Considering the applied potential, a K + concentration of 1.0 mol L − 1 was chosen for the following investigation. As mentioned above, the challenge of carbonate formation in the alkaline eCO 2 RR can be addressed by improving the carbon utilization efficiency by using acidic media 14 . To evaluate the carbon utilization efficiency of the Ag NPs-Skeleton in acidic electrolytes, the single-pass CO 2 conversion efficiency (SPCE) for the eCO 2 RR was measured at 100 mA cm − 2 with different CO 2 flow rates, as presented in Figure S8d . At a higher flow rate, the SPCE was relatively lower since the CO 2 input greatly exceeded the consumption. By gradually decreasing the flow rate of CO 2 to 3 sccm, the SPCE reached 58.6% for CO production, reflecting the high carbon utilization efficiency of the Ag NPs-Skeleton. Notably, Ag NPs-Skeleton exhibit excellent versatility in a wide range of pH environments, including acidic, buffered, neutral and alkaline electrolytes, with all CO selectivity above 90% at a current density of 100 mA cm − 2 (Fig. 2 c), making them promising candidates for the eCO 2 RR in different practical applications or for coupling with various anodic reactions. To make an intuitive comparison, the control samples, commercial silver nanoparticles (Ag NPs, 50–100 nm) and silver macroparticles (Ag MPs, 1–3 µm) coated on GDLs by the drop-casting method with the use of Nafion, were tested for the eCO 2 RR in acidic media. The commercial Ag NPs disperse along the porous carbon nanoparticle layer of the GDL as Ag NPs-Skeleton but are more retained on the surface of the GDL ( Figure S9a-c ). The commercial Ag MPs are uniformly distributed on the GDL surface without entering the skeleton due to their large size ( Figure S9d-f ). XRD patterns of these control samples are shown in Figure S9g to identify the material phases, which are identical to Ag NPs-Skeleton with metallic Ag phase. Obviously, Ag NPs and Ag MPs show much lower FEs, SPCEs and CO yield rates at the same current density as Ag NPs-Skeleton (Fig. 2 d and Figure S9h, i ), such as CO FEs of 58% and 47%, SPCEs of 35% and 29%, and CO yield rates of 3.4 and 3.0 mol g − 1 h − 1 at 100 mA cm − 2 , respectively. Compared with recently reported CO production electrocatalysts and the control powdery electrocatalysts used in this work, the Ag NPs-Skeleton show a higher current density, greater CO product FE, and lower pH of the bulk electrolyte, making their performance among the best in acidic media (Fig. 2 f, Table S1 ) 6 , 21 , 29 , 30 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 . More importantly, the synthesis method can be extended to other soluble Ag and Cu salts, such as silver tetrafluoroborate (AgBF 4 ) and copper nitrate (Cu(NO 3 ) 2 ). The structural characteristics and eCO 2 RR performance for Ag NPs-Skeleton with AgBF 4 as a precursor are shown in Figure S10 and are like these prepared with AgNO 3 . Similarly, Cu NPs-Skeleton using Cu(NO 3 ) 2 as a precursor (Figure S11) could achieve a significantly higher eCO 2 RR product FE of 75% than that of the commercial Cu nanoparticles coated on GDLs using the drop-casting method (FE 27%) in at 300 mA cm − 2 (Figure S12) . These results suggest that the targeted delivery of active sites to the porous carbon nanoparticle layer of the GDL give a great university for creating a favorable microenvironment for the electrocatalytic reaction sites, which is significant for promoting eCO 2 RR performance. 2.3. The role of the microenvironment in the eCO 2 RR Due to the isolation effect of the Ag NPs-Skeleton, most Ag sites are separated from the bulk electrolyte, raising questions of whether the Ag sites located in the skeleton could contribute to the eCO 2 RR. To address this inquiry, the surface of the Ag NPs-Skeleton was covered with multiwalled carbon nanotubes (MWCNTs, Figure S13a ) or washed with electrolyte for 1 h before in situ electroreduction ( Figure S13b ) to thoroughly avoid direct contact between the Ag NPs and the electrolyte and separate or wash the surface Ag NPs, respectively. The XRD patterns of these control samples revealed that the intensity of the typical Ag signal was much weaker than that of Ag NPs-Skeleton (Fig. 13c, Fig. 1 g). The thus-treated Ag NPs-Skeleton could still maintain a high CO production selectivity with an FE CO > 90% at current densities ranging from 25 to 400 mA cm − 2 (Fig. 3 a, 3 b, Figure S13d ), indicating that the Ag NPs within the 3D carbon skeleton could act as the main active sites for the eCO 2 RR, which can provide more active sites than that of the traditional surface coated method. To smoothly promote the eCO 2 RR, not only are electrocatalytic active sites needed but also a suitable microenvironment is indispensable. First, the presence of a cation (K + ) of 1.6 at% is verified by SEM-EDS mapping images of the Ag NPs-Skeleton electrode during the eCO 2 RR (Fig. 3 c), which shows that a large amount of K + disperses homogeneously across the carbon skeleton. This could help increase the local pH and stabilize key intermediates of the eCO 2 RR 54 . Afterwards, the critical proton provider, water 55 , was checked by connecting a buffering gas container equipped with a humidity meter at the gas chamber exit of the flow cell (Fig. 3 d). Due to the transpiration effect of CO 2 gas, the water could evaporate and pass through the GDL into the gas chamber even without the electrolysis process, resulting a humidity of 60% after 1 h. After applying the potential, the water evaporation became more severe at a humidity of 74% after 1 h, which possibly resulted from the heating effect during the eCO 2 RR. These results show that the Ag NPs-Skeleton could reach the available water to support the eCO 2 RR, and the amount of water vapor around the Ag active sites was much less than that in the surface liquid water, resulting in a comparatively high local CO 2 /H 2 O ratio, which is quite important for suppressing the HER and promoting the eCO 2 RR. To confirm the important role of the local CO 2 /H 2 O ratio for the eCO 2 RR on Ag NPs-Skeleton electrode, an electro-oxidation treatment of the GDL by a bias voltage was conducted to increase the surface hydrophilicity 56 . The water contact angle of the GDL decreased from 133.7° to 123.3° after applying 2 V vs Ag/AgCl for 1000 s ( Figure S14 ), thus providing a lower water contact angle for the electro-oxidation-treated GDL loaded Ag NPs-Skeleton (Ag NPs-Skeleton-Ot) than for the plain GDL loaded Ag NPs-Skeleton (Fig. 3 e). As expected, the Ag NPs-Skeleton-Ot show more water evaporation with a humidity of 84% after 1 h (Fig. 3 d) and an evidently lower FE CO from 25 to 200 mA cm − 2 in acidic media (Fig. 3 f). Furthermore, the local pH during the eCO 2 RR could be tested by pH test strips as they were pasted on the back of the cathode GDL because of water evaporation. Figure S15 shows that the Ag NPs-Skeleton electrode has a pH of ~ 9, which is higher than that of the Skeleton Ag NP-Ot electrode (pH = ~ 8). This suggests that the optimized Ag NPs-Skeleton electrode could maintain a local micro-alkaline microenvironment to suppress the HER. These results illustrate that the space confinement of active Ag NPs within the hydrophobic GDL skeleton can construct a favorable microenvironment through water evaporation, such as a high concentration of local cations and hydroxides and an increased CO 2 /H 2 O ratio, for the eCO 2 RR. 2.4 Bubble management at the reaction interface The evolution and transport of bubbles significantly complicate the gas/solid/liquid three-phase electrocatalytic reaction interface 57 , 58 , and an unambiguous understanding of bubble behaviors and their impacts on eCO 2 RR performance has been scarce. An in situ flow cell for the observation of gas bubble formation through an optical microscope was designed and is shown in Figure S16 . With no electrolysis, the top views of the catalyst surface of Ag NPs-Skeleton, Ag NPs and Ag MPs and the electrolyte surface all showed no bubble formation. Once the potential was applied, the Ag NPs-Skeleton provided a static electrolyte surface with no bubble inflation, while a few small gas bubbles and large bubbles on the Ag NPs and Ag MPs were observed at the same current density of 100 mA cm − 2 (Fig. 4 ) . Therefore, the appearance of bubbles is highly dependent on the location of the Ag active sites. For the Ag NPs-Skeleton, the Ag sites are mainly located within the framework of the GDL and do not directly contact the electrolyte; thus, the bubbles generated in the skeleton dissipate within the framework and do not enter the electrolyte layer. Conversely, Ag MPs are mainly located on the surface of the GDL and directly contact the electrolyte. The generation and dissolution of bubbles during the eCO 2 RR occurred in the electrolyte layer, which caused a turbulent three-phase interface and poor electrocatalytic stability. Ag NPs are located both on the surface and within the framework of the GDL. Hence, a portion of the generated bubbles dissipate within the framework, while others enter the electrolyte layer to destabilize the three-phase interface. As a result, the existence of vast bubbles hindered ion transport and led to voltage fluctuations ( Figure S17 ), resulting in much worse stability and lower CO FEs of Ag NPs and Ag MPs than for those of Ag NPs-Skeleton (Fig. 2 b). These results reveal that the skeleton loading mode of Ag NPs within the hydrophobic GDL skeleton can efficiently control bubble behaviors, such as decreasing bubble coverage, accelerating bubble detachment, and addressing gas accumulation issues in the flow cell. These factors are highly important for improving the mass transport, catalyst utilization, and stability of the eCO 2 RR. To further elucidate the intrinsic mechanism behind bubble evolution and transport in the eCO 2 RR, COMSOL Multiphysics simulation 59 , 60 , 61 , 62 was employed to study the motion characteristics of bubbles generated during the transport process of mixed gases CO 2 , CO, and H 2 under the effect of electric field force (Fig. 5 ). In general, because of the pore distribution, the gas inlet velocity of the pores on the GDL surface follows the sequence: Ag NPs-Skeleton < Ag NPs Ag NPs > Ag MPs, and the pore separation distance on the GDL surface follows the sequence: Ag NPs-Skeleton < Ag NPs < Ag MPs ( Figure S18 ). These factors are all contributing factors to the formation of bubbles. At a gas inlet velocity of 0.1 m s − 1 , no bubble was able to penetrate the pores and form a gas film within the computational time. When the inlet velocity was increased to 0.115 m s − 1 , only one bubble appeared and was able to enter the liquid phase ( Figure S19a ), confirming that the critical velocity was approximately 0.1 m s − 1 to avoid the appearance of bubbles. Furthermore, the influence of velocities ranging from 0.5 to 1.5 m s − 1 on the gas film length and bubble quantity was investigated (Fig. 5 a-b). It is evident that elevated velocities lead to more pronounced expansion of the gas film, rendering it more susceptible to shear forces and resulting in an increased frequency of bubble growth, which is applicable for the Ag MPs sample. The increase in the number of pores results in fewer bubbles, as revealed by the shorter gas film in the Ag NPs-Skeleton sample (Fig. 5 c). Furthermore, the quantity of bubbles follows a volcano-shaped curve in response to variations in the pore distance. In our model, three pores had separation distances ranging from 125 to 500 µm were simulated (Fig. 5 d and Figure S19b ). When the pore spacing separation distance decreases from 500 to 250 µm, the gas film at pore 1 rapidly ruptures upon reaching 250 µm due to the disruptive influence of gas film growth at pore 2, making bubble formation easier ( Figure S19c ). However, as the pore separation distance is further decreased to 125 µm, the growth process of the gas film completely covers both pore 1 and pore 2. At this point, the gas film growth and bubble detachment processes resemble those of a single pore ( Figure S19d and Figure S20 ). Therefore, a comparatively shorter pore separation distance of approximately 175 µm is conducive to preventing bubble formation. Additionally, considering that the Ag NPs-Skeleton could homogenize the gas pressure of the pores on the GDL surface, we changed the single gas inlet of the traditional flow cell (Fig. 5 e ) to multiple independent inlets in our simulation and observed the obvious suppression of liquid backfilling into the gas chamber, i.e., flooding (Fig. 5 f). Consequently, microenvironment regulation to achieve a relatively stable fluid field through smart catalyst loading and reactor design contributes to the long-term stability and high CO Faradaic efficiency of the eCO 2 RR at industrial current densities. 2.5 DFT calculations DFT calculations, widely used to understand eCO 2 RR reaction mechanisms 63 , 64 , were conducted to elucidate the enhanced selectivity and stability of the Ag NPs-Skeleton. The assumption is that the dramatically enhanced activity can be related to the specific crystalline structure, namely, evident vacancy defects on the Ag NPs-Skeleton (Fig. 1 e). Two simulation models, i.e., the Ag(111) surface and Ag(111) surface with vacancies (denoted as Ag111-v, Fig. 6 a and Figure S21a, b ), are employed to evaluate the CO formation pathway. As shown in Fig. 6 b, the potential-determining step energy (PDS), *COOH formation, of Ag111-v is ~ 0.2 eV lower than that of Ag(111), which facilitates CO formation, demonstrating that the existence of structural defects are responsible in promoting eCO 2 RR activity. In addition, we further evaluated the effect of the CO 2 /H 2 O ratio on the activity of Ag NPs-Skeleton (Fig. 6 c). The constructed CO 2 /H 2 O ratios ranged from 10 to 8.33×10 − 2 , indicating that the material was Ag(111)-v-CO 2 rich and Ag(111)-v-H 2 O rich (Fig. 6 a). With the high coverage of water on the Ag surface, the abundant Ag(111)-H 2 O provides a highly favorable energy for the HER. Compared to the Ag(111)-H 2 O-rich sample, the Ag(111)-CO 2 -rich sample evidently has a higher energy barrier for the HER. Coupled with the introduction of vacancies, the Ag(111)-v-CO 2 -rich catalyst further achieves an increased energy barrier for the HER in contrast to the bare Ag(111)-CO 2 -rich catalyst and Ag(111)-v. These results confirm that the HER can be effectively suppressed during the eCO 2 RR by regulating the CO 2 /H 2 O ratio and introducing active defects on the catalyst surface. Overall, as illustrated in Fig. 6 d, the underlying reason for the increase in the eCO 2 RR performance of the Ag NPs-Skeleton is based on the skeleton loading mode used for the delivery of the active Ag sites to the superior microenvironment. Specifically, compared to the conventional surface loading mode, the skeleton loading mode can embed active sites into the GDL framework and construct a beneficial local microenvironment for eCO 2 RR with a high CO 2 /H 2 O ratio, a low concentration of protons, and a static fluid field with a suppressed bubbles generation. Consequently, the Ag NPs-Skeleton show significantly enhanced CO FEs, yields and SPECs over a wide range of potentials, pH ranges, and decent long-term stabilities. 3. Conclusion In summary, a freestanding, binder-free electrode composed of activated Ag NPs catalysts located uniformly within GDL skeleton was successfully designed. The in situ reduction procedure ensures the intimate interactions between the catalysts and skeleton, and therefore promoting good electronic conductivity during the eCO 2 RR. The GDL skeleton effectively protects Ag NPs from direct erosion caused by the physical impacts of electrolyte flow and gas bubble evolution, leading to a greatly improved stability. As supported by the in situ observation of optical microscope and COMSOL Multiphysics simulation, delivering catalysts within the GDL also manifests the pore structures, leading to the reduction of bubble formation/coverage and the alleviation of gas accumulation issues, and thereby enhancing the eCO 2 RR performance. DFT calculations further demonstrate that the regulation of the catalyst structure (vacancy defect) and local microenvironment (CO 2 /H 2 O ratio) is responsible for improving the eCO 2 RR activity. The achievement of wide potential and wide pH adaptability for CO production allows for the coupling of the eCO 2 RR with other anodic reactions beyond the OER or tandem cathodic reactions to directly employ the in situ formed CO for higher reaction efficiency and more value-added products. Declarations Acknowledgements This work was financially supported by the National Natural Science Foundation of China (52201227, 52272088, 52331009, 22173066), Chinese education ministry’s Chunhui program (202200767), Zhejiang Provincial Natural Science Foundation of China (LQ23B030001, Q24B020025), and the open research fund of Songshan Lake Materials Laboratory (2023SLABFN09). References De Luna P, Hahn C, Higgins D, Jaffer SA, Jaramillo TF, Sargent EH. 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Supplementary Files AgCO2RRSI240705.docx TOC.png Table of Contents Cite Share Download PDF Status: Published Journal Publication published 24 Jan, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4692796","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":329959529,"identity":"88cfeef0-6d24-41e7-9d8c-0a01ed0461b6","order_by":0,"name":"Shun Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1ElEQVRIiWNgGAWjYDACCSjND6GYSdAi2UCyFoMDxGqRn91j9pin5o7d5hvpzyQYKqwTG9jPHsCrxeDOGXNjnmPPkrfdSEiTYDiTntjAk5eAX4tEjpl0DtvhZLPbCcckGNsOJzZI8Bjgd9gMkJZ/h5ONZye2STD+I0ILww2glty2w3YG0slsEowNRGgxuJFWJv2373CCxP1nzBYJx9KN23hyCDkseZvkjG+H7fl7jj+88aHGWraf/QwBh0FBYgOITABiNqLUA4E9sQpHwSgYBaNgBAIAB/dC3no6Jx4AAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0001-5305-5134","institution":"Wenzhou University","correspondingAuthor":true,"prefix":"","firstName":"Shun","middleName":"","lastName":"Wang","suffix":""},{"id":329959530,"identity":"6d9b8aae-506a-46e9-85e3-4e7a53389758","order_by":1,"name":"Ting Xu","email":"","orcid":"","institution":"Wenzhou University","correspondingAuthor":false,"prefix":"","firstName":"Ting","middleName":"","lastName":"Xu","suffix":""},{"id":329959531,"identity":"d4138972-4931-41bf-ae38-a961d6bf9a40","order_by":2,"name":"Hao 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University","correspondingAuthor":false,"prefix":"","firstName":"Jing-Jing","middleName":"","lastName":"Lv","suffix":""},{"id":329959537,"identity":"04726133-882b-4da8-89cd-ca77b9225605","order_by":6,"name":"Shaojun Zhu","email":"","orcid":"","institution":"Wenzhou university","correspondingAuthor":false,"prefix":"","firstName":"Shaojun","middleName":"","lastName":"Zhu","suffix":""},{"id":329959538,"identity":"46d1a273-6853-4895-903c-08722e09347b","order_by":7,"name":"Mingming Zhang","email":"","orcid":"","institution":"Wenzhou University","correspondingAuthor":false,"prefix":"","firstName":"Mingming","middleName":"","lastName":"Zhang","suffix":""},{"id":329959539,"identity":"d69c0d9c-b6e1-4b0b-abdf-95eb442d107c","order_by":8,"name":"Zheng-Jun Wang","email":"","orcid":"","institution":"Wenzhou University","correspondingAuthor":false,"prefix":"","firstName":"Zheng-Jun","middleName":"","lastName":"Wang","suffix":""},{"id":329959540,"identity":"fe4fff54-d8b1-4af2-a2a7-d321d8e2e434","order_by":9,"name":"Yifei Yuan","email":"","orcid":"https://orcid.org/0000-0002-2360-8794","institution":"Wenzhou University","correspondingAuthor":false,"prefix":"","firstName":"Yifei","middleName":"","lastName":"Yuan","suffix":""},{"id":329959541,"identity":"f28c9e4f-6c2f-4538-a2ee-e8e1495b16e7","order_by":10,"name":"Jun Li","email":"","orcid":"","institution":"Wenzhou University","correspondingAuthor":false,"prefix":"","firstName":"Jun","middleName":"","lastName":"Li","suffix":""},{"id":329959542,"identity":"40ca6ab2-f667-4285-95f2-02477b59c4ae","order_by":11,"name":"Jichang Wang","email":"","orcid":"","institution":"University of Windsor","correspondingAuthor":false,"prefix":"","firstName":"Jichang","middleName":"","lastName":"Wang","suffix":""},{"id":329959543,"identity":"14b8f21e-1975-45c5-acd4-b025dec4deea","order_by":12,"name":"Huile Jin","email":"","orcid":"","institution":"Wenzhou University","correspondingAuthor":false,"prefix":"","firstName":"Huile","middleName":"","lastName":"Jin","suffix":""},{"id":329959544,"identity":"466f8e87-176e-4028-8d05-13f8cf0777c2","order_by":13,"name":"Shuang Pan","email":"","orcid":"","institution":"Wenzhou University","correspondingAuthor":false,"prefix":"","firstName":"Shuang","middleName":"","lastName":"Pan","suffix":""},{"id":329959545,"identity":"8016eb29-d30b-4caa-a0aa-fb2039a9c34c","order_by":14,"name":"Xin Wang","email":"","orcid":"","institution":"City University of Hong Kong","correspondingAuthor":false,"prefix":"","firstName":"Xin","middleName":"","lastName":"Wang","suffix":""},{"id":329959546,"identity":"38fdd985-d4e1-47a3-87f0-9c878cb5d3ad","order_by":15,"name":"Tao Cheng","email":"","orcid":"https://orcid.org/0000-0003-4830-177X","institution":"Soochow University","correspondingAuthor":false,"prefix":"","firstName":"Tao","middleName":"","lastName":"Cheng","suffix":""}],"badges":[],"createdAt":"2024-07-05 14:10:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4692796/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4692796/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-025-56039-x","type":"published","date":"2025-01-24T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":60871824,"identity":"089ce54f-5dda-4dbf-b07e-3fe60f0d9ee9","added_by":"auto","created_at":"2024-07-23 05:01:32","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":693697,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStructural characterizations of Ag NPs-Skeleton\u003c/strong\u003e. (a) Cross-sectional FESEM image and (b) the corresponding EDS mapping images for Ag and C. (c) Cross-sectional FESEM image at high magnification. (d) TEM image. (e-f) HRTEM images of the structural defects in different regions. (g) Line profiles of the red line in (f). (h) XRD patterns of I: MPL surface (magenta), II: MPL skeleton (gray), III: MPL back (red), and IV: CFS surface (blue). (i) Ag 3d XPS spectrum.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4692796/v1/b664fbbc10cbad79b65de778.png"},{"id":60871826,"identity":"75904e6b-1048-49e1-8b68-8aea2151b21d","added_by":"auto","created_at":"2024-07-23 05:01:32","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":105706,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Potential and product FEs of Ag NPs-Skeleton at different current densities and (b) potential and FE\u003csub\u003eCO \u003c/sub\u003evariation of Ag NPs-Skeleton during long-term electrolysis at 100 mA cm\u003csup\u003e-2\u003c/sup\u003e in 20 mM H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e + 1 M KCl. (c) Potential and product FEs of Ag NPs-Skeleton with various electrolytes. (d) Product FEs of Ag NPs-Skeleton, Ag NPs, and Ag MP GDL in 20 mM H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e + 1 M KCl at 100 mA cm\u003csup\u003e-2\u003c/sup\u003e. (e) SPCE and CO yield rate of Ag NPs-Skeleton, Ag NPs and Ag MPs at 100 mA cm\u003csup\u003e-2\u003c/sup\u003e. (f) Comparison of the eCO\u003csub\u003e2\u003c/sub\u003eRR performance on the current density, CO product FE, and pH of the bulk electrolyte for Ag NPs-Skeleton with those of commercial Ag NPs, Ag MPs and other state-of-the-art electrocatalysts. This comparison is limited to reports with a pH ≤ 4.0 or with a total current density \u0026gt; 10 mA cm\u003csup\u003e−2\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4692796/v1/6a482a302211043e80f828d4.png"},{"id":60871825,"identity":"5919589c-7029-4a55-80e7-f608190e5e04","added_by":"auto","created_at":"2024-07-23 05:01:32","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":320822,"visible":true,"origin":"","legend":"\u003cp\u003eFE products of (a) Ag NPs-Skeleton covered by MWCNTs and (b) Ag NPs-Skeleton washed with electrolyte for 1 h in 20 mM H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e +1 M KCl at various current densities. (c) FESEM and EDS mapping images for K of the Ag NPs-Skeleton after eCO\u003csub\u003e2\u003c/sub\u003eRR at 100 mA cm\u003csup\u003e-2\u003c/sup\u003e for 20 min. (d) Humidity variation curves of the flow cell with/without electrolysis at a current density of 25 mA cm\u003csup\u003e-2\u003c/sup\u003e, (e) contact angles, and (f) FE\u003csub\u003eCO\u003c/sub\u003e of Ag NPs-Skeleton and Ag NPs-Skeleton-Ot.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4692796/v1/139bf80c3d01ef2276f583cb.png"},{"id":60871347,"identity":"c9d761a9-af7b-4c92-8103-b8f7d487d515","added_by":"auto","created_at":"2024-07-23 04:53:32","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":811798,"visible":true,"origin":"","legend":"\u003cp\u003eOptical microscopic detection of the bubble evolution process ascribed to CO exsolution produced during the eCO\u003csub\u003e2\u003c/sub\u003eRR on the electrodes of (a) Ag NPs-Skeleton, (b) Ag NPs and (c) Ag MPs.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4692796/v1/3aeb5dfb7afb683ba4ed50f0.png"},{"id":60871352,"identity":"e78a73fd-0d6d-4b2c-9b32-71e348978c17","added_by":"auto","created_at":"2024-07-23 04:53:32","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":473562,"visible":true,"origin":"","legend":"\u003cp\u003eCOMSOL Multiphysics simulations of Ag NPs-Skeleton. (a) Gas spreading film length curve at various gas velocities and (b) their corresponding velocity clouds. (c) Velocity cloud of the gas spreading film length with various pores. (d) Gas spreading film length between pore 2 and pore 3. Velocity cloud of (e) a single gas inlet and (f) a separate gas inlet at a 175 μm pore separation distance.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4692796/v1/e94d64c2df9761685b0f71dd.png"},{"id":60871349,"identity":"7675dd8d-0b8a-4714-9310-a97bcbfaeff0","added_by":"auto","created_at":"2024-07-23 04:53:32","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1919988,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Top view of Ag(111)-v, Ag(111)-v-CO\u003csub\u003e2\u003c/sub\u003e rich, Ag(111)-v-H\u003csub\u003e2\u003c/sub\u003eO rich, and Ag(111)-CO\u003csub\u003e2\u003c/sub\u003e rich configurations. (b) Calculated Gibbs free energy of the eCO\u003csub\u003e2\u003c/sub\u003eRR intermediates for CO formation on Ag(111) and Ag(111)-v surfaces. (c) Calculated Gibbs free energy of the HER on Ag(111)-v-, Ag(111)-v-CO\u003csub\u003e2\u003c/sub\u003e-rich, Ag(111)-v-H\u003csub\u003e2\u003c/sub\u003eO-rich, and Ag(111)-CO\u003csub\u003e2\u003c/sub\u003e-rich electrodes. (d) Schematic diagrams of the eCO\u003csub\u003e2\u003c/sub\u003eRR using skeleton loading mode compared with the surface loading mode.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4692796/v1/5e4a4994177c83017fa32837.png"},{"id":74719760,"identity":"ac1e32ff-af9e-490a-9158-2ae3ff93bfbd","added_by":"auto","created_at":"2025-01-25 08:07:14","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6830370,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4692796/v1/8eeb55bb-9203-4537-90b3-5c9c5dc54152.pdf"},{"id":60871351,"identity":"38f00bd7-0746-42fd-9da7-a7925f90c45e","added_by":"auto","created_at":"2024-07-23 04:53:32","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":16071937,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"AgCO2RRSI240705.docx","url":"https://assets-eu.researchsquare.com/files/rs-4692796/v1/4e5f07a83d6c11fefa4b479c.docx"},{"id":60871344,"identity":"7ea0360e-e8df-46aa-9d0b-e9f638f3d6ba","added_by":"auto","created_at":"2024-07-23 04:53:32","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":43651,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTable of Contents\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"TOC.png","url":"https://assets-eu.researchsquare.com/files/rs-4692796/v1/17cd83d7b9bd29bc05335f9d.png"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"\u003cp\u003eMicroenvironment engineering by targeted delivery of activated Ag NPs for boosting electrocatalytic CO\u003csub\u003e2\u003c/sub\u003e reduction reaction\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe electrocatalytic CO\u003csub\u003e2\u003c/sub\u003e reduction reaction (eCO\u003csub\u003e2\u003c/sub\u003eRR), when powered by renewable electricity, provides a sustainable and appealing pathway to convert the greenhouse gas CO\u003csub\u003e2\u003c/sub\u003e into value-added chemicals\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. To date, significant efforts have been directed towards the conversion of CO\u003csub\u003e2\u003c/sub\u003e to carbon monoxide (CO) due to its economic viability and extensive industrial applications\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Silver (Ag)-based catalysts have emerged as superior candidates for CO production, showing promising prospects for market feasibility based on techno-economic assessments.\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e High CO Faradaic efficiencies (FE) of up to 90% has been achieved over various Ag-based catalysts in neutral or alkali media\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. However, in acidic media, the hydrogen evolution reaction (HER) is normally predominant, resulting in poor catalytic activity. Considering that acidic media have been proved useful with high carbon utilization\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, developing catalysts that work well over a wide pH range is therefore important not only for understanding the different eCO\u003csub\u003e2\u003c/sub\u003eRR mechanisms occurring in acidic to alkaline media but also for determining their use under different pH conditions based on special requirements.\u003c/p\u003e \u003cp\u003eFrom a technical point of view, constructing a gas/solid/liquid interface in a flow cell, where a powdery Ag-based catalyst deposited on a gas diffusion layer (GDL) has generally served as the cathode, is crucial for achieving industrial-level reaction rates\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. To improve the eCO\u003csub\u003e2\u003c/sub\u003eRR performance of Ag-based catalysts at high current densities, extensive attention has been given to strategies for modulating the microenvironment around the electrocatalytic center\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. For examples, the surface modification of Ag catalyst with functional molecules\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e or polymer binders\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e, could increase the CO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO ratio, effectively inhibiting the HER and driving the eCO\u003csub\u003e2\u003c/sub\u003eRR. However, these additives may reduce conductivity and impede mass transport within active sites. Moreover, the thus-coated catalysts are prone to detach from the GDL under the impact of gas and electrolyte flush during electrocatalysis because of weak interfacial adhesion\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003ePrevious successful examples have demonstrated that the construction of metal sandwich electrodes\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e and self-supported metal species-decorated carbon membranes\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e can greatly enhance eCO\u003csub\u003e2\u003c/sub\u003eRR activity and stability in alkaline and neutral media. However, such three-dimensional (3D) skeleton-type electrodes have rarely been employed to optimize electrocatalytic eCO\u003csub\u003e2\u003c/sub\u003eRR behavior in acidic media, primarily due to the high concentration of protons and indispensable cations. In addition, the in-depth understanding of electrocatalytic mechanism involving the active sites and microenvironment of those electrodes remains elusive, challenged by the encapsulated state of the active sites within the 3D skeleton\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. Therefore, achieving targeted delivery of activated Ag NPs to a superior microenvironment that offers a safe shelter to prevent direct contact with the electrolyte and buffer gas flush, while preserving accessibility to the Ag active sites, is highly desirable for practical eCO\u003csub\u003e2\u003c/sub\u003eRR applications.\u003c/p\u003e \u003cp\u003eIn this work, activated Ag NPs catalysts were in situ generated within GDL skeleton, resulting in a binder free, self-supported electrode. Referred to as Ag NPs-Skeleton, this electrode utilizes a layer of carbon nanoparticles within the GDL to prevent direct contact between the Ag NPs and electrolyte, and buffer gas flush. Therefore, the Ag NPs-Skeleton exhibit a high local CO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO ratio and a high concentration of K\u003csup\u003e+\u003c/sup\u003e, favoring the formation of a highly active and stable solid-liquid-gas interfacial microenvironment. The Ag NPs-Skeleton exhibit a high CO FE of over 94% for the eCO\u003csub\u003e2\u003c/sub\u003eRR at a current density of 400 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in pH-universal (acidic, neutral and alkaline) electrolytes over a wide potential range. Impressively, high durability was also achieved for this binder-free electrode, with a remarkably high current density of 100 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for nearly 8 h in acidic media. In situ bubble observation by an optical microscope and COMSOL Multiphysics simulation revealed that the Ag NPs-Skeleton exposed more mass transporting pores and thus equalized the interfacial gas pressure and decreased the gas flow rate of each pore, which can efficiently address gas accumulation and flood issues, and stabilize the catalyst surface. Furthermore, density functional theory (DFT) calculations demonstrated that defect-rich Ag NPs with a high local CO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO ratio promoted H\u003csub\u003e2\u003c/sub\u003e suppression and CO production.\u003c/p\u003e"},{"header":"2. Results and discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Preparation of the Ag NPs-Skeleton\u003c/h2\u003e \u003cp\u003eThe Ag NPs-Skeleton were prepared by a simple in situ electrodeposition method. The silver nitrate (AgNO\u003csub\u003e3\u003c/sub\u003e) precursor (6 mg mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was sonicated in ethanol for dispersion and drop-casting in the GDL and then in situ electro-reduced at a constant current density of 25 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in a flow cell (\u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e). The cross-sectional field emission scanning electron microscopy (FESEM) image and corresponding X-ray energy-dispersive (EDS) mapping images in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea-c show that the bright Ag NPs are uniformly distributed within the three-dimensional GDL skeleton, heavily overlapping with the microporous layer (MPL) of carbon nanoparticles with traces in the carbon fiber substrate (CFS) of the GDL. Negligible amount of Ag NPs was located on the surface of the GDL, as shown in \u003cb\u003eFigure S2a-b\u003c/b\u003e, which shows no difference from the surface of the bare GDL in \u003cb\u003eFigure S2c\u003c/b\u003e. Transmission electron microscopy image (TEM, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed) and size distribution plot (\u003cb\u003eFigure S3\u003c/b\u003e) of the Ag NPs-Skeleton illustrate the distribution of Ag NPs with an average diameter of 60 nm. Importantly, high-resolution TEM (HRTEM) images of the Ag NPs (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee, \u003cb\u003eFigure S4\u003c/b\u003e) show the presence of a high density of structural defects along the Ag(111) plane\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e, as evidenced by the periodic stacking sequence in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef and Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg. The formation of structural defects in Ag NPs-Skeleton could be caused by the disruption of the surface atomic assembly under electroreduction conditions, which is beneficial for improving the adsorption energy and catalytic activity of the intermediates for the eCO\u003csub\u003e2\u003c/sub\u003eRR\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe crystal structures of the Ag NPs-Skeleton in the GDL, including the MPL surface, MPL skeleton, MPL back, and CFS surface, were identified by powder X-ray diffraction (XRD) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eh). All samples show diffraction peaks consistent with the face-centered cubic structure of Ag (JCPDs#04-0783)\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, with the intensity of the Ag signal following the order of MPL skeleton\u0026thinsp;\u0026gt;\u0026thinsp;MPL surface\u0026thinsp;\u0026gt;\u0026thinsp;MPL back\u0026thinsp;\u0026gt;\u0026thinsp;CFS surface, indicating that the Ag NPs are mainly distributed and seamlessly loaded within the MPL of the GDL. Ag NPs-Skeleton also exhibit a characteristic peak with the typical (002) plane feature of graphitic carbon (JCPDSs#41-1487) at 26.6\u0026deg; \u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. This intense and sharp peak indicates the highly crystalline nature of graphene in the GDL, which provides decent conductivity for electron transfer during electrolysis. In addition, the chemical state of the Ag NPs-Skeleton was examined by X-ray photoelectron spectroscopy (XPS), where the peaks at 374.3 and 368.3 eV (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ei) could be assigned to the Ag 3d\u003csub\u003e5/2\u003c/sub\u003e and Ag3d\u003csub\u003e3/2\u003c/sub\u003e peaks, respectively, suggesting the metallic Ag phase\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. In addition, the Ag signal intensity also follows sequence of MPL skeleton\u0026thinsp;\u0026gt;\u0026thinsp;MPL surface\u0026thinsp;\u0026gt;\u0026thinsp;MPL back\u0026thinsp;\u0026gt;\u0026thinsp;CFS surface (\u003cb\u003eFigure S5\u003c/b\u003e), which is consistent with the XRD results. Thus, these results underscore the effectiveness of a simple method involving drop coating silver precursors and in situ electroreduction to obtain evenly distributed Ag NPs-Skeleton with abundant structural defects located in the porous carbon nanoparticle layer of the GDL, enabling direct utilization as an electrode without any extra use of organic binder.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 eCO\u003csub\u003e2\u003c/sub\u003eRR performance in a flow cell\u003c/h2\u003e \u003cp\u003eThe electrochemical performance for the eCO\u003csub\u003e2\u003c/sub\u003eRR was firstly studied in acidic media by performing bulk electrolysis in 1 M KCl with the pH adjusted to 1.4 by 20 mM H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. A high concentration of K\u003csup\u003e+\u003c/sup\u003e cations can make the electrode-electrolyte interface alkaline when the current density increases, effectively suppressing the HER in acidic electrolytes\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. The only products of the Ag NPs-Skeleton produced were CO and H\u003csub\u003e2\u003c/sub\u003e, as evidenced by nuclear magnetic resonance (NMR) spectroscopy results with no signal from liquid products (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, \u003cb\u003eFigure S6\u003c/b\u003e). The CO and H\u003csub\u003e2\u003c/sub\u003e Faradaic efficiencies (FEs) reach close to 100%. Previous work from Fan et al.\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e reported that the FE for CO of commercial gold nanoparticles that were sprayed onto the surface of a GDL at pH\u0026thinsp;=\u0026thinsp;2 was 40% at current densities below 50 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Similar results were also obtained for a Ag-PTFE GDL with 53% FE\u003csub\u003eCO\u003c/sub\u003e\u003csup\u003e30\u003c/sup\u003e. The low FEs for CO production can be understood because the corresponding production of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e is not sufficient to neutralize the protons diffusing from the bulk acidic media toward the catalyst surface, thus favors the HER. In our case, the in situ formed OH\u003csup\u003e\u0026minus;\u003c/sup\u003e during the eCO\u003csub\u003e2\u003c/sub\u003eRR process can rapidly neutralize the local acidic environment because they are far away from the bulk electrolyte. As a result, the Ag NPs-Skeleton displayed superior selectivity for CO over a wide range of current densities from 25 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e to 400 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). The Ag NPs-Skeleton electrode can maintain nearly 85% of the FE\u003csub\u003eCO\u003c/sub\u003e during the 8 h stability test (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). Both the morphology and composition of the Ag NPs-Skeleton electrode remained stable, as indicated by the post-reaction XRD and TEM measurements (\u003cb\u003eFigure S7\u003c/b\u003e). However, over the extended time, due to the gradual variation in hydrophobicity and the presence of too many cracks on the GDL surface (\u003cb\u003eFigure S2)\u003c/b\u003e, the electrolyte gradually permeates into the gas layer as electrolysis proceeds, eventually leading to flooding. Future systematic research can focus on optimizing the GDL properties to further improve the eCO\u003csub\u003e2\u003c/sub\u003eRR stability.\u003c/p\u003e \u003cp\u003eSubsequently, we investigated the loading effect of the Ag NPs-Skeleton under the same conditions by conducting the eCO\u003csub\u003e2\u003c/sub\u003eRR under a constant current density of 100 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e with different catalyst loadings, and the results were summarized in \u003cb\u003eFigure S8a.\u003c/b\u003e No significant changes in CO selectivity were observed, but at a loading of 0.3 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, the electrode exhibits the lowest overpotential. Therefore, we chose a catalyst loading of 0.3 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for the subsequent investigations, which led us to achieve high CO yield rates of 6.3 mol g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 100 m A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 22.9 mol g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 400 m A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (\u003cb\u003eFigure S8b\u003c/b\u003e). Moreover, we examined the eCO\u003csub\u003e2\u003c/sub\u003eRR product distribution of Ag NPs-Skeleton in 20 mM H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e with different concentrations of K\u003csup\u003e+\u003c/sup\u003e at a current density of 100 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, which was expected to shed light on the key role of K\u003csup\u003e+\u003c/sup\u003e in suppressing the HER.\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e \u003cb\u003eFigure S8c\u003c/b\u003e shows that CO\u003csub\u003e2\u003c/sub\u003e can be converted with a high selectivity even at a low concentration of K\u003csup\u003e+\u003c/sup\u003e (0.01 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and a higher concentration of K\u003csup\u003e+\u003c/sup\u003e in the electrolyte results in a lower resistance and cell potential\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e. These results illustrate that the presence of K\u003csup\u003e+\u003c/sup\u003e is truly important for the selective eCO\u003csub\u003e2\u003c/sub\u003eRR in acidic media, and the local cation concentration of the Ag NPs-Skeleton is sufficient even at a low concentration of K\u003csup\u003e+\u003c/sup\u003e in the bulk electrolyte for the Ag NPs-Skeleton, possibly resulting from their skeleton configuration. Considering the applied potential, a K\u003csup\u003e+\u003c/sup\u003e concentration of 1.0 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was chosen for the following investigation. As mentioned above, the challenge of carbonate formation in the alkaline eCO\u003csub\u003e2\u003c/sub\u003eRR can be addressed by improving the carbon utilization efficiency by using acidic media\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. To evaluate the carbon utilization efficiency of the Ag NPs-Skeleton in acidic electrolytes, the single-pass CO\u003csub\u003e2\u003c/sub\u003e conversion efficiency (SPCE) for the eCO\u003csub\u003e2\u003c/sub\u003eRR was measured at 100 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e with different CO\u003csub\u003e2\u003c/sub\u003e flow rates, as presented in \u003cb\u003eFigure S8d\u003c/b\u003e. At a higher flow rate, the SPCE was relatively lower since the CO\u003csub\u003e2\u003c/sub\u003e input greatly exceeded the consumption. By gradually decreasing the flow rate of CO\u003csub\u003e2\u003c/sub\u003e to 3 sccm, the SPCE reached 58.6% for CO production, reflecting the high carbon utilization efficiency of the Ag NPs-Skeleton.\u003c/p\u003e \u003cp\u003eNotably, Ag NPs-Skeleton exhibit excellent versatility in a wide range of pH environments, including acidic, buffered, neutral and alkaline electrolytes, with all CO selectivity above 90% at a current density of 100 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec), making them promising candidates for the eCO\u003csub\u003e2\u003c/sub\u003eRR in different practical applications or for coupling with various anodic reactions. To make an intuitive comparison, the control samples, commercial silver nanoparticles (Ag NPs, 50\u0026ndash;100 nm) and silver macroparticles (Ag MPs, 1\u0026ndash;3 \u0026micro;m) coated on GDLs by the drop-casting method with the use of Nafion, were tested for the eCO\u003csub\u003e2\u003c/sub\u003eRR in acidic media. The commercial Ag NPs disperse along the porous carbon nanoparticle layer of the GDL as Ag NPs-Skeleton but are more retained on the surface of the GDL (\u003cb\u003eFigure S9a-c\u003c/b\u003e). The commercial Ag MPs are uniformly distributed on the GDL surface without entering the skeleton due to their large size (\u003cb\u003eFigure S9d-f\u003c/b\u003e). XRD patterns of these control samples are shown in \u003cb\u003eFigure S9g\u003c/b\u003e to identify the material phases, which are identical to Ag NPs-Skeleton with metallic Ag phase. Obviously, Ag NPs and Ag MPs show much lower FEs, SPCEs and CO yield rates at the same current density as Ag NPs-Skeleton (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed and \u003cb\u003eFigure S9h, i\u003c/b\u003e), such as CO FEs of 58% and 47%, SPCEs of 35% and 29%, and CO yield rates of 3.4 and 3.0 mol g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 100 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively. Compared with recently reported CO production electrocatalysts and the control powdery electrocatalysts used in this work, the Ag NPs-Skeleton show a higher current density, greater CO product FE, and lower pH of the bulk electrolyte, making their performance among the best in acidic media (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef, \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e)\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eMore importantly, the synthesis method can be extended to other soluble Ag and Cu salts, such as silver tetrafluoroborate (AgBF\u003csub\u003e4\u003c/sub\u003e) and copper nitrate (Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e). The structural characteristics and eCO\u003csub\u003e2\u003c/sub\u003eRR performance for Ag NPs-Skeleton with AgBF\u003csub\u003e4\u003c/sub\u003e as a precursor are shown in \u003cb\u003eFigure S10\u003c/b\u003e and are like these prepared with AgNO\u003csub\u003e3\u003c/sub\u003e. Similarly, Cu NPs-Skeleton using Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e as a precursor \u003cb\u003e(Figure S11)\u003c/b\u003e could achieve a significantly higher eCO\u003csub\u003e2\u003c/sub\u003eRR product FE of 75% than that of the commercial Cu nanoparticles coated on GDLs using the drop-casting method (FE 27%) in at 300 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e \u003cb\u003e(Figure S12)\u003c/b\u003e. These results suggest that the targeted delivery of active sites to the porous carbon nanoparticle layer of the GDL give a great university for creating a favorable microenvironment for the electrocatalytic reaction sites, which is significant for promoting eCO\u003csub\u003e2\u003c/sub\u003eRR performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. The role of the microenvironment in the eCO\u003csub\u003e2\u003c/sub\u003eRR\u003c/h2\u003e \u003cp\u003eDue to the isolation effect of the Ag NPs-Skeleton, most Ag sites are separated from the bulk electrolyte, raising questions of whether the Ag sites located in the skeleton could contribute to the eCO\u003csub\u003e2\u003c/sub\u003eRR. To address this inquiry, the surface of the Ag NPs-Skeleton was covered with multiwalled carbon nanotubes (MWCNTs, \u003cb\u003eFigure S13a\u003c/b\u003e) or washed with electrolyte for 1 h before in situ electroreduction (\u003cb\u003eFigure S13b\u003c/b\u003e) to thoroughly avoid direct contact between the Ag NPs and the electrolyte and separate or wash the surface Ag NPs, respectively. The XRD patterns of these control samples revealed that the intensity of the typical Ag signal was much weaker than that of Ag NPs-Skeleton (Fig.\u0026nbsp;13c, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg). The thus-treated Ag NPs-Skeleton could still maintain a high CO production selectivity with an FE\u003csub\u003eCO\u003c/sub\u003e \u0026gt; 90% at current densities ranging from 25 to 400 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, \u003cb\u003eFigure S13d\u003c/b\u003e), indicating that the Ag NPs within the 3D carbon skeleton could act as the main active sites for the eCO\u003csub\u003e2\u003c/sub\u003eRR, which can provide more active sites than that of the traditional surface coated method. To smoothly promote the eCO\u003csub\u003e2\u003c/sub\u003eRR, not only are electrocatalytic active sites needed but also a suitable microenvironment is indispensable. First, the presence of a cation (K\u003csup\u003e+\u003c/sup\u003e) of 1.6 at% is verified by SEM-EDS mapping images of the Ag NPs-Skeleton electrode during the eCO\u003csub\u003e2\u003c/sub\u003eRR (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec), which shows that a large amount of K\u003csup\u003e+\u003c/sup\u003e disperses homogeneously across the carbon skeleton. This could help increase the local pH and stabilize key intermediates of the eCO\u003csub\u003e2\u003c/sub\u003eRR\u003csup\u003e\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAfterwards, the critical proton provider, water\u003csup\u003e\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e, was checked by connecting a buffering gas container equipped with a humidity meter at the gas chamber exit of the flow cell (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Due to the transpiration effect of CO\u003csub\u003e2\u003c/sub\u003e gas, the water could evaporate and pass through the GDL into the gas chamber even without the electrolysis process, resulting a humidity of 60% after 1 h. After applying the potential, the water evaporation became more severe at a humidity of 74% after 1 h, which possibly resulted from the heating effect during the eCO\u003csub\u003e2\u003c/sub\u003eRR. These results show that the Ag NPs-Skeleton could reach the available water to support the eCO\u003csub\u003e2\u003c/sub\u003eRR, and the amount of water vapor around the Ag active sites was much less than that in the surface liquid water, resulting in a comparatively high local CO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO ratio, which is quite important for suppressing the HER and promoting the eCO\u003csub\u003e2\u003c/sub\u003eRR. To confirm the important role of the local CO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO ratio for the eCO\u003csub\u003e2\u003c/sub\u003eRR on Ag NPs-Skeleton electrode, an electro-oxidation treatment of the GDL by a bias voltage was conducted to increase the surface hydrophilicity\u003csup\u003e\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e. The water contact angle of the GDL decreased from 133.7\u0026deg; to 123.3\u0026deg; after applying 2 V vs Ag/AgCl for 1000 s (\u003cb\u003eFigure S14\u003c/b\u003e), thus providing a lower water contact angle for the electro-oxidation-treated GDL loaded Ag NPs-Skeleton (Ag NPs-Skeleton-Ot) than for the plain GDL loaded Ag NPs-Skeleton (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). As expected, the Ag NPs-Skeleton-Ot show more water evaporation with a humidity of 84% after 1 h (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed) and an evidently lower FE\u003csub\u003eCO\u003c/sub\u003e from 25 to 200 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in acidic media (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef). Furthermore, the local pH during the eCO\u003csub\u003e2\u003c/sub\u003eRR could be tested by pH test strips as they were pasted on the back of the cathode GDL because of water evaporation. \u003cb\u003eFigure S15\u003c/b\u003e shows that the Ag NPs-Skeleton electrode has a pH of ~\u0026thinsp;9, which is higher than that of the Skeleton Ag NP-Ot electrode (pH\u0026thinsp;=\u0026thinsp;~\u0026thinsp;8). This suggests that the optimized Ag NPs-Skeleton electrode could maintain a local micro-alkaline microenvironment to suppress the HER. These results illustrate that the space confinement of active Ag NPs within the hydrophobic GDL skeleton can construct a favorable microenvironment through water evaporation, such as a high concentration of local cations and hydroxides and an increased CO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO ratio, for the eCO\u003csub\u003e2\u003c/sub\u003eRR.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Bubble management at the reaction interface\u003c/h2\u003e \u003cp\u003eThe evolution and transport of bubbles significantly complicate the gas/solid/liquid three-phase electrocatalytic reaction interface\u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e, \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e, and an unambiguous understanding of bubble behaviors and their impacts on eCO\u003csub\u003e2\u003c/sub\u003eRR performance has been scarce. An in situ flow cell for the observation of gas bubble formation through an optical microscope was designed and is shown in \u003cb\u003eFigure S16\u003c/b\u003e. With no electrolysis, the top views of the catalyst surface of Ag NPs-Skeleton, Ag NPs and Ag MPs and the electrolyte surface all showed no bubble formation. Once the potential was applied, the Ag NPs-Skeleton provided a static electrolyte surface with no bubble inflation, while a few small gas bubbles and large bubbles on the Ag NPs and Ag MPs were observed at the same current density of 100 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e. Therefore, the appearance of bubbles is highly dependent on the location of the Ag active sites. For the Ag NPs-Skeleton, the Ag sites are mainly located within the framework of the GDL and do not directly contact the electrolyte; thus, the bubbles generated in the skeleton dissipate within the framework and do not enter the electrolyte layer. Conversely, Ag MPs are mainly located on the surface of the GDL and directly contact the electrolyte. The generation and dissolution of bubbles during the eCO\u003csub\u003e2\u003c/sub\u003eRR occurred in the electrolyte layer, which caused a turbulent three-phase interface and poor electrocatalytic stability. Ag NPs are located both on the surface and within the framework of the GDL. Hence, a portion of the generated bubbles dissipate within the framework, while others enter the electrolyte layer to destabilize the three-phase interface. As a result, the existence of vast bubbles hindered ion transport and led to voltage fluctuations (\u003cb\u003eFigure S17\u003c/b\u003e), resulting in much worse stability and lower CO FEs of Ag NPs and Ag MPs than for those of Ag NPs-Skeleton (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). These results reveal that the skeleton loading mode of Ag NPs within the hydrophobic GDL skeleton can efficiently control bubble behaviors, such as decreasing bubble coverage, accelerating bubble detachment, and addressing gas accumulation issues in the flow cell. These factors are highly important for improving the mass transport, catalyst utilization, and stability of the eCO\u003csub\u003e2\u003c/sub\u003eRR.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo further elucidate the intrinsic mechanism behind bubble evolution and transport in the eCO\u003csub\u003e2\u003c/sub\u003eRR, COMSOL Multiphysics simulation\u003csup\u003e\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e, \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e was employed to study the motion characteristics of bubbles generated during the transport process of mixed gases CO\u003csub\u003e2\u003c/sub\u003e, CO, and H\u003csub\u003e2\u003c/sub\u003e under the effect of electric field force (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). In general, because of the pore distribution, the gas inlet velocity of the pores on the GDL surface follows the sequence: Ag NPs-Skeleton\u0026thinsp;\u0026lt;\u0026thinsp;Ag NPs\u0026thinsp;\u0026lt;\u0026thinsp;Ag MPs, the pore quantity on the GDL surface follows the sequence: Ag NPs-Skeleton\u0026thinsp;\u0026gt;\u0026thinsp;Ag NPs\u0026thinsp;\u0026gt;\u0026thinsp;Ag MPs, and the pore separation distance on the GDL surface follows the sequence: Ag NPs-Skeleton\u0026thinsp;\u0026lt;\u0026thinsp;Ag NPs\u0026thinsp;\u0026lt;\u0026thinsp;Ag MPs (\u003cb\u003eFigure S18\u003c/b\u003e). These factors are all contributing factors to the formation of bubbles. At a gas inlet velocity of 0.1 m s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, no bubble was able to penetrate the pores and form a gas film within the computational time. When the inlet velocity was increased to 0.115 m s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, only one bubble appeared and was able to enter the liquid phase (\u003cb\u003eFigure S19a\u003c/b\u003e), confirming that the critical velocity was approximately 0.1 m s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to avoid the appearance of bubbles. Furthermore, the influence of velocities ranging from 0.5 to 1.5 m s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e on the gas film length and bubble quantity was investigated (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea-b). It is evident that elevated velocities lead to more pronounced expansion of the gas film, rendering it more susceptible to shear forces and resulting in an increased frequency of bubble growth, which is applicable for the Ag MPs sample. The increase in the number of pores results in fewer bubbles, as revealed by the shorter gas film in the Ag NPs-Skeleton sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec).\u003c/p\u003e \u003cp\u003eFurthermore, the quantity of bubbles follows a volcano-shaped curve in response to variations in the pore distance. In our model, three pores had separation distances ranging from 125 to 500 \u0026micro;m were simulated (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed \u003cb\u003eand Figure S19b\u003c/b\u003e). When the pore spacing separation distance decreases from 500 to 250 \u0026micro;m, the gas film at pore 1 rapidly ruptures upon reaching 250 \u0026micro;m due to the disruptive influence of gas film growth at pore 2, making bubble formation easier (\u003cb\u003eFigure S19c\u003c/b\u003e). However, as the pore separation distance is further decreased to 125 \u0026micro;m, the growth process of the gas film completely covers both pore 1 and pore 2. At this point, the gas film growth and bubble detachment processes resemble those of a single pore (\u003cb\u003eFigure S19d and Figure S20\u003c/b\u003e). Therefore, a comparatively shorter pore separation distance of approximately 175 \u0026micro;m is conducive to preventing bubble formation. Additionally, considering that the Ag NPs-Skeleton could homogenize the gas pressure of the pores on the GDL surface, we changed the single gas inlet of the traditional flow cell (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee\u003cb\u003e)\u003c/b\u003e to multiple independent inlets in our simulation and observed the obvious suppression of liquid backfilling into the gas chamber, i.e., flooding (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef). Consequently, microenvironment regulation to achieve a relatively stable fluid field through smart catalyst loading and reactor design contributes to the long-term stability and high CO Faradaic efficiency of the eCO\u003csub\u003e2\u003c/sub\u003eRR at industrial current densities.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 DFT calculations\u003c/h2\u003e \u003cp\u003eDFT calculations, widely used to understand eCO\u003csub\u003e2\u003c/sub\u003eRR reaction mechanisms\u003csup\u003e\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e\u003c/sup\u003e, were conducted to elucidate the enhanced selectivity and stability of the Ag NPs-Skeleton. The assumption is that the dramatically enhanced activity can be related to the specific crystalline structure, namely, evident vacancy defects on the Ag NPs-Skeleton (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee). Two simulation models, i.e., the Ag(111) surface and Ag(111) surface with vacancies (denoted as Ag111-v, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea \u003cb\u003eand Figure S21a, b\u003c/b\u003e), are employed to evaluate the CO formation pathway. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb, the potential-determining step energy (PDS), *COOH formation, of Ag111-v is ~\u0026thinsp;0.2 eV lower than that of Ag(111), which facilitates CO formation, demonstrating that the existence of structural defects are responsible in promoting eCO\u003csub\u003e2\u003c/sub\u003eRR activity. In addition, we further evaluated the effect of the CO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO ratio on the activity of Ag NPs-Skeleton (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). The constructed CO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO ratios ranged from 10 to 8.33\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, indicating that the material was Ag(111)-v-CO\u003csub\u003e2\u003c/sub\u003e rich and Ag(111)-v-H\u003csub\u003e2\u003c/sub\u003eO rich (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). With the high coverage of water on the Ag surface, the abundant Ag(111)-H\u003csub\u003e2\u003c/sub\u003eO provides a highly favorable energy for the HER. Compared to the Ag(111)-H\u003csub\u003e2\u003c/sub\u003eO-rich sample, the Ag(111)-CO\u003csub\u003e2\u003c/sub\u003e-rich sample evidently has a higher energy barrier for the HER. Coupled with the introduction of vacancies, the Ag(111)-v-CO\u003csub\u003e2\u003c/sub\u003e-rich catalyst further achieves an increased energy barrier for the HER in contrast to the bare Ag(111)-CO\u003csub\u003e2\u003c/sub\u003e-rich catalyst and Ag(111)-v. These results confirm that the HER can be effectively suppressed during the eCO\u003csub\u003e2\u003c/sub\u003eRR by regulating the CO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO ratio and introducing active defects on the catalyst surface.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOverall, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed, the underlying reason for the increase in the eCO\u003csub\u003e2\u003c/sub\u003eRR performance of the Ag NPs-Skeleton is based on the skeleton loading mode used for the delivery of the active Ag sites to the superior microenvironment. Specifically, compared to the conventional surface loading mode, the skeleton loading mode can embed active sites into the GDL framework and construct a beneficial local microenvironment for eCO\u003csub\u003e2\u003c/sub\u003eRR with a high CO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO ratio, a low concentration of protons, and a static fluid field with a suppressed bubbles generation. Consequently, the Ag NPs-Skeleton show significantly enhanced CO FEs, yields and SPECs over a wide range of potentials, pH ranges, and decent long-term stabilities.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Conclusion","content":"\u003cp\u003eIn summary, a freestanding, binder-free electrode composed of activated Ag NPs catalysts located uniformly within GDL skeleton was successfully designed. The in situ reduction procedure ensures the intimate interactions between the catalysts and skeleton, and therefore promoting good electronic conductivity during the eCO\u003csub\u003e2\u003c/sub\u003eRR. The GDL skeleton effectively protects Ag NPs from direct erosion caused by the physical impacts of electrolyte flow and gas bubble evolution, leading to a greatly improved stability. As supported by the in situ observation of optical microscope and COMSOL Multiphysics simulation, delivering catalysts within the GDL also manifests the pore structures, leading to the reduction of bubble formation/coverage and the alleviation of gas accumulation issues, and thereby enhancing the eCO\u003csub\u003e2\u003c/sub\u003eRR performance. DFT calculations further demonstrate that the regulation of the catalyst structure (vacancy defect) and local microenvironment (CO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO ratio) is responsible for improving the eCO\u003csub\u003e2\u003c/sub\u003eRR activity. The achievement of wide potential and wide pH adaptability for CO production allows for the coupling of the eCO\u003csub\u003e2\u003c/sub\u003eRR with other anodic reactions beyond the OER or tandem cathodic reactions to directly employ the in situ formed CO for higher reaction efficiency and more value-added products.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was financially supported by the National Natural Science Foundation of China (52201227, 52272088, 52331009, 22173066), Chinese education ministry’s Chunhui program (202200767), Zhejiang Provincial Natural Science Foundation of China (LQ23B030001, Q24B020025), and the open research fund of Songshan Lake Materials Laboratory (2023SLABFN09).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eDe Luna P, Hahn C, Higgins D, Jaffer SA, Jaramillo TF, Sargent EH. 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Electric field effects in electrochemical CO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003ereduction. \u003cem\u003eACS Catal\u003c/em\u003e \u003cstrong\u003e6\u003c/strong\u003e, 7133-7139 (2016).\u003c/li\u003e\n \u003cli\u003eLejaeghere K\u003cem\u003e, et al.\u003c/em\u003e Reproducibility in density functional theory calculations of solids. \u003cem\u003eScience\u003c/em\u003e \u003cstrong\u003e351\u003c/strong\u003e, aad3000 (2016).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4692796/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4692796/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTo boost the performance of electrocatalytic CO\u003csub\u003e2\u003c/sub\u003e reduction reaction (eCO\u003csub\u003e2\u003c/sub\u003eRR), a unique synthetic method that deploys the in situ reduction of precoated precursors was developed to produce activated Ag nanoparticles (NPs) within the gas diffusion layer (GDL), where the thus-obtained Ag NPs-Skeleton could block direct contact between the active Ag sites and electrolyte. Specifically, compared to the conventional surface loading mode in the acidic media, our freestanding and binder free electrode could achieve obvious higher CO selectivity of 94%, CO production rate of 23.3 mol g\u003csup\u003e-1\u003c/sup\u003e h\u003csup\u003e-1\u003c/sup\u003e, single-pass CO\u003csub\u003e2\u003c/sub\u003e conversion of 58.6%, and enhanced long-term stability of 8 hours. Our study shows that delivering catalysts within the GDL does not only gain the desired physical protection from GDL skeleton to achieve a superior local microenvironment for more efficient pH-universal eCO\u003csub\u003e2\u003c/sub\u003eRR, but also manifests the pore structures to effectively address gas accumulation and flood issues, thereby stabilizing the catalysts.\u003c/p\u003e","manuscriptTitle":"Microenvironment engineering by targeted delivery of activated Ag NPs for boosting electrocatalytic CO2 reduction reaction","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-23 04:53:27","doi":"10.21203/rs.3.rs-4692796/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"4063968c-4d00-4a27-a54e-4f7ccf58d78b","owner":[],"postedDate":"July 23rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":34984523,"name":"Physical sciences/Chemistry/Catalysis/Electrocatalysis"},{"id":34984524,"name":"Earth and environmental sciences/Environmental sciences/Environmental chemistry/Atmospheric chemistry"}],"tags":[],"updatedAt":"2025-01-25T08:07:06+00:00","versionOfRecord":{"articleIdentity":"rs-4692796","link":"https://doi.org/10.1038/s41467-025-56039-x","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-01-24 05:00:00","publishedOnDateReadable":"January 24th, 2025"},"versionCreatedAt":"2024-07-23 04:53:27","video":"","vorDoi":"10.1038/s41467-025-56039-x","vorDoiUrl":"https://doi.org/10.1038/s41467-025-56039-x","workflowStages":[]},"version":"v1","identity":"rs-4692796","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4692796","identity":"rs-4692796","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}