Localized mass transport channels for electro-upgrade of dilute CO2 toward high-yield C2+ products

Localized mass transport channels for electro-upgrade of dilute CO2 toward high-yield C2+ products | 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 Localized mass transport channels for electro-upgrade of dilute CO 2 toward high-yield C 2+ products Zhongwei Chen, Bohua Ren, Xiaowen Zhang, Leixin Yang, Guobin Wen, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5984755/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 25 Sep, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Electrocatalytic upgrade of CO 2 offers a promising approach for the recycling of global CO 2 emissions, facilitating the achievement of carbon neutrality. Nevertheless, the purification of CO 2 is costly and direct utilization of practical dilute CO 2 is urgently important yet rather difficult. The main challenge for continuous electrocatalysis of dilute CO 2 is to balance the reaction kinetics and mass transport of CO 2 to the catalytic sites, which is hindered by the large mass transport resistance. Herein, we propose coordinating the local environment and active catalyst by constructing covalent organic frameworks (COF) on single-atomic In-doped Cu 2 O (In 1 @Cu 2 O) for a high tolerance of CO 2 inlet concentrations (15–100%). The optimized amounts of COF functionalized by the trifluoromethyl group act as the local CO 2 /CO diffusion channels via steric confinement effects and C∙∙∙F electronic effects. Besides, the formation of key intermediates for C 2+ products is greatly facilitated by the promoted COOH adsorption. Hence, a total current of 81.7 A is realized in a 4×100 cm 2 electrolyzer stack with over 770 mmol/h C 2+ products at an inlet of dilute CO 2 . Such new electrode architecture sheds light on the high-yield electrochemical conversion using dilute CO 2 at the potential industrial scale for practical applications. Physical sciences/Chemistry/Electrochemistry/Electrocatalysis Earth and environmental sciences/Environmental sciences/Environmental chemistry/Atmospheric chemistry electrocatalysis dilute CO2 mass transport channels steric confinement local environment Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Recycling CO 2 emissions at ambient conditions by electrocatalytic conversion with renewable electricity grants an elegant carbon-neutral route. 1 – 3 Such electrochemical CO 2 reduction reactions (CO 2 RR) have shown techno-economic viability to synthesize valuable chemicals and feedstocks. 4 Nevertheless, the imbalance of reaction kinetics and mass transport with an increasing conversion rate and industrial dilute CO 2 limits the large-scale applications of this technique. So far, most of the research on CO 2 RR is focused on pure CO 2 gas to benchmark catalyst or device performances. 5 – 7 However, the general CO 2 concentration is only around 70–95% after capture and separation by the membrane plants from flue gas (15–20%). 8–10 Hence, the direct utilization of impure or dilute CO 2 inlets is highly significant. The intrinsic challenge for continuous electrolysis of dilute CO 2 is that the solubility or partial pressure of CO 2 becomes too low to be fed sufficiently to the catalytic sites. 11 , 12 Therefore, a concerted manner of concentrating CO 2 at a local level and efficiently converting CO 2 is urgently needed for further practical developments. Particularly, it is crucial to manage both localized reaction environments and catalytic sites for enrichments of local reactants or intermediates and improvements of conversion rate, respectively. Researchers have been investigating the use of covalent organic frameworks (COFs) as sorption materials for capturing CO 2 because of a high affinity for CO 2 . 13 Meanwhile, COF-based materials have also been extensively studied as potential catalysts for CO 2 RR, either by introducing metals onto COFs or using them as molecular catalysts with functionalized groups. 14 Attributed to the unique porous configuration and conjugated electronic structure, COF materials can also be employed as diffusion channels to regulate the local environment. Herein, we coordinate reaction kinetic promotions and mass transport regulations for the scale-up of the electrolyzer stack with industrial-level electrosynthesis C 2+ products from dilute CO 2 . As shown in Fig. 1 a, through constructing mass transport channels with a COF layer on the single atomic In doped Cu 2 O (In 1 @Cu 2 O), CO 2 concentrating and converting processes are coupled together. Hence, the dilute CO 2 (70–90%) and even simulated flue gas (15% CO 2 ) are efficiently converted into C 2+ products at ambient conditions. In detail, a COF functionalized by the trifluoromethyl group (TfCOF) acts as localized channels for localized CO 2 /CO mass transport. Besides, active In 1 @Cu 2 O is found to strengthen the adsorption of *COOH for the production of CO key intermediate toward C 2+ products. 15 Correspondingly, such TfCOF-In 1 @Cu 2 O electrode converts dilute CO 2 with a Faradaic efficiency for C 2+ products (FE C2+ ) of 83.5% at E cell of 3.4 V, presenting only a 3.4% decrease in FE C2+ compared with the performance testing under 100% pure CO 2 inlet. Such high selectivity is well maintained for over 96 hours with a current density of over 700 mA/cm 2 . Additionally, a 4×100 cm 2 electrolyzer stack is assembled to achieve over 770 mmol/h C 2+ products with a total current of 81.7 A with a dilute CO 2 inlet. Results and Discussions Electrode synthesis and in-situ activation The TfCOF is proposed to tune the mass transport at the local environment near the catalytic sites, which is synthesized from 1,3,5-triformyl phloroglucinol (Tp) and 2,2'-Bis(trifluoromethyl)benzidine (BTBD) with the formation of Enol-imine form and further Keto-enamine form (Fig. 1 b). The structures of TfCOF are illustrated as shown in Figs. 1 c, S1, and S2. The pore sizes are characterized by the wide-angle X-ray scattering (WAXS, Fig. 1 d), which is around 18 Å. The high crystallinity and the compositions of TfCOF are also observed by the crystalline lattice in transmission electron microscopy (TEM) images and elemental mapping images (Fig. 1 e), respectively. On the other hand, the active site is also delicately designed to promote the reaction kinetics of CO 2 -to-C 2+ products. As reported, 16 In doping of Cu-In alloy highly suppresses the hydrogen evolution and regulates the electronic structure of Cu for selective synthesis of CO intermediate. Therefore, single atomic In is further introduced to modify the surface Cu 2 O site. The detailed synthesis process of TfCOF-In 1 @Cu 2 O catalyst is presented in Figure S3. An epoxide gelation method was firstly employed to prepare In-Cu gel, which consists of Cu 2 (OH) 3 Cl and In(OH) 3 . This In-Cu gel was aged in the oven for 24 hours, and then it was mixed with TfCOF to prepare catalyst ink, which was drop-casting on the carbon paper to form the electrode (Figure S4). Under CO 2 RR conditions, the synthesized electrode was subjected to in-situ electrochemical activation at a constant potential for 30 minutes, and then TfCOF-In 1 @Cu 2 O electrode was ultimately yielded. It is revealed by scanning electron microscopy (SEM) images that abundant interlaced channels are formed in the as-prepared TfCOF-In 1 @Cu 2 O by cross-linking of nanoparticles (Figure S5). To further investigate this material, the high-resolution TEM (HRTEM) is examined as depicted in Figures S6 and S7. It is found that such nanoparticles are quite fine and highly dispersed. Moreover, as shown in the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, isolated bright spots are identified as representing atomically dispersed In atoms in the Cu 2 O matrix (Fig. 1 f). The lattice fringe with a d-spacing of 0.24 nm corresponds to the Cu 2 O (111) plane and the existence of single atomic In over the Cu 2 O matrix is further confirmed. 17 As shown in Fig. 1 g,h, the 3D visualization and element mapping images further depict the distribution of single atomic In atoms. Synchrotron X-ray absorption spectroscopy (XAS) characterizations are further performed to reveal the local electronic structures and coordination environment of Cu and In in TfCOF-In 1 @Cu 2 O catalyst. 18 , 19 The Cu K-edge of X-ray absorption near-edge structure (XANES) for TfCOF-In 1 @Cu 2 O is depicted in Fig. 2 a, as well as the spectra of copper foil, Cu 2 O, and CuO references. The near-edge absorption peak of TfCOF-In 1 @Cu 2 O is located between those of Cu foil and Cu 2 O, indicating the chemical valence of copper species is between 0 and + 1, and close to + 1. 20,21 As for the catalyst modification, it is well known that monovalent Cu(I)-based catalysts are favorable for C–C bond formation, 22 – 24 while single-atom alloys are reported to steer the electronic features of host material with the introduction of foreign atoms. 25 With the analyses of the extended X-ray absorption fine structure (EXAFS) for Cu K-edge (Fig. 2 b), the peak in R space at 1.46 Å is ascribed to the contribution of Cu-O bonds from Cu 2 O. 26 , 27 The broad peak at 2.35 Å is ascribed to the co-existence of Cu-In and Cu-Cu paths. 21 , 28 Meanwhile, EXAFS curves of In K-edge for TfCOF-In 1 @Cu 2 O, indium foil, and In 2 O 3 references are shown in Fig. 2 c. Two peaks at 1.64 Å and 2.47 Å are attributed to In-O and In-Cu paths, respectively. 29 Notably, there is no In-In coordination in TfCOF-In 1 @Cu 2 O, revealing that indium is atomically dispersed on Cu 2 O. In addition, the near-edge absorption of In atom in TfCOF-In 1 @Cu 2 O occurs at a higher energy than that of In 2 O 3 , indicating that In atoms are possessed of a higher valence state than In 2 O 3 (Figure S8). Single atomic In is formed during the in-situ activation step, and such evolution of crystal structures and 3D elemental distribution of TfCOF-In 1 @Cu 2 O is captured by operando synchrotron 2D-WAXS measurements as shown in Fig. 2 d-g. Before the in-situ activation (0 min), the crystal patterns of Cu 2 (OH) 3 Cl (JCPDS#50-1559) and In(OH) 3 (JCPDS#16–0161) are presented. Notably, these peaks gradually disappear and the existence of Cu 2 O (JCPDS#78-2076) can be detected as the activation proceeds. 21 , 30 It is worth noting that no indium-associated peaks are observed for the TfCOF-In 1 @Cu 2 O material, which further confirmed that there are no In particles formed. These results are further clearly verified by the integrated XRD curves in Fig. 2 e,f. The In(OH) 3 (2 theta = 5.04) leaches out rapidly, while Cu 2 (OH) 3 Cl (2 theta = 3.65, Figure S9) is converted to Cu 2 O (2 theta = 8.27). Time-of-flight secondary-ion mass spectroscopy (TOF-SIMS) with vacuum interconnection was also performed to analyze the elemental distribution in different depths of the electrode. 31 After the activation in the glove box, the electrodes were transferred to the test station for TOF-SIMS measurements immediately. The 3D rendering of Cu and In species in the electrode before and after the activation step is depicted in Fig. 2 g. In elements are observed to be distributed along different depths of the electrode before the activation step. Then the content of In is greatly reduced after the activation step (Figure S10), which is consistent with the 2D-WAXS results. These results reveal that a large amount of In atoms leach out during the in-situ activation process. The distribution of other elements for TfCOF-In 1 @Cu 2 O catalysts is shown in Figures S11 and S12. Notably, the uniform distribution of K element in Figure S11b indicates that the TfCOF-In 1 @Cu 2 O catalyst holds porous structures for electrolyte penetrations. Additionally, quasi in-situ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is performed to further elucidate the evolution of electronic structure and chemical states. 32 , 33 As shown in Figure S13, the binding energy of all Cu 2p 3/2 spectra for TfCOF-In 1 @Cu 2 O catalyst is around 932.7 eV, attributing to Cu 0 or Cu + peaks. 21,34 The Cu LMM Auger spectra further clarify the major Cu + species in the material after the activation step (Fig. 2 h). Moreover, according to In 3d spectra in Fig. 2 i, the In 3+ peaks of In-Cu gel are located at 452.5 eV and 444.9 eV, which show a positive shift of about 0.23 eV after the activation step. The result indicates that In atom has a higher valence state than In 3+ , which is consistent with the EXAFS results. According to the operando and quasi in-situ characterizations, a schematic is drawn to show the evolution of atomic structures as presented in Figure S14, where only Cu, O, and a small amount of In atoms are retained after the in-situ activation, with a large outflow of In, Cl, O, and H atoms. Localized mass transport channels for dilute CO 2 electrolysis We employ TfCOF-In 1 @Cu 2 O for regulating both catalytic sites and localized diffusion channels to simultaneously promote the reaction kinetics and local mass transport for efficient dilute CO 2 electrolysis (Fig. 3 a). In detail, In 1 @Cu 2 O plays the role of accelerating the production of CO key species for C-C coupling via enhancing the adsorption of *COOH intermediate as illustrated in the following Density Functional Theory (DFT) simulations. On the other hand, the TfCOF layer acts as the CO and CO 2 diffusion channels and makes it possible for them to contact with electrons from the catalyst and protons from the electrolyte as illustrated by combined Mulphysic simulations and Molecular dynamic simulations. It is worth mentioning that the TfCOF layer also avoids the rapid departure of CO species to the electrolyte. With the target of extending the commercial utilization of CO 2 RR systems, we employ a customized flow cell with a CO 2 -saturated aqueous inlet to deliver the carbon sources, 3 which are bubbled by a series of pure and impure CO 2 gas: 100%, 90%, 80%, and 70% CO 2 . These typical concentrations are selected to simulate the CO 2 waste gas after the membrane plants from fuel gases. 9 , 10 As shown in Figure S15, FE toward total carbon-containing products (FE Ctot ) shows a sharp decrease from 82.6–49.4% at E cell of 3.4 V on pure Cu 2 O when changing the inlet from pure CO 2 to 80% CO 2 . It is attributed to that low concentrations of CO 2 inlet reduce the partial pressure of CO 2 (P CO2 ) and further decrease the solubility of CO 2 , 35 which highly reduces the selectivity of CO 2 RR on pure Cu 2 O. Dilute CO 2 is concentrated according to the electrostatic interaction by the modifications of TfCOF in the electrode. 13 , 14 , 36 As shown in Figures S16a and S17, Faradaic efficiency toward total carbon-containing products (FE Ctot ) is promoted to 86.9% using TfCOF-Cu 2 O and 80% CO 2 inlet. Nevertheless, the selectivity of C 2+ products is still less than 75%. The possible reason is the production and concentration of CO intermediate adsorbed on the catalysts are too low to proceed for the further C-C coupling on pure Cu 2 O for impure CO 2 electrolysis. Meanwhile, it is found that In 1 @Cu 2 O has a higher ability to produce CO than Cu 2 O (Figure S18), which confirms the critical role of single atomic In doping for the facilitating of reaction kinetics. As expected, the selectivity of C 2+ products on TfCOF-In 1 @Cu 2 O demonstrates strong tolerance on a wide CO 2 concentration window, which shows high FE Ctot and FE C2+ in the flow cell as shown in Fig. 3 b. A maximum value of 86.3 ± 2.4% at E cell of 3.4V is delivered for pure CO 2 electrolysis. The obtained FE Ctot and FE C2+ using 90% CO 2 inlet are almost the same as those using pure inlet at a wide potential window between 2.6 V and 3.6V (Figure S18a). Meanwhile, FE C2+ reaches 83.5% and FE Ctot is 95.5% at E cell of 3.4 V with 80% CO 2 inlet, showing comparable performance with 100% pure CO 2 and the performance damping is less than 5%. The high selectivity and activity are attributed to the balance of effective capture of CO 2 by TfCOF and faster reaction kinetic by In 1 @Cu 2 O. FE Ctot drops when the inlet changes to 70% CO 2 , which is around 85.8% ± 2.2% at E cell of 3.4 V (Figure S3b). The 11.7% reduction in FE Ctot compared with pure inlet is likely due to the limited CO 2 supply for the reactions, 37 which is more evident under larger cell voltages. With the inlet of simulated flue gas of 15% CO 2 , TfCOF-In 1 @Cu 2 O still presents a high conversion ability of CO 2 , and the FE Ctot is over 60% at E cell between 2.8 V and 3.6V (Figs. 3 d and S18b). To reveal the effect of the TfCOF layer on the localized concentrations and coverages of CO and CO 2 , Multiphysics simulations coupled with MD calculations are employed with considerations of the mass transport, buffer reactions, and electrochemical reactions in the near-surface region of the catalyst (Fig. 3 e,f). 38 , 39 The diffusion coefficients of CO and CO 2 in the catholyte with diffusion channels are calculated from Mean Squared Displacement (MSD) functions from MD calculations (Figure S19), which are the inlet parameters used for Multiphysics simulations. It can be seen that the local concentrations of CO and CO 2 around the catalyst are much higher after the modification by TfCOF (Fig. 1 f and S20). Additionally, the coverage of adsorbed CO (*CO) varies from 0.06 to 0.28 after adopting TfCOF layer, which shows 4.7 times promotion. This high coverage of *CO provides sufficient *CO for further reduction, which accounts for the higher FE C2+ on TfCOF-In 1 @Cu 2 O than that on In 1 @Cu 2 O. The addition of such TfCOF also facilitates the coverage of *CO 2 , swinging from 0.22 to 0.31, which provides more carbon sources for CO 2 electrolysis on the catalytic sites. 40 The simulated results reveal that the existence of TfCOF layer could highly increase the coverage and localized concentration of CO and CO 2 . 41 , 42 The enrichment of these species around active sites can realize the further reduction reactions toward valuable C 2+ products. Besides Multiphysics numerical simulation, the calculated CO 2 distribution probability using MD simulations is also shown in the middle inset of Fig. 3 a. The red dots in the pores of TfCOF indicate the distribution possibilities of CO 2 accumulation region. High possibilities occur at the corners of nanopores in TfCOF, which reflect the special steric confinement effect on CO 2 by TfCOF. 43 TfCOF holds a large amount of CO 2 with ample adsorption sites (Table S1 ), ascribing to the high electrostatic interaction of CO 2 . Such TfCOF additive layer further breaks the solubility limitations from the low pCO 2 and promotes the local concentration of CO 2 for the reactions, which further improves the tolerance of lower inlet concentrations of CO 2 . High yield and stability with impure CO inlets The synthesized TfCOF-In 1 @Cu 2 O not only presents a high selectivity for C 2+ products but also exhibits improved current densities and yields. As shown in Fig. 4 a, the total current density (J) for TfCOF-In 1 @Cu 2 O exceeds 1400 mA/cm 2 at E cell of 3.8V with the inlet of pure CO 2 in the flow cell. FE Ctot is also over 87% at such a high current, which suggests a pronounced catalytic activity and CO 2 utilization. With the inlets of dilute 90% and 80% CO 2 , the total current densities remain high at E cell of 3.8V, which are 1355 mA/cm 2 and 1245 mA/cm 2 , respectively. TfCOF-In 1 @Cu 2 O also presents a total current density of 200 mA/cm 2 at E cell of 3.4V for the direct conversion of simulated flue gas with 15% CO 2 . Meanwhile, the maximum selectivity of C 2 H 4 reaches 72.9 ± 2.2% at E cell of 3.4 V, with FE C2+ of 83.5% and FE Ctot of 95.5% when using the 80% CO 2 inlet. Likewise, we observe that TfCOF-In 1 @Cu 2 O electrode delivers a superior partial current density toward C 2+ products (J C2+ ) of 837 mA/cm 2 at 3.4V with pure CO 2 inlet, while it remains 768 mA/cm 2 with 80% impure CO 2 inlet (Fig. 4 b), showing only 9% decrease in the production rate with 20% decrease of CO 2 concentration at such a high current density. As depicted in Fig. 4 c, we realize the total yield for carbon products of 3.45 mmol/h/cm 2 at E cell of 3.6 V with the impure inlet of 80% CO 2 , and the C 2 H 4 yield is 2.36 mmol/h/cm 2 . It is worth mentioning that the separations of C 2 H 4 from CO and CH 4 are comparatively mature industrial processes, which makes the TfCOF-In 1 @Cu 2 O catalyst a promising material for CO 2 electrolysis. The efficient conversion of dilute CO 2 is ascribed to the simultaneous steric confinement effect and electronic effects of TfCOF on CO 2 and CO as discussed previously. Specifically, dilute CO 2 molecules are concentrated by TfCOF with ample adsorption sites, 44 and the adsorption energies are revealed by the DFT simulations (Figures S21 and S22). Different amounts of TfCOF additives are also conducted with weight ratios of 0.1, 0.2, and 0.3 relative to the In-Cu gel (Figure S23). The amount of TfCOF is critical to ensure the high yield of the C 2+ products and the optimized ratio of TfCOF is around 0.2. The morphologies of different additions of TfCOF remain similar to the fine particles after the in-situ activations (Figures S24 and S25). The J C2+ of 698 mA/cm 2 with 80% dilute CO 2 inlet is realized on the catalyst with TfCOF(0.3), showing around 10% reduction compared with that of TfCOF-In 1 @Cu 2 O. On the other hand, TfCOF(0.1)-In 1 @Cu 2 O shows 18.5% decrease of J C2+ compared with that of TfCOF-In 1 @Cu 2 O (Figs. 4 d and S26). The stability of TfCOF-In 1 @Cu 2 O is also measured with 80% CO 2 inlet. A current density of 760 mA/cm 2 is well maintained for 96 hours at E cell of 3.4V with FE Ctot over 95% and FE C2+ over 80% during continuous operation (Figs. 4 e and S27). The high yield of C 2 H 4 is around 2.1 mmol/h/cm 2 , which is about 200 mmol after a four-day electrochemical CO 2 upgrade with 1 cm 2 electrode. Such high yield and stability performance with 80% CO 2 inlet surpasses lots of reports with pure CO 2 inlet (Table S2). With the target of potential industrial applications, an electrolyzer stack is further assembled as shown in Fig. 4 f, which consistents of four 10×10 cm 2 modules connected in series. 3 , 45 , 46 The maximum production rate of C 2+ products is over 770 mmol/h with an inlet of 80% CO 2 , corresponding to a total current of 81.7 A (Fig. 4 g). With the utilization of pure CO 2 inlet, the maximum total current of 95.9 A is achieved with the C 2+ production rate of around 800 mmol/h. Therefore, such a dual strategy of mass transport regulations and reaction kinetics promotions is scalable for potential industrial-level applications. Underling mechanism To evaluate the catalytic site of a single atomic In dopant combined with monovalent Cu(I) on CO formation, we firstly set up three surface models by the periodic DFT computations: Cu (111), In 1 @Cu (111) and In 1 @Cu 2 O (111) as shown in Figures S28, S29 and S30, respectively. The reaction energies are depicted in Fig. 5 a for the pathways of CO production, in which the initial step of electron-proton transfer to form COOH* is the rate-limiting step. 47 – 49 Among the three surface models, In 1 @Cu 2 O (111) shows the lowest Gibbs free energy for COOH* formation, indicating the promoting effect from single atomic In doping in Cu 2 O. To better understand the intrinsic mechanism for the enhanced activity for CO formation on In 1 @Cu 2 O, the projected density of states (PDOS) of the C atom in the key COOH* adsorbate and corresponding surface Cu atoms in Cu(111), In 1 @Cu (111) and In 1 @Cu 2 O (111) were calculated. The electron density and the wave function are decomposed to reveal the atomic orbital contributions. 50 , 51 As shown in Fig. 5 b, the harmonic overlaps between the C-2p and Cu-3d states on In 1 @Cu 2 O are the largest among all the models, which shows the strong interaction between the C and Cu atoms. 52 Importantly, compared with the d-band of Cu, incorporating In into a Cu 2 O modifies the broadness of the Cu d-band below the Fermi level (E f ). 53 In contrast, the harmonic overlaps between the C-2p and Cu-3d states are the smallest for In 1 @Cu (Figure S29), which is consistent with the highest reaction energy toward CO (Fig. 5 a) and the reported higher selectivity for formate instead of CO. 25 Hence, such a strategic combination of foreign In atomic In atoms doped in oxidized monovalent Cu(I) leads to the highest selectivity towards CO by holding specific electronics and features that are rather different from their counterpart metals. The proposed mechanism is also depicted by the schematic of Fig. 5 c. Incorporating single atomic In into Cu 2 O results in a larger energy split of hybrid orbitals when incorporated with the *COOH. 32,53 Such modifications drive the antibonding level near to Femi level and decrease the energy barrier of charge transfer, 53 – 55 enabling a stronger extent of Cu-COOH orbital mixing. 53 TfCOF possesses unique 3D porous structures, which can availably promote the mass transport and enrichments of CO and CO 2 near the catalyst surface. The electrostatic potential of the F atom becomes larger after interacting with CO (Fig. 5 d), which is attributed to the electron density transfer from F atom of TfCOF to C atom in CO. Hence, the negative regions in the molecular electrostatic potential maps extend to the oxygen atom of CO. The distance of C and F atoms is found to be 2.25 Å (Figs. 5 e and S32). Such C∙∙∙F interactions make the TfCOF become CO diffusion channels near the catalytic surface. As revealed, the strong electrostatic interaction between CO and TfCOF is further confirmed by the radial distribution function (RDF) and coordination numbers (CN) around TfCOF. The CNs of CO near TfCOF are much higher than that between CO 2 and TfCOF, indicating a larger number density of CO. The distributions of CO and CO 2 are shown in the lattice for the MD simulation (Figs. 5 e, f and S33). The random TfCOF molecules are gathering around 5 nm away from the catalytic surface. This assembled structure is likely causing the existence of multiple layers of CO between the TfCOF layer and catalytic surface due to different electrostatic interactions, which results in the analogous normal density distribution of it along the Z-direction (Fig. 5 f). The inner layers of CO are enriched by TfCOF layer ascribed to the stronger van der Waals’ interactions, while the outer layers of CO with moderate interactions are close to the catalytic sites (around 1 nm in the simulation lattice) and can be released from TfCOF to the catalytic surface for further reduction. This is the proposed mechanism for the simultaneous capturing and releasing of CO and CO 2 molecules by TfCOF with the C \(\:\cdots\:\) F electronic effect and steric effect, respectively. Such mass transport regulation effects are further depicted by the experimental confirmations with in-situ electrochemical attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy to monitor the intermediates of In 1 @Cu 2 O/COF at various potentials (Fig. 5 h,j). 56 – 58 The important intermediates for the generation of C 2+ products were observed, including the CO* (at 2065 cm - 1 ), 59 and CO bound to the copper surface (at 1967, 1919 cm - 1 ). 60 The intensity of these peaks increased with the cathode potentials, indicating the high coverage of *CO species. The enhancement in *CO adsorption promoted the subsequent C−C coupling. Moreover, the characteristic peak at 1541, 1423, and 1396 cm - 1 corresponds to COOH* and *COO - (two O coordinated), respectively. 15 , 61 , 62 The *H 2 O peak is observed at 1649 cm - 1 (Fig. 5 i). 59 The peaks at 1743, 1554, and 1519 cm - 1 are attributed to CO 3 2- species. 63 The pronounced peak at 2344 cm - 1 is assigned to the CO 2 * (Figure S34), demonstrating the adsorption of CO 2 on TfCOF-In 1 @Cu 2 O. These findings further demonstrate the effective regulations of CO and CO 2 species near the catalytic sites by the TfCOF. Discussion Efficient electrolysis of dilute CO 2 (70–90% and 15%) toward C 2+ products is realized through employing combined TfCOF and single-atom active sites of In 1 @Cu 2 O. Supported by the multi-scale simulation and experimental characterizations, TfCOF is proved to be the local diffusion channels of CO 2 /CO and optimized amounts of TfCOF provide the proper concentrating of these molecules. In 1 @Cu 2 O plays the role of promoting the production of CO key intermediate for C-C coupling. Hence, the maximum FE C2+ of 83.5% and FE Ctot of 95.5% are obtained at E cell of 3.4 V when using the 80% CO 2 inlet. The high C 2 H 4 yield of 2.1 mmol/h/cm 2 is delivered for four days with an impure CO 2 inlet. Such a dual strategy is further scalable to the electrolyzer stack with a high yield of C 2+ products of over 770 mmol/h. The coupled design strategy of mass transport regulation and reaction kinetics promotion lays the foundation for the practical developments of dilute CO 2 electrolysis. Declarations Competing interests The authors declare no competing interests. Supplementary materials Supplementary Information accompanies this paper at XXX. Acknowledgements B. R., X. Z., and L. Y. contributed equally to this work. The authors appreciate Dr. Graham King and Dr. Al Rahemtulla for the synchrotron WAXS on BXDS-WHE beamline at the Canadian Light Source (CLS). The authors thank Dr. Ning Chen, Dr. Roman Chernikov, and Dr. Emilio Heredia for XAS characterizations on HXMA and BioXAS beamlines at CLS. The authors also acknowledge the technical support for quasi in-situ NAP-XPS characterizations from Nano-X from Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (SINANO). This work is financially supported by the National Natural Science Foundation of China (22472049) and Changsha Natural Science Foundation (kq2402051). The authors gratefully acknowledge the computational resources provided by the National Supercomputer Center in Guangzhou. References Wang G et al (2021) Electrocatalysis for CO 2 conversion: from fundamentals to value-added products. Chem Soc Rev 50:4993–5061 Wen G et al (2023) Bridging Trans-Scale Electrode Engineering for Mass CO 2 Electrolysis. JACS Au 3:2046–2061 Wen G et al (2022) Continuous CO 2 electrolysis using a CO 2 exsolution-induced flow cell. 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Supplementary Files SupportingInformationCuIn1.docx Supporting Information ForTableofContentsOnly.docx Cite Share Download PDF Status: Published Journal Publication published 25 Sep, 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-5984755","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":416920705,"identity":"455e743e-e7a1-4ef0-8e8f-e9fb5bbd3073","order_by":0,"name":"Zhongwei Chen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAuElEQVRIiWNgGAWjYHACNiC2YWwjVUsa6VoOMzYQrV5+RvKzBx93nJftYz97gOFHDYO8OSEtjDPSzA1nnrlt3MaTl8DYc4zBcCch+5ilc9ikedtuJ7ZJ8Bgw8DYwJBgcIKCFDaTlb9s5sBbGv8Ro4QFpYWw7ANbCTJQtEvLPzCR725LBfjksc0zCcAMhLfI9h59J/Gyzk53ffvbgwzc1NvIEbUF2IwNQsQTx6sFaRsEoGAWjYBRgBQAIMzj/CRCZxQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-3463-5509","institution":"Power Battery and Systems Research Center, State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences","correspondingAuthor":true,"prefix":"","firstName":"Zhongwei","middleName":"","lastName":"Chen","suffix":""},{"id":416920706,"identity":"3cbf12dc-384e-47fe-979c-063617b90fb7","order_by":1,"name":"Bohua Ren","email":"","orcid":"","institution":"University of Waterloo","correspondingAuthor":false,"prefix":"","firstName":"Bohua","middleName":"","lastName":"Ren","suffix":""},{"id":416920707,"identity":"01eb0e73-457f-4f28-9a2b-df97450b538c","order_by":2,"name":"Xiaowen Zhang","email":"","orcid":"","institution":"Institute of Carbon Neutrality, Zhejiang Wanli University","correspondingAuthor":false,"prefix":"","firstName":"Xiaowen","middleName":"","lastName":"Zhang","suffix":""},{"id":416920708,"identity":"21e56dc9-01d1-4332-9cea-25d850685c12","order_by":3,"name":"Leixin Yang","email":"","orcid":"","institution":"Tianjin University of Science \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Leixin","middleName":"","lastName":"Yang","suffix":""},{"id":416920709,"identity":"95c05f64-0b2d-4f04-8144-fa0149a5aaf9","order_by":4,"name":"Guobin Wen","email":"","orcid":"https://orcid.org/0000-0002-2191-6734","institution":"Hunan University","correspondingAuthor":false,"prefix":"","firstName":"Guobin","middleName":"","lastName":"Wen","suffix":""},{"id":416920710,"identity":"a2ceb9fa-2549-4a83-9c02-6b0308a208f8","order_by":5,"name":"Silong Dong","email":"","orcid":"","institution":"Institute of Carbon Neutrality, Zhejiang Wanli University","correspondingAuthor":false,"prefix":"","firstName":"Silong","middleName":"","lastName":"Dong","suffix":""},{"id":416920711,"identity":"83c19beb-9a88-4fd3-b185-75335e654715","order_by":6,"name":"Haoyang Xiong","email":"","orcid":"","institution":"Institute of Carbon Neutrality, Zhejiang Wanli University","correspondingAuthor":false,"prefix":"","firstName":"Haoyang","middleName":"","lastName":"Xiong","suffix":""},{"id":416920712,"identity":"55165c37-358c-4fdb-94e6-0d3cd9fb9bcb","order_by":7,"name":"Yinyi Liu","email":"","orcid":"","institution":"Institute of Carbon Neutrality, Zhejiang Wanli University","correspondingAuthor":false,"prefix":"","firstName":"Yinyi","middleName":"","lastName":"Liu","suffix":""},{"id":416920713,"identity":"7afec996-ec6d-40ce-a929-9fec42daca59","order_by":8,"name":"Xiaoman Duan","email":"","orcid":"","institution":"Division of Biomedical Engineering, College of Engineering, University of Saskatchewan","correspondingAuthor":false,"prefix":"","firstName":"Xiaoman","middleName":"","lastName":"Duan","suffix":""},{"id":416920714,"identity":"43fc0e50-abb4-4fe6-b28a-31cb6af52183","order_by":9,"name":"Lichao Tan","email":"","orcid":"","institution":"Zhejiang Wanli University","correspondingAuthor":false,"prefix":"","firstName":"Lichao","middleName":"","lastName":"Tan","suffix":""},{"id":416920715,"identity":"40821eec-3412-43ca-8cac-19d8825f46c9","order_by":10,"name":"Xin Wang","email":"","orcid":"","institution":"Zhejiang Wanli University","correspondingAuthor":false,"prefix":"","firstName":"Xin","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2025-02-08 03:20:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5984755/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5984755/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-025-63178-8","type":"published","date":"2025-09-25T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":76678245,"identity":"5faa9f16-15b9-4da8-ab83-7d33799c0e79","added_by":"auto","created_at":"2025-02-19 14:41:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1344529,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eConcept, fabrication and characterizations of TfCOF-In\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e@Cu\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO electrode. \u003c/strong\u003e(a) Schematic of relationships among reaction kinetics, mass transport, and industrial-level electrosynthesis. TfCOF layer on single atomic In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO surface acting as localized channels for CO and CO\u003csub\u003e2\u003c/sub\u003e diffusion, which synergistically balances the reaction kinetics promotions and facilitates the scale-up of electrolyzer stacks. (b) Synthetic scheme of TfCOF by an ion-exchange process. Tp is 1,3,5-triformyl phloroglucinol and BTBD is 2,2' Bis(trifluoromethyl)benzidine. (c) The schematic structure of TfCOF with the pore size of 18 Å. (d) WAXS patterns of TfCOF and the carbon paper background. (e) TEM, STEM and element mapping images of TfCOF. (f) HAADF-STEM image of TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO. The yellow circles highlight representative single In atoms, which are brighter compared with Cu atoms. (g) Three-dimensional visualization of region \u0026nbsp;in (e) to depict single atomic In atoms. (h) Element mapping images of TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO. \u0026nbsp;\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-5984755/v1/050732456da38c41b1d02983.png"},{"id":76678288,"identity":"6867fb2f-5769-4c36-885a-f94e6e47fe03","added_by":"auto","created_at":"2025-02-19 14:41:45","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":945412,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStructural characterizations and evolutions of TfCOF-In\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e@Cu\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO with \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003ein-situ\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e activation under CO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eRR. \u003c/strong\u003e(a) XANES spectra of Cu K-edge. EXAFS spectra of (b) Cu K-edge and (c) In K-edge, respectively. (d) \u003cem\u003eOperando \u003c/em\u003eWAXS patterns detected during the activation process. \u003cem\u003eOperando\u003c/em\u003e WAXS spectra of (e) In(OH)\u003csub\u003e3\u003c/sub\u003e leaching and (f) Cu\u003csub\u003e2\u003c/sub\u003eO generation during the activation step. (g) 3D images of TOF-SIMS elemental depth distribution of Cu and In elements before and after \u003cem\u003ein-situ\u003c/em\u003e activation step. The bottom images are the surface distributions of single atomic In formation. Quasi \u003cem\u003ein-situ\u003c/em\u003e NAP-XPS spectra of (h) Cu LMM and (i) In 3d spectra during the activation process.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-5984755/v1/dbede008de01b495da07ac16.png"},{"id":76678312,"identity":"e3635df3-fc25-48e8-8237-25da2df445d1","added_by":"auto","created_at":"2025-02-19 14:42:13","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":672695,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eConstruction of localized mass transport channels for dilute CO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e electrolysis.\u003c/strong\u003e (a) Schematic diagram of the specialized roles for In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO and TfCOF to promote reaction kinetics and regulate mass transport, respectively. Inset in the middle revealing the steric effect for CO\u003csub\u003e2\u003c/sub\u003e by calculating CO\u003csub\u003e2\u003c/sub\u003e adsorption distribution. (b) FEs of different products for Cu\u003csub\u003e2\u003c/sub\u003eO and TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO with dilute 80 % CO\u003csub\u003e2\u003c/sub\u003e inlets. The cell voltage of E\u003csub\u003ecell\u003c/sub\u003e is reported without \u003cem\u003eiR\u003c/em\u003e correction. The error bars represent the standard deviation from the measurement of three independent electrodes. (c) FFs toward total carbon products (FE\u003csub\u003eCtot\u003c/sub\u003e) and (d) C\u003csub\u003e2+\u003c/sub\u003e products (FE\u003csub\u003eC2+\u003c/sub\u003e) for TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO in a flow cell with different concentrations of CO\u003csub\u003e2\u003c/sub\u003e inlets. The simulated flue gas is 15% CO\u003csub\u003e2\u003c/sub\u003e and 85% N\u003csub\u003e2\u003c/sub\u003e. (e) Calculated 2D distributions of CO concentration around electrodes with and without TfCOF layer with Multiphysics simulations. (f) Calculated coverages of adsorbed *CO and CO\u003csub\u003e2\u003c/sub\u003e on the catalytic surface.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-5984755/v1/230fa4acf381affec8e2f7f3.png"},{"id":76678273,"identity":"945708f3-bc11-4ef2-a938-b4324a8b4992","added_by":"auto","created_at":"2025-02-19 14:41:31","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":568345,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eContinuous upgrade of dilute CO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e by TfCOF-In\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e@Cu\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO in the flow cell. \u003c/strong\u003e(a) Total current densities of TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO with different CO\u003csub\u003e2\u003c/sub\u003e concentrations. (b) Partial current densities toward C\u003csub\u003e2+\u003c/sub\u003e products under different potentials and CO\u003csub\u003e2\u003c/sub\u003e concentrations. (c) Yield of CO, CH\u003csub\u003e4\u003c/sub\u003e, C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eOH and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003e with the inlet of 80 % CO\u003csub\u003e2\u003c/sub\u003e. The yield for C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003e is not shown in the figures due to the low selectivity (FE \u0026lt; 3%). (d) Total current density and partial current density for C\u003csub\u003e2+\u003c/sub\u003e and C\u003csub\u003e1\u003c/sub\u003e products with different adding amounts of TfCOF. (e) Stability measurements of TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO at E\u003csub\u003ecell\u003c/sub\u003e of 3.4 V with inlet of 80 % CO\u003csub\u003e2\u003c/sub\u003e. (f) Photograph of 4×100 cm\u003csup\u003e2\u003c/sup\u003e electrolyzer stack. (g) Total current and partial current for C\u003csub\u003e2+\u003c/sub\u003e and C\u003csub\u003e1\u003c/sub\u003e products with stack potentials in the electrolyzer stack with inlet of 80% and 100% CO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-5984755/v1/0c0f2f764d4cb3a9c4b507f0.png"},{"id":76678249,"identity":"ed5e5d66-da1a-48ba-9c38-ee9d03ebcd9f","added_by":"auto","created_at":"2025-02-19 14:41:21","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1273023,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMechanism analysis\u003c/strong\u003e \u003cstrong\u003eand calculations.\u003c/strong\u003e (a) Relative Gibbs free energy (Δ\u003cem\u003eG\u003c/em\u003e)\u003cem\u003e \u003c/em\u003eprofiles of the CO\u003csub\u003e2\u003c/sub\u003e-to-CO reaction\u003cstrong\u003e \u003c/strong\u003eon Cu(111), In\u003csub\u003e1\u003c/sub\u003e@Cu (111) and In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO (111) facets. (b) Projected density of states (PDOS) of Cu-3d, In-4d, and C-2p orbitals with adsorbed COOH* on In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO and Cu surfaces. (c) Schematic of the impact of metal d-band broadness. (d) C⋯F electronic effect for CO, and the molecular electrostatic potential map of CO interacted with TfCOF. Inset: representative snapshots showing the pure TfCOF and close interactions of CO-TfCOF, respectively. Cyan, red, blue, white, and pink sticks: C, O, N, H, and F atoms. (e) Radial distribution function and coordination numbers of CO and CO\u003csub\u003e2\u003c/sub\u003e with the distance from TfCOF. Inset is the representative snapshot showing close interactions of TfCOF-CO. (f) CO and CO\u003csub\u003e2\u003c/sub\u003e distributions in the lattice implemented in the MD simulation considering Cu surface (yellow), K\u003csup\u003e+\u003c/sup\u003e (blue balls), H\u003csub\u003e2\u003c/sub\u003eO (red dots), HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e (short-stick structures, red, white, cyan: O, H, C) and TfCOF (long-stick structures, blue, white, and pink sticks: N, H, and F). The element color of (e) is the same as (f). (g) The density distribution of CO along the Z-direction of the modeling lattice. (h, i) \u003cem\u003eIn-situ\u003c/em\u003e FTIR spectrum of TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO for CO\u003csub\u003e2\u003c/sub\u003eRR in different wavenumber regions.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-5984755/v1/711f72488da528d9e19836bc.png"},{"id":92235072,"identity":"7859b109-dfa5-4937-80fd-571a8a842352","added_by":"auto","created_at":"2025-09-26 07:09:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6082540,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5984755/v1/30261c8a-85f5-4cd9-ae14-af9cd8dd3fb5.pdf"},{"id":76678282,"identity":"1b7eef1a-d695-4c65-8456-e212b552f6bb","added_by":"auto","created_at":"2025-02-19 14:41:39","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":24785886,"visible":true,"origin":"","legend":"Supporting Information","description":"","filename":"SupportingInformationCuIn1.docx","url":"https://assets-eu.researchsquare.com/files/rs-5984755/v1/52f42ef23a0297aa526b92af.docx"},{"id":76678306,"identity":"134a3c94-847d-44db-b986-9c7a9c814afa","added_by":"auto","created_at":"2025-02-19 14:42:05","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":139692,"visible":true,"origin":"","legend":"","description":"","filename":"ForTableofContentsOnly.docx","url":"https://assets-eu.researchsquare.com/files/rs-5984755/v1/d5f80e99b56a76ea300b1115.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"\u003cp\u003eLocalized mass transport channels for electro-upgrade of dilute CO\u003csub\u003e2\u003c/sub\u003e toward high-yield C\u003csub\u003e2+\u003c/sub\u003e products\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eRecycling CO\u003csub\u003e2\u003c/sub\u003e emissions at ambient conditions by electrocatalytic conversion with renewable electricity grants an elegant carbon-neutral route.\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e Such electrochemical CO\u003csub\u003e2\u003c/sub\u003e reduction reactions (CO\u003csub\u003e2\u003c/sub\u003eRR) have shown techno-economic viability to synthesize valuable chemicals and feedstocks.\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e Nevertheless, the imbalance of reaction kinetics and mass transport with an increasing conversion rate and industrial dilute CO\u003csub\u003e2\u003c/sub\u003e limits the large-scale applications of this technique. So far, most of the research on CO\u003csub\u003e2\u003c/sub\u003eRR is focused on pure CO\u003csub\u003e2\u003c/sub\u003e gas to benchmark catalyst or device performances.\u003csup\u003e\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e However, the general CO\u003csub\u003e2\u003c/sub\u003e concentration is only around 70\u0026ndash;95% after capture and separation by the membrane plants from flue gas (15\u0026ndash;20%).\u003csup\u003e8\u0026ndash;10\u003c/sup\u003e Hence, the direct utilization of impure or dilute CO\u003csub\u003e2\u003c/sub\u003e inlets is highly significant.\u003c/p\u003e \u003cp\u003eThe intrinsic challenge for continuous electrolysis of dilute CO\u003csub\u003e2\u003c/sub\u003e is that the solubility or partial pressure of CO\u003csub\u003e2\u003c/sub\u003e becomes too low to be fed sufficiently to the catalytic sites.\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e Therefore, a concerted manner of concentrating CO\u003csub\u003e2\u003c/sub\u003e at a local level and efficiently converting CO\u003csub\u003e2\u003c/sub\u003e is urgently needed for further practical developments. Particularly, it is crucial to manage both localized reaction environments and catalytic sites for enrichments of local reactants or intermediates and improvements of conversion rate, respectively. Researchers have been investigating the use of covalent organic frameworks (COFs) as sorption materials for capturing CO\u003csub\u003e2\u003c/sub\u003e because of a high affinity for CO\u003csub\u003e2\u003c/sub\u003e.\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e Meanwhile, COF-based materials have also been extensively studied as potential catalysts for CO\u003csub\u003e2\u003c/sub\u003eRR, either by introducing metals onto COFs or using them as molecular catalysts with functionalized groups.\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e Attributed to the unique porous configuration and conjugated electronic structure, COF materials can also be employed as diffusion channels to regulate the local environment.\u003c/p\u003e \u003cp\u003eHerein, we coordinate reaction kinetic promotions and mass transport regulations for the scale-up of the electrolyzer stack with industrial-level electrosynthesis C\u003csub\u003e2+\u003c/sub\u003e products from dilute CO\u003csub\u003e2\u003c/sub\u003e. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, through constructing mass transport channels with a COF layer on the single atomic In doped Cu\u003csub\u003e2\u003c/sub\u003eO (In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO), CO\u003csub\u003e2\u003c/sub\u003e concentrating and converting processes are coupled together. Hence, the dilute CO\u003csub\u003e2\u003c/sub\u003e (70\u0026ndash;90%) and even simulated flue gas (15% CO\u003csub\u003e2\u003c/sub\u003e) are efficiently converted into C\u003csub\u003e2+\u003c/sub\u003e products at ambient conditions. In detail, a COF functionalized by the trifluoromethyl group (TfCOF) acts as localized channels for localized CO\u003csub\u003e2\u003c/sub\u003e/CO mass transport. Besides, active In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO is found to strengthen the adsorption of *COOH for the production of CO key intermediate toward C\u003csub\u003e2+\u003c/sub\u003e products.\u003csup\u003e15\u003c/sup\u003e Correspondingly, such TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO electrode converts dilute CO\u003csub\u003e2\u003c/sub\u003e with a Faradaic efficiency for C\u003csub\u003e2+\u003c/sub\u003e products (FE\u003csub\u003eC2+\u003c/sub\u003e) of 83.5% at E\u003csub\u003ecell\u003c/sub\u003e of 3.4 V, presenting only a 3.4% decrease in FE\u003csub\u003eC2+\u003c/sub\u003e compared with the performance testing under 100% pure CO\u003csub\u003e2\u003c/sub\u003e inlet. Such high selectivity is well maintained for over 96 hours with a current density of over 700 mA/cm\u003csup\u003e2\u003c/sup\u003e. Additionally, a 4\u0026times;100 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e electrolyzer stack is assembled to achieve over 770 mmol/h C\u003csub\u003e2+\u003c/sub\u003e products with a total current of 81.7 A with a dilute CO\u003csub\u003e2\u003c/sub\u003e inlet.\u003c/p\u003e"},{"header":"Results and Discussions","content":"\u003cp\u003e \u003cb\u003eElectrode synthesis and\u003c/b\u003e \u003cb\u003ein-situ\u003c/b\u003e \u003cb\u003eactivation\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe TfCOF is proposed to tune the mass transport at the local environment near the catalytic sites, which is synthesized from 1,3,5-triformyl phloroglucinol (Tp) and 2,2'-Bis(trifluoromethyl)benzidine (BTBD) with the formation of Enol-imine form and further Keto-enamine form (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The structures of TfCOF are illustrated as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec, S1, and S2. The pore sizes are characterized by the wide-angle X-ray scattering (WAXS, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed), which is around 18 \u0026Aring;. The high crystallinity and the compositions of TfCOF are also observed by the crystalline lattice in transmission electron microscopy (TEM) images and elemental mapping images (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee), respectively.\u003c/p\u003e \u003cp\u003eOn the other hand, the active site is also delicately designed to promote the reaction kinetics of CO\u003csub\u003e2\u003c/sub\u003e-to-C\u003csub\u003e2+\u003c/sub\u003e products. As reported,\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e In doping of Cu-In alloy highly suppresses the hydrogen evolution and regulates the electronic structure of Cu for selective synthesis of CO intermediate. Therefore, single atomic In is further introduced to modify the surface Cu\u003csub\u003e2\u003c/sub\u003eO site. The detailed synthesis process of TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO catalyst is presented in Figure S3. An epoxide gelation method was firstly employed to prepare In-Cu gel, which consists of Cu\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e3\u003c/sub\u003eCl and In(OH)\u003csub\u003e3\u003c/sub\u003e. This In-Cu gel was aged in the oven for 24 hours, and then it was mixed with TfCOF to prepare catalyst ink, which was drop-casting on the carbon paper to form the electrode (Figure S4). Under CO\u003csub\u003e2\u003c/sub\u003eRR conditions, the synthesized electrode was subjected to \u003cem\u003ein-situ\u003c/em\u003e electrochemical activation at a constant potential for 30 minutes, and then TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO electrode was ultimately yielded.\u003c/p\u003e \u003cp\u003eIt is revealed by scanning electron microscopy (SEM) images that abundant interlaced channels are formed in the as-prepared TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO by cross-linking of nanoparticles (Figure S5). To further investigate this material, the high-resolution TEM (HRTEM) is examined as depicted in Figures S6 and S7. It is found that such nanoparticles are quite fine and highly dispersed. Moreover, as shown in the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, isolated bright spots are identified as representing atomically dispersed In atoms in the Cu\u003csub\u003e2\u003c/sub\u003eO matrix (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef). The lattice fringe with a d-spacing of 0.24 nm corresponds to the Cu\u003csub\u003e2\u003c/sub\u003eO (111) plane and the existence of single atomic In over the Cu\u003csub\u003e2\u003c/sub\u003eO matrix is further confirmed.\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg,h, the 3D visualization and element mapping images further depict the distribution of single atomic In atoms.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSynchrotron X-ray absorption spectroscopy (XAS) characterizations are further performed to reveal the local electronic structures and coordination environment of Cu and In in TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO catalyst.\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e The Cu K-edge of X-ray absorption near-edge structure (XANES) for TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, as well as the spectra of copper foil, Cu\u003csub\u003e2\u003c/sub\u003eO, and CuO references. The near-edge absorption peak of TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO is located between those of Cu foil and Cu\u003csub\u003e2\u003c/sub\u003eO, indicating the chemical valence of copper species is between 0 and +\u0026thinsp;1, and close to +\u0026thinsp;1.\u003csup\u003e20,21\u003c/sup\u003e As for the catalyst modification, it is well known that monovalent Cu(I)-based catalysts are favorable for C\u0026ndash;C bond formation,\u003csup\u003e\u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e while single-atom alloys are reported to steer the electronic features of host material with the introduction of foreign atoms.\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eWith the analyses of the extended X-ray absorption fine structure (EXAFS) for Cu K-edge (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb), the peak in R space at 1.46 \u0026Aring; is ascribed to the contribution of Cu-O bonds from Cu\u003csub\u003e2\u003c/sub\u003eO.\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e The broad peak at 2.35 \u0026Aring; is ascribed to the co-existence of Cu-In and Cu-Cu paths.\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e Meanwhile, EXAFS curves of In K-edge for TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO, indium foil, and In\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e references are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec. Two peaks at 1.64 \u0026Aring; and 2.47 \u0026Aring; are attributed to In-O and In-Cu paths, respectively.\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e Notably, there is no In-In coordination in TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO, revealing that indium is atomically dispersed on Cu\u003csub\u003e2\u003c/sub\u003eO. In addition, the near-edge absorption of In atom in TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO occurs at a higher energy than that of In\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, indicating that In atoms are possessed of a higher valence state than In\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (Figure S8).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSingle atomic In is formed during the \u003cem\u003ein-situ\u003c/em\u003e activation step, and such evolution of crystal structures and 3D elemental distribution of TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO is captured by \u003cem\u003eoperando\u003c/em\u003e synchrotron 2D-WAXS measurements as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed-g. Before the \u003cem\u003ein-situ\u003c/em\u003e activation (0 min), the crystal patterns of Cu\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e3\u003c/sub\u003eCl (JCPDS#50-1559) and In(OH)\u003csub\u003e3\u003c/sub\u003e (JCPDS#16\u0026ndash;0161) are presented. Notably, these peaks gradually disappear and the existence of Cu\u003csub\u003e2\u003c/sub\u003eO (JCPDS#78-2076) can be detected as the activation proceeds.\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e It is worth noting that no indium-associated peaks are observed for the TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO material, which further confirmed that there are no In particles formed. These results are further clearly verified by the integrated XRD curves in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee,f. The In(OH)\u003csub\u003e3\u003c/sub\u003e (2 theta\u0026thinsp;=\u0026thinsp;5.04) leaches out rapidly, while Cu\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e3\u003c/sub\u003eCl (2 theta\u0026thinsp;=\u0026thinsp;3.65, Figure S9) is converted to Cu\u003csub\u003e2\u003c/sub\u003eO (2 theta\u0026thinsp;=\u0026thinsp;8.27).\u003c/p\u003e \u003cp\u003eTime-of-flight secondary-ion mass spectroscopy (TOF-SIMS) with vacuum interconnection was also performed to analyze the elemental distribution in different depths of the electrode.\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e After the activation in the glove box, the electrodes were transferred to the test station for TOF-SIMS measurements immediately. The 3D rendering of Cu and In species in the electrode before and after the activation step is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg. In elements are observed to be distributed along different depths of the electrode before the activation step. Then the content of In is greatly reduced after the activation step (Figure S10), which is consistent with the 2D-WAXS results. These results reveal that a large amount of In atoms leach out during the \u003cem\u003ein-situ\u003c/em\u003e activation process. The distribution of other elements for TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO catalysts is shown in Figures S11 and S12. Notably, the uniform distribution of K element in Figure S11b indicates that the TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO catalyst holds porous structures for electrolyte penetrations.\u003c/p\u003e \u003cp\u003eAdditionally, quasi \u003cem\u003ein-situ\u003c/em\u003e near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is performed to further elucidate the evolution of electronic structure and chemical states.\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e As shown in Figure S13, the binding energy of all Cu 2p\u003csub\u003e3/2\u003c/sub\u003e spectra for TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO catalyst is around 932.7 eV, attributing to Cu\u003csup\u003e0\u003c/sup\u003e or Cu\u003csup\u003e+\u003c/sup\u003e peaks.\u003csup\u003e21,34\u003c/sup\u003e The Cu LMM Auger spectra further clarify the major Cu\u003csup\u003e+\u003c/sup\u003e species in the material after the activation step (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh). Moreover, according to In 3d spectra in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei, the In\u003csup\u003e3+\u003c/sup\u003e peaks of In-Cu gel are located at 452.5 eV and 444.9 eV, which show a positive shift of about 0.23 eV after the activation step. The result indicates that In atom has a higher valence state than In\u003csup\u003e3+\u003c/sup\u003e, which is consistent with the EXAFS results. According to the \u003cem\u003eoperando\u003c/em\u003e and quasi \u003cem\u003ein-situ\u003c/em\u003e characterizations, a schematic is drawn to show the evolution of atomic structures as presented in Figure S14, where only Cu, O, and a small amount of In atoms are retained after the \u003cem\u003ein-situ\u003c/em\u003e activation, with a large outflow of In, Cl, O, and H atoms.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eLocalized mass transport channels for dilute CO\u003csub\u003e2\u003c/sub\u003e electrolysis\u003c/h2\u003e \u003cp\u003eWe employ TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO for regulating both catalytic sites and localized diffusion channels to simultaneously promote the reaction kinetics and local mass transport for efficient dilute CO\u003csub\u003e2\u003c/sub\u003e electrolysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). In detail, In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO plays the role of accelerating the production of CO key species for C-C coupling via enhancing the adsorption of *COOH intermediate as illustrated in the following Density Functional Theory (DFT) simulations. On the other hand, the TfCOF layer acts as the CO and CO\u003csub\u003e2\u003c/sub\u003e diffusion channels and makes it possible for them to contact with electrons from the catalyst and protons from the electrolyte as illustrated by combined Mulphysic simulations and Molecular dynamic simulations. It is worth mentioning that the TfCOF layer also avoids the rapid departure of CO species to the electrolyte.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWith the target of extending the commercial utilization of CO\u003csub\u003e2\u003c/sub\u003eRR systems, we employ a customized flow cell with a CO\u003csub\u003e2\u003c/sub\u003e-saturated aqueous inlet to deliver the carbon sources,\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e which are bubbled by a series of pure and impure CO\u003csub\u003e2\u003c/sub\u003e gas: 100%, 90%, 80%, and 70% CO\u003csub\u003e2\u003c/sub\u003e. These typical concentrations are selected to simulate the CO\u003csub\u003e2\u003c/sub\u003e waste gas after the membrane plants from fuel gases.\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e As shown in Figure S15, FE toward total carbon-containing products (FE\u003csub\u003eCtot\u003c/sub\u003e) shows a sharp decrease from 82.6\u0026ndash;49.4% at E\u003csub\u003ecell\u003c/sub\u003e of 3.4 V on pure Cu\u003csub\u003e2\u003c/sub\u003eO when changing the inlet from pure CO\u003csub\u003e2\u003c/sub\u003e to 80% CO\u003csub\u003e2\u003c/sub\u003e. It is attributed to that low concentrations of CO\u003csub\u003e2\u003c/sub\u003e inlet reduce the partial pressure of CO\u003csub\u003e2\u003c/sub\u003e (P\u003csub\u003eCO2\u003c/sub\u003e) and further decrease the solubility of CO\u003csub\u003e2\u003c/sub\u003e,\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e which highly reduces the selectivity of CO\u003csub\u003e2\u003c/sub\u003eRR on pure Cu\u003csub\u003e2\u003c/sub\u003eO.\u003c/p\u003e \u003cp\u003eDilute CO\u003csub\u003e2\u003c/sub\u003e is concentrated according to the electrostatic interaction by the modifications of TfCOF in the electrode.\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e As shown in Figures S16a and S17, Faradaic efficiency toward total carbon-containing products (FE\u003csub\u003eCtot\u003c/sub\u003e) is promoted to 86.9% using TfCOF-Cu\u003csub\u003e2\u003c/sub\u003eO and 80% CO\u003csub\u003e2\u003c/sub\u003e inlet. Nevertheless, the selectivity of C\u003csub\u003e2+\u003c/sub\u003e products is still less than 75%. The possible reason is the production and concentration of CO intermediate adsorbed on the catalysts are too low to proceed for the further C-C coupling on pure Cu\u003csub\u003e2\u003c/sub\u003eO for impure CO\u003csub\u003e2\u003c/sub\u003e electrolysis. Meanwhile, it is found that In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO has a higher ability to produce CO than Cu\u003csub\u003e2\u003c/sub\u003eO (Figure S18), which confirms the critical role of single atomic In doping for the facilitating of reaction kinetics.\u003c/p\u003e \u003cp\u003eAs expected, the selectivity of C\u003csub\u003e2+\u003c/sub\u003e products on TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO demonstrates strong tolerance on a wide CO\u003csub\u003e2\u003c/sub\u003e concentration window, which shows high FE\u003csub\u003eCtot\u003c/sub\u003e and FE\u003csub\u003eC2+\u003c/sub\u003e in the flow cell as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb. A maximum value of 86.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4% at E\u003csub\u003ecell\u003c/sub\u003e of 3.4V is delivered for pure CO\u003csub\u003e2\u003c/sub\u003e electrolysis. The obtained FE\u003csub\u003eCtot\u003c/sub\u003e and FE\u003csub\u003eC2+\u003c/sub\u003e using 90% CO\u003csub\u003e2\u003c/sub\u003e inlet are almost the same as those using pure inlet at a wide potential window between 2.6 V and 3.6V (Figure S18a). Meanwhile, FE\u003csub\u003eC2+\u003c/sub\u003e reaches 83.5% and FE\u003csub\u003eCtot\u003c/sub\u003e is 95.5% at E\u003csub\u003ecell\u003c/sub\u003e of 3.4 V with 80% CO\u003csub\u003e2\u003c/sub\u003e inlet, showing comparable performance with 100% pure CO\u003csub\u003e2\u003c/sub\u003e and the performance damping is less than 5%. The high selectivity and activity are attributed to the balance of effective capture of CO\u003csub\u003e2\u003c/sub\u003e by TfCOF and faster reaction kinetic by In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO.\u003c/p\u003e \u003cp\u003eFE\u003csub\u003eCtot\u003c/sub\u003e drops when the inlet changes to 70% CO\u003csub\u003e2\u003c/sub\u003e, which is around 85.8% \u0026plusmn; 2.2% at E\u003csub\u003ecell\u003c/sub\u003e of 3.4 V (Figure S3b). The 11.7% reduction in FE\u003csub\u003eCtot\u003c/sub\u003e compared with pure inlet is likely due to the limited CO\u003csub\u003e2\u003c/sub\u003e supply for the reactions,\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e which is more evident under larger cell voltages. With the inlet of simulated flue gas of 15% CO\u003csub\u003e2\u003c/sub\u003e, TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO still presents a high conversion ability of CO\u003csub\u003e2\u003c/sub\u003e, and the FE\u003csub\u003eCtot\u003c/sub\u003e is over 60% at E\u003csub\u003ecell\u003c/sub\u003e between 2.8 V and 3.6V (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed and S18b).\u003c/p\u003e \u003cp\u003eTo reveal the effect of the TfCOF layer on the localized concentrations and coverages of CO and CO\u003csub\u003e2\u003c/sub\u003e, Multiphysics simulations coupled with MD calculations are employed with considerations of the mass transport, buffer reactions, and electrochemical reactions in the near-surface region of the catalyst (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee,f).\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e,\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e The diffusion coefficients of CO and CO\u003csub\u003e2\u003c/sub\u003e in the catholyte with diffusion channels are calculated from Mean Squared Displacement (MSD) functions from MD calculations (Figure S19), which are the inlet parameters used for Multiphysics simulations.\u003c/p\u003e \u003cp\u003eIt can be seen that the local concentrations of CO and CO\u003csub\u003e2\u003c/sub\u003e around the catalyst are much higher after the modification by TfCOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef and S20). Additionally, the coverage of adsorbed CO (*CO) varies from 0.06 to 0.28 after adopting TfCOF layer, which shows 4.7 times promotion. This high coverage of *CO provides sufficient *CO for further reduction, which accounts for the higher FE\u003csub\u003eC2+\u003c/sub\u003e on TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO than that on In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO. The addition of such TfCOF also facilitates the coverage of *CO\u003csub\u003e2\u003c/sub\u003e, swinging from 0.22 to 0.31, which provides more carbon sources for CO\u003csub\u003e2\u003c/sub\u003e electrolysis on the catalytic sites.\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e The simulated results reveal that the existence of TfCOF layer could highly increase the coverage and localized concentration of CO and CO\u003csub\u003e2\u003c/sub\u003e.\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e,\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e The enrichment of these species around active sites can realize the further reduction reactions toward valuable C\u003csub\u003e2+\u003c/sub\u003e products.\u003c/p\u003e \u003cp\u003eBesides Multiphysics numerical simulation, the calculated CO\u003csub\u003e2\u003c/sub\u003e distribution probability using MD simulations is also shown in the middle inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. The red dots in the pores of TfCOF indicate the distribution possibilities of CO\u003csub\u003e2\u003c/sub\u003e accumulation region. High possibilities occur at the corners of nanopores in TfCOF, which reflect the special steric confinement effect on CO\u003csub\u003e2\u003c/sub\u003e by TfCOF.\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e TfCOF holds a large amount of CO\u003csub\u003e2\u003c/sub\u003e with ample adsorption sites (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e), ascribing to the high electrostatic interaction of CO\u003csub\u003e2\u003c/sub\u003e. Such TfCOF additive layer further breaks the solubility limitations from the low pCO\u003csub\u003e2\u003c/sub\u003e and promotes the local concentration of CO\u003csub\u003e2\u003c/sub\u003e for the reactions, which further improves the tolerance of lower inlet concentrations of CO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eHigh yield and stability with impure CO inlets\u003c/h3\u003e\n\u003cp\u003eThe synthesized TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO not only presents a high selectivity for C\u003csub\u003e2+\u003c/sub\u003e products but also exhibits improved current densities and yields. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, the total current density (J) for TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO exceeds 1400 mA/cm\u003csup\u003e2\u003c/sup\u003e at E\u003csub\u003ecell\u003c/sub\u003e of 3.8V with the inlet of pure CO\u003csub\u003e2\u003c/sub\u003e in the flow cell. FE\u003csub\u003eCtot\u003c/sub\u003e is also over 87% at such a high current, which suggests a pronounced catalytic activity and CO\u003csub\u003e2\u003c/sub\u003e utilization. With the inlets of dilute 90% and 80% CO\u003csub\u003e2\u003c/sub\u003e, the total current densities remain high at E\u003csub\u003ecell\u003c/sub\u003e of 3.8V, which are 1355 mA/cm\u003csup\u003e2\u003c/sup\u003e and 1245 mA/cm\u003csup\u003e2\u003c/sup\u003e, respectively. TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO also presents a total current density of 200 mA/cm\u003csup\u003e2\u003c/sup\u003e at E\u003csub\u003ecell\u003c/sub\u003e of 3.4V for the direct conversion of simulated flue gas with 15% CO\u003csub\u003e2\u003c/sub\u003e. Meanwhile, the maximum selectivity of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003e reaches 72.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2% at E\u003csub\u003ecell\u003c/sub\u003e of 3.4 V, with FE\u003csub\u003eC2+\u003c/sub\u003e of 83.5% and FE\u003csub\u003eCtot\u003c/sub\u003e of 95.5% when using the 80% CO\u003csub\u003e2\u003c/sub\u003e inlet. Likewise, we observe that TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO electrode delivers a superior partial current density toward C\u003csub\u003e2+\u003c/sub\u003e products (J\u003csub\u003eC2+\u003c/sub\u003e) of 837 mA/cm\u003csup\u003e2\u003c/sup\u003e at 3.4V with pure CO\u003csub\u003e2\u003c/sub\u003e inlet, while it remains 768 mA/cm\u003csup\u003e2\u003c/sup\u003e with 80% impure CO\u003csub\u003e2\u003c/sub\u003e inlet (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb), showing only 9% decrease in the production rate with 20% decrease of CO\u003csub\u003e2\u003c/sub\u003e concentration at such a high current density.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, we realize the total yield for carbon products of 3.45 mmol/h/cm\u003csup\u003e2\u003c/sup\u003e at E\u003csub\u003ecell\u003c/sub\u003e of 3.6 V with the impure inlet of 80% CO\u003csub\u003e2\u003c/sub\u003e, and the C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003e yield is 2.36 mmol/h/cm\u003csup\u003e2\u003c/sup\u003e. It is worth mentioning that the separations of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003e from CO and CH\u003csub\u003e4\u003c/sub\u003e are comparatively mature industrial processes, which makes the TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO catalyst a promising material for CO\u003csub\u003e2\u003c/sub\u003e electrolysis. The efficient conversion of dilute CO\u003csub\u003e2\u003c/sub\u003e is ascribed to the simultaneous steric confinement effect and electronic effects of TfCOF on CO\u003csub\u003e2\u003c/sub\u003e and CO as discussed previously. Specifically, dilute CO\u003csub\u003e2\u003c/sub\u003e molecules are concentrated by TfCOF with ample adsorption sites,\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e and the adsorption energies are revealed by the DFT simulations (Figures S21 and S22).\u003c/p\u003e \u003cp\u003eDifferent amounts of TfCOF additives are also conducted with weight ratios of 0.1, 0.2, and 0.3 relative to the In-Cu gel (Figure S23). The amount of TfCOF is critical to ensure the high yield of the C\u003csub\u003e2+\u003c/sub\u003e products and the optimized ratio of TfCOF is around 0.2. The morphologies of different additions of TfCOF remain similar to the fine particles after the \u003cem\u003ein-situ\u003c/em\u003e activations (Figures S24 and S25). The J\u003csub\u003eC2+\u003c/sub\u003e of 698 mA/cm\u003csup\u003e2\u003c/sup\u003e with 80% dilute CO\u003csub\u003e2\u003c/sub\u003e inlet is realized on the catalyst with TfCOF(0.3), showing around 10% reduction compared with that of TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO. On the other hand, TfCOF(0.1)-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO shows 18.5% decrease of J\u003csub\u003eC2+\u003c/sub\u003e compared with that of TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed and S26). The stability of TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO is also measured with 80% CO\u003csub\u003e2\u003c/sub\u003e inlet. A current density of 760 mA/cm\u003csup\u003e2\u003c/sup\u003e is well maintained for 96 hours at E\u003csub\u003ecell\u003c/sub\u003e of 3.4V with FE\u003csub\u003eCtot\u003c/sub\u003e over 95% and FE\u003csub\u003eC2+\u003c/sub\u003e over 80% during continuous operation (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee and S27). The high yield of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003e is around 2.1 mmol/h/cm\u003csup\u003e2\u003c/sup\u003e, which is about 200 mmol after a four-day electrochemical CO\u003csub\u003e2\u003c/sub\u003e upgrade with 1 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e electrode. Such high yield and stability performance with 80% CO\u003csub\u003e2\u003c/sub\u003e inlet surpasses lots of reports with pure CO\u003csub\u003e2\u003c/sub\u003e inlet (Table S2).\u003c/p\u003e \u003cp\u003eWith the target of potential industrial applications, an electrolyzer stack is further assembled as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef, which consistents of four 10\u0026times;10 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e modules connected in series.\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e The maximum production rate of C\u003csub\u003e2+\u003c/sub\u003e products is over 770 mmol/h with an inlet of 80% CO\u003csub\u003e2\u003c/sub\u003e, corresponding to a total current of 81.7 A (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg). With the utilization of pure CO\u003csub\u003e2\u003c/sub\u003e inlet, the maximum total current of 95.9 A is achieved with the C\u003csub\u003e2+\u003c/sub\u003e production rate of around 800 mmol/h. Therefore, such a dual strategy of mass transport regulations and reaction kinetics promotions is scalable for potential industrial-level applications.\u003c/p\u003e\n\u003ch3\u003eUnderling mechanism\u003c/h3\u003e\n\u003cp\u003eTo evaluate the catalytic site of a single atomic In dopant combined with monovalent Cu(I) on CO formation, we firstly set up three surface models by the periodic DFT computations: Cu (111), In\u003csub\u003e1\u003c/sub\u003e@Cu (111) and In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO (111) as shown in Figures S28, S29 and S30, respectively. The reaction energies are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea for the pathways of CO production, in which the initial step of electron-proton transfer to form COOH* is the rate-limiting step.\u003csup\u003e\u003cspan additionalcitationids=\"CR48\" citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e Among the three surface models, In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO (111) shows the lowest Gibbs free energy for COOH* formation, indicating the promoting effect from single atomic In doping in Cu\u003csub\u003e2\u003c/sub\u003eO.\u003c/p\u003e \u003cp\u003eTo better understand the intrinsic mechanism for the enhanced activity for CO formation on In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO, the projected density of states (PDOS) of the C atom in the key COOH* adsorbate and corresponding surface Cu atoms in Cu(111), In\u003csub\u003e1\u003c/sub\u003e@Cu (111) and In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO (111) were calculated. The electron density and the wave function are decomposed to reveal the atomic orbital contributions.\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e,\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, the harmonic overlaps between the C-2p and Cu-3d states on In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO are the largest among all the models, which shows the strong interaction between the C and Cu atoms.\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eImportantly, compared with the d-band of Cu, incorporating In into a Cu\u003csub\u003e2\u003c/sub\u003eO modifies the broadness of the Cu d-band below the Fermi level (E\u003csub\u003ef\u003c/sub\u003e).\u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e In contrast, the harmonic overlaps between the C-2p and Cu-3d states are the smallest for In\u003csub\u003e1\u003c/sub\u003e@Cu (Figure S29), which is consistent with the highest reaction energy toward CO (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea) and the reported higher selectivity for formate instead of CO.\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e Hence, such a strategic combination of foreign In atomic In atoms doped in oxidized monovalent Cu(I) leads to the highest selectivity towards CO by holding specific electronics and features that are rather different from their counterpart metals. The proposed mechanism is also depicted by the schematic of Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec. Incorporating single atomic In into Cu\u003csub\u003e2\u003c/sub\u003eO results in a larger energy split of hybrid orbitals when incorporated with the *COOH.\u003csup\u003e32,53\u003c/sup\u003e Such modifications drive the antibonding level near to Femi level and decrease the energy barrier of charge transfer,\u003csup\u003e\u003cspan additionalcitationids=\"CR54\" citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e enabling a stronger extent of Cu-COOH orbital mixing.\u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eTfCOF possesses unique 3D porous structures, which can availably promote the mass transport and enrichments of CO and CO\u003csub\u003e2\u003c/sub\u003e near the catalyst surface. The electrostatic potential of the F atom becomes larger after interacting with CO (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed), which is attributed to the electron density transfer from F atom of TfCOF to C atom in CO. Hence, the negative regions in the molecular electrostatic potential maps extend to the oxygen atom of CO. The distance of C and F atoms is found to be 2.25 \u0026Aring; (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee and S32). Such C∙∙∙F interactions make the TfCOF become CO diffusion channels near the catalytic surface. As revealed, the strong electrostatic interaction between CO and TfCOF is further confirmed by the radial distribution function (RDF) and coordination numbers (CN) around TfCOF. The CNs of CO near TfCOF are much higher than that between CO\u003csub\u003e2\u003c/sub\u003e and TfCOF, indicating a larger number density of CO.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe distributions of CO and CO\u003csub\u003e2\u003c/sub\u003e are shown in the lattice for the MD simulation (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee, f and S33). The random TfCOF molecules are gathering around 5 nm away from the catalytic surface. This assembled structure is likely causing the existence of multiple layers of CO between the TfCOF layer and catalytic surface due to different electrostatic interactions, which results in the analogous normal density distribution of it along the Z-direction (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef). The inner layers of CO are enriched by TfCOF layer ascribed to the stronger van der Waals\u0026rsquo; interactions, while the outer layers of CO with moderate interactions are close to the catalytic sites (around 1 nm in the simulation lattice) and can be released from TfCOF to the catalytic surface for further reduction. This is the proposed mechanism for the simultaneous capturing and releasing of CO and CO\u003csub\u003e2\u003c/sub\u003e molecules by TfCOF with the C\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\cdots\\:\\)\u003c/span\u003e\u003c/span\u003eF electronic effect and steric effect, respectively.\u003c/p\u003e \u003cp\u003eSuch mass transport regulation effects are further depicted by the experimental confirmations with \u003cem\u003ein-situ\u003c/em\u003e electrochemical attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy to monitor the intermediates of In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO/COF at various potentials (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eh,j).\u003csup\u003e\u003cspan additionalcitationids=\"CR57\" citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e The important intermediates for the generation of C\u003csub\u003e2+\u003c/sub\u003e products were observed, including the CO* (at 2065 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e),\u003csup\u003e\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e and CO bound to the copper surface (at 1967, 1919 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e).\u003csup\u003e\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e The intensity of these peaks increased with the cathode potentials, indicating the high coverage of *CO species. The enhancement in *CO adsorption promoted the subsequent C\u0026minus;C coupling. Moreover, the characteristic peak at 1541, 1423, and 1396 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e corresponds to COOH* and *COO\u003csup\u003e-\u003c/sup\u003e (two O coordinated), respectively.\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e,\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e The *H\u003csub\u003e2\u003c/sub\u003eO peak is observed at 1649 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ei).\u003csup\u003e\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e The peaks at 1743, 1554, and 1519 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e are attributed to CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e species.\u003csup\u003e\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e The pronounced peak at 2344 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e is assigned to the CO\u003csub\u003e2\u003c/sub\u003e* (Figure S34), demonstrating the adsorption of CO\u003csub\u003e2\u003c/sub\u003e on TfCOF-In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO. These findings further demonstrate the effective regulations of CO and CO\u003csub\u003e2\u003c/sub\u003e species near the catalytic sites by the TfCOF.\u003c/p\u003e\n\u003ch3\u003eDiscussion\u003c/h3\u003e\n\u003cp\u003eEfficient electrolysis of dilute CO\u003csub\u003e2\u003c/sub\u003e (70\u0026ndash;90% and 15%) toward C\u003csub\u003e2+\u003c/sub\u003e products is realized through employing combined TfCOF and single-atom active sites of In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO. Supported by the multi-scale simulation and experimental characterizations, TfCOF is proved to be the local diffusion channels of CO\u003csub\u003e2\u003c/sub\u003e/CO and optimized amounts of TfCOF provide the proper concentrating of these molecules. In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO plays the role of promoting the production of CO key intermediate for C-C coupling. Hence, the maximum FE\u003csub\u003eC2+\u003c/sub\u003e of 83.5% and FE\u003csub\u003eCtot\u003c/sub\u003e of 95.5% are obtained at E\u003csub\u003ecell\u003c/sub\u003e of 3.4 V when using the 80% CO\u003csub\u003e2\u003c/sub\u003e inlet. The high C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003e yield of 2.1 mmol/h/cm\u003csup\u003e2\u003c/sup\u003e is delivered for four days with an impure CO\u003csub\u003e2\u003c/sub\u003e inlet. Such a dual strategy is further scalable to the electrolyzer stack with a high yield of C\u003csub\u003e2+\u003c/sub\u003e products of over 770 mmol/h. The coupled design strategy of mass transport regulation and reaction kinetics promotion lays the foundation for the practical developments of dilute CO\u003csub\u003e2\u003c/sub\u003e electrolysis.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003ch2\u003eSupplementary materials\u003c/h2\u003e \u003cp\u003eSupplementary Information accompanies this paper at XXX.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eB. R., X. Z., and L. Y. contributed equally to this work. The authors appreciate Dr. Graham King and Dr. Al Rahemtulla for the synchrotron WAXS on BXDS-WHE beamline at the Canadian Light Source (CLS). The authors thank Dr. Ning Chen, Dr. Roman Chernikov, and Dr. Emilio Heredia for XAS characterizations on HXMA and BioXAS beamlines at CLS. The authors also acknowledge the technical support for quasi \u003cem\u003ein-situ\u003c/em\u003e NAP-XPS characterizations from Nano-X from Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (SINANO). This work is financially supported by the National Natural Science Foundation of China (22472049) and Changsha Natural Science Foundation (kq2402051). The authors gratefully acknowledge the computational resources provided by the National Supercomputer Center in Guangzhou.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWang G et al (2021) Electrocatalysis for CO\u003csub\u003e2\u003c/sub\u003e conversion: from fundamentals to value-added products. Chem Soc Rev 50:4993\u0026ndash;5061\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWen G et al (2023) Bridging Trans-Scale Electrode Engineering for Mass CO\u003csub\u003e2\u003c/sub\u003e Electrolysis. 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ACS Catal 13:2374\u0026ndash;2385\u003c/span\u003e\u003c/li\u003e \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":"electrocatalysis, dilute CO2, mass transport channels, steric confinement, local environment","lastPublishedDoi":"10.21203/rs.3.rs-5984755/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5984755/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eElectrocatalytic upgrade of CO\u003csub\u003e2\u003c/sub\u003e offers a promising approach for the recycling of global CO\u003csub\u003e2\u003c/sub\u003e emissions, facilitating the achievement of carbon neutrality. Nevertheless, the purification of CO\u003csub\u003e2\u003c/sub\u003e is costly and direct utilization of practical dilute CO\u003csub\u003e2\u003c/sub\u003e is urgently important yet rather difficult. The main challenge for continuous electrocatalysis of dilute CO\u003csub\u003e2\u003c/sub\u003e is to balance the reaction kinetics and mass transport of CO\u003csub\u003e2\u003c/sub\u003e to the catalytic sites, which is hindered by the large mass transport resistance. Herein, we propose coordinating the local environment and active catalyst by constructing covalent organic frameworks (COF) on single-atomic In-doped Cu\u003csub\u003e2\u003c/sub\u003eO (In\u003csub\u003e1\u003c/sub\u003e@Cu\u003csub\u003e2\u003c/sub\u003eO) for a high tolerance of CO\u003csub\u003e2\u003c/sub\u003e inlet concentrations (15\u0026ndash;100%). The optimized amounts of COF functionalized by the trifluoromethyl group act as the local CO\u003csub\u003e2\u003c/sub\u003e/CO diffusion channels via steric confinement effects and C∙∙∙F electronic effects. Besides, the formation of key intermediates for C\u003csub\u003e2+\u003c/sub\u003e products is greatly facilitated by the promoted COOH adsorption. Hence, a total current of 81.7 A is realized in a 4\u0026times;100 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e electrolyzer stack with over 770 mmol/h C\u003csub\u003e2+\u003c/sub\u003e products at an inlet of dilute CO\u003csub\u003e2\u003c/sub\u003e. Such new electrode architecture sheds light on the high-yield electrochemical conversion using dilute CO\u003csub\u003e2\u003c/sub\u003e at the potential industrial scale for practical applications.\u003c/p\u003e","manuscriptTitle":"Localized mass transport channels for electro-upgrade of dilute CO2 toward high-yield C2+ products","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-02-19 14:38:27","doi":"10.21203/rs.3.rs-5984755/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":"42ee687c-2873-490f-bc47-ac4fbfc6972c","owner":[],"postedDate":"February 19th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":44575852,"name":"Physical sciences/Chemistry/Electrochemistry/Electrocatalysis"},{"id":44575853,"name":"Earth and environmental sciences/Environmental sciences/Environmental chemistry/Atmospheric chemistry"}],"tags":[],"updatedAt":"2025-09-26T07:08:51+00:00","versionOfRecord":{"articleIdentity":"rs-5984755","link":"https://doi.org/10.1038/s41467-025-63178-8","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-09-25 04:00:00","publishedOnDateReadable":"September 25th, 2025"},"versionCreatedAt":"2025-02-19 14:38:27","video":"","vorDoi":"10.1038/s41467-025-63178-8","vorDoiUrl":"https://doi.org/10.1038/s41467-025-63178-8","workflowStages":[]},"version":"v1","identity":"rs-5984755","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5984755","identity":"rs-5984755","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}