paper12-afm-2025-cu-cu2o-quinoline-hydrogenation

Electrochemical Hydrogenation of Quinoline Enabled by Cu0‐Cu+ Dual Sites Coupled with Efficient Biomass Valorization in Aqueous Solution

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RESEARCH ARTICLE www.afm-journal.de Electrochemical Hydrogenation of Quinoline Enabled by Cu0-Cu+ Dual Sites Coupled with Efficient Biomass Valorization in Aqueous Solution Yaoling Pan, Zhenyu Bao, Chen Wang, Zhengyu Wang, Penghui Xu, Xinwen Bai, Xiaowei Shi, Huajun Zheng, Hong-En Wang,* and Lingxia Zheng* The hydrogenation of nitrogen-containing heterocyclic precursors in aqueous medium is challenging, especially at ambient temperature and pressure. Elec- trochemical hydrogenation (ECH) of quinoline to 1,2,3,4-tetrahydroquinoline (THQ) at mild conditions using water as the hydrogen source is demonstrated with splendid activity on a Cu-based nonprecicous catalyst. The yield of THQ is up to ≈100% with ≈100% selectivity at −1.275 V vs Hg/HgO. The real active sites and key intermediates are deciphered, where the Lewis acid-base sites on the heterointerface of Cu/Cu2O are beneficial to the quinoline adsorption in a dual-site coordination configuration and water dissociation to afford H*. The presence of Cu0 plays a vital role in inhibiting the binding of H*, which ensures good Faradaic efficiency. In addition, a novel co-production system by coupling benzyl alcohol oxidation at the anode is established, achieving dual benefits in both energy utilization efficiency and economic benefits.

1. Introduction Among the heterocyclic compounds, which account for ≈60% of all drug substances, nitrogen-containing heterocycles are the most important compound class in the pharmaceutical and pesticide industries. In particular, the tetrahydroquinoline (THQ) ring system is a very common structural motif found in Y. Pan, Z. Bao, C. Wang, Z. Wang, P. Xu, X. Bai, X. Shi, H. Zheng, L. Zheng Department of Applied Chemistry Petroleum and Chemical Industry Key Laboratory of Organic Electrochemical Synthesis Zhejiang University of Technology Hangzhou 310014, P. R. China E-mail: lxzheng@zjut.edu.cn H.-E.Wang Collegeof Physics andElectronics Information Yunnan Key Laboratory of OptoelectronicInformation Technology Key Laboratory of AdvancedTechnique& Preparation forRenewableEnergy Materials Ministry of Education Yunnan Normal University Kunming 650500, P.R.China E-mail: hongen.wang@ynnu.edu.cn The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.202414120 DOI: 10.1002/adfm.202414120 massive biologically active natural prod- ucts and pharmacologically meaningful therapeutic drugs.[1] Thus, developing new methods for synthesizing THQ rings continues to be a very active research field.[1b,2] Various reductive catalytic proto- cols have been explored by heterogeneous catalysts to synthesize THQ, such as transfer hydrogenation using ammonia borane (NH3·BH3)[3] or formic acid)[4] as a hydrogen source, photocatalytic hydrogenation[5] and sequential dearoma- tive hydroboration and hydrogenation.[6] To date, the traditional catalytic hydrogena- tion using transitional metals requires molecular hydrogen as the reducing agent (6–20 bar of H2) at high temperatures (generally ≥100 °C, Scheme 1a).[1a,7] Al- though impressive achievements have been accomplished, the utilization of high-pressure flammable H2 leads to special apparatus, cautious operation, and additional fuel energy input. Moreover, the thermocatalytic process might lead to the production of 5,6,7,8-tetrahydroquinoline and decahydro- quinoline byproducts. Therefore, it is of paramount importance to establish selective hydrogenation of quinoline with a sustain- able, safe, and convenient hydrogen source. Electrochemical hydrogenation (ECH) has inspired this field given the advantages of ambient reaction conditions, easily controllable selectivity, and employment of sustainable electrical energy by directly utilizing water as the hydrogen source.[8] However, it still faces technical challenges because of the diffi- culty in the activation of quinoline and water enabled by suitable electrocatalysts. Recently, Zhang et al.[9] have made significant progress in the ECH of quinoline with ca. 99% selectivity in 1 m KOH over a Co-F catalyst (Scheme 1b). However, the productivity of THQ was unsatisfactory as well as the undesired Faradaic efficiency (FE) caused by the dominant competing hydrogen evolution reaction (HER). Regarding this, it is imperative to develop nonprecious highly efficient electrocatalysts with high yield and FE. On the other hand, the ECH of quinoline occurs at the cathode as a half-reaction, and the sluggish anodic oxygen evolution reaction (OER, 1.23 V vs RHE) severely limits the overall electrolytic efficiency with the generation of low-value O2 product. It is advantageous to establish a co-electrolytic system in an aqueous media by coupling with anodic biomass upgrading with lower energy input and higher value-added products. Adv. Funct. Mater. 2025, 35, 2414120 © 2024 Wiley-VCH GmbH 2414120 (1 of 10)

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www.advancedsciencenews.com www.afm-journal.de Scheme 1. Comparison between the a) traditional method and b) electrochemical method of the conversion of quinoline to THQ. c) The proposed co-production system in this work over Cu-based electrodes. Herein, an array of CuNWs catalysts with mixed Cu0 and Cu+ dual sites (denoted as Cu-LR, Scheme 1c) is prepared and utilized first for the ECH of quinoline with outstanding performance. Quasi-operando Auger electron spectroscopy and in situ electro- chemical impedance spectroscopy are performed to unveil the structure-activity-potential relationship. The Lewis acid-base sites on the Cu/Cu2O heterointerface enable a mixed N and C dual ad- sorption configuration of quinoline and promote the water dis- sociation to afford H*. The presence of Cu0 plays a vital role in inhibiting the binding of H*, which ensures good FE. Moreover, the two-electrode electrolyzer (Cu-LR||CuO) is successfully estab- lished by coupling ECH of quinoline and benzyl alcohol oxidation reaction (BAOR) to produce THQ and benzoic acid simultane- ously, which demonstrates boosted energy utilization efficiency in an economical manner. 2. Results and Discussion 2.1. Morphology and Microstructure of Catalysts The preparation route of three different Cu-based catalysts is schematically illustrated (Figure 1a) and the corresponding scan- ning electron microscopy (SEM) images have been displayed in Figure 1b–f. Generally, the 1D nanowire morphology is well- maintained after thermal calcination and electrochemical reduc- tion, in contrast to the Cu(OH)2 precursor (Figure S1, Support- ing Information) with very smooth surface and CuO nanowires (NWs) with rough surface (Figure S2, Supporting Information). The nanowires become even rough with sporadic particles on top for Cu-LR (Figure 1b,c) when using a low cathodic potential (−1 V) to reduce CuO to Cu. The other two counterparts reduced at different conditions turn out to exhibit varied morphologies. For Cu-HR (Figure 1d,e) generated by reducing CuO at a higher ca- thodic potential (−2 V), many fissures are readily observed in the nanowires and the surface remains clean. While much coarser nanowires are obtained which are made of irregular large and dense nanosized grains for Cu-DR (Figure 1f,g) when reducing Cu(OH)2 precursor at −1 V. Besides the distinct difference in mi- crostructures, transmission electron microscopy (TEM) results disclose the presence of Cu/Cu2O heterostructures in the three catalysts (Figure 2b,e,i), which is very likely to be the active phase for electrocatalysis. Small nanoparticles are assembled into 1D wire shape with readily observed pores in Cu-LR (Figure 2a). The lattice spacings of 0.245 and 0.207 nm correspond to the (111) of Cu2O and (111) of Cu (Figure 2b), respectively. The se- lected area electron diffraction (SAED) graph (Figure 2c) presents Adv. Funct. Mater. 2025, 35, 2414120 © 2024 Wiley-VCH GmbH 2414120 (2 of 10) 16163028, 2025, 4, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202414120 by Zhejiang University Of Technology, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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www.advancedsciencenews.com www.afm-journal.de Figure 1. a) Schematic illustration of the synthetic routes for three catalysts. SEM images of b,c) Cu-LR, d,e) Cu-HR, and f,g) Cu-DR. Figure 2. a,d) TEM, b,e) HRTEM images, and c,f) SAED of Cu-LR and Cu-HR, respectively. g,h) TEM and i) HRTEM images of Cu-DR. Adv. Funct. Mater. 2025, 35, 2414120 © 2024 Wiley-VCH GmbH 2414120 (3 of 10) 16163028, 2025, 4, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202414120 by Zhejiang University Of Technology, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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www.advancedsciencenews.com www.afm-journal.de Figure 3. a) XRD patterns. b) Cu 2p XPS spectra. c) Cu LMM Auger electron spectra and d) O 1s XPS spectra of Cu-HR, Cu-LR and Cu-DR. a series of concentric rings, manifesting the polycrystalline na- ture of Cu-LR and the coexistence of Cu+ and Cu0. A clean sur- face without pores is observed in Cu-DR (Figure 2d). The lattice fringes (Figure 2e) along with the two concentric rings verify the co-existence of Cu and Cu2O (Figure 2f). For Cu-DR, irregular nanoparticles are formed into 1D morphology but with much thicker wires (Figure 2g,h). The results demonstrate that differ- ent microstructures can be obtained on Cu (hydro) oxide precur- sors via a facile electrochemical reduction process. X-ray diffraction (XRD) patterns are examined to reveal the compositions of the materials. Five diffraction peaks in Cu(OH)2 precursor match well with Cu(OH)2 (PDF # 72–0140) (Figure S3, Supporting Information).[10] While both CuO and Cu2O can be found in CuO precursor. The diffraction peaks at 2𝜃of 35.6° and 38.8° correspond to the (−111) and (200) of CuO (PDF # 80– 1916),[11] and the peak at 36.7° belongs to (111) plane of Cu2O (PDF # 78–2076).[12] For the three electrochemical reduced Cu catalysts (Figure 3a), the (111) facet of Cu2O (2𝜃= 36.7°) can be found for both Cu-HR and Cu-LR but with different peak in- tensities while (110) facet is dominant in Cu-DR (2𝜃= 29.4°). It is worth noticing that the oxide and hydroxide precursors not only affect the microstructures of the reduced catalysts but also the exposed facets, which exert great influence on the catalytic activity toward ECH of quinoline.[13] In the Cu 2p X-ray photo- electron spectroscopy (XPS, Figure 3b), the peaks at 952.27 and 932.47 eV pertain to Cu 2p3/2 and Cu 2p1/2, respectively. The miss- ing of obvious satellite peaks suggests the absence of CuO. To further distinguish Cu+ or Cu0 species,[14] Cu LMM Auger spec- tra were performed and the results are presented in Figure 3c. The peak at 570.0 eV is assigned to Cu+ (Cu2O), while Cu0 auger peak is at 568.1 eV and the other two peaks at ≈573.6 and 565.8 eV represent an additional transition.[15] Impressively, the contents of Cu0 follow the order: Cu-LR<Cu-HR<Cu-DR. And Cu-LR en- dows the highest level of Cu+ (48.82%) and the lowest level of Cu0 (19.95%). The O 1s spectra can be deconvoluted into three peaks (Figure 3d). The one at 530.4 eV corresponds to the lattice oxygen bonded with metal (Olatt, Cu–O), and the peak at 531.4 eV is at- tributed to the oxygen vacancies (Ov), while the peak at 531.9 eV is attributed to the adsorbed oxygen on the surface (Oads). The much higher level of Olatt and lower amount of OV further confirm the largest content of Cu2O, consistent with the Cu LLM spectra. 2.2. ECH of Quinoline Given the merits of mild reaction condition, renewable electric- ity as the driving force, and water as the hydrogen source in- stead of hydrogen molecule, the ECH of quinoline (Figure 4a) to value-added THQ was performed at room temperature and ambient condition. Upon addition of 10 mm quinoline, the cur- rent densities increase obviously in comparison with the Lin- ear sweep voltammetry (LSV) curve tested in 1 m KOH with- out quinoline (dashed lines, Figure 4b), which verifies the fa- vorable reaction kinetics of ECH in contrast to HER, the dom- inant competing reaction at the cathode. The current densi- ties at varied potentials of three catalysts follow the order: Cu- LR>Cu-HR>Cu-DR, indicating the best ECH activity of Cu-LR (Figure 4c). It reaches −65.4 mA cm−2 at −1.275 V vs Hg/HgO, ≈3.6 times that of Cu-DR (−18.1 mA cm−2), and ≈3.6 times that of Cu-HR (−44.5 mA cm−2) (Table S1, Supporting Information). The Tafel slopes have been plotted to examine the kinetic pro- cesses. As shown in Figure 4d, the Tafel slope values of the three Adv. Funct. Mater. 2025, 35, 2414120 © 2024 Wiley-VCH GmbH 2414120 (4 of 10) 16163028, 2025, 4, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202414120 by Zhejiang University Of Technology, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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www.advancedsciencenews.com www.afm-journal.de Figure 4. a) Scheme of ECH of quinoline to THQ. b) LSV curves, c) current density obtained at varied potentials, d) Tafel plots, e) conversion of quinoline and FE obtained after electrolysis at −1.275 V vs Hg/HgO. f) The ECH performance comparison of the three catalysts. g) The fitted double- layer capacitance (Cdl) results. h) The electrolysis results at different potentials over Cu-LR. Potential-dependent Bode phase plots of Cu-LR in i) KOH and j) KOH+ quinoline. catalysts for H2 evolution are all larger than 120 mV dec−1, in- dicating that the Volmer step is the rate-determining step in HER.[16] Cu-LR with the smallest Tafel slope endows the highest H* coverage. Thus, the ECH of quinoline, which consumes pro- tons from H* would be more favorable kinetically on Cu-LR. As a result, the decreased Tafel slope (from 146.4 to 99.7 mV dec−1) is obtained in the order of Cu-LR <Cu-HR< Cu-DR for ECH. The results suggest that the ECH of quinoline with water as hydro- gen donor is kinetically favorable on Cu-LR. Electrolysis at con- stant potentials was performed to evaluate the ECH performance and the quantity of reduction products was examined by high- performance liquid chromatography (HPLC) using an external reference method (Figure S4, Supporting Information). Upon electrolysis at −1.275 V vs Hg/HgO for 1 h, the Faradaic effi- ciency (FE) is calculated to be 51.9%, 43.2%, and 6.3% for Cu-LR, Cu-HR, and Cu-DR, respectively (Figure 4e), along with the con- version (Conv.) of quinoline to be ≈100%, 77.2%, and 7.5% (Table S2, Supporting Information). Note that there is no other byprod- uct for all the catalysts and the THQ selectivity (Sel.) is ≈100%. The comparison of overall ECH performance including current density at −1.275 V vs Hg/HgO, Conv. of quinoline, yield, and Sel. of THQ and FE is disclosed in the Radar graph (Figure 4f), definitely unveiling the outstanding ECH activity of Cu-LR. The electrochemical active surface area (ECSA) is evaluated by fitting the double-layer capacitance (Cdl, Figure 4g) based on the cyclic voltammetry (CV) curves obtained at varied scanning rates (Figure S5, Supporting Information). Cu-LR undoubtedly en- dows the largest Cdl and ECSA, manifesting the numerous active sites accessible for quinoline and water adsorption. Accordingly, the ECSA-normalized LSV curves (Figure S6, Supporting Infor- mation) have been plotted and it suggested that the superior ECH activity is partially originated from the great ECSA. The much smaller impedance resistances of Cu-LR (intrinsic resistance Rs of 0.65 Ω and charge transfer resistance Rct of 0.018 Ω) (Figure S7 and Table S1, Supporting Information) suggest outstanding charge-transfer kinetics toward quinoline reduction, also con- tributing to high ECH activity. Five different potentials were used for electrolysis. Increasing the cathodic potential from −1.225 to −1.275 V vs Hg/HgO, the Conv. of quinoline increases from 58.8% to ≈100% along with FE increasing from 40.9% to 51.9% (Figure 4h). Further increasing the cathodic potential, the Conv. remains ≈100% but FE decreases. The optimal electrolytic poten- tial is found to be −1.275 V vs Hg/HgO. The results suggest that the conversion and FE of quinoline reduction is highly potential dependent. Potential-dependent electrochemical impedance spectra (EIS) were performed to examine the reaction dynamics to disclose the potential-structure-activity relationship. With the cathodic potential increasing from −1.125 to −1.325 V vs Hg/HgO, the decrease in the numerical value of Rct indicates that the charge Adv. Funct. Mater. 2025, 35, 2414120 © 2024 Wiley-VCH GmbH 2414120 (5 of 10) 16163028, 2025, 4, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202414120 by Zhejiang University Of Technology, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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www.advancedsciencenews.com www.afm-journal.de Figure 5. In situ FTIR spectra a) during ECH and b) during HER at different potentials over Cu-LR. c) Cu LMM spectra after electrolysis at different potentials. d) LSV curves with and without KSCN. e) LSV curves in 1 m K2CO3 with H2O or D2O as solvent. f) EPR trapping for hydrogen () and carbon (#) radicals. g) The proposed reaction mechanism. transfer becomes more facilitated for both HER (Figure 4i) and ECH (Figure 4j). The amplitude of the phase angle for HER is significantly larger than that for ECH at the same potential, resulting in higher Rct (Tables S3 and S4, Supporting Informa- tion) and lower charge diffusion capacity, which thereby verifies more superior charge transfer ability for ECH. In situ, Fourier Transform infrared (FTIR) spectroscopy was performed in 0.5 m Na2SO4 upon increasing the cathodic potential from −0.9 to −1.5 V vs Hg/HgO. The peaks at 1250,1500, 1600,1680, and 3020 cm−1 can be assigned to quinoline (Figure 5a).[17] In addi- tion, the peak at 1360 cm−1 can be attributed to the stretching vibration of C-N derived from THQ.[18] One broad peak appears at 3440 cm−1 is attributed to the stretching of O-H and the other peak at 1630 cm−1 is attributed to the bending of O-H, along with the detection of OH (3660 cm−1) species, suggesting the adsorption/activation and conversion of H2O,[19] which is also observed during HER (Figure 5b). 2.3. Active Sites and Key Intermediates Identification To figure out the real active sites, quasi-operando Auger electron spectroscopy (AES) was conducted on Cu-LR after electrolysis at different potentials, and the results are displayed in Figure 5c. Compared to that of fresh Cu-LR (48.82%, Figure 3c), the con- tent of Cu+ decreases, as it can be reduced to Cu0 during ECH in the strong reduction environment. The more negative the po- tential, the lower the Cu+ content, except that at −1.325 V vs Hg/HgO. The content of Cu+ appears to be the lowest at the optimal electrolytic potential −1.275 V vs Hg/HgO (Figure S8, Adv. Funct. Mater. 2025, 35, 2414120 © 2024 Wiley-VCH GmbH 2414120 (6 of 10) 16163028, 2025, 4, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202414120 by Zhejiang University Of Technology, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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www.advancedsciencenews.com www.afm-journal.de Supporting Information). During ECH, the Cu+ on the surface of the catalyst would be reduced to Cu0, while the simultane- ously generated hydroxyl radicals (OH*) from water dissociation with strong oxidability[20] would oxidize Cu0 to Cu+, forming a competitive reaction between the two. Thereby, the “seesaw ef- fect” between the reduction and oxidation of Cu species results in the content change of Cu+ species and it is highly possible that Cu+ is the actual active sites in the ECH of quinoline. To verify it, the electrolysis at −1.275 V vs Hg/HgO was conducted for five runs, and slight decrease of conversion (100%–86.2%) and FE (51.9%–44.3%) can be obtained but with THQ selectivity of ≈100% (Figure S9, Supporting Information). Detailed charac- terizations were performed on post Cu-LR to explore the slight performance deterioration. TEM and HRTEM images (Figure S10, Supporting Information) disclose the formation of an amor- phous layer outside the nanowires on the post Cu-LR, signifying the phase reconstruction. Noticeably, XRD patterns (Figure S11, Supporting Information) reveal that the intensity of the Cu2O (111) diffraction peak in the spent sample becomes very weak compared to that of fresh Cu-LR. Consistently, the decreased con- tent in Olatt level (O 1s XPS spectrum, Figure S12, Supporting Information) and the increase in OV level also confirm the de- creased content of Cu2O. The results confirm that the Cu2O (111) is more active for quinoline reduction. As reported,[16b] SCN−can adsorb Cu+ by forming an complex of SCN−—Cu+, which can be used to poison the Cu2O species. As shown in Figure 5d, the onset cathodic potential increases and the current density dramatically decreases upon the addition of KSCN, indicating a significant deterioration in the ECH perfor- mance. Further electrolysis at −1.275 and −1.325 V vs Hg/HgO, no THQ product can be found (Figure S13, Supporting Informa- tion), revealing that the participation of Cu+ in the ECH of quino- line is essential. On the other hand, LSV curves and electrolysis at −1.275 V vs Hg/HgO were performed (Figure S14, Supporting Information) on Cu foam, and THQ was also hardly found, which manifests that bulk copper (Cu0) exhibits negligible ECH activ- ity. In contrast, the Cu2O delivers only 16.0% conversion upon electrolysis, much lower than Cu-LR (Figure S15, Supporting In- formation), revealing the significant role of Cu0. It can be safe to deduce that both Cu0 and Cu+ are responsible for the superior ECH performance. Moreover, tertiary butanol (t-BuOH), a commonly used scav- enger for hydrogen radicals,[9] was added to the system to exam- ine the key role of in situ formed H* via water dissociation. As shown in Figure S16 (Supporting Information), the current den- sities are severely impeded and the yield of THQ decreases from 100% to 47.5%, manifesting the necessity of H* intermediate.[21] The kinetic isotope effect (KIE) of H2O/D2O results (Figure 5e) show that the current densities reduce significantly when replac- ing H2O by D2O in the K2CO3 solution with and without quino- line, further confirming the crucial role of H* from water dis- sociation. In situ electron paramagnetic resonance (EPR) spec- tra were performed by using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the radical spin-trapping reagent (Figure 5f). No sig- nals appear in the absence of quinoline and electricity. A com- plex nine-fold signal appears (labeled by ), which is a direct sign of hydrogen radicals from water splitting (Figure S17, Support- ing Information) with electricity.[22] Impressively, a new six-fold signal emerges with electricity and quinoline attributing to C radical (Figure S18, Supporting Information).[23] The decreased intensity of H signals indicates the consumption due to THQ formation.[24] Collectively, a possible reaction pathway is pro- posed (Figure 5g). First, water molecules are adsorbed onto the catalyst surface and dissociated to produce H*.[25] Then quino- line molecules are also adsorbed through Cu+-Cu0 dual site con- figurations to produce C*. Finally, the H* is transfer to couple with C* accompanied by electron transfer to produce THQ, which is then desorbed from the catalyst to refresh the active sites for the next reaction cycle. To further evaluate the universality of Cu- LR catalyst, quinoline substrates, and other N-heterocycles were electrolyzed at −1.275 V for 1 h, and the conversion results have been shown in Table S5 (Supporting Information). Overall, Cu- LR exhibits catalytic activity toward quinoline compounds. The electronic and steric hindrance effects caused by different nitro- gen substitution positions and numbers affect slightly the ECH activity of Cu-LR. 2.4. Theoretical Exploration of the Structure-Activity Relationship First-principle density functional theory (DFT) calculations were performed to examine the structure-activity relationship. For Cu (111), the adsorption of quinoline (Figure 6a) and THQ (Figure 6c) is mainly governed by van der Waals forces, result- ing in the weakest Eads values (−1.80 and −2.64 eV, respectively, Figure 6j). This dominance of van der Waals forces is evidenced by the differential charge distribution in Figure 6b. On the Cu2O (111) surface, the adsorption of quinoline leads to the formation of Cu─N bonds and hydrogen bonds at the interface (Figure 6d), resulting in a stronger Eads (−2.91 eV). The primary charge trans- fer occurs through the Cu─N bond (Figure 6e). Similarly, the adsorption of THQ forms interfacical C─Cu bonds and hydro- gen bonds (Figure 6f), resulting in the strongest Eads (−3.63 eV). In contrast, the Cu/Cu2O adsorps quinoline through the forma- tion of multiple Cu─C bonds where Cu from both Cu3 clus- ter and Cu2O slab, so-called dual-site adsorption configuration (Figure 6g), with an Eads of −2.29 eV. The charge transfer is influ- enced by both the Cu at the heterojunction and the Cu from Cu2O (Figure 6h). The generated THQ predominantly adsorbs through van der Waals interaction and hydrogen bonding (Figure 6i), with an Eads of −3.14 eV. The moderate adsorption strength toward quinoline and THQ enabled by Cu/Cu2O verify the facilitated ECH process and both Cu+ and Cu0 play crucial roles in the re- actant and product adsorption/desorption behaviors. On the other hand, the H2O molecule can chemically adsorb on the Cu (111) surface by forming a Cu─O bond with a length of 2.31 Å (Figure S19a, Supporting Information), yielding an Eads of −0.66 eV (Figure 6j). For Cu2O, one H atom from H2O tends to form a hydrogen bond with one O atom from Cu2O (Figure S19b, Supporting Information), resulting in an Eads of −0.97 eV. In contrast, the H2O molecule on Cu/Cu2O cannot form a stable chemical adsorption but tends to spontaneously dissociate. The generated OH group adsorbs above one Cu atom from Cu3 clus- ter, while the H bonds with one surface O atom from Cu2O at the interface (Figure S19c, Supporting Information). Moreover, the adsorption of a single H atom on the three structures was inves- tigated. The H atom can form coordinative adsorption with three Cu atoms (Figure S20a, Supporting Information), resulting in an Adv. Funct. Mater. 2025, 35, 2414120 © 2024 Wiley-VCH GmbH 2414120 (7 of 10) 16163028, 2025, 4, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202414120 by Zhejiang University Of Technology, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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www.advancedsciencenews.com www.afm-journal.de Figure 6. Calculation results. Optimized adsorption configurations of a,d,g) quinoline and b,e,h) Charger transfer and Bader charges on Cu, Cu2O, and Cu/Cu2O. Optimized adsorption configurations of THQ product on c) Cu, f) Cu2O, and i) Cu/Cu2O. The yellow color denotes charge deplection and the cyan signifies charge accumulation. j) Adsorption energies and k) HER Gibbs free energies. Eads value of −0.66 eV for Cu. On the Cu2O (111) surface, one H atom can form H─O bond (0.98 Å) with a surface-exposed O atom (Figure S20b, Supporting Information), resulting in an Eads of −0.75 eV. The H atom also tends to adsorb on a surface O atom from Cu2O for Cu/Cu2O (Figure S20c, Supporting Information), with an Eads of −0.56 eV. According to the Sabatier principle,[26] the catalyst’s adsorption of hydrogen that is too strong or too weak is unfavorable. Therefore, compared to Cu and Cu2O, the mod- erate adsorption toward hydrogen on Cu/Cu2O is beneficial for the proceeding of HER. The smaller Gibbs free energies (△GH*) obtained on Cu/Cu2O (−0.27 eV, Figure 6k) also confirm the facil- itated generation of H* key intermediate.[27] The results suggest that the effective ECH enabled by Cu/Cu2O is mainly attributed to the modulated adsorption behaviors of key species including quinoline, H2O, and THQ. 2.5. Hybrid Coupled System for co-Production Given a much lower thermodynamics potential (0.48 V vs RHE), the electrochemical oxidation of benzyl alcohol (BA) turns out to be a promising alternative to the sluggish oxygen evolution reaction (OER, 1.23 V vs RHE) at the anode.[28] It is highly im- perative to pair the ECH of quinoline with BA oxidation reac- tion (BAOR) to co-produce value-added chemicals in aqueous so- lution, which would increase electron economy and maximize the cell utilization efficiency.[8a,29] The hybrid coupled system (de- noted ECH||BAOR) is schemed in Figure 7a,b in a home-made flow cell with a size of 1.5 × 1.5 cm2, where the CuO precursor is employed as the anode catalyst and Cu-LR is the cathode catalyst (Cu-LR||CuO). The LSV curves of CuO (Figure 7c) show much lower onset potential and higher current density when adding BA. The potential is ≈150 mV smaller than that of OER to deliver a current density of 20 mA cm−2, verifying more favorable kinet- ics and thermodynamics. The electrolysis of 10 mm BA at 0.65 V vs Hg/HgO was performed for five consecutive runs and the oxi- dation products were determined from HPLC traces based on the external standard method (Figure S21, Supporting Information). The conversion of BA remains ≈100% with benzoic acid selec- tivity of ≈94% and FE of ≈88% after 1 h of electrolysis (Figure S22, Supporting Information), suggesting outstanding catalytic stability. The XRD patterns (Figure S23, Supporting Information) and XPS spectra (Figure S24, Supporting Information) of post- CuO remain unchanged, which confirms robust structural in- tegrity. The onset cell voltage (E2) of ECH||BAOR hybrid system is ≈1.43 V (Figure 7d), which is significantly smaller than that of ECH||OER (1.5 V), suggesting the advantages of the hybrid sys- tem. The cell LSV curves (Figure 7e) reveal a much lower onset voltage and higher current density of ECH||BAOR with respect to ECH||OER. The voltage is ≈214 mV lower at 50 mA, illustrating the notable kinetic advantage of the hybrid co-electrolysis system. We further explore the productivity upon electrolysis at different currents. As shown in Figure 7f, the productivities of THQ and ben- zoic acid increase gradually with the increase of current. Upon electrolysis at 30 mA, the productivity of THQ and benzoic acid is 0.189 mmol h−1 and 0.173 mmol h−1, respectively, verifying the feasibility of the hybrid co-production system. The calculated Adv. Funct. Mater. 2025, 35, 2414120 © 2024 Wiley-VCH GmbH 2414120 (8 of 10) 16163028, 2025, 4, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202414120 by Zhejiang University Of Technology, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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www.advancedsciencenews.com www.afm-journal.de Figure 7. The ECH of quinoline coupled with benzyl alcohol oxidation reaction (BAOR) ECH||BAOR co-electrolysis system. The scheme of a) flow cell and b) electrochemical reactor. c) LSV curves of CuO with and without BA. d) Onset cell voltage (Ecell) of the ECH||OER and ECH||BAOR systems. e) Cell LSV curves. f) Productivities of products in ECH||BAOR systems at different electrolytic currents. g) Comparison of the energy consumptions at 30 mA after 1h of reaction. h) Technoeconomic analysis (TEA). electric energy consumption is 0.155 W h mmol−1 products of ECH||BAOR hybrid system, which exhibits a ≈53.6% energy savings in contrast to that of ECH||OER system (0.334 W h mmol−1 products) (Figure 7g). In addition, we conducted a preliminary technoeconomic analysis (TEA) using a model adapted from literature,[30] including the costs of input chemi- cals, operation, installation, capital, and maintenance, to inves- tigate the feasibility of the hybrid coupled system. The cost and revenue of the ECH||OER are estimated to be ≈$2232/tonTHQand\approx$3201/ton THQ (Figure 7h), respectively, and the profit is ≈$969/ton THQ. For the ECH||BAOR system, benzoic acid is obtained instead of O2 at the anode, which further increases the technoeconomic value to ≈1551/ton THQ, which results in a 60% increase in net profits. 3. Conclusion The ECH of quinoline using water as the hydrogen source is first achieved on nonprecious Cu-based electrocatalysts, with high productivity and moderate FE. Benefited from the enlarged ECSA and reduced Rct, Cu-LR outperforms the other two catalysts. With the help of in situ and ex situ characterization techniques and DFT calculations, the underlying mechanism for ECH of quino- line has been thoroughly investigated and the results reveal that the Lewis acid-base sites on Cu+-Cu0 dual sites play a vital role in the adsorption behaviors, facilitating the electrochemical hydro- genation through the proton-coupled electron transfer (PCET) process. The new co-production system (ECH||BAOR) with lower cell voltage and higher productivity can enhance the cell uti- lization efficiency and deliver high-value benefits, which hold promise for the achievement of carbon neutrality goals. Supporting Information Supporting Information is available from the Wiley Online Library or from the author. Acknowledgements Y.L. P. and Z.Y.B. contribute equally to this work. The financial support from the Natural Science Foundation of Zhejiang Province (LY21B030005), the NSFC (51702287 and 21902143), and the Key R&D Program of Zhejiang Province (2021C03018) is gratefully acknowledged. Adv. Funct. Mater. 2025, 35, 2414120 © 2024 Wiley-VCH GmbH 2414120 (9 of 10) 16163028, 2025, 4, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202414120 by Zhejiang University Of Technology, Wiley Online Library on [02/06/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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