www.acsami.org Research Article Engineering the Interfacial Microenvironment via Surface Hydroxylation to Realize the Global Optimization of Electrochemical CO2 Reduction Xu Han,○ Ting Zhang,○ Martí Biset-Peiró, Xuan Zhang, Jian Li,* Weiqiang Tang,* Pengyi Tang, Joan Ramon Morante, and Jordi Arbiol* Cite This: ACS Appl. Mater. Interfaces 2022, 14, 32157−32165 Read Online ACCESS Metrics & More Article Recommendations * sı Supporting Information ABSTRACT: The adsorption and activation of CO2 on the electrode interface is a prerequisite and key step for electrocatalytic CO2 reduction reaction (eCO2 RR). Regulating the interfacial microenvironment to promote the adsorption and activation of CO2 is thus of great significance to optimize overall conversion efficiency. Herein, a CO2- philic hydroxyl coordinated ZnO (ZnO−OH) catalyst is fabricated, for the first time, via a facile MOF-assisted method. In comparison to the commercial ZnO, the as-prepared ZnO−OH exhibits much higher selectivity toward CO at lower applied potential, reaching a Faradaic efficiency of 85% at −0.95 V versus RHE. To the best of our knowledge, such selectivity is one of the best records in ZnO-based catalysts reported till date. Density functional theory calculations reveal that the coordinated surficial −OH groups are not only favorable to interact with CO2 molecules but also function in synergy to decrease the energy barrier of the rate-determining step and maintain a higher charge density of potential active sites as well as inhibit undesired hydrogen evolution reaction. Our results indicate that engineering the interfacial microenvironment through the introduction of CO2-philic groups is a promising way to achieve the global optimization of eCO2 RR via promoting adsorption and activation of CO2. KEYWORDS: ZnO, surficial hydroxyls, CO2 adsorption, CO2 activation, metal−organic frameworks (MOFs) 1. INTRODUCTION enhance the eCO2 RR efficiency.18−21 For example, an The electrochemical CO2 reduction reaction (eCO2 RR) into increased number of active sites could be induced by various fuels and value-added chemicals is a promising method modulating the ZnO morphology to expose abundant edge to eliminate excessive greenhouse gas and realize energy reuse facets;17 the ratio of H2/CO obtained on ZnO electrocatalysts toward carbon recycling.1−4 Considering the products of eCO2 could be tuned through controlling the defects and facets.19 RR, carbon monoxide (CO), an important raw material for However, almost no attention has been paid to the interfacial top-level organic chemical products, has high industrial microenvironment between ZnO catalysts and CO2, a key value.5−7 Theoretically, CO2-to-CO conversion goes through factor to affect its adsorption and activation. Generally, the the following steps: (1) adsorption of CO2 and activation adsorption and activation of non-polar CO2 occur only at the through a proton-coupled electron transfer process to generate interface of the solid electrocatalyst with the liquid electrolyte COOH* intermediates; (2) the adsorbed COOH* inter- and CO2 molecules by weak interactions.11,22−25 mediate is further reduced to form CO* and water; and (3) Introducing carbon dioxide-philic functional groups, which CO* is desorbed from the surface of the catalyst to form the have strong interaction with CO2 molecules, is an appealing CO product.8−12 Due to the poor solubility of CO2 in the route to manipulate the interface to enhance CO 2 aqueous electrolyte, the transformation of CO2 from the gas affinities.11,26−30 It is also anticipated that the CO2-philic feed to the surface of active sites is a minimum prerequisite for the follow-up steps of eCO2 RR, thus limiting the overall Received: May 23, 2022 conversion efficiency.13,14 Accepted: June 29, 2022 Zinc oxide (ZnO), characterized by its huge reserves and for Published: July 11, 2022 being cost-friendly, has been widely investigated for generating CO with moderate selectivity.15−21 The oxidation state of Zn in ZnO as a clear active site provides infinite possibilities to © 2022 The Authors. Published by American Chemical Society https://doi.org/10.1021/acsami.2c09129 32157 ACS Appl. Mater. Interfaces 2022, 14, 32157−32165 ACS Applied Materials & Interfaces www.acsami.org Research Article Figure 1. (a) Schematic illustration for the formation process of the ZnO−OH. SEM image of (b) ZIF-8, (c) Zn5(OH)8(NO3)2(H2O)2 and (d) ZnO−OH. functional groups on the surface could modulate the electronic Subsequently, the samples were placed in a tube furnace and heated at structure of the catalyst to further manipulate the formation of 400 °C in air for 90 min to yield ZnO−OH (10 °C/min). Similarly, the sequent intermediates in the CO2-to-CO conversion.11,29 L-ZnO-OH and H−ZnO−OH were prepared by pyrolysis of With this in mind, −OH groups, a kind of CO2-philic Zn5(OH)8(NO3)2(H2O)2 that were treated by 0.4 or 0.6 g Zn(NO3)2·6H2O, respectively. functional groups, for the first time, were introduced on the 2.2.4. Preparation of D−ZnO. The as-prepared ZIF-8 powders surface of ZnO catalysts (ZnO−OH) via a simple ZIF-8- were put at the porcelain boat with a direct pyrolysis at 400 °C for 90 assisted (ZIF stands for zeolitic imidazolate frameworks) min to yield D−ZnO. method. Compared to the commercial ZnO, the ZnO−OH 2.3. Ink Preparation. 5 mg of the powder sample and 100 μL of exhibited much higher selectivity toward CO at a relatively Nafion solutions (5 wt %) were dissolved in 1 mL of ethanol under lower applied potential and reached a FECO maximum of 85% ultrasonication to form a homogeneous solution. 500 μL of the above at −0.95 V versus RHE, which is one of the best values among inks were dropped onto the surface of the carbon paper (1 × 1 cm2). ZnO-based catalysts reported till date (see Table S4). Density The loading mass of the catalyst was determined as ∼3 mg/cm2. functional theory (DFT) calculations indicated the existence of 2.4. Electrochemical Characterization. The electrocatalytic performance was characterized in a three-electrode H-type cell system strong attraction between the ZnO−OH and the CO2 with two-compartments separated by a Nafion N-117 membrane, molecule, which is beneficial to the adsorption of CO2. including a reference electrode (Ag/AgCl electrode), a counter Furthermore, the hydroxyl groups play an important role in electrode (Pt plate), and a working electrode (catalyst-loaded carbon facilitating the formation of the follow-up intermediates paper). All potentials were referred to the RHE with ERHE = E0Ag/AgCl (COOH* and CO*), simultaneously limiting the undesired + EAg/AgCl + 0.059 × pH.32,33 A BioLogic VMP3 electrochemical hydrogen evolution reaction (HER). All the results reveal the workstation was used to perform electrochemical experiments. crucial role of CO2-philic −OH groups in promoting the During electrochemical CO2 reduction experiments, the CO2 gas interfacial adsorption and activation of CO2 to realize the was delivered with a rate of 20 mL min−1 into the cell, and gas global optimization of CO2 electroreduction, which benefits chromatography was used to test the final gas phase composition every 20 min. Meanwhile, we collected data three times to get an the understanding of the relevant mechanism in eCO2 RR and average value. rational design of future high-efficient electrocatalysts. 2. EXPERIMENTAL SECTION 3. RESULTS AND DISCUSSION 2.1. Chemicals. If not specified, all chemical reagents were 3.1. Characterization of the Sample. In order to obtained from Sigma-Aldrich and used directly. Zinc nitrate understand the influence of the −OH group on the CO2 hexahydrate [Zn(NO3)2·6H2O], 2-methylimidazole (2-mim), com- adsorption, DFT was first used to calculate the free energy of mercial zinc oxide (ZnO), ethanol, and sodium bicarbonate CO2 adsorption on two representative models for ZnO and (NaHCO3) were all of analytical grade. The Nafion membrane (N- ZnO−OH (Figure S1). Compared to the negligible adsorption 117, 0.18 mm thick) and carbon paper were obtained from Alfa Aesar. 2.2. Material Preparation. 2.2.1. Preparation of ZIF-8. The Gibbs free energy of CO2 molecule on the pristine ZnO fabrication process of ZIF-8 is similar to the process reported in the (−0.0028 eV), a much larger adsorption energy of −0.1466 eV literature.31 50 mL of methanol aqueous solution containing 2-mim was observed on ZnO−OH, revealing that the CO2 adsorption (1.230 g) was added into the methanol aqueous solution of on the ZnO−OH is more feasible. The increase in the CO2 Zn(NO3)2·6H2O (50 mL, 1.115 g) with magnetic stirring to form adsorption affinity is beneficial for the following eCO2 RR and, homogeneous solution. After 24 h reaction without stirring at room in parallel, inhibits the reduction of protons (hydrogen temperature, the white solid was then taken out, washed by methanol evolution) in the electrolyte.26,29 several times, and vacuum dried overnight. With the guidance of above DFT calculations, ZnO with rich 2.2.2. Preparation of Zn5(OH)8(NO3)2(H2O)2. 100 mg of ZIF-8 was surficial −OH was synthesized via a novel MOF-assisted etched by immersing into an ethanol solution (100 mL) containing 0.5 g of Zn(NO3)2·6H2O with stirring for 30 min. The obtained procedure (Figure 1a). In brief, ZIF-8 as a precursor was first Zn5(OH)8(NO3)2(H2O)2 sample was then taken out, washed with transformed into a hydroxide intermediate by virtue of adding ethanol, and dried in vacuum oven overnight. a given amount of Zn(NO3)2 solution at room temperature. 2.2.3. Preparation of ZnO−OH. The as-prepared Afterward, the ZnO with rich surficial −OH (ZnO−OH) was Zn5(OH)8(NO3)2(H2O)2 powders were put at the porcelain boat. obtained through pyrolysis of the above hydroxide inter- 32158 https://doi.org/10.1021/acsami.2c09129 ACS Appl. Mater. Interfaces 2022, 14, 32157−32165 ACS Applied Materials & Interfaces www.acsami.org Research Article Figure 2. (a) XRD patterns. (b) Bright field TEM images showing the morphology of the ZnO−OH sample. The inset corresponds to a magnified detail of the studied area; (c) HRTEM image (left) and corresponding magnified detail (middle) with the corresponding indexed fast Fourier transform spectrum (right); (d) high-angle annular dark field scanning transmission electron microscopy (HAADF STEM) image; (e) HAADF STEM image and representative EELS chemical composition maps obtained from the red squared area in the STEM micrograph. Individual maps obtained from the Zn L2,3-edges at 1020 eV (red), O K-edges at 532 eV (blue), and Zn−O composite map. Inset in (e) shows a 3D atomic supercell model of a ZnO nanoparticle (Zn and O atoms are represented in red and blue, respectively). Figure 3. (a) XPS survey spectra and (b) high-resolution XPS spectra of Zn 2p and (c) O 1s for ZnO−OH (top), C−ZnO (middle), and D−ZnO (bottom). 32159 https://doi.org/10.1021/acsami.2c09129 ACS Appl. Mater. Interfaces 2022, 14, 32157−32165 ACS Applied Materials & Interfaces www.acsami.org Research Article Figure 4. Electrocatalytic performance tests for ZnO−OH, D−ZnO and C−ZnO. (a) Total current density at various potentials. (b) FE of CO. (c) Current density of CO and (d) FE of H2. (e) Current density of H2 on ZnO−OH, D−ZnO, and C−ZnO. (f) Stability test for the ZnO−OH catalyst at −0.95 V vs RHE. mediate under air. The high crystallinity of the as-prepared through direct pyrolysis under air of an as-prepared ZIF-8 ZIF-8 and the corresponding hydroxide intermediate were first sample without Zn(NO3)2 treatment. Meanwhile, commercial confirmed by powder X-ray diffraction (XRD) measurements. ZnO was also used as a reference sample and was labeled as The ZIF-8 samples exhibited similar crystal patterns as C−ZnO. As shown in Figure 2a, all samples clearly showed a expected for the standard ZIF-8 structure (Figure S2a).31,34 similar diffraction pattern with that of simulated ZnO, In the case of the hydroxide intermediate sample, new indicating the successful synthesis of the ZnO skeleton.18,19 diffraction peaks belonging to the Zn5(OH)8(NO3)2(H2O)2 To investigate the morphology and phase evolution processes, phase appeared, indicating that the treatment changed the SEM and TEM images of the three ZnO-based samples were crystal structure of the pristine ZIF-8 (Figure S2b).35,36 Field obtained (Figures 1d, 2 and S7−10). The as-prepared ZnO− emission scanning electron microscopy revealed that sheet- OH and the corresponding ZnO-based samples exhibited shaped nanostructures were formed for the similar quasi-spherical shapes with irregular sizes. HRTEM Zn5(OH)8(NO3)2(H2O)2 sample, different from the character- analyses showed that all the ZnO-based samples displayed the istic rhombic dodecahedral morphology of the ZIF-8 sample typical hexagonal wurtzite ZnO phase (space group = P63/ (Figures 1b,c and S3). Elemental composition maps indicated mmc) with a = b = 3.2900 Å and c = 5.3000 Å.37−40 Electron the existence of an additional O signal in the energy loss spectroscopy (EELS) demonstrated the uniform Zn5(OH)8(NO3)2(H2O)2 sample (Figures S4 and S5), while distributions of Zn and O throughout all samples. high-resolution TEM (HRTEM) analyses (Figure S6) further X-ray photoelectron spectroscopy (XPS) was used to proved that ZIF-8 successfully transformed into the characterize the chemical valence state and surface composi- Zn5(OH)8(NO3)2(H2O)2 structure. tions of the different catalysts. Figure 3a shows the presence of In order to clarify the uniqueness of the ZnO−OH obtained C, O, and Zn elements in all samples. The Zn 2p XPS core by our method, a reference D−ZnO sample was synthesized level spectra for all samples can be deconvoluted into two 32160 https://doi.org/10.1021/acsami.2c09129 ACS Appl. Mater. Interfaces 2022, 14, 32157−32165 ACS Applied Materials & Interfaces www.acsami.org Research Article Figure 5. DFT studies of CO2 RR. Free-energy profiles for the (a) CO2 RR to CO at 0 and (b) −0.95 V (vs RHE) on the simulated models. Charge density difference for CO2, CO, and *COOH adsorbed on a (c−e) ZnO slab and a (f−h) ZnO−OH slab. The gray, red, brown, and pink spheres represent Zn, O, C, and H atoms, respectively. peaks, corresponding to Zn 2p3/2 and Zn 2p1/2 centered at surface −OH groups of ZnO−OH promoted CO2 adsorption around 1021 and 1044 eV, respectively, which indicates the remarkably, consistent with the DFT results (Figure S1). presence of Zn2+ in all samples (Figure 3b).19,31 The high- 3.2. eCO2 RR Performance. Next, electrochemical CO2 resolution XPS spectra obtained on the O 1s show three peaks RR performances of the different samples were evaluated in 0.5 in all three samples, corresponding to the typical metal− M NaHCO3. All electrodes were pre-treated in an Ar-saturated oxygen bond (Zn−O, 529.8 eV),18,19 oxygen vacancy (Ov, electrolyte at −0.70 V versus RHE for 30 min to reach a stable 531.0 eV),41 and −OH (531.7 eV),42−44 respectively (Figure current (Figure S13). The eCO2 RR performance on the 3c). It is worth noting that there is a significant signal ZnO−OH sample was first evaluated by linear sweep enhancement of the corresponding −OH peak obtained on the voltammetry in both Ar- and CO2-saturated electrolytes ZnO−OH sample in comparison to the C−ZnO and D−ZnO, (Figure S14). A large increase in the current density observed which is ascribed to the higher density of surficial −OH on the ZnO−OH sample after replacement of an Ar groups. The integral-area ratios of the peak of surficial −OH atmosphere by CO2 suggested that CO2 was electrochemically groups to the peak of oxygen vacancy were calculated to be reduced by the ZnO−OH sample.46,47 Meanwhile, no obvious 51.3, 2.1, and 1.3 for ZnO−OH, C−ZnO, and D−ZnO. In redox peaks were observed in the CO2-saturated aqueous comparison to C−ZnO, the much stronger FTIR peaks at solution, which displayed that ZnO−OH tended to react with around 1500 and 3400 cm−1 for ZnO−OH (Figure S11), CO2 molecules instead of suffering from self-reduction.26 which are attributed to the O−H stretch mode,45 further Figure 4a summarizes the measured total current density for confirmed the existence of large amount of −OH groups on ZnO−OH, D−ZnO, and C−ZnO samples. Although ZnO− the surface of ZnO−OH. All these observations demonstrated OH and C−ZnO showed similar total reduction current that the prepared ZnO−OH maintained the basic skeleton of densities, ZnO−OH showed the highest selectivity toward CO ZnO with large amount of −OH groups on the surface. CO2 in a potential range from −0.80 to −1.15 V versus RHE, adsorption measurements on different samples were further reaching the maximum Faradaic efficiency (FE) (CO) (85%) performed to support the strong interaction between −OH at −0.95 V versus RHE (Figure 4b). To the best of our groups and CO2 experimentally (Figure S12). The higher CO2 knowledge, such high selectivity for CO at a low applied uptake is observed on ZnO−OH sample, with the order potential is the best record in ZnO-based catalysts reported so following ZnO−OH (15.44 m2/g) > D−ZnO (5.93 m2/g) > far (Table S4). The largest potential-dependent CO partial C−ZnO (1.64 m2/g). Such results demonstrated that the current densities observed on ZnO−OH further demonstrated 32161 https://doi.org/10.1021/acsami.2c09129 ACS Appl. Mater. Interfaces 2022, 14, 32157−32165 ACS Applied Materials & Interfaces www.acsami.org Research Article the excellent activity and selectivity toward CO (Figure 4c). A −0.63 eV, respectively. The stronger stabilization of surface decreasing trend in FE (CO) for ZnO−OH and C−ZnO was COOH* on the ZnO−OH could increase the selectivity for observed when the potential shifted to more negative values, the desired product CO. Besides, the following dissociation of which mainly stems from the dominance of the H2 generation COOH* assisted by the proton-electron transfer to produce over the eCO2 RR (Figure 4d). This assumption was further CO* and H2O is an endothermic and the RDS. To our confirmed by the potential-dependent H2 current densities for excitement, ΔG increases by 1.72 and 1.5 eV on ZnO and the different catalysts (Figure 4e). The intrinsic activity of the ZnO−OH catalyst models, respectively, which means that the catalysts was disclosed by the electrochemical active surface process of the CO* generation on the ZnO−OH slab is area (ECSA).32 As shown in Figure S15, the Cdl of ZnO−OH, thermodynamically more favorable than that on the ZnO slab. D−ZnO, and C−ZnO samples was 0.05, 0.07, and 0.02 μF As for the final step of CO desorption, the ΔG over the cm−2, respectively, which indicated that the ECSA is not reference ZnO and the ZnO−OH catalyst is −0.59 and −0.26 responsible for the activity of ZnO−OH. A similar eV, respectively. Such a relatively weak binding of CO* and phenomenon could be observed on the nitrogen adsorption− above stronger stabilization of COOH* steer the electron and desorption isotherms and BET surface area (Figure S16). It is proton transfer to the formation of the CO product. Similar well known that those electrocatalysts with high specific surface area should endow the efficient exposure of electro- trends are also observed on the free-energy profiles at −0.95 V catalytic active sites, fast electrolyte penetration/diffusion, and (vs RHE) (Figure 5b). The differential charge density for CO2, free diffusion of intermediates.48,49 In our case, the specific CO, and COOH* on the ZnO−OH and ZnO slabs was also surface area of the ZnO−OH was much lower than that of D− calculated and is shown in Figure 5c−h. The charge ZnO, which suggests that the intrinsic catalytic activity of accumulation and deficit between them and the corresponding ZnO−OH sample arise from the presence of surficial −OH surface were presented with yellow and cyan iso-surfaces. groups instead of the specific surface area. Through contrastive analysis, the charge density difference of To investigate the reaction kinetics on ZnO−OH during CO on the ZnO−OH slab was more prominent than that on eCO2 RR, Tafel slopes derived from the static state current the ZnO slab. To summarize, the ZnO−OH slab stabilizes the densities for CO were calculated. The C−ZnO samples exhibit key intermediates via electronic interactions, which in synergy a Tafel slope of 36 mV dec−1, close to 39 mV dec−1, indicating leads to an enhanced CO selectivity. More importantly, the that the rate-determining step (RDS) of CO2 RR on C−ZnO Gibbs free energy for the CO2 activation process on ZnO with powder corresponds to the initial proton-coupled electron two surficial −OH decreased by ca. 0.17 eV with respect to the transfer (Figure S17).50 The much lower Tafel slopes (30 mV ZnO with only one surficial −OH, which revealed that more dec−1) for the ZnO−OH catalyst indicated its remarkably surficial −OH coverage enhanced the adsorption of CO2 improved kinetics toward CO conversion.51−55 In addition, the (Figure S22). These calculated results were in good agreement effects of ZnO−OH samples treated by different amounts of with the experimental observations that the ZnO−OH sample Zn(NO3)2 on the CO2 RR activity were also studied, which exhibited better selectivity for CO2 RR in comparison to the were denoted as L−ZnO−OH and H−ZnO−OH, respec- C−ZnO catalyst. Additionally, HER as a competing side tively. Both the referential samples showed similar crystal reaction is also studied here (Figure S23). The stronger patterns with simulated ZnO (Figure S18a) and morphology in stability of H* on the surface could suppress HER effectively. comparison with spherical ZnO−OH (Figure S18b,c). It can be concluded that the HER is less active on ZnO−OH However, the selectivity of L−ZnO−OH and H−ZnO−OH than that on the reference ZnO sample (−1.87 and −1.67 eV, changed negatively (Figure S19), which is due to the decreased respectively), suggesting that HER occurs more easily on ZnO ratio between surficial −OH groups and oxygen vacancy (Figure S20). without the surficial −OH coverage. Taken in all, the surface To further investigate the stability of the ZnO−OH during hydroxyls can not only facilitate the formation of COOH* and the eCO2 RR, a 10 h stability measurement was conducted. A CO* via electronic interactions but also limit the undesired current density of ca. −8.2 mA cm−2 and a FE(CO) over 80% HER. were maintained during the 10 h test (Figure 4f). After the stability test, TEM analyses were performed to reveal the 4. CONCLUSIONS morphology and phase changes on the ZnO−OH sample, as In summary, ZnO covered by surficial −OH groups was shown in Figure S21. EELS compositional maps demonstrate synthesized through a novel MOF-assisted method, which that most of the ZnO−OH areas showed a uniform delicately optimize the interfacial microenvironment to distribution of Zn and O. HRTEM analyses showed the promote the interfacial adsorption and activation of CO2. presence of some metallic Zn nanoparticles with hexagonal phase (space group = P63/mmc). The presence of reduced Zn The synthesized −OH-rich ZnO presents a FECO maximum of nanostructure can explain the slight efficiency loss after the 85% at −0.95 V versus RHE, which is one of the best records stability test, evidencing the competition in the metal oxides among the state-of-the-art ZnO-based catalysts. DFT calcu- between self-reduction and CO2 reduction.26,56 lations confirmed that the surface −OH first boosts the 3.3. DFT Calculations. The CO2 RR process for the ZnO adsorption of CO2 at the interface and then promotes the and ZnO−OH models was studied by DFT calculations to generation of COOH* and CO* intermediates. Our findings illustrate the origin of the improved CO2 RR. The free-energy revealed that tuning the interfacial microenvironment via the profiles at a potential of 0 V versus RHE for the three introduction of dioxide-philic functional groups is a promising elementary steps and the two important intermediates way to achieve the global optimization via promotion of (COOH* and CO*) in the CO2 RR process are shown in interfacial adsorption and activation of CO2, which paves a Figure 5a. The ΔG for the formation of COOH* over new way to rationally design future highly active electro- commercial ZnO and the ZnO−OH catalysts is −0.52 and catalysts for eCO2 RR. 32162 https://doi.org/10.1021/acsami.2c09129 ACS Appl. Mater. Interfaces 2022, 14, 32157−32165 ACS Applied Materials & Interfaces www.acsami.org Research Article ■ ASSOCIATED CONTENT * Supporting Information sı work has been performed in the framework of Universitat Autònoma de Barcelona Materials Science PhD program. X.H. The Supporting Information is available free of charge at thanks China Scholarship Council for scholarship support https://pubs.acs.org/doi/10.1021/acsami.2c09129. (201804910551). Additional characterizations, DFT results, and electro- catalytic testing curves (PDF) ■ REFERENCES (1) Jin, S.; Hao, Z.; Zhang, K.; Yan, Z.; Chen, J. Advances and ■ AUTHOR INFORMATION Corresponding Authors Challenges for the Electrochemical Reduction of CO2 to CO: From Fundamentals to Industrialization. Angew. Chem., Int. Ed. 2021, 60, 20627−20648. Jian Li − Laboratory of Renewable Energy Science and (2) Zhong, M.; Tran, K.; Min, Y.; Wang, C.; Wang, Z.; Dinh, C.-T.; Engineering, Institute of Mechanical Engineering EPFL, 1015 De Luna, P.; Yu, Z.; Rasouli, A. S.; Brodersen, P.; Sun, S.; Voznyy, O.; Lausanne, Switzerland; Email: jian.li@epfl.ch Tan, C.-S.; Askerka, M.; Che, F.; Liu, M.; Seifitokaldani, A.; Pang, Y.; Weiqiang Tang − State Key Laboratory of Chemical Lo, S.-C.; Ip, A.; Ulissi, Z.; Sargent, E. H. Accelerated Discovery of Engineering and School of Chemical Engineering, East China CO2 Electrocatalysts Using Active Machine Learning. Nature 2020, University of Science and Technology, 200237 Shanghai, 581, 178−183. China; orcid.org/0000-0002-7726-4130; (3) Yang, B.; Liu, K.; Li, H.; Liu, C.; Fu, J.; Li, H.; Huang, J. E.; Ou, Email: wqtang@ecust.edu.cn P.; Alkayyali, T.; Cai, C.; Duan, Y.; Liu, H.; An, P.; Zhang, N.; Li, W.; Jordi Arbiol − Catalan Institute of Nanoscience and Qiu, X.; Jia, C.; Hu, J.; Chai, L.; Lin, Z.; Gao, Y.; Miyauchi, M.; Cortés, E.; Maier, S. A.; Liu, M. Accelerating CO2 Electroreduction to Nanotechnology (ICN2), CSIC and BIST, Barcelona 08193 Multicarbon Products via Synergistic Electric−Thermal Field on Catalonia, Spain; ICREA, Barcelona 08010 Catalonia, Copper Nanoneedles. J. Am. Chem. Soc. 2022, 144, 3039−3049. Spain; orcid.org/0000-0002-0695-1726; Email: arbiol@ (4) Li, H.; Zhou, H.; Zhou, Y.; Hu, J.; Miyauchi, M.; Fu, J.; Liu, M. icrea.cat Electric-Field Promoted C−C Coupling over Cu Nanoneedles for CO2 Electroreduction to C2 Products. Chin. J. Catal. 2022, 43, 519− Authors 525. Xu Han − Catalan Institute of Nanoscience and (5) Guo, Q.; Liang, F.; Li, X.-B.; Gao, Y.-J.; Huang, M.-Y.; Wang, Y.; Nanotechnology (ICN2), CSIC and BIST, Barcelona 08193 Xia, S.-G.; Gao, X.-Y.; Gan, Q.-C.; Lin, Z.-S.; Tung, C.-H.; Wu, L.-Z. Catalonia, Spain Efficient and Selective CO2 Reduction Integrated with Organic Ting Zhang − Catalan Institute of Nanoscience and Synthesis by Solar Energy. Chem 2019, 5, 2605−2616. Nanotechnology (ICN2), CSIC and BIST, Barcelona 08193 (6) Yuan, X.; Wu, Y.; Jiang, B.; Wu, Z.; Tao, Z.; Lu, X.; Liu, J.; Qian, Catalonia, Spain; Catalonia Institute for Energy Research T.; Lin, H.; Zhang, Q. Interface Engineering of Silver-Based (IREC), Barcelona 08930 Catalonia, Spain Heterostructures for CO2 Reduction Reaction. ACS Appl. Mater. Martí Biset-Peiró − Catalonia Institute for Energy Research Interfaces 2020, 12, 56642−56649. (7) Navarro, R. M.; Peña, M. A.; Fierro, J. L. G. Hydrogen (IREC), Barcelona 08930 Catalonia, Spain Production Reactions from Carbon Feedstocks: Fossil Fuels and Xuan Zhang − Department of Materials Engineering, KU Biomass. Chem. Rev. 2007, 107, 3952−3991. Leuven, 3001 Leuven, Belgium (8) Rosen, B. A.; Salehi-Khojin, A.; Thorson, M. R.; Zhu, W.; Pengyi Tang − State Key Laboratory of Information Whipple, D. T.; Kenis, P. J. A.; Masel, R. I. Ionic Liquid-Mediated Functional Materials, 2020 X-Lab, Shanghai Institute of Selective Conversion of CO2 to CO at Low Overpotentials. Science Microsystem and Information Technology, Chinese Academy 2011, 334, 643−644. of Sciences, 200050 Shanghai, China; orcid.org/0000- (9) Zhu, D. D.; Liu, J. L.; Qiao, S. Z. Recent Advances in Inorganic 0002-2306-095X Heterogeneous Electrocatalysts for Reduction of Carbon Dioxide. Joan Ramon Morante − Catalonia Institute for Energy Adv. Mater. 2016, 28, 3423−3452. Research (IREC), Barcelona 08930 Catalonia, Spain; (10) Zhang, W.; Hu, Y.; Ma, L.; Zhu, G.; Wang, Y.; Xue, X.; Chen, Department of Physics, Universitat de Barcelona, Barcelona R.; Yang, S.; Jin, Z. Progress and Perspective of Electrocatalytic CO2 Reduction for Renewable Carbonaceous Fuels and Chemicals. Adv. 08028 Catalonia, Spain Sci. 2018, 5, 1700275. Complete contact information is available at: (11) Huang, Q.; Li, Q.; Liu, J.; Wang, Y. R.; Wang, R.; Dong, L. Z.; https://pubs.acs.org/10.1021/acsami.2c09129 Xia, Y. H.; Wang, J. L.; Lan, Y.-Q. Disclosing CO2 Activation Mechanism by Hydroxyl-Induced Crystalline Structure Transforma- Author Contributions tion in Electrocatalytic Process. Matter 2019, 1, 1656−1668. ○ X.H. and T.Z. contributed equally to this paper. (12) Zhang, X.; Zhou, Y.; Zhang, H.; Li, H.; Liu, K.; Li, H.; Pan, H.; Hu, J.; Fu, J.; Chen, S.; Liu, M. Tuning the Electron Structure Enables Notes the Nizn Alloy for CO2 Electroreduction to Formate. J. Energy Chem. The authors declare no competing financial interest. 2021, 63, 625−632. ■ ACKNOWLEDGMENTS The authors acknowledge funding from Generalitat de (13) Xu, S.; Carter, E. A. Theoretical Insights into Heterogeneous (Photo)electrochemical CO2 Reduction. Chem. Rev. 2019, 119, 6631−6669. Catalunya 2017 SGR 327 and 2017 SGR 1246. X.H., T.Z., (14) Zhao, K.; Quan, X. Carbon-Based Materials for Electrochemical J.R.M., and J.A. acknowledge funding from the projects Reduction of CO2 to C2+ Oxygenates: Recent Progress and Remaining Challenges. ACS Catal. 2021, 11, 2076−2097. (PID2020-116093RB-C42 and -C43), funded by MCIN/ (15) Tan, D.; Lee, W.; Kim, Y. E.; Ko, Y. N.; Youn, M. H.; Jeon, Y. AEI/10.13039/501100011033/. ICN2 is supported by the E.; Hong, J.; Jeong, S. K.; Park, K. T. SnO2/ZnO Composite Hollow Severo Ochoa program from Spanish MINECO (grant no. Nanofiber Electrocatalyst for Efficient CO2 Reduction to Formate. SEV-2017-0706). ICN2 and IREC are funded by the CERCA ACS Sustain. Chem. Eng. 2020, 8, 10639−10645. Programme/Generalitat de Catalunya. X.Z. acknowledges (16) Nguyen, D. L. T.; Jee, M. S.; Won, D. H.; Jung, H.; Oh, H.-S.; funding from FWO project (12ZV320N). Part of the present Min, B. K.; Hwang, Y. J. Selective CO2 Reduction on Zinc 32163 https://doi.org/10.1021/acsami.2c09129 ACS Appl. Mater. Interfaces 2022, 14, 32157−32165 ACS Applied Materials & Interfaces www.acsami.org Research Article Electrocatalyst: The Effect of Zinc Oxidation State Induced by (33) Zhang, T.; Han, X.; Liu, H.; Biset-Peiró, M.; Li, J.; Zhang, X.; Pretreatment Environment. ACS Sustain. Chem. Eng. 2017, 5, 11377− Tang, P.; Yang, B.; Zheng, L.; Morante, J. R.; Arbiol, J. Site-Specific 11386. Axial Oxygen Coordinated FeN4 Active Sites for Highly Selective (17) Xiang, Q.; Li, F.; Wang, J.; Chen, W.; Miao, Q.; Zhang, Q.; Electroreduction of Carbon Dioxide. Adv. Funct. Mater. 2022, 32, Tao, P.; Song, C.; Shang, W.; Zhu, H.; Deng, T.; Wu, J. 2111446. Heterostructure of ZnO Nanosheets/Zn with a Highly Enhanced (34) Saliba, D.; Ammar, M.; Rammal, M.; Al-Ghoul, M.; Hmadeh, Edge Surface for Efficient CO2 Electrochemical Reduction to CO. M. Crystal Growth of ZIF-8, ZIF-67, and Their Mixed-Metal ACS Appl. Mater. Interfaces 2021, 13, 10837−10844. Derivatives. J. Am. Chem. Soc. 2018, 140, 1812−1823. (18) Geng, Z.; Kong, X.; Chen, W.; Su, H.; Liu, Y.; Cai, F.; Wang, (35) Schwenzer, B.; Pop, L. Z.; Neilson, J. R.; Sbardellati, T. B.; G.; Zeng, J. Oxygen Vacancies in ZnO Nanosheets Enhance CO2 Morse, D. E. Nanostructured ZnS and CdS Films Synthesized Using Electrochemical Reduction to CO. Angew. Chem., Int. Ed. 2018, 57, Layered Double Hydroxide Films as Precursor and Template. Inorg. 6054−6059. Chem. 2009, 48, 1542−1550. (19) Daiyan, R.; Lovell, E. C.; Huang, B.; Zubair, M.; Leverett, J.; (36) Shinagawa, T.; Watanabe, M.; Mori, T.; Tani, J.-i.; Chigane, M.; Zhang, Q.; Lim, S.; Horlyck, J.; Tang, J.; Lu, X.; Kalantar-Zadeh, K.; Izaki, M. Oriented Transformation from Layered Zinc Hydroxides to Hart, J. N.; Bedford, N. M.; Amal, R. Uncovering Atomic-Scale Nanoporous ZnO: A Comparative Study of Different Anion Types. Stability and Reactivity in Engineered Zinc Oxide Electrocatalysts for Inorg. Chem. 2018, 57, 13137−13149. Controllable Syngas Production. Adv. Energy Mater. 2020, 10, (37) Utama, M. I. B.; Belarre, F. J.; Magen, C.; Peng, B.; Arbiol, J.; 2001381. Xiong, Q. Incommensurate van der Waals Epitaxy of Nanowire (20) Franco, F.; Rettenmaier, C.; Jeon, H. S.; Roldan Cuenya, B. Arrays: A Case Study with ZnO on Muscovite Mica Substrates. Nano Transition Metal-Based Catalysts for the Electrochemical CO2 Lett. 2012, 12, 2146−2152. Reduction: From Atoms and Molecules to Nanostructured Materials. (38) de la Mata, M.; Magen, C.; Gazquez, J.; Utama, M. I. B.; Heiss, Chem. Soc. Rev. 2020, 49, 6884−6946. M.; Lopatin, S.; Furtmayr, F.; Fernández-Rojas, C. J.; Peng, B.; (21) Liu, Y.; Yu, L.; Hu, Y.; Guo, C.; Zhang, F.; Lou, X. W. A Morante, J. R.; Rurali, R.; Eickhoff, M.; Fontcuberta i Morral, A.; Magnetically Separable Photocatalyst Based on Nest-Like γ-Fe2O3/ Xiong, Q.; Arbiol, J. Polarity Assignment in ZnTe, GaAs, ZnO, and ZnO Double-Shelled Hollow Structures with Enhanced Photo- GaN-AlN Nanowires from Direct Dumbbell Analysis. Nano Lett. catalytic Activity. Nanoscale 2012, 4, 183−187. 2012, 12, 2579−2586. (22) Resasco, J.; Chen, L. D.; Clark, E.; Tsai, C.; Hahn, C.; Jaramillo, (39) de la Mata, M.; Zamani, R. R.; Martí-Sánchez, S.; Eickhoff, M.; T. F.; Chan, K.; Bell, A. T. Promoter Effects of Alkali Metal Cations Xiong, Q.; Fontcuberta i Morral, A.; Caroff, P.; Arbiol, J. The Role of on the Electrochemical Reduction of Carbon Dioxide. J. Am. Chem. Polarity in Nonplanar Semiconductor Nanostructures. Nano Lett. 2019, 19, 3396−3408. Soc. 2017, 139, 11277−11287. (40) Li, J.; Slassi, A.; Han, X.; Cornil, D.; Ha-Thi, M. H.; Pino, T.; (23) Resasco, J.; Lum, Y.; Clark, E.; Zeledon, J. Z.; Bell, A. T. Effects Debecker, D. P.; Colbeau-Justin, C.; Arbiol, J.; Cornil, J.; Ghazzal, M. of Anion Identity and Concentration on Electrochemical Reduction N. Tuning the Electronic Bandgap of Graphdiyne by H-Substitution of CO2. ChemElectroChem 2018, 5, 1064−1072. to Promote Interfacial Charge Carrier Separation for Enhanced (24) Liu, P.; Zheng, N. Coordination Chemistry of Atomically Photocatalytic Hydrogen Production. Adv. Funct. Mater. 2021, 31, Dispersed Catalysts. Natl. Sci. Rev. 2018, 5, 636−638. 2100994. (25) Wang, Q.; Liu, K.; Fu, J.; Cai, C.; Li, H.; Long, Y.; Chen, S.; (41) Lei, F.; Sun, Y.; Liu, K.; Gao, S.; Liang, L.; Pan, B.; Xie, Y. Liu, B.; Li, H.; Li, W.; Qiu, X.; Zhang, N.; Hu, J.; Pan, H.; Liu, M. Oxygen Vacancies Confined in Ultrathin Indium Oxide Porous Sheets Atomically Dispersed s-Block Magnesium Sites for Electroreduction for Promoted Visible-Light Water Splitting. J. Am. Chem. Soc. 2014, of CO2 to CO. Angew. Chem., Int. Ed. 2021, 60, 25241−25245. 136, 6826−6829. (26) Deng, W.; Zhang, L.; Li, L.; Chen, S.; Hu, C.; Zhao, Z.-J.; (42) Bang, S.; Lee, S.; Ko, Y.; Park, J.; Shin, S.; Seo, H.; Jeon, H. Wang, T.; Gong, J. Crucial Role of Surface Hydroxyls on the Activity Photocurrent Detection of Chemically Tuned Hierarchical ZnO and Stability in Electrochemical CO2 Reduction. J. Am. Chem. Soc. Nanostructures Grown on Seed Layers Formed by Atomic Layer 2019, 141, 2911−2915. Deposition. Nanoscale Res. Lett. 2012, 7, 290. (27) Yang, P.; Zhao, Z.-J.; Chang, X.; Mu, R.; Zha, S.; Zhang, G.; (43) Kim, Y. H.; Kim, D. G.; Maduwu, R. D.; Jin, H. C.; Moon, D. Gong, J. The Functionality of Surface Hydroxy Groups on the K.; Kim, J. H. Organic Electrolytes Doped ZnO Layer as the Electron Selectivity and Activity of Carbon Dioxide Reduction over Cuprous Transport Layer for Bulk Heterojunction Polymer Solar Cells. Sol. Oxide in Aqueous Solutions. Angew. Chem., Int. Ed. 2018, 57, 7724− RRL 2018, 2, 1800086. 7728. (44) Jiang, L.; Li, J.; Huang, K.; Li, S.; Wang, Q.; Sun, Z.; Mei, T.; (28) Peng, Y.; Wang, L.; Luo, Q.; Cao, Y.; Dai, Y.; Li, Z.; Li, H.; Wang, J.; Zhang, L.; Wang, N.; Wang, X. Low-Temperature and Zheng, X.; Yan, W.; Yang, J.; Zeng, J. Molecular-Level Insight into Solution-Processable Zinc Oxide Transistors for Transparent How Hydroxyl Groups Boost Catalytic Activity in CO2 Hydro- Electronics. ACS Omega 2017, 2, 8990−8996. genation into Methanol. Chem 2018, 4, 613−625. (45) Hu, Z.-A.; Xie, Y.-L.; Wang, Y.-X.; Xie, L.-J.; Fu, G.-R.; Jin, X.- (29) Cui, C.; Han, J.; Zhu, X.; Liu, X.; Wang, H.; Mei, D.; Ge, Q. Q.; Zhang, Z.-Y.; Yang, Y.-Y.; Wu, H.-Y. Synthesis of α-Cobalt Promotional Effect of Surface Hydroxyls on Electrochemical Hydroxides with Different Intercalated Anions and Effects of Reduction of CO2 over Snox/Sn Electrode. J. Catal. 2016, 343, Intercalated Anions on Their Morphology, Basal Plane Spacing, and 257−265. Capacitive Property. J. Phys. Chem. C 2009, 113, 12502−12508. (30) Yao, D.; Tang, C.; Vasileff, A.; Zhi, X.; Jiao, Y.; Qiao, S. Z. The (46) Liu, S.; Yang, H. B.; Hung, S. F.; Ding, J.; Cai, W.; Liu, L.; Gao, Controllable Reconstruction of Bi-MOFs for Electrochemical CO2 J.; Li, X.; Ren, X.; Kuang, Z.; Huang, Y.; Zhang, T.; Liu, B. Elucidating Reduction through Electrolyte and Potential Mediation. Angew. the Electrocatalytic CO2 Reduction Reaction over a Model Single- Chem., Int. Ed. 2021, 60, 18178−18184. Atom Nickel Catalyst. Angew. Chem., Int. Ed. 2020, 59, 798−803. (31) Dou, S.; Song, J.; Xi, S.; Du, Y.; Wang, J.; Huang, Z. F.; Xu, Z. (47) Zhang, T.; Han, X.; Liu, H.; Biset-Peiró, M.; Zhang, X.; Tan, P.; J.; Wang, X. Boosting Electrochemical CO2 Reduction on Metal− Tang, P.; Yang, B.; Zheng, L.; Morante, J. R.; Arbiol, J. Quasi-Double- Organic Frameworks via Ligand Doping. Angew. Chem., Int. Ed. 2019, Star Nickel and Iron Active Sites for High-Efficiency Carbon Dioxide 58, 4041−4045. Electroreduction. Energy Environ. Sci. 2021, 14, 4847−4857. (32) Zhang, T.; Du, J.; Xi, P.; Xu, C. Hybrids of Cobalt/Iron (48) Ni, W.; Xue, Y.; Zang, X.; Li, C.; Wang, H.; Yang, Z.; Yan, Y.- Phosphides Derived from Bimetal−Organic Frameworks as Highly M. Fluorine Doped Cagelike Carbon Electrocatalyst: An Insight into Efficient Electrocatalysts for Oxygen Evolution Reaction. ACS Appl. the Structure-Enhanced CO Selectivity for CO2 Reduction at High Mater. Interfaces 2017, 9, 362−370. Overpotential. ACS Nano 2020, 14, 2014−2023. 32164 https://doi.org/10.1021/acsami.2c09129 ACS Appl. Mater. Interfaces 2022, 14, 32157−32165 ACS Applied Materials & Interfaces www.acsami.org Research Article (49) Liu, Y.; Liu, Z.; Lu, N.; Preiss, E.; Poyraz, S.; Kim, M. J.; Zhang, X. Facile Synthesis of Polypyrrole Coated Copper Nanowires: A New Concept to Engineered Core−Shell Structures. Chem. Commun. 2012, 48, 2621−2623. (50) Dunwell, M.; Luc, W.; Yan, Y.; Jiao, F.; Xu, B. Understanding Surface-Mediated Electrochemical Reactions: CO2 Reduction and Beyond. ACS Catal. 2018, 8, 8121−8129. (51) Zhao, C.; Wang, Y.; Li, Z.; Chen, W.; Xu, Q.; He, D.; Xi, D.; Zhang, Q.; Yuan, T.; Qu, Y.; Yang, J.; Zhou, F.; Yang, Z.; Wang, X.; Wang, J.; Luo, J.; Li, Y.; Duan, H.; Wu, Y.; Li, Y. Solid-Diffusion Synthesis of Single-Atom Catalysts Directly from Bulk Metal for Efficient CO2 Reduction. Joule 2019, 3, 584−594. (52) Li, C. W.; Kanan, M. W. CO2 Reduction at Low Overpotential on Cu Electrodes Resulting from the Reduction of Thick Cu2O Films. J. Am. Chem. Soc. 2012, 134, 7231−7234. (53) Gu, J.; Hsu, C.-S.; Bai, L.; Chen, H. M.; Hu, X. Atomically Dispersed Fe3+ Sites Catalyze Efficient CO2 Electroreduction to CO. Science 2019, 364, 1091−1094. (54) Chen, K.; Cao, M.; Ni, G.; Chen, S.; Liao, H.; Zhu, L.; Li, H.; Fu, J.; Hu, J.; Cortés, E.; Liu, M. Nickel Polyphthalocyanine with Electronic Localization at the Nickel Site for Enhanced CO2 Reduction Reaction. Appl. Catal., B 2022, 306, 121093. (55) Zhu, L.; Lin, Y.; Liu, K.; Cortés, E.; Li, H.; Hu, J.; Yamaguchi, A.; Liu, X.; Miyauchi, M.; Fu, J.; Liu, M. Tuning the Intermediate Reaction Barriers by a CuPd Catalyst to Improve the Selectivity of CO2 Electroreduction to C2 Products. Chin. J. Catal. 2021, 42, 1500− 1508. (56) Luo, W.; Zhang, Q.; Zhang, J.; Moioli, E.; Zhao, K.; Züttel, A. Electrochemical Reconstruction of ZnO for Selective Reduction of CO2 to CO. Appl. Catal., B 2020, 273, 119060. 32165 https://doi.org/10.1021/acsami.2c09129 ACS Appl. Mater. Interfaces 2022, 14, 32157−32165