Electrodeposition Of Zn Research Articles

Boosting Zn2+ kinetics via the multifunctional pre-desolvation interface for dendrite-free Zn anodes

Aqueous zinc ion batteries (AZIBs) are an advanced secondary battery technology to supplement lithium-ion batteries. It has been widely concerned and developed recently based on the element abundance and safety advantages. However, AZIBs still suffer from serious problems such as dendrites Zn, hydrogen evolution corrosion, and surface passivation, which hinder the further commercial application of AZIBs. Herein, an in-situ ZnCr2O4 (ZCO) interface endows AZIBs with dendrite-free and ultra-low polarization by realizing Zn2+ pre-desolvation, constraining H2O-induced corrosion, and boosting Zn2+ transport/deposition kinetics. The ZCO@Zn anode harvests an ultrahigh cumulative capacity of ∼20000 mA h cm−2 (cycle time: over 4000 h) at a high current density of 10 mA cm−2, indicating excellent reversibility of Zn deposition. Such superior performance is among the best cyclability in AZIBs. Moreover, the multifunctional ZCO interface improves the Coulombic efficiency (CE) to 99.7% for more than 2600 cycles. The outstanding electrochemical performance is also verified by the long-term cycle stability of ZCO@Zn//α-MnO2 full cells. Notably, the as-proposed method is efficient and low-cost enough to enable mass production. This work provides new insights into the uniform Zn electrodeposition at the scale of interfacial Zn2+ pre-desolvation and kinetics improvement.

Deposition of Horizontally Stacked Zn Crystals on Single Layer 1T‐VSe2 for Dendrite‐Free Zn Metal Anodes

AbstractOwing to the moderate redox potential and high safety, Zn metal anodes have been garnering great attention. However, the poor reversibility and limited‐service period caused by side reactions and dendrites hinder their applications. Here, a novel anode material consisting of a hexagonal 1T‐Vanadium diselenide (1T‐VSe2) film on graphene is developed as a zincophilic template to epitaxially electrodeposit hexagonal closest packed Zn to replace the conventional metal substrates in Zn batteries. The 1T‐VSe2/Zn anode induces a horizontally (002)‐oriented plate‐like Zn crystal deposition morphology instead of randomly oriented grains that prompts the compact Zn deposition. According to density functional theory calculations, the VSe2 substrate exhibits a higher Zn adsorption (−0.54 eV) than the graphene (−0.38 eV) or neat Zn (−0.48 eV) counterparts, leading to the enhanced zincophilicity and a lower nucleation overpotential, in agreement with the experimental results. The force field‐based molecular dynamics simulations visualize Zn nucleation and morphological evolution at the atomistic level. The rapid adatom diffusion on VSe2 leads to layer‐by‐layer Zn electrodeposits with higher fraction of the (002) facets to effectively prohibit dendrite formation. The symmetric cell with 1T‐VSe2/Zn delivers an ultra‐stable cyclic life of 2500 h with 50 mV overpotential at 1 mA cm−2 and 1 mAh cm−2.

Design of a permselective interface for highly stable Zn electrodeposition

In aqueous electrolytes, the deterioration of Zn electrodes is mainly due to the electrolyte species (e.g., H2O, Zn2+, SO42−, etc.) involved side reactions happened at the Zn|electrolyte interface (ZEI). Here, we design a permselective polyelectrolyte (PPE) that is rich in hydrophobic ethylhexyl and anion-blocking sulfonate (–SO3−) groups for Zn electrodes. During Zn electrodeposition, the PPE coating serves as a “screener” to suppress the transportation of undesired electrolyte species (e.g., H2O and SO42−) while homogenizing the Zn-ion flux. The as-designed PPE significantly suppresses the side reactions and prolongs the cycling life of the Zn electrodes. Even with a PPE layer as thin as ∼ 220 nm, the protected Zn electrode delivers an exceptional stability of > 3400 h at an areal capacity of 2 mAh cm−2 and > 1200 h at a higher capacity of 10 mAh cm−2, superior to those of the control cells.

Zn metal anodes stabilized by an intrinsically safe, dilute, and hydrous organic electrolyte

Rechargeable Zn batteries hold great promise for large-scale energy storage applications but their reversibility is limited by non-compact and dendritic Zn deposition along with interfacial parasitic reactions in conventional electrolytes. Herein, we report an intrinsically safe, dilute, and hydrous organic electrolyte by coupling hydrated Zn(BF4)2 salt with trimethyl phosphate (TMP) solvent for highly reversible Zn batteries, without the need of concentrated electrolyte strategies. The formulated 1 m Zn(BF4)2/TMP enables spatially compact, dendrite-free, and corrosion-free Zn electrodeposition even at high areal capacity (5 and 10 mAh cm−2) using a pressure-free electrolytic cell. Moreover, the hydrous organic electrolyte with low water activity expands the electrochemical window to 3 V (versus Zn2+/Zn) and in-situ forms a protective ZnF2-Zn3(PO4)2-rich interphase on Zn. The resultant Zn electrode achieves long-term cycling over 4200 h with a superhigh cumulative plating capacity of 10500 mAh cm−2 under 5 mA cm−2 in Zn//Zn cell and exhibits high efficiency of 99.5% over 600 cycles in Zn//Cu cell (1 mA cm−2; 1 mAh cm−2). Moreover, this electrolyte supports the stable operation of a full Zn//V2O5·nH2O battery by significantly suppressing cathode dissolution. This work would enlighten the design of hydrous organic electrolytes for practical Zn batteries.

Investigating Formate, Sulfate, and Halide Anions in Reversible Zinc Electrodeposition Dynamic Windows.

Reversible metal electrodeposition (RME) is an emerging and promising method for designing dynamic windows with electrically controllable transmission, excellent color neutrality, and wide dynamic range. Zn is a viable option for metal-based dynamic windows due to its fast switching kinetics and reversibility despite its very negative deposition voltage. In this manuscript, we study the effect of the supporting electrolyte anions for Zn electrodeposition on transparent tin-doped indium oxide. Through systematic additions or removal of components of the electrolytes, we are able to establish a link between the anions and the effectiveness of Zn RME. This insight allows us to design practical two-electrode 25 cm2 Zn dynamic windows that switch to <1% within 20 s. Lastly, we demonstrate that the accumulation of Zn(OH)2 species on the working electrode degrades the optical contrast of Zn windows during long-term cycling. However, the elimination of these species through acid immersion allows the windows to cycle at least 500 times. Reversible Zn electrodeposition in the presence of a polyethylene glycol additive further improves the cycle life to greater than 1000 cycles. Taken together, these studies highlight important design principles for the construction of robust dynamic windows based on Zn RME.

An Analytical Study on the Electrochemical Behavior and Nucleation Mechanism of a Zn‐Ni Alloy in a Choline Chloride‐Urea Deep Eutectic Solvent

AbstractIn this work, the electrochemical behavior and reversibility of electrodeposition of Zn−Ni alloys were investigated by cyclic voltammetry (CV) in the Choline chloride Urea (ChCl‐Urea) system. The results show that the electrodeposition of Zn−Ni alloy follows the normal co‐deposition mechanism and is an irreversible process controlled by diffusion. Timing current method (CA) shows that the electrocrystallization mechanism of Zn−Ni alloy follow three‐dimensional instantaneous nucleation, involving several processes: adsorption process (jads), diffusion‐controlled three‐dimensional nucleation/growth process (j3D‐DC), and water reduction process(jWR). The charge of each process was calculated: Qads, Q3D‐DC, and QWR, and it was found that changing potential could control the charge contribution rate. According to the kinetic parameters, the number density N0 (cm−2) and nucleation rate A (S−1) were obtained. According to the best fitting results, Zn−Ni alloy coating was obtained. The microstructure and phase composition of the coating were analyzed by scanning electron microscopy (SEM) and X‐ray diffraction (XRD).

(Digital Presentation) The Role of Iron in the Zinc Electrodeposition from Chloride Media for Recovering Zinc from Spent Pickling Liquors

Electrodeposition of Zn from chloride media had been studied by potentiodynamic method to understand the characteristics of Zn recovery from spent pickling liquor (SPL). Various concentration, pH, agitation speed and impurities contamination were examined in the series of experiments. The influence of Zn concentration in the range of 30-150 g/dm3 relevant to the real SPL were studied along with acidity level change (pH 1.5-5.5). It was found that the cathodic deposition started with the uniform patern followed by sponge-like deposit and as the concentration of the electrolyte near the cathode surface decreased, the dendritic deposition start to grow, especially at the edge of the cathodes.It was found that the effect of iron concentration on the polarization curves of zinc from SPL is complex. Initially it has a negative effect on the generated cathodic current because of the enhancement of hydrogen bubble formation. At a higher concentration range, however, iron deposits at a relatively higher rate. Further increased iron concentrations may make the composition of the Zn-Fe deposit dominantly in favor of iron, resulting in a hydrogen dominated cathodic mechanism. It is also characterised by the loss of the dendritic structure – attributed mostly of zinc deposition when hydrogen bubbles are not blocking the cathode. As the gas evolution becomes more characteristic, the deposit tends to become more powdery. Under such conditions the cathode becomes smoother and the active surface is reduced. Increasing the stirring speed, the powder was easily detached from the cathode surface. Iron, however can enhance the cathodic deposition process of zinc. With 30 – 60 g/dm3 iron in the 90 g/dm3 Zn solution, an increased iron concentration resulted in a significant increase in the mass of the deposited zinc. This may be interpreted by a beneficial effect of the increased hydrogen evolution enhancing the zinc ion transport to the electrode surface. However further increments of iron had a contrary effect, possibly by the locally increased – and generally detected – pH of the solution indirectly causing a superficial precipitation of hydroxides. Technically pure zinc could be deposited from only low-iron (< < 30 g/dm3) zinc solutions (of 90 g/dm3 Zn) at relatively vigorous stirring speeds. High iron concentration in the solution is definitely unsuitable for obtaining the aimed quality of cathode zinc.

Non‐chromate conversion process for zinc coating with durable hydrophobicity and enhanced corrosion resistance

AbstractA Zn‐based coating with durable hydrophobicity and good corrosion resistance was formed on a mild steel substrate, which involves electroplating Zn from a non‐aqueous electrolyte, followed by passivation in an oleic acid (OA) solution. The electrodeposited Zn coatings were porous, which facilitated the formation of a chemical conversion layer of Zn oleate (ZO) during OA passivation. The Zn coating after passivation had a two‐layer structure, which included an outer layer of ZO with a thickness of ∼26 μm and an inner layer of Zn with a thickness of ∼6 μm. The outer layer ZO is a type of metal soap with a smooth surface and durable hydrophobicity, such that water droplets can easily slip off its surface. Corrosion testing and electrochemical measurements in 3.5 wt.% NaCl aqueous solution indicate that the Zn coating after OA passivation exhibits outstanding anti‐corrosion properties compared with those exhibited by pure Zn coating. The corrosion products and mechanism of the two‐layer coating were explored. This study shows that smooth metal oleate coatings can provide hydrophobicity and corrosion resistance simultaneously to mild steel substrates.

Nanoscale visualization of metallic electrodeposition in a well-controlled chemical environment

Liquid phase transmission electron microscopy (TEM) provides a useful means to study a wide range of dynamics in solution with near-atomic spatial resolution and sub-microsecond temporal resolution. However, it is still a challenge to control the chemical environment (such as the flow of liquid, flow rate, and the liquid composition) in a liquid cell, and evaluate its effect on the various dynamic phenomena. In this work, we have systematically demonstrated the flow performance of an in situ liquid TEM system, which is based on ‘on-chip flow’ driven by external pressure pumps. We studied the effects of different chemical environments in the liquid cell as well as the electrochemical potential on the deposition and dissolution behavior of Cu crystals. The results show that uniform Cu deposition can be obtained at a higher liquid flow rate (1.38 μl min−1), while at a lower liquid flow rate (0.1 μl min−1), the growth of Cu dendrites was observed. Dendrite formation could be further promoted by in situ addition of foreign ions, such as phosphates. The generality of this technique was confirmed by studying Zn electrodeposition. Our direct observations not only provide new insights into understanding the nucleation and growth but also give guidelines for the design and synthesis of desired nanostructures for specific applications. Finally, the capability of controlling the chemical environment adds another dimension to the existing liquid phase TEM technique, extending the possibilities to study a wide range of dynamic phenomena in liquid media.

Toward practical aqueous zinc-ion batteries for electrochemical energy storage

Chang Li is a PhD candidate in the Department of Chemistry at University of Waterloo, under the supervision of Professor Linda F. Nazar. He received his bachelor's degree from the Department of Materials Science and Engineering at Huazhong University of Science and Technology in 2019. His current research focuses on developing novel electrolyte systems for Zn²⁺-exclusive intercalation cathodes and advanced anodes for aqueous zinc-ion batteries. Shuo Jin is a PhD candidate in the Smith School of Chemical and Biomolecular Engineering at Cornell University, under the supervision of Professor Lynden Archer. He received his bachelor's degree from South China University of Technology in 2018 and MS degree from Cornell University in 2020, both in chemical engineering. His current research focuses on understanding the effects of Zn electrodeposit crystallography on electrochemical reversibility of Zn anodes. Lynden Archer is the James A. Friend Family Distinguished Professor and Joseph Silbert dean of engineering at Cornell University. He is a member of the National Academy of Engineering and fellow of the American Physical Society and the Society of Rheology. His research focuses on fluid dynamics of simple and complex liquids at liquid solid interfaces, as well as their application for morphological control of battery anodes. Linda Nazar is a fellow of the Royal Society of London, an officer of the Order of Canada, and holds a Tier 1 Canada Research Chair in solid state energy materials. She was awarded the Materials Research Society Medal in 2020 for her outstanding contributions to advanced materials design, synthesis, and characterization for energy storage, particularly Li battery technologies. Dr. Nazar carries out research in solid state chemistry/ionics, electrochemistry, and materials chemistry and has published more than 270 academic papers. Dr. Nazar is identified as a highly cited researcher (Web of Science; 2014–2021), with multiple highly cited papers that are defined as those ranking in the top 1% by citations for chemistry.

Uniform and oriented zinc deposition induced by artificial Nb2O5 Layer for highly reversible Zn anode in aqueous zinc ion batteries

Zn metal has recently emerged as a promising candidate for stable and reversible anode in aqueous rechargeable batteries. However, despite the high reversibility of Zn metal in aqueous media, Zn metal anode utilization is limited owing to unavoidable dilemmas, such as dendrite growth, hydrogen gas evolution, and “dead Zn”, eventually leading to battery breakdown. Herein, we propose a Nb2O5 film as an effective coating layer to guarantee uniform ion flux and a rapid transportation pathway for Zn ions through Maxwell–Wagner polarization, resulting in homogeneous Zn electrodeposition under the Nb2O5 layer. The artificial Nb2O5 layer coated on the Zn surface (Nb2O5@Zn) acted as a guide for Zn deposition, enabling a dense and uniform morphology of electrodeposited Zn oriented in a specific direction. The symmetric Nb2O5@Zn anode system exhibited stable plating/stripping for up to 1000 h. Outstanding durability and resilience (220 h at 5 mA cm−2/5 mAh cm−2) and rapid plating/stripping with excellent recovery (returning to 1 from 10 mA cm−2) were verified under harsh cycling conditions. The excellent characteristics of Nb2O5 layer resulted in high electrochemical stability and performance for a full cell with a VO2 cathode for practical applications.

Synergistic effect of Zn electrodeposition and cerium conversion coating on the corrosion performance of low carbon steel

The present research is based on the comparison of the results obtained from low carbon steel samples treated by different approaches for formation of coating primers. The treatments included electrodeposition of a galvanic Zn-layer, spontaneous deposition of a cerium conversion coating (CeCC), and combination of them. The obtained layers were exposed for 24 h to a 0.01 M NaCl model corrosive medium (MCM) and were then assessed by two electrochemical methods: Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Scanning (PDS). The formed protective layers were examined using a variety of instrumental analytical techniques. The composition of the surfaces was determined by performing X-Ray Photoelectron Spectroscopy (XPS) and Energy Dispersion X-ray (EDX) analyses. Their topologies were observed by means of Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), which also enabled to define the roughness of the films. In addition, their color characteristics and surface hydrophobicity were also evaluated. As main result, the synergism between the cerium conversion coating and the galvanically deposited Zn underlayer was evinced by all the used analytical methods. Finally, a conceptual model on the mechanism of the formation of the combined double layer coating primer was proposed.

Lorentz-Force-Mediated Zn Electrodeposition and Br- Ion Convection for Improved Performance in Aqueous Zn-Br2 Static Batteries

Redox flow batteries are one of the prominent electrochemical energy storage devices with large-scale storage and high energy density.1 The highly reversible Zn/Zn2+ (-0.76 V vs. RHE) and Br-/Br2 (1.08 V vs. RHE) redox couple have been employed in Zn-Br2 flow batteries (1.84 V vs. RHE). However, the dendritic growth of Zn electrodeposits during the repetitive discharge process triggers an internal short-circuit between the anode and the cathode.1 Besides this, cross-diffusion of the highly soluble Br- (Br3 -) ion causes a severe self-discharge of the system and reduced cycle life.2 Additives and ion-selective membranes have been employed to mitigate these challenges for improved cycle life and coulombic efficiency in Zn-Br2 batteries.3 Here, we fabricate an aqueous Zn-Br2 static battery with internally contained and moderate magnetic fields, (~ 30, 40, 50 and 60 mT) at the anode and cathode by incorporating 1 mm thick Nd permanent magnets. A solid complex of tetrapropylammonium tribromide was supported on activated carbon and employed as the positive electrode. Introducing a magnetic field can generate the Lorentz force (acting on Br- and Zn2+ ions), and create a controllable magnetohydrodynamic mass transport during the charge-discharge processes. Among the various magnetic fields, ~50 mT resulted in the highest coulombic efficiency (99 % for 100 cycles) and suppressed Zn dendritic growth. To rationalize the effect of magnetic fields on the efficiency and cycle life, Raman analysis, X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry (for the calculation of diffusion coefficient of Br- ion) are performed on the positive and negative electrodes of Zn-Br2 battery.

Achieving Ultrahigh-Rate Planar and Dendrite-Free Zinc Electroplating for Aqueous Zinc Battery Anodes.

Despite being one of the most promising candidates for grid-level energy storage, practical aqueous zinc batteries are limited by dendrite formation, which leads to significantly compromised safety and cycling performance. In this study, by using single-crystal Zn-metal anodes, reversible electrodeposition of planar Zn with a high capacity of 8 mAh cm-2 can be achieved at an unprecedentedly high current density of 200mA cm-2 . This dendrite-free electrode is well maintained even after prolonged cycling (>1200 cycles at 50 mA cm- 2 ). Such excellent electrochemical performance is due to single-crystal Zn suppressing the major sources of defect generation during electroplating and heavily favoring planar deposition morphologies. As so few defect sites form, including those that would normally be found along grain boundaries or to accommodate lattice mismatch, there is little opportunity for dendritic structures to nucleate, even under extreme plating rates. This scarcity of defects is in part due to perfect atomic-stitching between merging Zn islands, ensuring no defective shallow-angle grain boundaries are formed and thus removing a significant source of non-planar Zn nucleation. It is demonstrated that an ideal high-rate Zn anode should offer perfect lattice matching as this facilitates planar epitaxial Zn growth and minimizes the formation of any defective regions.

Analysis of the behavior of Zn atoms with a Pb additive on the surface during Zn electrodeposition

Zn has attracted considerable attention as an effective anode material in post-Li secondary batteries for large-scale, next-generation energy storage. The use of metal additives such as Pb is effective in suppressing undesirable morphological changes in the electrode during charging. More efficient additives can be obtained by investigating the behavior of deposited Zn in the presence of Pb at the atomic level. This study investigates the morphological and structural characteristics of Zn electrodeposition with the addition of Pb. Galvanostatic electrodeposition indicates that distinctive pillar-like Zn grows in the presence of Pb, which is oriented to (0001) in the hexagonal close-packed (hcp) structure, with its side wall oriented toward the hcp-(0–110) structure. The electrodeposited Zn is covered by a top layer of Pb(111). Density functional theory calculations confirm this layer structure by showing that the deposited Zn atoms can penetrate the Pb top layer to reach the Zn underlayer as a surfactant. This feature allows pillars to grow continuously. Understanding the behavior of such deposited atoms also provides insights into the effects and working mechanisms of additives in general.

A Kinetically Superior Rechargeable Zinc-Air Battery Derived from Efficient Electroseparation of Zinc, Lead, and Copper in Concentrated Solutions.

Zinc electrodeposition is currently a hot topic because of its widespread use in rechargeable zinc‐air batteries. However, Zn deposition has received little attention in organic solvents with much higher ionic conductivity and current efficiency. In this study, a Zn‐betaine complex is synthesized by using ZnO and betainium bis[(trifluoromethyl)sulfonyl]imide and its electrochemical behavior for six organic solvents and electrodeposited morphology are studied. Acetonitrile allowed dendrite‐free Zn electrodeposition at room temperature with current efficiencies of up to 86 %. From acetonitrile solutions in which Zn, Pb, and Cu complexes are dissolved in high concentrations, Zn and Pb/Cu are efficiently separated electrolytically under potentiostatic control, allowing the purification of solutions prepared directly from natural ores. Additionally, a highly flexible Zn anode with excellent kinetics is obtained by using a carbon fabric substrate. A rechargeable zinc‐air battery with these electrodes shows an open‐circuit voltage of 1.63 V, is stable for at least 75 cycles at 0.5 mA cm−2 or 33 cycles at 20 mA cm−2, and allows intermediate cycling at 100 mA cm−2.

In-situ observation of the Zn electrodeposition on the planar electrode in the alkaline electrolytes with different viscosities

As the dendrite issue is prominent in Zn-based batteries, the regulation of Zn electrodeposition to inhibit the dendrite formation and growth is crucial. Herein, the in-situ observation of electrodeposition process on a planar electrode is performed in this work. The scenarios of operating conditions and electrolyte viscosities are investigated by adjusting charging currents and adding polymer molecules with different concentrations. It is found that the Zn electrodeposition process can be divided into uniform and non-uniform regions, and high currents and high viscosities can prolong the uniform region. Besides, with the increases of current and viscosity, the deposition Zn becomes thinner and compact in the uniform region. The mechanism is proposed as the high current can provide enough electrons which can make the deposition occur besides the deposition tips. The increase in viscosity hinders ion transport, which makes the effect of distance more obvious. Thus, using a high charging current (e.g., pulse charging) and/or an electrolyte with high viscosity are favorable for the uniform deposition of Zn. This work lays the foundation for the improvement of alkaline Zn-based batteries. The optical in-situ observation technology used here is also favorable to explore the deposition process in other electrochemical systems.

NONISOTHERMAL SIMULATION OF ELECTRODEPOSITION

The simulation of electrochemical deposition is developed by using a non-isothermal model. The model consists of two parts; the first is a continuum part that simulates the transport of heat and mass and the voltage distributions, and the second is a stochastic noncontinuum part that simulates the bulk diffusion, surface diffusion, and adsorption of the particles. The finite element method is used to solve the differential-algebraic governing equations of the continuum part whereas the Kinetic Monte Carlo method is used to simulate the particle actions in the non-continuum part. The model is applied to the electrodeposition of Zn in ZnSO4 additive-free electrolyte. A comparison is made between the experimental and the simulated results including the surface morphology and the temperature distributions. The results indicated that the simulation model is very promising to be used for such a complicated process.

Multiscale Simulation of Irregular Shape Evolution during the Initial Stage of Zn Electrodeposition on a Negative Electrode Surface

Multiscale Simulation of Irregular Shape Evolution during the Initial Stage of Zn Electrodeposition on a Negative Electrode Surface

The Role of Undercoordinated Sites on Zinc Electrodes for CO2 Reduction to CO

AbstractThe electrochemical CO2 reduction reaction (CO2RR) using renewable energies is a promising route toward global carbon neutrality. Recently, the use of copper catalysts and CO feedstocks, instead of CO2, has been shown to enhance the selectivity toward multicarbon products, leading to increased efforts in developing tandem electrocatalytic systems. State‐of‐the‐art CO2‐to‐CO electrocatalysts are mainly based on noble metals such as silver and gold. Earth‐abundant zinc, in contrast, displays poorer selectivity and activity. Herein, the use of porous dendritic oxidederived zinc (OD‐Zn) catalysts for CO2RR is reported. These catalysts can reduce CO2 to CO with a maximum Faradaic efficiency of 86% at −0.95 V versus reversible hydrogen electrode (RHE) and partial current density of −266 mA cm–2 at −1.00 V vs RHE. OD‐Zn is further found to have a higher amount of undercoordinated sites and exhibits higher CO2RR activity and CO selectivity than electrodeposited Zn metal. While oxygen vacancies have been previously implicated as active sites, detailed experiments and density functional theory calculations show that Zn sites with a high degree of undercoordination provide even higher activity, in view of their nearly optimal *COOH adsorption energies. These findings showcase Zn‐Oderived particles with plentiful undercoordinated sites as cost‐effective electrocatalysts for CO production.