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The oxidation of a carbon anode with air and CO2 occurs during the electrolysis of alumina in Hall-Héroult cells, resulting in a significant overconsumption of carbon and dusting. Boron is well known to decrease the rate of this reaction for graphite. In this work, the application of boron oxide has been investigated to evaluate its inhibition effect on the air oxidation reaction, and to provide an effective protection for anodes. Different methods of impregnation coating have been explored. Impregnated anode samples were gasified under air at 525 °C according to the standard measurement methods. X-ray tomography was used to obtain the microstructural information of the samples before and after air-burning tests. The impregnated samples showed a very low oxidation reaction rate and dust generation.

The oxygen-evolving IrO2-Ta2O5/Ti anode (OEA), primarily used in electrolyzers for plating, metal powder production, electrowinning (EW), and water electrolysis, is analyzed. This study focuses on the distribution of oxygen evolution reaction (OER) activity and the associated operational loss over the randomized OEA texture. The OER activity and its distribution across the IrO2-Ta2O5 coating surface are key factors that influence EW operational challenges and the lifecycle of OEA in EW processes. To understand the OER activity distribution over the coating’s randomized texture, we performed analyses using anode polarization in acid solution at both low and high (EW operation relevant) overpotentials and electrochemical impedance spectroscopy (EIS) during the OER. These measurements were conducted on anodes in both their as-prepared and deactivated states. The as-prepared anode was deactivated using an accelerated stability test in an acid solution, the EW simulating electrolyte. The obtained data are correlated with fundamental electrochemical properties of OEA, such as structure-related pseudocapacitive responses at open circuit potential in the same operating environment. OER and Ir dissolution kinetics, along with the physicochemical anode state upon deactivation, are clearly characterized based on current and potential dependent charge transfer resistances and associated double layer capacitances obtained by EIS. This approach presents a useful tool for elucidating, and consequently tailoring and predicting, anode OER activity and electrolytic operational stability in industrial electrochemical applications.

The instability of Zn anode resulting from corrosion and dendritic growth remain impeding the development of aqueous zinc‐ion batteries (AZIBs). In addition, the desolvation on the Zn surface is sluggish, which hinders the reaction kinetics and fast charge/discharge behavior of AZIBs. Herein, the uniform Zn deposition and fast desolvation are realized by using a hydrophilic fumed nano‐silica coating with zinc alginate (Alg) as a functional binder (Alg/SiO2@Zn). Combined theoretical calculation and experimental investigations show the interaction between the H2O in the solvation structure and ‐OH functional group of SiO2 facilitates the desolvation process. In addition to the Zn2+ guiding effect of Alg, the fast Zn2+ diffusion along SiO2 endows the homogeneous Zn deposition. Consequently, Alg/SiO2@Zn symmetric cell demonstrates exceptional plating/stripping reversibility and excellent long‐term cycle life at both 1 and 10 mAh cm−2. A full cell assembled with Alg/SiO2@Zn and NaV3O8·xH2O cathode achieves a high capacity of 129 mAh g−1 at 4 A g−1 over 2650 cycles. Even under −20 °C, the battery maintains a high capacity of 136.5 mAh g−1 at 1 A g−1 after 1000 stable cycles. This study provides a facile strategy to achieve a highly stable Zn anode and gains deep insight into desolvation modulation via surface modification. The uniform Zn deposition and fast desolvation of Zn anode are realized by using a hydrophilic fumed nano‐silica coating with zinc alginate (Alg) as a functional binder. The interaction between the H2O in the solvation structure and ‐OH functional group of SiO2 facilitates the desolvation process. In addition to the Zn2+ guiding effect of Alg, the fast Zn2+ diffusion along SiO2 endows the homogeneous Zn deposition.

A highly polar perovskite SrTiO3 (STO) layer is considered as one of the promising artificial protective layers for the Zn metal anode of aqueous zinc-ion batteries (AZIBs). Although it has been reported that oxygen vacancies tend to promote Zn(II) ion migration in the STO layer and thereby effectively suppress Zn dendrite growth, there is still a lack of a basic understanding of the quantitative effects of oxygen vacancies on the diffusion characteristics of Zn(II) ions. In this regard, we comprehensively studied the structural features of charge imbalances caused by oxygen vacancies and how these charge imbalances affect the diffusion dynamics of Zn(II) ions by utilizing density functional theory and molecular dynamics simulations. It was found that the charge imbalances are typically localized close to vacancy sites and those Ti atoms that are closest to them, whereas differential charge densities close to Sr atoms are essentially non-existent. We also demonstrated that there is virtually no difference in structural stability between the different locations of oxygen vacancies by analyzing the electronic total energies of STO crystals with the different vacancy locations. As a result, although the structural aspects of charge distribution strongly rely on the relative vacancy locations within the STO crystal, Zn(II) diffusion characteristics stay almost consistent with changing vacancy locations. No preference for vacancy locations causes isotropic Zn(II) ion transport inside the STO layer, which subsequently inhibits the formation of Zn dendrites. Due to the promoted dynamics of Zn(II) ions induced by charge imbalance near the oxygen vacancies, the Zn(II) ion diffusivity in the STO layer monotonously increases with the increasing vacancy concentration ranging from 0% to 16%. However, the growth rate of Zn(II) ion diffusivity tends to slow down at relatively high vacancy concentrations as the imbalance points become saturated across the entire STO domain. The atomic-level understanding of the characteristics of Zn(II) ion diffusion demonstrated in this study is expected to contribute to developing new long-life anode systems for AZIBs.

The propensity of metals to form irregular and nonplanar electrodeposits at liquid-solid interfaces has emerged as a fundamental barrier to high-energy, rechargeable batteries that use metal anodes. We report an epitaxial mechanism to regulate nucleation, growth, and reversibility of metal anodes. The crystallographic, surface texturing, and electrochemical criteria for reversible epitaxial electrodeposition of metals are defined and their effectiveness demonstrated by using zinc (Zn), a safe, low-cost, and energy-dense battery anode material. Graphene, with a low lattice mismatch for Zn, is shown to be effective in driving deposition of Zn with a locked crystallographic orientation relation. The resultant epitaxial Zn anodes achieve exceptional reversibility over thousands of cycles at moderate and high rates. Reversible electrochemical epitaxy of metals provides a general pathway toward energy-dense batteries with high reversibility.

Alkaline fuel cells enable the use of earth-abundant elements to replace Pt but are hindered by the sluggish kinetics of the hydrogen oxidation reaction (HOR) in alkaline media. Precious metal–free HOR electrocatalysts need to overcome two major challenges: their low intrinsic activity from too strong a hydrogen-binding energy and poor durability due to rapid passivation from metal oxide formation. Here, we designed a Ni-based electrocatalyst with a 2-nm nitrogen-doped carbon shell (Ni@CNₓ) that serves as a protection layer and significantly enhances HOR kinetics. A Ni@CNₓ anode, paired with a Co–Mn spinel cathode, exhibited a record peak power density of over 200 mW/cm² in a completely precious metal–free alkaline membrane fuel cell. Ni@CNₓ exhibited superior durability when compared to a Ni nanoparticle catalyst due to the enhanced oxidation resistance provided by the CNₓ layer. Density functional theory calculations suggest that graphitic carbon layers on the surface of the Ni nanoparticles lower the H binding energy to Ni, bringing it closer to the previously predicted value for optimal HOR activity, and single Ni atoms anchored to pyridinic or pyrrolic N defects of graphene can serve as the HOR active sites. The strategy described here marks a milestone in electrocatalyst design for low-cost hydrogen fuel cells and other energy technologies with completely precious metal–free electrocatalysts.

This study investigated the microstructure and corrosion behavior of 30MnB5 hot-stamped steel after applying a zinc coating using the cold-spraying method followed by heat treatment (HT). Al-10 wt%Si coating is essential for improving the high-temperature corrosion resistance of 30MnB5 steel during the hot-stamping process. Before HT, the coating layer primarily consisted of Al, whereas after HT, Fe–Al-based intermetallic compounds were formed throughout the layer. The Zn in the coating layer applied using the cold-spraying method was not uniformly distributed before HT. However, during HT, the low-melting-point Zn melted and re-solidified, allowing it to combine with Fe diffusing from the substrate. Consequently, Zn–Al–Fe-based intermetallic compounds were formed on the surface of the coating layer. In the Zn-coated specimens, the current density near the corrosion potential tends to be lower than that of the Al–Si-coated specimens because Zn corrodes preferentially owing to its sacrificial anode effect, thereby protecting the underlying Al–Si-coated layer and steel.

HighlightsAlternating positively and negatively charged surface controlled by pH expedites and homogenizes Zn2+ flux, endowing the Zn- silk fibroin (SF) anode with low polarization voltage and stable stripping/plating.Experimental analyses with theoretical calculations suggest that SF coating facilitates the desolvation of [Zn(H2O)6]2+ and provides nucleation sites for uniform deposition.Symmetric battery of Zn–SF anodes delivers high-rate performance (up to 20 mA cm−2) and excellent stability (1500 h at 1 mA cm−2; 500 h at 10 mA cm−2) with cumulative capacity of 2.5 Ah cm−2.Metallic interface engineering is a promising strategy to stabilize Zn anode via promoting Zn2+ uniform deposition. However, strong interactions between the coating and Zn2+ and sluggish transport of Zn2+ lead to high anodic polarization. Here, we present a bio-inspired silk fibroin (SF) coating with amphoteric charges to construct an interface reversible electric field, which manipulates the transfer kinetics of Zn2+ and reduces anodic polarization. The alternating positively and negatively charged surface as a build-in driving force can expedite and homogenize Zn2+ flux via the interplay between the charged coating and adsorbed ions, endowing the Zn-SF anode with low polarization voltage and stable plating/stripping. Experimental analyses with theoretical calculations suggest that SF can facilitate the desolvation of [Zn(H2O)6]2+ and provide nucleation sites for uniform deposition. Consequently, the Zn-SF anode delivers a high-rate performance with low voltage polarization (83 mV at 20 mA cm−2) and excellent stability (1500 h at 1 mA cm−2; 500 h at 10 mA cm−2), realizing exceptional cumulative capacity of 2.5 Ah cm−2. The full cell coupled with ZnxV2O5·nH2O (ZnVO) cathode achieves specific energy of ~ 270.5/150.6 Wh kg−1 (at 0.5/10 A g−1) with ~ 99.8% Coulombic efficiency and retains ~ 80.3% (at 5.0 A g−1) after 3000 cycles.

The anode electrode of microbial fuel cell (MFC) is the key component to determine its power generation performance because it is the habitat and electron transfer center of the electricity-producing microorganisms. Carbon-based anodes have been confirmed to improve MFC performance. Its large surface area, excellent conductivity and low cost make it very suitable for electrode materials used in MFC. However, the low biocompatibility and instability of common carbon-based materials restrict their practical application in MFC. In this work, a bimetal oxide MnFe2O4 was prepared and used to modify carbon felt anode by a simple drop coating method. The influence of the amount of MnFe2O4 material on the performance of MFC was systematically studied. The results showed that the power density of the carbon felt anode with a MnFe2O4 modified amount of 1 mg/cm2 increased by 66.9% compared with the unmodified anode. Meanwhile, the MFC cycle using MnFe2O4 modified anode was more stable. After 6 months of long-term operation, the power density reached 3836 mW/m2. The anode modified by MnFe2O4 has capacitance characteristics, good biocompatibility and fast electron transmission rate, which significantly improves the power generation performance of MFC. In addition, the use of a simple drop coating method to prepare electrodes can reduce the difficulty of electrode fabrication and the cost of MFC, laying a certain foundation for the industrialization of MFC.

Improving zinc metal (Zn0) reversibility and minimizing the N/P ratio are critical to boosting the energy density of Zn0 batteries. However, in reality, an excess Zn source is usually adopted to offset the irreversible zinc loss and guarantee sufficient zinc cycling, which sacrifices the energy density and leads to poor practicability of Zn0 batteries. To address the above conundrum, here, we report a lean‐Zn and hierarchical anode based on metal–organic framework (MOF)‐derived carbon, where trace Zn0 is pre‐reserved within the anode structure to make up for any irreversible zinc source loss. This allows us to construct low N/P ratio Zn0 full cells when coupling the lean‐Zn anode with Zn‐containing cathodes. Impressively, high Zn0 reversibility (average Coulombic efficiency of 99.4% for 3000 cycles) and long full‐cell lifetime (92% capacity retention after 900 cycles) were realized even under the harsh lean‐Zn condition (N/P ratio: 1.34). The excellent Zn reversibility is attributed to the hierarchy structure that homogenizes zinc ion flux and electric field distribution, as confirmed by theoretical simulations, which therefore stabilizes Zn0 evolution. The lean‐Zn anode design strategy will provide new insights into construction of high‐energy Zn0 batteries for practical applications. A lean‐Zn and hierarchical anode material for low N/P ratio zinc metal batteries is reported for the first time. The innovative anode structure shows a large number of active sites and abundant ionic migration channels that jointly homogenize the ionic flux and electric field distribution, thus stabilizing Zn plating/stripping with high reversibility.