Manufacturing and Characterization of Metallic Electrode Materials

1. Introduction and Scope

In recent years, the growing demand for resources has driven the development of energy storage devices and related technologies, particularly the application of metal electrode materials, which are of particular importance in lithium, sodium, potassium, and zinc-based ion batteries, metal batteries, and solar energy storage and catalytic technologies. However, in practical applications, metal electrode materials demonstrate several drawbacks in relation to large-scale manufacturing and application. To meet the energy storage requirements for electrode materials, many researchers have explored and developed modified metal electrode materials and, through advanced characterization techniques, have improved the structural properties and energy storage efficiency of these materials.

Traditional metal electrode preparation involves casting molten metals (such as copper, aluminum, and sodium) into ingots at high temperatures, followed by rolling and stamping to obtain sheet-like or foil-like electrode materials. Not only does this method result in relatively simple electrode materials, moreover, it cannot be used to prepare nanomaterials with complex structures. Therefore, researchers have developed methods that involve mixing metal particles with carbon materials such as graphene and carbon nanotubes (CNTs) or polymers such as poly (3,4-ethylenedioxythiophene) (PEDOT) and poly (styrenesulfonate) (PSS). Additionally, they have used porous polymer templates or metal–organic framework-derived materials mixed with metal ions to form in situ-grown metal-derived composite electrode materials. Although the preparation process for these materials is relatively complex, it effectively enhances the structural stability and electrochemical properties of metal batteries while suppressing dendrite formation. This method has been widely adopted in energy storage and electrocatalysis fields.

During catalysis and electrochemical charge–discharge processes, ion migration is the primary source of these phenomena. Characterizing the structural distortion and morphological changes in metal electrode materials during this process can build a foundation for determining whether their properties have changed. This requires comparison with standards, such as the X-ray diffraction (XRD) analysis of metal electrode materials. This not only determines the crystal structure of the material but also allows for the assessment of structural changes based on variations in peak intensity, particularly in terms of different metal contents and charge–discharge cycles. Electrochemical and kinetic characterization is used to assess whether the electrochemical properties and ion migration rates have improved and serves as the primary basis for evaluating performance. Through the characterization of actual applications of metal electrode materials, their cost-effectiveness and applicability can be assessed and the feasibility of their commercial production can be enhanced.

2. Contributions

Chen et al. [Contribution 1] reveal the compression deformation mechanism of Ti/Al layered composite materials through molecular dynamics simulations. Their study shows that during compression, dislocations preferentially nucleate in the Al phase (1/6<211> and 1/6<112> types), and some dislocations (1/2<101> and 1/6<211>) can cross the interface and propagate into the Ti phase. Increased temperature promotes early dislocation nucleation, leading to reduced strength but enhanced plasticity; when T > 400 K, the formation of ordered intermetallic compounds at the interface slows the rate of strength decline. The material strength increases with increasing Ti content: at low Ti content, the plasticity is concentrated in the Ti phase (dominated by 1/6<112> dislocations), while with equal proportions, it shifts to the Al phase (dominated by 1/2<110> and 1/2<011> dislocations), resulting in reduced plasticity. Optimal performance is achieved at a Ti volume fraction of 40%, exhibiting the best strength-to-ductility balance, providing important guidance for composite material design.

Metal electrode materials also have widespread applications in the field of catalytic hydrogen production. Zhang et al. [Contribution 2] used metal electrode materials to prepare MgH₂-NaH composite materials with different composition ratios through different ball milling times. Studies have shown that increasing the NaH content can significantly improve the hydrogen production rate and kinetic performance of composite materials. However, as the ball milling time increases, the hydrogen production rate exhibits a trend of first increasing and then decreasing. Additionally, after one hour of ball milling, the hydrolysis processing of composite materials in deionized water also showed a significant improvement in reaction kinetics, releasing 1119 mL·g⁻¹ of hydrogen within 30 s, with a conversion rate of 69.2%. At 30 °C in deionized water, the composite material ground for 10 h exhibited a maximum hydrolysis hydrogen production rate of 1360 mL·g⁻¹, a hydrogen conversion rate of 83.7%, and a hydrolysis activation energy of 17.7 kJ·mol⁻¹. The significant improvement in the hydrolysis performance of the MgH₂-NaH composite material provides new insights that can inform future catalytic studies.

Traditional metal electrode materials undergo indentation deformation during preparation, which significantly affects their electrochemical properties. Zhou et al. [Contribution 3] investigated the effect of plastic deformation on the indentation behaviors of commercially pure titanium alloy. Titanium was subjected to various deformations during cold rolling, and indentation behaviors were measured using micro-indentation. The results showed that the samples with the greatest deformation exhibited the highest indentation resistance and the highest dislocation density and that the indentation size influenced the indentation behaviors of commercial pure titanium (CP-Ti). This study provides an analytical framework for reducing deformation in pure metal electrodes and offers guidance for the production of metal electrode materials.

In capacitors using composite electrode materials, composite metal electrode materials have seen widespread application. Sun et al. [Contribution 4] employed MnO₂/MXene composite electrode materials in a capacitive deionization (CDI) system and conducted a systematic evaluation of their performance. This composite material exhibits a unique synergistic effect: low-crystallinity MnO₂ nanoparticles are uniformly distributed on the MXene substrate, where MnO₂ serves as an intercalation-type pseudocapacitive material to provide high capacitance, while the three-dimensional conductive network formed by MXene significantly improves the charge transport efficiency. At a working voltage of 1.2 V, the composite material shows an excellent desalination performance (30.5 mg·g⁻¹), far exceeding that of the single-component materials (pure MXene and MnO₂). Mechanistic studies reveal that the charge storage process simultaneously involves electric double-layer capacitance (contributing 50.3%) and diffusion-controlled Faradaic processes. This work offers new design insights and technical pathways to inform the development of efficient CDI electrode materials.

Li et al. [Contribution 5] innovatively developed a Cu_xO@N-doped porous carbon network (Cu_xO@NPC) composite material with a stress-dispersing structure, effectively addressing key scientific issues in the application of transition metal oxides in supercapacitors. The study employed in situ freeze drying combined with a one-step carbonization method, successfully achieving the uniform anchoring of highly active copper oxide nanoparticles within the porous carbon network and constructing a three-dimensional conductive network with a high nitrogen doping level of 10.7%. This unique structural design enables the material to exhibit outstanding specific capacitance (392 F·g⁻¹ @ 0.5 A·g⁻¹) in a three-electrode system (6 mol·L⁻¹ KOH electrolyte). More importantly, in a two-electrode system test, the material demonstrated exceptional cycling stability (97% capacity retention after 10,000 cycles), overcoming the cycling performance bottleneck caused by agglomeration effects in traditional transition metal oxides. This study provides a new structural design strategy for developing high-performance supercapacitors using metal electrode materials.

Wu et al. [Contribution 6] successfully developed a Co₃O₄ nanosheet electrode with oxygen vacancies (OVs) and nickel foam (NF) (Co₃O_4−x/NF), achieving the efficient electrocatalytic reduction of nitrates to ammonia. The presence of OV in the material was confirmed through X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) characterization, and these defect structures significantly enhanced the electronic conductivity and electrochemical active surface area of the electrode. In terms of catalytic performance, the electrode demonstrated excellent NO₃⁻-N removal efficiency (93.7%) and NH₄⁺-N selectivity (85.4%). Mechanistic studies revealed that the increase in the Co²⁺/Co³⁺ ratio during the reaction highlights the critical role of Co²⁺ in the catalytic cycle, while oxygen vacancies effectively promote reaction kinetics by optimizing electron transfer processes. This work not only provides an efficient solution for nitrate wastewater treatment but also opens up new avenues for green ammonia synthesis, with significant implications for the development of sustainable environmental governance and energy conversion technologies.

Additionally, certain metallic electrode materials can neutralize the toxicity of waste materials, and the resource recovery of SO₂ from flue gas represents a critical challenge in the green development of the metallurgy industry. Liu et al. [Contribution 7] innovatively developed an electrochemical resource recovery technology for SO₂ based on lead cathodes. The study found that lead electrodes exhibit excellent catalytic activity and selectivity in the reduction of SO₂ to elemental sulfur (S⁰) but face severe sulfur poisoning issues. Through the introduction of sodium dodecyl benzene sulfonate (SDBS) surfactant, the sulfur content on the electrode surface was significantly reduced from 31.82% to 2.17%, effectively addressing this technical bottleneck. Under optimized conditions of pH = 0.25, E = −0.8 V vs. a saturated calomel electrode (SCE), this method achieved an 83% selective conversion rate of SO₂ to elemental sulfur (S⁰).

With the widespread emergence of electric vehicles, drones, and other electronic devices, there is a growing demand for higher energy density in energy storage devices. Lithium–sulfur batteries (LSBs) are considered a highly promising next-generation energy storage system due to their exceptional high theoretical specific capacity and energy density. However, the severe shuttle effect of soluble lithium polysulfides (LiPSs) and their slow redox kinetics result in low sulfur utilization and poor cycle stability, significantly hindering the commercialization of LSBs. To address this challenge, numerous researchers have introduced various catalytic materials as solutions. High-entropy materials (HEMs), as cutting-edge materials, exhibit unique surface and electronic structural characteristics and expose a large number of catalytic active sites, offering a novel approach to regulating the redox kinetics of LiPS. Yao et al. [Contribution 8] provide a comprehensive and in-depth review of the latest research progress in LSBs based on HEMs, covering their design principles, detailed explanations of their mechanical electrocatalytic functions, and in-depth analyses from a practical perspective.

3. Conclusions and Outlook

Metal electrode materials hold immense potential for energy storage applications, not only in the fields of electrochemistry and electrocatalysis but also in hydrogen production and waste recycling. Today, as the demand for energy storage and catalytic efficiency continues to rise, metal electrode materials have become a key research focus in related fields. However, current metal electrode materials still show considerable room for improvement, not only in terms of material preparation and characterization methods but also in terms of their commercial value. This Special Issue provides a comprehensive overview of the latest advancements in the manufacturing and characterization of metallic electrode materials and showcases the versatility of various metal electrode materials across different fields.

Not only are the preparation and characterization of electrode metal materials applicable to the field of electrochemistry, the inherent properties of the metals themselves make them suitable for additional research directions. The works in this Special Issue also advance the development of energy storage and catalysis and enhance applications of metal electrode materials in large-scale industries.

In conclusion, the field of metallic electrode materials is rich with opportunities for innovation and discovery. This Special Issue is designed to serve as a platform for ongoing advancements and set the stage for future breakthroughs.

As the Guest Editor, I extend my grateful gratitude to all the contributors, reviewers, readers, and editors of Metals whose dedication and expertise have made this Special Issue possible.