Flower-like NiCo2O4–CN as efficient bifunctional electrocatalyst for Zn-Air battery

Cobalt Oxide-Based Electrocatalysts with Bifunctionality for High-Performing Rechargeable Zinc-Air Batteries

In recent years, the rapid growth in renewable energy applications has created a significant demand for efficient energy storage solutions on a large scale. Among the various options, rechargeable zinc-air batteries (ZABs) have emerged as an appealing choice in green energy storage technology due to their higher energy density, sustainability, and cost-effectiveness. Regarding this fact, a spotlight is shaded on air electrode for constructing high-performance ZABs. Cobalt oxide-based electrocatalysts on the air electrode have gained significant attention due to their extraordinary features. Particularly, exploration and integration of bifunctional behavior for energy storage has remarkably promoted both ORR and OER to facilitate the overall performance of the battery. The plot of this review is forwarded towards in-depth analysis of the latest advancements in electrocatalysts that are based on cobalt oxide and possess bifunctional properties along with an introduction of the fundamental aspects of ZABs, Additionally, the topic entails an examination of the morphological variations and mechanistic details mentioning about the synthesis processes. Finally, a direction is provided for future research endeavors through addressing the challenges and prospects in the advancement of next-generation bifunctional electrocatalysts to empower high-performing ZABs with bifunctional cobalt oxide.

Self-Adaptive Electronic Structure of Amphoteric Conjugated Ligand-Modified 3 d Metal-C3 N4 Smart Electrocatalyst by pH Self-Response Realizing Electrocatalytic Self-Adjustment

Constructing pH-responsive smart material provides a new opportunity to address the problem that traditional electrocatalysts cannot achieve both alkaline oxygen evolution reaction (OER) and acidic hydrogen evolution reaction (HER) activities. In this study, amphoteric conjugated ligand (2-aminoterephthalic acid, BDC-NH₂ )-modified 3d metal-anchored graphitic carbon nitride (3d metal-C₃ N₄ ) smart electrocatalysts are constructed, and self-adaptation of the electronic structure is realized by self-response to pH stimulation, which results in self-adjustment of alkaline OER and acidic HER. Specifically, the amino and carboxyl functional groups in BDC-NH₂ undergo protonation and deprotonation respectively under different pH stimulation to adapt to environmental changes. Through DFT calculations, the increase or decrease of electron delocalization range brought by the self-response characteristic is found to lead to redistribution of the Bader charge around the modified active sites. The OER and HER activities are greatly promoted roughly 4.8 and 8.5 times over Co-C₃ N₄ after BDC-NH₂ -induced self-adaptive processes under different environments, arising from the reduced energy barrier of O* to OOH* and ΔG_H* . Impressively, the proposed BDC-NH₂ -induced smart regulation strategy is applicable to a series of 3d metal anchors for C₃ N₄ , including Co, Ni and Fe, providing a general structural upgrading method for constructing smart electrocatalytic systems.

Dealloying-Derived Porous Spinel Oxide for Bifunctional Oxygen Electrocatalysis and Rechargeable Zinc-Air Batteries: Promotion of Activity Via Hereditary Al-Doping

The large-scale fabrication of highly efficient and low-cost bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical to the development of rechargeable zinc-air batteries (ZABs). Herein, a scalable dealloying strategy was proposed to obtain hierarchically porous spinel-type oxide with minor hereditary Al doping. Benefiting from the well-structured porosity and native dopant, O-np-Ni₅ Co₁₀ (Al), namely Al-NiCo₂ O₄ , exhibited excellent electrocatalytic ORR and OER activities, giving a small potential gap of 0.71 V. The rechargeable ZAB with O-np-Ni₅ Co₁₀ (Al) as cathode catalyst delivered a high specific capacity of 757 mAh g^-1 , a competitive peak power density of 142 mW cm^-2 , and a long-term discharge-charge cycling stability. Furthermore, density functional theory calculations evidenced that appropriate Al doping into NiCo₂ O₄ could significantly reduce the Gibbs free energy difference to 1.71 eV. This work is expected to inspire the design of performance-oriented bifunctional electrocatalysts for wider applications in renewable energy systems.

Tunable dual cationic redox couples boost bifunctional oxygen electrocatalysis for long-term rechargeable Zn-air batteries

Efficient nonprecious bifunctional electrocatalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for improving the electrochemical performance of Zinc-air (Zn-air) batteries. Herein, we report a cobalt-doped Mn₂(OH)₃VO₃ catalyst prepared by facile hydrothermal method, and the ratios of cationic redox couples of catalysts were tuned with different Co doping amounts. The as-prepared Mn_1.8Co_0.2(OH)₃VO₃ (MnCoVO-1) catalyst achieves the highest ratio of (Mn³⁺Mn⁴⁺)/Mn²⁺ and Co³⁺/Co²⁺ redox couples which serve as ORR and OER active sites respectively, and exhibits the enhanced electrocatalytic performance. Furthermore, when employed as air-cathode catalyst for rechargeable Zn-air batteries, the MnCoVO-1 catalyst reveals a high power density (278 mW cm^-2), enhanced rate performance and outstanding long-term stability of over 270 h. This work demonstrates the Co-doped Mn₂(OH)₃VO₃ with optimized electronic structure by rational doping engineering can serve as a promising bifunctional catalyst for oxygen electrocatalysis and rechargeable Zn-air batteries.

Magnesium lignosulfonate-derived N, S co-doped 3D flower-like hierarchically porous carbon as an advanced metal-free electrocatalyst towards oxygen reduction reaction

The development of metal-free electrocatalytic materials that are economical, friendly to the environment, and efficiency towards the oxygen reduction reaction (ORR) is of significant interest. Hence, this paper synthesizes nitrogen and sulfur co-doped three-dimensional magnesium lignosulfonate (MLS-derived) flower-like hierarchical porous carbon (NSLPC) materials by a simple and green method. The synthesized NSLPC uses magnesium lignosulfonate as the sulfur source and carbon precursor, melamine as nitrogen source, MgO as hard template, and ZnCl₂ as the activator. We also investigated the effect of the ratio of MgO to ZnCl₂ on the catalyst performance. When the ratio of MgO to ZnCl₂ is 10:0.5, NSLPC-1005 possesses the highest ORR activity with an enormous surface area (1752.54 m² g^-1), abundant active sites, and a hierarchical porous network structure. In alkaline media, NSLPC-1005 has an initial potential of 0.97 V, as well as an excellent half-potential of 0.86 V (vs. Hg/HgO), and an ultimate current density of 5.35 mA cm^-2. It exhibits attractive ORR performance as well as outstanding cyclic stability that are comparable to commercial Pt/C electrocatalysts. This research developed an effective approach to synthesize metal-free carbon materials with high activity and long-term durability as electrocatalysts, which have a promising application in sustainable energy conversion technology.

N-Doped carbon coated NiCo2O4 nanorods for efficient electrocatalytic oxygen evolution

Hybrid architectures composed of NiCo₂O₄ nanorods coated N-doped carbon (NiCo₂O₄@NC) are synthesized through the pyrolysis of Bi-metallic MOFs, which exhibit excellent electrochemical performance for oxygen evolution reaction.

Three-Dimensional-Order Macroporous AB2O4 Spinels (A, B =Co and Mn) as Electrodes in Zn-Air Batteries

In this work, atomically substituted three-dimensionally ordered macroporous (3DOM) spinels based on Co and Mn (MnCo₂O₄ and CoMn₂O₄) were synthetized and used as cathodic electrocatalysts in a primary Zn-air battery. Scanning/transmission electron microscopy images show a 3DOM structure for both materials. Skeleton sizes of 114.4 and 140.8 nm and surface areas of 65.3 and 74.6 m² g^-1 were found for MnCo₂O₄ and CoMn₂O₄, respectively. The increase in surface area and higher presence of Mn³⁺ and Mn⁴⁺ species in the CoMn₂O₄ 3DOM material improved battery performance with a maximum power density of 101.6 mW cm^-2 and a specific capacity of 1440 mA h g^-1, which shows the highest battery performance reported to date using similar spinel materials. The stability performance of the electrocatalyst was evaluated in half-cell and battery cell systems, showing the higher durability of CoMn₂O₄, which was related to its better capability to perform the electrocatalytic process as adsorption, electron transfer, and desorption. It was found through density functional theory calculations that the CoMn₂O₄ spinel has a higher density of states in the Fermi level vicinity and better conductivity. Finally, the unique shape of 3DOM spinels promoted a high interaction between electroactive species and catalytic sites, making them suitable for oxygen reduction reaction applications.