Interface engineering of Co3S4@Co3O4/N, S-doped carbon core@shell nanostructures serve as an excellent bifunctional ORR/OER electrocatalyst for rechargeable Zn-air battery

Hierarchically Ordered Macro-/Mesoporous N,P-Codoped Carbon with Fe-Co Dual Sites for Efficient Electrocatalytic Oxygen Reduction

The development of high-performance, low-cost non-precious-metal electrocatalysts as alternatives to Pt-based catalysts for the oxygen reduction reaction (ORR) is crucial for promoting the commercial application of fuel cells and metal-air batteries. In this work, we report a novel type of ORR electrocatalyst with Fe and Co sites anchored on N,P-codoped hierarchically ordered macro-/mesoporous carbon (FeCo/NP-HOMMC) through a facile one-pot, controllable synthesis method with the aid of dual-templating technique. The FeCo/NP-HOMMC catalyst shows robust ORR performance under alkaline conditions with a half-wave potential (E1/2) of 0.90 V vs. reversible hydrogen electrode (RHE), significantly surpassing the commercial 20 wt% Pt/C catalyst, while also exhibiting remarkable long-term stability and great methanol tolerance. Control experiments reveal that the superior performance of the FeCo/NP-HOMMC catalyst for ORR benefits from the synergistic catalysis of highly dispersed Fe and Co dual active sites, and the advantages of the unique hierarchically ordered macro-/mesoporous structure, which can provide improved active site accessibility, excellent conductivity, and maximized mass/charge transport.

Low-Level Fe Doping in CoMoO4 Enhances Surface Reconstruction and Electronic Modulation Creating an Outstanding OER Electrocatalyst for Water Splitting

Efficient and stable nonprecious metal-based oxygen evolution reaction (OER) electrocatalysts are pivotal for water electrolysis technology. Herein, we are reporting an effective strategy for fabricating efficient Co-based OER electrocatalysts by low-level Fe doping in CoMoO4 to boost surface reconstruction and electronic modulation, which resulted in excellent OER electroactivity consequently. Our findings reveal that a mere 5.30% (wt %) of Fe doping can raise the O 2p band center energy nearer to the Fermi level, reduce the energy barrier for oxygen vacancy (VO) formation, and significantly enhance OER electrocatalytic activity. Additionally, the fast dissolution of Mo in the initial reaction facilitated surface reconstruction to form active oxyhydroxide species and stabilized Fe and Co from leaching. As a result, the optimized catalyst Fe-CoMoO4-0.2 exhibited a low overpotential of 276 mV at 10 mA cm-2 in 1 M KOH and can operate stably at a current density of 20 mA cm-2 for at least 24 h under water splitting conditions. This work provides an excellent example of regulating the surface structure and electronic properties of the OER catalysts.

Graphene Supported NiFe-LDH and PbO2 Catalysts Prepared by Plasma Process for Oxygen Evolution Reaction

The development of efficient catalysts for water electrolysis is crucial for advancing the low-carbon transition and addressing the energy crisis. This work involves the fabrication of graphene-based catalysts for the oxygen evolution reaction (OER) by integrating NiFe-LDH and PbO2 onto graphene using plasma treatment. The plasma process takes only 30 min. Graphene's two-dimensional structure increases the available reaction surface area and improves surface electron transport. Plasma treatment further improves catalyst performance by facilitating nanoparticle attachment and creating carbon defects and sulfur vacancies. Density functional theory (DFT) calculations at the PBE provide valuable insights into the role of vacancies in enhancing catalyst performance for OER. The catalyst's conductivity and electronic structure are greatly impacted by vacancies. While modifications to the electronic structure increase the kinetics of charge transfer, the vacancy structure can produce more active sites and improve the adsorption and reactivity of OER intermediates. This optimization of intermediate adsorption and electronic properties leads to increased overall OER activity. The catalyst NiFe-PbO2/S/rGO-45, synthesized through plasma treatment, demonstrated an overpotential of 230 mV at 50 mA·cm-2 and a Tafel slope of 44.26 mV dec-1, exhibiting rapid reaction kinetics and surpassing the OER activity of commercial IrO2. With its excellent performance, the prepared catalyst has broad prospects in commercial applications such as water electrolysis and air batteries.

Constructing heterogeneous interface between Co3O4 and RuO2 with enhanced electronic regulation for efficient oxygen evolution reaction at large current density

Exploring effective strategies for developing new high-efficiency catalysts for water splitting is essential for advancing hydrogen energy technology. Herein, Co3O4/RuO2 heterojunction interface is construct through ion exchange reaction and pyrolysis. The as-synthesized Co3O4/RuO2-4 exhibits outstanding oxygen evolution reaction (OER) activity at the current density of 100 mA cm-2 with a low overpotential of 276 mV, and remarkable stability (maintaining activity for 60 h at 100 mA cm-2). Experimental results and theoretical calculations reveal that the electrons around the heterogeneous interface transferred from RuO2 to Co3O4, resulting in electron redistribution and optimization of energy barriers for OER intermediates. This unique composite catalyst structure offers a new potential for designing efficient oxygen electrocatalysts at large current density.

Phosphorus-doped nickel cobalt oxide (NiCo2O4) wrapped in 3D hierarchical hollow N-doped carbon nanoflowers as highly efficient bifunctional electrocatalysts for overall water splitting

Properly design and fabricate capable electrocatalysts with 3D hierarchical hollow framework to realize cost-effective and efficacious overall water splitting (OWS) are particularly meaningful for the large-scale arrangement of pivotal energy technology. In this study, P-doped NiCo2O4 nanoparticles encapsulated in N-doped carbon hierarchical hollow nanoflowers (P-NiCo2O4@NCHHNFs) were constructed using the hydrothermal-pyrolysis-phosphorization approach. This fascinating architecture can not merely serve as a conductive pathway for electron transfer, but at the same time effectively inhibited the aggregation and corrosion of the NiCo2O4 nanoparticles. Additionally, the P doping not only regulates electronic structure configuration to boost the intrinsic activity of the catalyst, but also enhance electrochemical surface areas to reveal more accessible active sites. Attributing to these characteristics, the as-prepared P-NiCo2O4@NCHHNFs exhibit preeminent electrocatalytic performance with low overpotentials of 283 mV and 162 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) (at 10 mA cm-2), respectively. Specifically, by using the P-NiCo2O4@NCHHNFs as bifunctional catalysts, a low potential of 1.56 V (at 10 mA cm-2) is sufficient to drive overall water splitting with splendid durability. This study proposed an innovative strategy for the conceiving and fabricating high-performance catalysts via heteroatom-doping.

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.

Carbon cloth supporting spinel CuMn0.5Co2O4 nanoneedles with the regulated electronic structure by multiple metal elements as catalysts for efficient oxygen evolution reaction

Developing transition metal oxide catalysts to replace the noble metal oxide catalysts for efficient oxygen evolution reaction (OER) is essential to promote the practical application of water splitting. Herein, we designed and constructed the carbon cloth (CC) supporting spinel CuMn_0.5Co₂O₄ nanoneedles with regulated electronic structure by multiple metal elements with variable chemical valences in the spinel CuMn_0.5Co₂O₄. The carbon cloth not only provided good conductivity for the catalytic reaction but also supported the well-standing spinel CuMn_0.5Co₂O₄ nanoneedles arrays with a large special surface area. Meanwhile, the well-standing nanoneedles arrays and mesoporous structure of CuMn_0.5Co₂O₄ nanoneedles enhanced their wettability and facilitated access for electrolyte to electrochemical catalysis. Besides, the regulated electronic structure and generated oxygen vacancies of CuMn_0.5Co₂O₄/CC by multiple metal elements improved the intrinsic catalytic activity and the durability of OER activity. Profiting from these merits, the CuMn_0.5Co₂O₄/CC electrode exhibited superior OER activity with an ultralow overpotential of 189 mV at the current density of 10 mA⋅cm^-2 and a smaller Tafel slope of 64.1 mV⋅dec^-1, which was competitive with the noble metal oxides electrode. And the CuMn_0.5Co₂O₄/CC electrode also exhibited long-term durability for OER with 95.3% of current retention after 1000 cycles. Therefore, the competitive OER activity and excellent cycling durability suggested that the CuMn_0.5Co₂O₄/CC electrode is a potential candidate catalyst for efficient OER.