Heterogeneous Bimetallic Organic Coordination Polymer-Derived Co/Fe@NC Bifunctional Catalysts for Rechargeable Li-O2 Batteries

Synergistic Zn and MoS2 Tailored Co-N/C Environments Enabling Bifunctional ORR/OER Electrocatalysis for Advanced Li-O2 Batteries

To better adapt lithium-oxygen batteries (LOBs) and overcome their sluggish oxygen reduction and evolution reactions (ORR/OER) kinetics, designing efficient bifunctional ORR/OER catalytic materials is essential. In this study, we successfully constructed a bifunctional ZnCo-N/C@MoS2 catalyst by tailoring the Co-N/C center with Zn incorporation and MoS2 encapsulation. Surprisingly, Zn atoms, which are typically considered to promote the Co atoms isolation, exhibit a promoting effect on the ORR performance of Co-N/C centers and enhance their stability under harsh conditions. Introducing MoS2 establishes Mo-N coupling centers, enhancing electron transfer and adjusting the charge density of Co active centers, thereby compensating OER activity limitation of ZnCo-N/C. In Li-O2 batteries, Zn and MoS2 synergistically optimize intermediate interactions and regulate LiO2 formation/decomposition, while Zn's environmental adaptability and MoS2's encapsulating protection jointly enhance operational stability. Results show that ZnCo-N/C@MoS2, serving as the oxygen electrode in Li-O2 batteries, achieves a low overpotential of 1.01 V, an ultra-high specific capacity of 25,026 mAh g-1, and a long cycle life of 298 cycles. This work achieves bifunctionality in single-atom catalysts through precise dual modulation of the catalytic environment, providing a novel strategy for the development of lithium-oxygen batteries.

Tailoring Cationic Cobalt Vacancies in Molybdenum-Cobalt Selenide Derived from POM@ZIF-67 for Enhanced Electrocatalysis in Lithium-Oxygen Batteries

Slow reaction kinetics during redox reactions limits the utilization of the high theoretical energy density of lithium-oxygen batteries (LOBs). Vacancy engineering, a potential strategy for modulating active sites, is critical in the development of high performance catalysts. This study investigates cobalt vacancies in Mo-CoSe2 nanoparticles created by selenization of phosphomolybdic acid (POM) embedded into zeolitic imidazolate framework-67 (ZIF-67). The nanomaterial exhibits an outstanding electrochemical performance, characterized by high specific capacitance and excellent cycle durability. The LOBs with cobalt vacancies in the Mo-CoSe2 electrode material exhibit a discharge capacity of 21 836 mAh g-1 at a current density of 100 mA g-1 and exhibit stable cycling performance over 194 cycles at 300 mA g-1. Additionally, density functional theory (DFT) calculations suggest that the presence of cobalt vacancies increases the distance between the surface selenium atoms and the subsurface cobalt atoms. In addition, cobalt vacancies modify the electronic structure of the d-orbitals, lowering the energy barriers of the reaction and accelerating the reaction kinetics by improving the adsorption of the reactants. The research introduces a strategy for the rational design of efficient cathode materials in LOBs.

Geometric and Electronic Engineering in Co/VN Nanoparticles to Boost Bifunctional Oxygen Electrocatalysis for Aqueous/Flexible Zn-Air Batteries

Modulating metal-metal and metal-support interactions is one of the potent tools for augmenting catalytic performance. Herein, highly active Co/VN nanoparticles are well dispersed on three-dimensional porous carbon nanofoam (Co/VN@NC) with the assistance of dicyandiamide. Studies certify that the consequential disordered carbon substrate reinforces the confinement of electrons, while the coupling of diverse components optimizes charge redistribution among species. Besides, theoretical analyses confirm that the regulated electron configuration can significantly tune the binding strength between the active sites and intermediates, thus optimizing reaction energy barriers. Therefore, Co/VN@NC exhibits a competitive potential difference (ΔE, 0.65 V) between the half-wave potential of ORR and OER potential at 10 mA cm-2, outperforming Pt/C+RuO2 (0.67 V). Further, catalyst-based aqueous/flexible ZABs present superior performances with peak power densities of 156 and 85 mW cm-2, superior to Pt/C-based counterparts (128 and 73 mW cm-2). This research provides a pivotal foundation for the evolution of bifunctional catalysts in the energy sector.

A Bifunctional Electrocatalyst for OER and ORR based on a Cobalt(II) Triazole Pyridine Bis-[Cobalt(III) Corrole] Complex

As alternative energy sources are essential to reach a climate-neutral economy, hydrogen peroxide (H2O2) as futuristic energy carrier gains enormous awareness. However, seeking for stable and electrochemically selective H2O2 ORR electrocatalyst is yet a challenge, making the design of-ideally-bifunctional catalysts extremely important and outmost of interest. In this study, we explore the application of a trimetallic cobalt(II) triazole pyridine bis-[cobalt(III) corrole] complex CoIITP[CoIIIC]2 3 in OER and ORR catalysis due to its remarkable physicochemical properties, fast charge transfer kinetics, electrochemical reversibility, and durability. With nearly 100 % selective catalytic activity towards the two-electron transfer generated H2O2, an ORR onset potential of 0.8 V vs RHE and a cycling stability of 50 000 cycles are detected. Similarly, promising results are obtained when applied in OER catalysis. A relatively low overpotential at 10 mA cm-2 of 412 mV, Faraday efficiency 98 % for oxygen, an outstanding Tafel slope of 64 mV dec-1 combined with superior stability.

A Bifunctional Electrocatalyst for OER and ORR based on a Cobalt(II) Triazole Pyridine Bis-[Cobalt(III) Corrole] Complex

As alternative energy sources are essential to reach a climate-neutral economy, hydrogen peroxide (H2 O2 ) as futuristic energy carrier gains enormous awareness. However, seeking for stable and electrochemically selective H2 O2 ORR electrocatalyst is yet a challenge, making the design of-ideally-bifunctional catalysts extremely important and outmost of interest. In this study, we explore the application of a trimetallic cobalt(II) triazole pyridine bis-[cobalt(III) corrole] complex CoII TP[CoIII C]2 3 in OER and ORR catalysis due to its remarkable physicochemical properties, fast charge transfer kinetics, electrochemical reversibility, and durability. With nearly 100 % selective catalytic activity towards the two-electron transfer generated H2 O2 , an ORR onset potential of 0.8 V vs RHE and a cycling stability of 50 000 cycles are detected. Similarly, promising results are obtained when applied in OER catalysis. A relatively low overpotential at 10 mA cm-2 of 412 mV, Faraday efficiency 98 % for oxygen, an outstanding Tafel slope of 64 mV dec-1 combined with superior stability.

Boosting the activity and stability via synergistic catalysis of Co nanoparticles and MoC to construct a bifunctional electrocatalyst for high-performance and long-life rechargeable zinc-air batteries

The high overpotential of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) leading to slow air cathode kinetics is still a major challenge for zinc-air batteries (ZABs), hindering the commercialization of ZABs. With the advantages of cost-effectiveness and feasibility of synthesis at room temperature, zeolite imidazole frameworks (ZIFs) are regarded as advanced precursors. But a majority of ZIF-derived catalysts show only one catalytic activity, which limits their performance in ZABs as well as the cycling stability. In addition, molybdenum carbide (MoC) is recognized as an excellent candidate for renewable energy conversion due to its good chemical resistance and thermal stability. Herein, we report a ZIF-67-derived Co/MoC-NC multiphase doped carbon bifunctional ORR/OER catalyst with multiple active sites for the cathode of ZABs. The synergistic catalysis of Co nanoparticles and MoC nanoparticles in Co/MoC-NC which are embedded in a thin layer of N-doped graphitic carbon and immobilized on N-doped graphitic carbon, respectively, demonstrates superior ORR catalytic performance and durability both under alkaline and acidic conditions (E_1/2 = 0.87 V in 1.0 M KOH and E_1/2 = 0.76 V in 0.5 M H₂SO₄). Simultaneously, Co/MoC-NC also exhibits favorable OER performance (10 mA cm^-2, η = 320 mV) in 1 M KOH. Furthermore, a remarkable peak-power density of 215.36 mW cm^-2 and great cycling stability could be achieved while applying Co/MoC-NC in the cathode of ZABs (over 300 h). This work will provide a viable design concept for designing and synthesizing multifunctional catalysts to construct rechargeable ZABs.

Anchoring NiO Nanosheet on the Surface of CNT to Enhance the Performance of a Li-O2 Battery

Li₂O₂, as the cathodic discharge product of aprotic Li-O₂ batteries, is difficult to electrochemically decompose. Transition-metal oxides (TMOs) have been proven to play a critical role in promoting the formation and decomposition of Li₂O₂. Herein, a NiO/CNT catalyst was prepared by anchoring a NiO nanosheet on the surface of CNT. When using the NiO/CNT as a cathode catalyst, the Li-O₂ battery had a lower overpotential of 1.2 V and could operate 81 cycles with a limited specific capacity of 1000 mA h g⁻¹ at a current density of 100 mA g⁻¹. In comparison, with CNT as a cathodic catalyst, the battery could achieve an overpotential of 1.64 V and a cycling stability of 66 cycles. The introduction of NiO effectively accelerated the generation and decomposition rate of Li₂O₂, further improving the battery performance. SEM and XRD characterizations confirmed that a Li₂O₂ film formed during the discharge process and could be fully electrochemical decomposed in the charge process. The internal network and nanoporous structure of the NiO/CNT catalyst could provide more oxygen diffusion channels and accelerate the decomposition rate of Li₂O₂. These merits led to the Li-O₂ battery’s better performance.