Electrical Pulse Induced One-step Formation of Atomically Dispersed Pt on Oxide Clusters for Ultra-Low-Temperature Zinc-Air Battery

FeNiCo|MnGaOx Heterostructure Nanoparticles as Bifunctional Electrocatalyst for Zn-Air Batteries

Driven by the pressing demand for stable energy systems, zinc-air batteries (ZABs) have emerged as crucial energy storage solutions. However, the quest for cost-effective catalysts to enhance vital oxygen evolution and reduction reactions remains challenging. FeNiCo|MnGaOx heterostructure nanoparticles on carbon nanotubes (CNTs) are synthesized using liquid-phase reduction and H2 calcination approach. Compared to its component, such FeNiCo|MnGaOx/CNT shows a high synergistic effect, low impedance, and modulated electronic structure, leading to a superior bifunctional catalytic performance with an overpotential of 255 mV at 10 mA cm-2 and half-wave potential of 0.824 V (ω = 1600 rpm and 0.1 m KOH electrolyte). Moreover, ZABs based on FeNiCo|MnGaOx/CNT demonstrate notable features, including a peak power density of 136.1 mW cm-2, a high specific capacity of 808.3 mAh gZn -1, and outstanding stability throughout >158 h of uninterrupted charge-discharge cycling. Theoretical calculations reveal that the non-homogeneous interface can introduce more carriers and altered electronic structures to refine intermediate adsorption reactions, especially promoting O* formation, thereby enhancing electrocatalytic performance. This work demonstrates the importance of heterostructure interfacial modulation of electronic structure and enhancement of adsorption capacity in promoting the implementation of OER/ORR, ZABs, and related applications.

Well-dispersed Pt/Nb2O5on zeolitic imidazolate framework derived nitrogen-doped carbon for efficient oxygen reduction reaction

In this work, an advanced hybrid material was constructed by incorporating niobium pentoxide (Nb2O5) nanocrystals with nitrogen-doped carbon (NC) derived from ZIF-8 dodecahedrons, serving as a support, referred to as Nb2O5/NC. Pt nanocrystals were dispersed onto Nb2O5/NC using a simple impregnation reduction method. The obtained Pt/Nb2O5/NC electrocatalyst showed high oxygen reduction reaction (ORR) activity due to three-phase mutual contacting structure with well-dispersed Pt and Nb2O5NPs. In addition, the conductive NC benefits electron transfer, while the induced Nb2O5can regulate the electronic structure of Pt element and anchor Pt nanocrystals, thereby enhancing the ORR activity and stability. The half-wave potential (E1/2) for Pt/Nb2O5/NC is 0.886 V, which is higher than that of Pt/NC (E1/2= 0.826 V). The stability examinations demonstrated that Pt/Nb2O5/NC exhibited higher electrocatalytic durability than Pt/NC. Our work provides a new direction for synthesis and structural design of precious metal/oxides hybrid electrocatalysts.

Engineering Electronic Structure of Nitrogen-Carbon Sites by sp3 -Hybridized Carbon and Incorporating Chlorine to Boost Oxygen Reduction Activity

Development of efficient and easy-to-prepare low-cost oxygen reaction electrocatalysts is essential for widespread application of rechargeable Zn-air batteries (ZABs). Herein, we mixed NaCl and ZIF-8 by simple physical milling and pyrolysis to obtain a metal-free porous electrocatalyst doped with Cl (mf-pClNC). The mf-pClNC electrocatalyst exhibits a good oxygen reduction reaction (ORR) activity (E1/2 =0.91 V vs. RHE) and high stability in alkaline electrolyte, exceeding most of the reported transition metal carbon-based electrocatalysts and being comparable to commercial Pt/C electrocatalysts. Likewise, the mf-pClNC electrocatalyst also shows state-of-the-art ORR activity and stability in acidic electrolyte. From experimental and theoretical calculations, the better ORR activity is most likely originated from the fact that the introduced Cl promotes the increase of sp3 -hybridized carbon, while the sp3 -hybridized carbon and Cl together modify the electronic structure of the N-adjacent carbons, as the active sites, while NaCl molten-salt etching provides abundant paths for the transport of electrons/protons. Furthermore, the liquid rechargeable ZAB using the mf-pClNC electrocatalyst as the cathode shows a fulfilling performance with a peak power density of 276.88 mW cm-2 . Flexible quasi-solid-state rechargeable ZAB constructed with the mf-pClNC electrocatalyst as the cathode exhibits an exciting performance both at low, high and room temperatures.

Electrolyte Modulation Strategies for Low-Temperature Zn Batteries

Aqueous rechargeable Zn metal batteries (ARZBs) are extensively studied recently because of their low-cost, high-safety, long lifespan, and other unique merits. However, the terrible ion conductivity and insufficient interfacial redox dynamics at low temperatures restrict their extended applications under harsh environments such as polar inspections, deep sea exploration, and daily use in cold regions. Electrolyte modulation is considered to be an effective way to achieve low-temperature operation for ARZBs. In this review, first, the fundamentals of the liquid-solid transition of water at low temperatures are revealed, and an in-depth understanding of the critical factors for inferior performance at low temperatures is given. Furthermore, the electrolyte modulation strategies are categorized into anion/concentration regulation, organic co-solvent/additive introduction, anti-freezing hydrogels construction, and eutectic mixture design strategies, and emphasize the recent progress of these strategies in low-temperature Zn batteries. Finally, promising design principles for better electrolytes are recommended and future research directions about high-performance ARZBs at low temperatures are provided.

Engineering Mn-Nx sites on porous carbon via molecular assembly strategy for long-life zinc-air batteries

Nitrogen-coordinated manganese atoms on carbon materials denoted as MnNC, serve as the highly active non-precious metal electrocatalysts for oxygen reduction reaction (ORR) in zinc-air batteries (ZABs). Nonetheless, a significant challenge arises from the tendency of Mn atoms to aggregate during heat treatment, thereby compromising ORR performance in ZABs. In this work, the molecular assembly strategy based on the hydrogen bond interaction was employed to fabricate the MnNC electrocatalyst. This approach promotes the dispersion of Mn atoms, creating abundant Mn-Nx active sites. Furthermore, the resulting three-dimensional porous nanostructure, formed by molecular assembly, significantly enhances accessibility to the Mn-Nx active sites. The porous nanostructure not only shortens the diffusion path of reactants and charges but also improves mass transfer. The MnNC exhibits impressive ORR catalytic performance with a half-wave potential of 0.90 V (vs. RHE). The liquid-type ZAB based on MnNC displays a high specific capacity of 816.6 mAh/g and an extended charge-discharge cycle life of 1000 h. Quasi-solid-state ZAB based on MnNC can operate stably for 24 h. This work presents an effective strategy to synthesize transition metal-nitrogen-carbon (MNC) electrocatalysts tailored for long-life zinc-air battery.

Ultrafine Pt Nanoparticles Anchored on 2D Metal-Organic Frameworks as Multifunctional Electrocatalysts for Water Electrolysis and Zinc-Air Batteries

Multifunctional electrocatalysts are crucial to cost-effective electrochemical energy conversion and storage systems requiring mutual enhancement of disparate reactions. Embedding noble metal nanoparticles in 2D metal-organic frameworks (MOFs) are proposed as an effective strategy, however, the hybrids usually suffer from poor electrochemical performance and electrical conductivity in operating conditions. Herein, ultrafine Pt nanoparticles strongly anchored on thiophenedicarboxylate acid based 2D Fe-MOF nanobelt arrays (Pt@Fe-MOF) are fabricated, allowing sufficient exposure of active sites with superior trifunctional electrocatalytic activity for hydrogen evolution, oxygen evolution, and oxygen reduction reactions. The interfacial Fe─O─Pt bonds can induce the charge redistribution of metal centers, leading to the optimization of adsorption energy for reaction intermediates, while the dispersibility of ultrafine Pt nanoparticles contributes to the high mass activity. When Pt@Fe-MOF is used as bifunctional catalysts for water-splitting, a low voltage of 1.65 V is required at 100 mA cm-2 with long-term stability for 20 h at temperatures (65 °C) relevant for industrial applications, outperforming commercial benchmarks. Furthermore, liquid Zn-air batteries with Pt@Fe-MOF in cathodes deliver high open-circuit voltages (1.397 V) and decent cycling stability, which motivates the fabrication of flexible quasisolid-state rechargeable Zn-air batteries with remarkable performance.

Tailoring Oxygen Reduction Reaction Kinetics on Perovskite Oxides via Oxygen Vacancies for Low-Temperature and Knittable Zinc-Air Batteries

High kinetics oxygen reduction reaction (ORR) electrocatalysts under low temperature are critical and highly desired for temperature-tolerant energy conversion and storage devices, but remain insufficiently investigated. Herein, oxygen vacancy-rich porous perovskite oxide (CaMnO3 ) nanofibers coated with reduced graphene oxide coating (V-CMO/rGO) are developed as the air electrode catalyst for low-temperature and knittable Zn-air batteries. V-CMO/rGO exhibits top-level ORR activity among perovskite oxides and shows impressive kinetics under low temperature. Experimental and theoretical calculation results reveal that the synergistic effect between metal atoms and oxygen vacancies, as well as the accelerated kinetics and enhanced electric conductivity and mass transfer over the rGO coated nanofiber 3D network contribute to the enhanced catalytic activity. The desorption of ORR intermediate is promoted by the regulated electron filling. The V-CMO/rGO drives knittable and flexible Zn-air batteries under a low temperature of -40 °C with high peak power density of 56 mW cm-2 and long cycle life of over 80 h. This study provides insight of kinetically active catalyst and facilitates the ZABs application in harsh environment.

Single-Atom Nano-Islands (SANIs): A Robust Atomic-Nano System for Versatile Heterogeneous Catalysis Applications

Academician Tao Zhang from China and co-workers designed the first Pt₁ /FeO_x single-atom catalysts (SACs) in 2011, and they proposed the concept of "single-atom catalysis" in the field of heterogeneous catalysis. Generally, it is easy for active metal single-atom sites on a carrier to migrate and aggregate, which results in poor performance; or the chemical bond between the metal atom and carrier is too strong (immovable), which results in passivation of the active site. Recently, "nano-island" type SACs were designed, in which the active metal atoms are isolated on the "islands", and can move within the respective "island", but the migration across the "island" is blocked, to achieve a dynamic confinement design of single atoms (that is, a "moving but not aggregating" design philosophy). Herein, a new concept of "single-atom nano-islands (SANIs)" is proposed to describe these congeneric "atomic-nano" systems in heterogeneous catalysis fields. Particularly, the SANIs are divided into three categories: "one-island-one-atom", "one-island-multi-atoms", and "island-sea synergism" architectures. The scientific significance and application principles of SANIs in versatile heterogeneous catalysis fields (i.e., thermocatalysis, electrocatalysis, and photocatalysis) are summarized. The challenges and proposals of SANIs are also provided.

Competitive Trapping of Single Atoms onto a Metal Carbide Surface

Controlling atomic adjustment of single-atom catalysts (SACs) can directly change its local configuration, regulate the energy barrier of intermediates, and further optimize reaction pathways. Herein, we report an atom manipulating process to synthesize Ni atoms stabilized on vanadium carbide (Ni_SA-VC) through a nanofiber-medium thermodynamically driven atomic migration strategy. Experimental and theoretical results systematically reveal the tunable migration pathway of Ni atom from Ni nanoparticles to neighboring N-doped carbon (NC) and finally to metal carbide that was obtained by regulating the competitive adsorption energies between VC and NC for capturing Ni atoms. For CO₂-to-CO electroreduction, Ni_SA-VC exhibits an industrial current density of -180 mA cm^-2 at -1.0 V vs reversible hydrogen electrode and the highest Faradaic efficiency for CO production (FE_CO) of 96.8% at -0.4 V vs RHE in a flow cell. Significant electron transfers occurring in Ni_SA-VC structures contribute to the activation of CO₂, facilitate the reaction free energy, regulate *CO desorption as the rate-determining step, and promote the activity and selectivity. This study provides an understanding on how to design powerful SACs for electrocatalysis.

Tunable Heterogeneous FeCo Alloy-Mo0.82N Bifunctional Electrocatalysts for Temperature-Adapted Zn-Air Batteries

The practical applications of temperature-tolerant Zn-air batteries (ZABs) rely on highly active and stable bifunctional catalysts that accelerate cathodic oxygen reduction (ORR) and oxygen evolution (OER) reactions. Herein, we successfully integrated fascinating transition metal nitrides and FeCo alloys through a simple coordination assembly and pyrolysis process. Importantly, the alloy-to-nitride ratio in the heterogeneous catalyst can be carefully regulated through the subsequent etching process. Moreover, the composition-dependent ORR/OER performance of the FeCo-Mo_0.82N catalysts was revealed. Aqueous ZABs using the optimized FeCo-Mo_0.82N-60 as a cathode exhibit a high peak power density of 149.7 mW cm^-2 and an impressive stability of 600 h with a low charge-discharge voltage gap decay rate of 0.025 mV h^-1, which exceeds those of most of recent reports. Furthermore, the FeCo-Mo_0.82N-60-based flexible ZABs display a small specific capacity degradation (3%) from 40 to -10 °C, demonstrating excellent temperature tolerance.