Tailoring the d-band electronic structure of deficient LaMn0.3Co0.7O3-δ perovskite nanofibers for boosting oxygen electrocatalysis in Zn-Air batteries

A Potassium-Doped Perovskite-Based Nanocomposite as an Efficient Bifunctional Oxygen Electrocatalyst for Rechargeable Zn-Air Batteries

Bifunctional oxygen electrocatalysts play a crucial role in the performance of rechargeable zinc-air batteries (ZABs), directly impacting key parameters such as capacity, round-trip efficiency, and durability. The ideal electrocatalysts for ZAB air electrodes must exhibit high catalytic activity for both oxygen reduction and oxygen evolution reactions in alkaline medium. This study presents a potassium-ion doping strategy to engineer the electron and defect structures of the perovskite oxide main phase, promoting phase separation to form a nanocomposite consisting of a perovskite phase and a secondary phase with an intergrowth structure. The resulting nanocomposite catalyst exhibits increased concentrations of Co3+ and oxygen vacancies, enhanced hydrophilicity, and improved adsorption of oxygen intermediates. As a result, the catalyst with the optimized composition demonstrates exceptional bifunctional activity and superior durability, leading to extended cycling stability and improved energy conversion efficiency in ZABs. Notably, it achieves a 42% increase in power density compared to the potassium-free pristine catalyst, a reduced voltage gap (ΔE = 0.83 V), and an extended cycle life of over 250 h. This work introduces a novel design paradigm for advanced metal-air battery catalysts through potassium-promoted defect-engineered heterostructure manipulation of perovskite oxides.

Decorated and reconstructed perovskite-oxide electrodes for oxygen electrocatalysis and Zn-air batteries

Although decorated nanoparticles offer a great potential to generate extra active sites, their preparation usually requires time- and energy-consuming approaches. We report the remarkable activity and durability augmentation for the oxygen evolution reaction (OER) via effective and facile on-site electrochemical manipulation, using LaNiO3 as a model catalyst. When compared to the pristine LaNiO3, the electrochemically manipulated LaNiO3 cycled in Fe3+-containing 0.1 M KOH (i.e., E-LNO+Fe) exhibits an almost three-fold improvement in current density at 1.65 V. It is experimentally and theoretically shown that the electrochemical manipulation leads to the creation of defective LaNiO3-δ and NiO on the surfaces, which accelerate phase transformation to (oxy)hydroxides and hence the OER. Furthermore, a Zn-air battery assembled with E-LNO+Fe has demonstrated superior activity by presenting 171 mW cm-2. Thus, our work demonstrates that substantial performance increases may be achieved by decorating and reconstructing perovskite-oxide electrodes via on-site electrochemical modification.

Manipulating d-Band Center of Nickel by Single-Iodine-Atom Strategy for Boosted Alkaline Hydrogen Evolution Reaction

Ni-based electrocatalysts have been predicted as highly potential candidates for hydrogen evolution reaction (HER); however, their applicability is hindered by an unfavorable d-band energy level (Ed). Moreover, precise d-band structural engineering of Ni-based materials is deterred by appropriative synthesis methods and experimental characterization. Herein, we meticulously synthesize a special single-iodine-atom structure (I-Ni@C) and characterize the Ed manipulation via resonant inelastic X-ray scattering (RIXS) spectroscopy to fill this gap. The complex catalytic mechanism has been elucidated via synchrotron radiation-based multitechniques (SRMS) including X-ray absorption fine structure (XAFS), in situ synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectroscopy, and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). In particular, RIXS is innovatively applied to reveal the precise regulation of Ni Ed of I-Ni@C. Consequently, the role of such single-iodine-atom strategy is confirmed to not only facilitate the moderate Ed of the Ni site for balancing the adsorption/desorption capacities of key intermediates but also act as a bridge to enhance the electronic interaction between Ni and the carbon shell for forming a localized polarized electric field conducive to H2O dissociation. As a result, I-Ni@C exhibits an enhanced alkaline hydrogen evolution performance with an overpotential of 78 mV at 10 mA/cm2 and superior stability, surpassing the majority of the reported Ni-based catalysts. Overall, this study has managed to successfully tailor the d-band center of materials from the SRMS perspective, which has crucial implications for nanotechnology, chemistry, catalysis, and other fields.

Nitrogen, sulfur co-coordinated iron single-atom catalysts with the optimized electronic structure for highly efficient oxygen reduction in Zn-air battery and fuel cell

Atomically dispersed iron-nitrogen-carbon (FesbndNsbndC) materials have been considered ideal catalysts for the oxygen reduction. Unfortunately, designing and adjusting the electronic structure of single-atom Fe sites to boost the kinetics and activity still faces grand challenges. In this work, the coordination environment engineering is developed to synthesize the FeSA/NSC catalyst with the tailored N, S co-coordinated Fe atomic site (Fe-N3S site). The structural characterizations and theoretical calculations demonstrate that the incorporation of sulfur can optimize the charge distribution of Fe atoms to weaken the adsorption of OH* and facilitate the desorption of OH*, thus leading to enhanced kinetics process and intrinsic activity. As a result, the S-modified FeSA/NSC exhibits outstanding catalytic activity with the half-wave potentials (E1/2) of 0.915 V and 0.797 V, as well as good stability, in alkaline and acidic electrolytes, respectively. Impressively, the excellent performance of FeSA/NSC is further confirmed in Zn-air batteries (ZABs) and fuel cells, with high peak power densities (146 mW cm-2 and 0.259 W cm-2).

Leaf-like Multiphase Metal Phosphides as Bifunctional Oxygen Electrocatalysts toward Rechargeable Zinc-Air Batteries

Developing a bifunctional oxygen electrocatalyst is crucial to improve the reversibility and cycle life of a rechargeable zinc-air battery (RZAB). Here, transition metal phosphides (TMPs) with a leaf-like hierarchical structure and multiphase composition can be synthesized by the "alloying-dealloying-phosphating" strategy. The as-prepared P-NiCo(1:1) electrode takes advantage of its internal dense nanoholes and synergistic effects induced by NiCoP-containing polyphase to reveal multifunctional catalysis, such as OER and ORR. In combination of these advantages, P-NiCo(1:1) exhibits an extremely low OER overpotential of 220 mV at 10 mA cm-2, a higher half-wave potential of 0.79 V for ORR, and a smaller potential difference (ΔE) of 0.66 V. The liquid RZAB with P-NiCo(1:1) as a cathodic bifunctional catalyst delivers a higher open-circuit voltage (OCV), a larger power density of 175 mW cm-2, and longer cycling life for more than 180 h. Even when applied in solid-state flexible RZABs, the lightweight module could start high-power devices. With theoretical confirmation, the major phase NiCoP of P-NiCo(1:1) is helpful to increase the density of states, regulate the d-band center, and decrease the energy barrier to 2.13 eV, which are significantly superior to those of Co2P and Ni2P. It is believable that the synthetic strategy and activity-promoting mechanism acquired from this research can offer a guide to designing a promising rechargeable zinc-air battery system.

Engineering dual-crystal configurations in perovskite oxides boosts electrocatalysis of lithium-oxygen batteries

Sculpting crystal configurations can vastly affect the charge and orbital states of electrocatalysts, fundamentally determining the catalytic activity of lithium-oxygen (Li-O2) batteries. However, the crucial role of crystal configurations in determining the electronic states has usually been neglected and needs to be further examined. Herein, we introduce orthorhombic and trigonal system into 0.5La0.6Sr0.4MnO3-0.5LaMn0.6Co0.4O3 (LSMCO) by selectively incorporating Sr and Co cations into the LaMnO3 framework during the sol-gel process, which is used to explore the relationship among crystal structure, electronic states and catalytic performance. Based on both experimental and theoretical calculations, the dual-crystal configurations induce strong lattice distortion, which promotes MnO6 octahedra vibration and shortened MnO bonds. Furthermore, the suppressed Jahn-Teller distortion weakens the orbital arrangement and accelerates the charge delocalization, leading to the conversion of Mn3+ to Mn4+ and optimized electronic states. Ultimately, this resulted in optimized Mn 3d and O 2p orbital hybridization and activated lattice oxygen function, leading to a significant improvement in electrocatalytic activity. The LSMCO catalyzed Li-O2 battery achieves enhanced discharge capacity of 14498.7 mAh/g and cycling stability of 258 cycles. This work highlights the significance of inner structure and presents a feasible strategy for engineering crystal configurations to boost electrocatalysis of Li-O2 batteries.