Vinod K. Paidi

By quantitatively linking Ni charge heterogeneity to irreversible lithium loss, our study provides a mechanistic foundation for mitigating IRC loss and optimizing Ni-rich cathode performance.

We explored the electrochemical behaviour of an iron-nitrogen-carbon catalyst in the electrochemical CO2 reduction reaction (CO2RR). The catalyst was prepared by pyrolysis from carbon-supported iron porphyrin to ensure a high concentration of FeN4 moieties and low amount of side phases. In situ X-ray absorption spectroscopy and X-ray emission spectroscopy were applied to determine average oxidation state, average spin state for the ex situ catalyst, electrode and various potential conditions. Nuclear forward scattering enabled us to determine the hyperfine interaction parameters associated with all individual iron coordination sites for different potentials as well as ex situ. Together with DFT calculations, this approach enabled us to discriminate the contributions of pyridinic and pyrrolic FeN4 moieties in the catalyst. Control experiments (without CO2 saturation) showed the formation of a pyrrolic ferryl FeN4 moiety with an oxygen ligand, caused by the unavoidable presence of oxygen from air. This intermediate belongs to the oxygen reduction reaction cycle that we elucidated in our previous work (doi: 10.1021/jacs.2c04865). In the presence of CO2, however, the main changes are associated with pyridinic FeN4 moieties. Aided by the identification of different intermediates, we deduce a CO2RR mechanism for the relevant pyridinic FeN4 moieties.

While Fe–N–C materials have shown promising initial oxygen reduction reaction (ORR) activity, they lack durability in acidic medium. Key degradation mechanisms include FeN₄ site demetallation and deactivation by reactive oxygen species. Here we show for mainstream Fe–N–Cs that adding 1 wt.% Pt nanoparticles via a soft polyol method results in well-defined and stable Pt/Fe–N–C hybrids. The Pt addition strongly reduces the H₂O₂ production and Fe leaching rate during ORR, while post mortem Mössbauer spectroscopy reveals that the highly active but unstable Fe(III)N₄ site is partially stabilized. The similar H₂O₂ electroreduction activity of Pt/Fe–N–C and Fe–N–C and other analyses point toward a long-distance electronic effect of Pt nanoparticles in stabilizing FeN₄ sites. Computational chemistry reveals that spin polarization of distant Pt atoms mitigates the structural changes of FeN₄ sites upon adsorption of oxygenated species atop Fe, especially in high-spin state.

Synergistic coupling of Cu LSPR, charge carrier separation via SMSI at the Cu–TiO₂ interface, and O-vacancy defects stabilized by SMSI collectively enhance the photocatalytic CO₂ reduction performance of the DFNS-supported hybrid catalyst.

Heterogeneous catalysts have emerged as a potential key for closing the carbon cycle by converting carbon dioxide (CO ₂ ) into value-added chemicals. In this work, we report a highly active and stable ceria (CeO ₂ )-based electronically tuned trimetallic catalyst for CO ₂ to CO conversion. A unique distribution of electron density between the defective ceria support and the trimetallic nanoparticles (of Ni, Cu, Zn) was established by creating the strong metal support interaction (SMSI) between them. The catalyst showed CO productivity of 49,279 mmol g ⁻¹ h ⁻¹ at 650 °C. CO selectivity up to 99% and excellent stability (rate remained unchanged even after 100 h) stemmed from the synergistic interactions among Ni-Cu-Zn sites and their SMSI with the defective ceria support. High-energy-resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) confirmed this SMSI, further corroborated by in situ electron energy loss spectroscopy (EELS) and density functional theory (DFT) simulations. The in situ studies (HERFD-XAS & EELS) indicated the key role of oxygen vacancies of defective CeO ₂ during catalysis. The in situ transmission electron microscopy (TEM) imaging under catalytic conditions visualized the movement and growth of active trimetallic sites, which completely stopped once SMSI was established. In situ FTIR (supported by DFT) provided a molecular-level understanding of the formation of various reaction intermediates and their conversion into products, which followed a complex coupling of direct dissociation and redox pathway assisted by hydrogen, simultaneously on different active sites. Thus, sophisticated manipulation of electronic properties of trimetallic sites and defect dynamics significantly enhanced catalytic performance during CO ₂ to CO conversion.

Precise positioning of cation at tetrahedral site of Na-layer renders ‘layered’ Na-transition metal oxide totally water-stable by directly blocking the spontaneous Na ⁺ /H ⁺ exchange pathway, facilitating ‘aqueous’ processing of such cathodes for SIBs.

Oxygen vacancies and their correlation with the nanomagnetism and electronic structure are crucial for applications in dilute magnetic semiconductors design applications. Here, we report on cobalt single atom-incorporated titanium dioxide (TiO₂) monodispersed nanoparticles synthesized using a thermodynamic redistribution strategy. Using advanced synchrotron-based X-ray techniques and simulations, we find trivalent titanium is absent, indicating trivalent cations do not influence ferromagnetic (FM) stability. Density functional theory calculations show that the FM stability between Co²⁺ions is very weak. However, electron doping from additional oxygen vacancies can significantly enhance this FM stability, which explains the observed room-temperature ferromagnetism. Moreover, our calculations illustrate enhanced FM interactions between Co_Ti+ V_Ocomplexes with additional oxygen vacancies. This study explores the electronic structure and room-temperature ferromagnetism using monodispersed nanocrystallites with single-atom-incorporated TiO₂nanostructures. The strategies described herein offer promise in revealing magnetism in other single-atom-incorporated nanostructures.

Fe cations produced during the reduction of O ₂ on Fe–N–C materials transform into Fe-oxides due to a local increase in pH.

Sodium‐ion batteries (SIBs) have emerged as a compelling alternative to lithium‐ion batteries (LIBs), exhibiting comparable electrochemical performance while capitalizing on the abundant availability of sodium resources. In SIBs, P2/O3 biphasic cathodes, despite their high energy, require furthur improvements in stability to meet current energy demands. This study introduces a systematic methodology that leverages the meta‐heuristically assisted NSGA‐II algorithm to optimize multi‐element doping in electrode materials, aiming to transcend conventional trial‐and‐error methods and enhance cathode capacity by the synergistic integration of P2 and O3 phases. A comprehensive phase analysis of the meta‐heuristically designed cathode material Na_0.76Ni_0.20Mn_0.42Fe_0.30Mg_0.04Ti_0.015Zr_0.025O₂ (D‐NFMO) is presented, showcasing its remarkable initial reversible capacity of 175.5 mAh g⁻¹ and exceptional long‐term cyclic stability in sodium cells. The investigation of structural composition and the stabilizing mechanisms is performed through the integration of multiple characterization techniques. Remarkably, the irreversible phase transition of P2→OP4 in D‐NFMO is observed to be dramatically suppressed, leading to a substantial enhancement in cycling stability. The comparison with the pristine cathode (P‐NFMO) offers profound insights into the long‐term electrochemical stability of D‐NFMO, highlighting its potential as a high‐voltage cathode material utilizing abundant earth elements in SIBs. This study opens up new possibilities for future advancements in sodium‐ion battery technology.