Parama Chakraborty Banerjee

The structure type and phase assemblage of “layered” Na-transition metal (TM) oxides dictate their performance as cathode materials, resulting in an impetus toward developing biphasic or hybrid Na-TM-oxides. However, a fundamental understanding as to what drives the formation of such biphasic structures, instead of a single phase, remains unestablished. This also means that a coherent strategy to rationally design hybrid Na-TM-oxides and tune the relative contents of the constituent phases is missing. Against this backdrop, we report a simple strategy and an associated descriptor, that is based on the overall covalency of cation−oxygen bonds in the TMO2-“slab”, viz., the average charge-to-radius ratio of the cation combination in the TM-layer. Tuning the above parameter gives access to compositions leading to either phase-pure or biphase/hybrid O3/P2-type structures with varied relative contents of the constituent phases (at least in qualitative terms) for a fixed Na-content. The usage of this simple descriptor and the associated phase map has been successfully demonstrated here by developing a series of phase-pure and hybrid P2/O3-structured Na-TM-oxides based on two Na-contents using the same synthesis protocol. This confirms the suitability of this rational design strategy across various compositions, which can be adapted for widespread development of biphasic/hybrid “layered” TM-oxides for usage as cathode materials for Na-ion batteries and beyond.

Cobalt single‐atom catalysts (SACs) have the potential to act as bi‐functional electrocatalysts for the oxygen‐redox reactions in metal‐air batteries. However, achieving both high performance and stability in these SACs has been challenging. Here, a novel and facile synthesis method is used to create cobalt‐doped‐nitrogen‐carbon structures (Co‐N‐C) containing cobalt‐SACs by carbonizing a modified ZIF‐11. HAADF‐STEM images and EXAFS spectra confirmed that the structure with the lowest cobalt concentration contains single cobalt atoms coordinated with four nitrogen atoms (Co‐N₄). Electrochemical tests showed that this electrocatalyst performed exceptionally well in both oxygen reduction reaction (ORR) (E1/2 ≈ 0.859 V) and oxygen evolution reaction (OER) (Ej = 10: 1.544 V), with excellent stability. When used as a bi‐functional electrocatalyst in the air cathode of a rechargeable zinc‐air battery (ZAB), a peak power density of 178.6.1 mW cm ⁻² , a specific capacity of 799 mA h g _Zn ⁻¹ and a cycle‐life of 1580 is achieved. Density functional theory (DFT) calculations revealed that the concentration and the position of the pyridinic nitrogen with Co play a critical role in determining the overpotential of this electrocatalyst for oxygen‐redox reactions. The unprecedented performance of this electrocatalyst can bring paradigm changes in the practical realization and application of metal‐air batteries.

This review article focuses on metal–organic framework (MOF) composites and the impact of mixing MOFs with other materials, such as polymers, carbon-based materials, and magnetic particles, to increase their performance to remove metals from water.

Owing to their suitable mechanical property and biocompatibility as well as the technological possibility of controlling their high corrosion rates, magnesium and its alloys have attracted significant attention as temporary bio-implants. Though the ability of magnesium to harmlessly biodegrade and its inherent biocompatibility make magnesium alloys a suitable choice for a temporary implant, their high corrosion rates limit their practical application, as the implants can potentially corrode away even before the healing process has completed. Different approaches, such as alloying, surface modification, and conversion coatings, have been explored to improve the corrosion resistance of various magnesium alloys. However, the corrosion behavior of magnesium implants with and without a surface modification has been generally investigated under in-vitro conditions, and studies under in-vivo conditions are limited, which has contributed to the lack of translation of magnesium implants in practical applications. This paper comprehensively reviews the prospects of magnesium alloy implants and the current challenges due to their rapid degradation in a physiological environment. This paper also provides a comprehensive review of the corrosion mitigation measures for these temporary implants.

We illustrate a novel concept in tailoring the architecture of MOF-derived carbons by doping MOF crystals with transition metal ions prior to carbon structure growth via chemical vapor deposition (CVD). MOF-5 was isomorphously doped with various concentrations of Ni²⁺ during synthesis and was subsequently subjected to CVD to grow a labyrinth of carbon nanofibers (CNF) with high electrical conductivity and higher surface area than that of the parent MOF. TEM of the inner structure of the CNFs revealed a chevron arrangement with ~0.34 nm visible fringe spacing. The CNF diameters increased with increasing Ni concentration. This is attributed to the decreasing distance between Ni dopants with increasing Ni concentration, which may facilitate coalescence of the Ni catalyst during the heat treatment and thereby increase the diameter of the resultant CNF. However, Ni doping concentration greater than 30% led to large agglomerations of Ni particles which eventually ceased CNF growth. The electrical conductivity and the electrochemical double layer capacitance of the CNFs also increased with increasing Ni concentrations. The highest electrochemical double layer capacitance and the lowest resistance was observed at a Ni doping concentration of 30%. An alkaline electrolyte was used to engage the Ni particles inside the CNFs to participate in a reversible redox reaction shuttling between Ni and Ni(OH)₂, which resulted in a specific capacitance as high as 349 F/g. The possibility of doping transition metals into a wide variety of MOF structures can provide a new method to synthesize novel carbon structures with high energy storage capabilities.

Magnesium and its alloys are attractive potential materials for construction of biodegradable temporary implant devices. However, their rapid degradation in human body fluid before the desired service life is reached necessitate the application of suitable coatings. To this end, WZ21 magnesium alloy surface was modified by hexagonal boron nitride (hBN)-impregnated silane coating. The coating was chemically characterised by Raman spectroscopy. Potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) of the coated alloy in Hanks’ solution showed a five-fold improvement in the corrosion resistance of the alloy due to the composite coating. Post-corrosion analyses corroborated the electrochemical data and provided a mechanistic insight of the improvement provided by the composite coating.