Baskar Senthilkumar

Earth‐Abundant Alkali Iron Phosphates (AFePO4) as Efficient Electrocatalysts for the Oxygen Reduction Reaction in Alkaline Solution

Water‐splitting systems are essential for clean energy production. The oxygen reduction reaction (ORR) is a key reaction involved in water splitting, which requires a catalyst. The current work explores the possible application of sodium and potassium iron phosphates (AFePO4, A=Na and K) as electrocatalysts for ORR activity. These earth‐abundant iron phosphates were synthesized by the solution combustion synthesis (SCS) technique by using ascorbic acid both as fuel and reducing agent for Fe. The crystal structure was analyzed by Rietveld refinement. The formation of carbon coating was identified by thermogravimetric analysis and Raman spectroscopy. Electrocatalytic properties of AFePO4 were investigated in alkali electrolytes for the first time by using linear sweep voltammetry with a rotating disk electrode (RDE). The ORR activities of these alkali iron phosphates are comparable to that of the Pt/C system. The Tafel slope and electron transfer number of the alkali iron phosphates were calculated. The ORR activity of NaFePO4 was found to be better than KFePO4 and FePO4. This work demonstrates alkali iron phosphates as alternate cost‐effective, novel electrocatalysts for productive ORR activity in alkaline solution.

Improved electrochemical performances of LiMnPO4 synthesized by a hydrothermal method for Li-ion supercapatteries

Developing high-performance positrode materials are essential to attain high energy supercapatteries. In this regard, the electrochemical performances of the hydrothermally synthesized LiMnPO4 are studied. The crystal structures of the materials are elucidated using Full-profile XRD Rietveld refinement. The LiMnPO4 particles showed uniform elongated spherical shape with rice-like morphology. The rice-like LiMnPO4 showed a higher specific capacity of 492xa0Cxa0g−1 at 2xa0mVxa0s−1 than highly agglomerated particles synthesized through sol–gel thermolysis method (191xa0Cxa0g−1) in 1xa0M LiOH aqueous electrolyte. The supercapattery is fabricated with rice-like LiMnPO4 and activated carbon (AC) as positrode and negatrode, respectively. The supercapattery (AC||LMP-H) delivered a higher capacitance around 99xa0Fxa0g−1 along with an improved energy density of 31xa0Whxa0kg−1. On the other hand, the LiMnPO4 prepared by sol–gel thermolysis method exhibited a very low capacitance of 35xa0Fxa0g−1 at 0.6xa0mA for the fabricated device (AC||LMP-S) with the lesser energy density about 11xa0Whxa0Kg−1 at a power density of 198xa0Wxa0kg−1. The reason behind the improved performance is explained based on the crystal structure as well as lower charge transfer resistance.

Enhanced storage ability by using a porous pyrrhotite@N-doped carbon yolk–shell structure as an advanced anode material for sodium-ion batteries

Sodium-ion batteries (SIBs) are undoubtedly the most promising alternatives to lithium-ion batteries considering the natural abundance, distribution and cost of sodium resources. Still, SIBs face challenges in the development of suitable anode materials due to the large volume change during sodiation/de-sodiation, which results in inferior cycling stability. Herein, we synthesized a yolk–shell structured pyrrhotite (Fe1−xS)@N-doped carbon (FS@NC) through a solution-based method and investigated its electrochemical properties for use in SIBs as an anode material. The optimized yolk–shell structured FS@NC with distinctive voids and a core exhibited a high reversible capacity of 594 mA h g−1 over 100 cycles at 100 mA g−1, excellent rate capability and superior cycling performance compared to core–shell and pristine Fe1−xS materials. During the charge and discharge cycles, the synergistic effect of the porous core (Fe1−xS) with empty voids and a defective carbon shell configuration provided a large electrode/electrolyte contact area and shortened the diffusion path for electrons and sodium ions. It also mitigated the structural degradation by accommodating the volume change during continuous cycles, which was confirmed by ex situ SEM and TEM analyses. To demonstrate a practical application, we assembled a sodium-ion full cell with an O3-type NaCo0.5Fe0.5O2 cathode and a yolk–shell structured FS@NC anode, and the results showed superior energy storage performance.

In-situ deposition of sodium titanate thin film as anode for sodium-ion micro-batteries developed by pulsed laser deposition

Sodium-ion thin-film micro-batteries form a niche sector of energy storage devices. Sodium titanate, Na2Ti6O13 (NTO) thin films were deposited by pulsed laser deposition (PLD) using solid-state synthesized polycrystalline Na2Ti6O13 compound. The phase-purity and crystallinity of NTO in bulk and thin-film forms were confirmed by Rietveld refinement. Electron microscopy and atomic force microscopy revealed the formation of uniform ∼100u202fnm thin film with roughness of ∼4u202fnm consisting of homogeneous nanoscale grains. These PLD-deposited NTO thin-films, when tested in Na-half cell architecture, delivered a near theoretical reversible capacity close to 42u202fmAu202fhu202fg-1 involving Ti4+/Ti3+ redox activity along with good cycling stability and rate kinetics. Na2Ti6O13 can work as an efficient and safe anode in designing sodium-ion thin-film micro-batteries.