2 results
Electrocatalytic Activity of Some Cobalt Based Sodium Phosphates in Alkaline Solution
- Debasmita Dwibedi, Ritambhara Gond, Krishnakanth Sada, Baskar Senthilkumar, Prabeer Barpanda
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- Journal:
- MRS Advances / Volume 3 / Issue 22 / 2018
- Published online by Cambridge University Press:
- 30 January 2018, pp. 1215-1220
- Print publication:
- 2018
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The development of efficient water oxidation catalyst is a major path to realize water splitting systems, which could benefit high performance and cost-effective metal-air batteries, fuel cells and solar energy conversion. To date, the rare crustal abundant platinum group metals rule this sector with Pt-alloys being the best for oxygen reduction reaction (ORR) and ruthenium oxides for oxygen evolution reaction (OER) in acidic solution. However, they show poor stability and are too expensive for large scale applications. Moreover, oxygen reduction in basic solutions can otherwise be catalysed by metal oxide with non-precious earth abundant transition metals (e.g. Fe, Co, Ni). Hence, there is a massive demand to explore noble metal free bifunctional electrocatalysts. In this work, we present the electrocatalytic activity of three cobalt based sodium phosphates namely NaCoPO4 (with one phosphate), Na2CoP2O7 (with two phosphate) NaFe2Co(PO4)3 (with three phosphate). Synthesized by solution combustion route, all these phosphates confirmed phase purity. NaCoPO4 and Na2CoP2O7 adopted orthorhombic structure with Pnma and Pna21 space group respectively; whereas NaFe2Co(PO4)3 crystallized in monoclinic (C2/c) framework. Electrocatalytic activity of these cobalt phosphates were inspected by linear sweep voltammetry with rotating disk electrode (RDE). All three showed promising bifunctional activity. In fact, the ORR activities of both orthorhombic cobalt phosphates are comparable to Vulcan carbon and Pt/C. OER activity of Na2CoP2O7 overrode other phosphates. The bifunctional activity and good stability of these sodium cobalt phosphates stem from cobalt ions and stabilization of the catalytic centres by the phosphate frameworks. The present work builds a detail structure-property correlation in these phosphate systems and also demonstrates the possibility of utilizing these sodium cobalt phosphates as alternate cost-effective, novel electrocatalysts for efficient OER/ORR activity in alkaline solution.
Sodium Metal Sulphate Alluaudite Class of High Voltage Battery Insertion Materials
- Debasmita Dwibedi, Prabeer Barpanda
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- Journal:
- MRS Advances / Volume 3 / Issue 22 / 2018
- Published online by Cambridge University Press:
- 30 January 2018, pp. 1209-1214
- Print publication:
- 2018
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Electrochemical energy storage has recently seen an exponential demand in the large-scale (power) grid storage sector. Earth abundant sodium-ion batteries are competent to enable this goal with economic viability. In a recent report in sodium-ion battery research, alluaudite framework Na2Fe2(SO4)3 has been reported with the highest Fe3+/Fe2+ redox potential (ca. 3.8 V, P. Barpanda, G. Oyama, S. Nishimura, S. C. Chung, and A. Yamada., Nature Commun. 5: 4358, 2014) with energy density comparable to the state-of-the-art Li-ion batteries. Material discovery is as essential as optimization of the existing materials to yield better performance for efficient energy storage. In a goal to optimize the synthesis of the reported alluaudite, this work first time reports the aqueous based Pechini synthesis for sodium metal sulphate alluaudite. It is a two-step method, where complexing agent plays a crucial role in holding the metal ions reserving their oxidation states. In the 2nd step, this complexing agent leaves the product with porous morphology. Taking advantage of its porous as well as 3D conductive framework, the complex attains fast electron/ion transport and sodium intercalation. Moreover, the single-phase reaction mechanism during sodium intercalation is reflected in its cycling property. It performs as a desirable cathode with operating potential as high as 3.7 V. While pursuing the synthesis, we observed an excess amount of sodium sulphate in the precursor mixture is needed to reduce the amount of impurities. To optimize the composition of the alluaudite phase and to explore novel compounds, we have carefully surveyed the Na2SO4-FeSO4 binary system. This work explores the possible compositional and structural flexibility in the Pechini synthesized alluaudites. A comparative study between compositional and redox activity in these samples will further inspire improvement of the alluaudite-type sodium metal sulphates for advanced sodium-ion batteries.