to battery driven (electric) mobility. While a multibillion-dollar industry has come up catering various needs, the manifold consumption of Li-based resources has led to steep price rise and concerns over future geo-political tension due to its nonuniform geographic distribution. To combat this imminent issue, various alternative battery chemistries (termed as "Beyond Li-ion batteries") are widely pursued, particularly to replace Li-ion batteries in applications unrestricted by gravimetric and/or volumetric energy density. In this case, sodium-ion batteries (NIBs) are touted as the emerging futuristic battery chemistry owing to the widespread availability of sodium-based resources and well-understood electrochemical operation involving the Na + charge carriers. [1][2][3][4][5] In the quest to build robust sodiumion batteries, various 2D layered transition metal oxides and 3D polyanionic framework materials have been unraveled. While the oxide cathodes can deliver high theoretical (and reversible) capacity, they suffer from lower redox potential owing to strong covalence nature. [6] It is more so acute in case of Na-ion batteries considering the higher potential of Na/Na + (−2.71 V vs normal hydrogen electrode (NHE)) vis-à-vis Li/Li + (−3.03 V vs NHE). This issue can be circumvented by implementing polyanionic cathode materials with tunable crystal structure, robust framework providing safe operation and higher redox potential due to inductive effect. [7,8] Following the inductive effect principle, plethora of cathodes with polyanionic units [(XO 4 ) m n− : X = B, P, Si, S, W, Mo, As, Ti, V, etc.] have been discovered both for Li-ion and Na-ion batteries. [9,10] Moving a step further with polyanionic chemistry, off late, materials discovery has been realized by using different types of polyanion units. These subclass of materials are known as "mixed polyanionic" cathode materials, which can be designed by simultaneously having i) polyanionic units [(XO 4 ) m n− , X = P, S, V, etc.] along with other single anions [Y − = F − /OH − /O 2− /N 3− ], ii) different structural units of same polyanion units [(XO m ) (X 2 O m ), e.g., PO 4 -P 2 O 7 , BO 3 -B 2 O 5 , SO 4 -S 2 O 3 , etc.], and iii) two different oxyanionic [(XO 4 ) m n− ] units (e.g., PO 4 -SO 4 , PO 4 -NO 3 , PO 4 -CO 3 , etc.) as illustrated in Figure 1. These polyanionic combinations can lead to rich structural diversity and multi ple electron redox activity leading to robust electrochemical "Building better batteries" remains an ongoing process to cater diverse energy demands starting from small-scale consumer electronics to large-scale automobiles and grid storage. While Li-ion batteries have carried this burden over the last three decades, the ever-growing and highly diverse applications (based on size, energy-density, and stationary vs mobile usages) have led to an era of "beyond lithium-ion batteries." In this postlithium-battery era, sodium-ion batteries (NIBs) have emerged as a pragmatic option particularly for large-scale applications. They attract...
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.
Bifunctional electrocatalysts are pre-eminent to achieve high capacity, cycling stability, and high Coulombic efficiency for rechargeable hybrid sodium–air batteries. The current work introduces metaphosphate (Na)KCo(PO3)3 nanostructures as noble metal-free bifunctional electrocatalysts suitable for the rechargeable aqueous sodium–air battery. Prepared by the scalable solution combustion method, the metaphosphate class of (Na)KCo(PO3)3 with spherical morphology exhibited robust oxygen reduction as well as evolution activity similar to the state-of-the-art catalysts. NaCo(PO3)3 metaphosphate, when employed as an air cathode in hybrid sodium–air batteries, delivered reasonably low overpotential along with excellent cycling stability with a round-trip energy efficiency of 78%. Cobalt metaphosphates thus form a new class of economical bifunctional catalysts to develop hybrid sodium–air batteries.
Rechargeable batteries based on Li-ion and post Li-ion chemistry have come a long way since their inception in early 1980s. The last four decades have witnessed steady development and discovery...
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