Dihydrogen phosphate ion functionalized nanocrystalline thallium ruthenium oxide pyrochlore as a bifunctional electrocatalyst for aqueous Na-air batteries

Abstract

Abstract The sodium-air (Na–air) batteries are considered as a new promising energy storage devices due to their 1683\u2009W h kg−1 of high theoretical specific energy density. However, these outstanding theoretical energy density performances cannot be achieved because undesirable sluggish oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) reaction kinetics on the air cathode side causes the high overpotential gap and low round-trip efficiencies during charge-discharge process. Therefore, the development of highly active bifunctional oxygen electrocatalysts is the key strategy to obtain the low overpotential gap with high energy density performance of Na-air batteries. In this work, a novel single crystalline thallium ruthenium oxide (Tl2Ru2O7) with pyrochlore structure was firstly revealed as an effective bifunctional electrocatalyst. Moreover, in order to enhance the surface chemical reactivity of Tl2Ru2O7, the surface of Tl2Ru2O7 is functionalized by using the dihydrogen phosphate ion (P-Tl2Ru2O7) for achieving the effective and rapid charge transfer behavior. The superior bifunctional catalytic activity of P-Tl2Ru2O7 can be explained by the degree of covalency of Ru-O bonds in Tl2Ru2O7 and enhanced covalent character by functionalized dihydrogen phosphate ion, which can afford favorable oxidation nature to Tl and Ru ions.