Development of renewable energy resources requires high-efficiency energy conversion and large-scale, low-cost, high-density energy storage devices. The energy density of traditional Li ion batteries is inadequate to meet the increased requirements, especially for electric or hybrid electric vehicles. Metal air batteries1-5
have attracted a great deal of attention mainly because of the extremely high energy density of the metal-air battery system, which is close to the energy density of fossil fuels. One advantage of Na–air batteries over Li-ion or Li–air batteries is its low material cost and its natural abundance, as sodium is 30 times cheaper than lithium. Moreover, the energy density of a Na–air battery is similar to the maximum practical energy density of a Li–air battery (1600 Wh/kg).6
As a common challenge to be addressed for all air-based battery technologies, excessive discharge products can accumulate on the cathode surface; most of these have very low electrical conductivity, and thus tend to inactivate surface reaction sites and block oxygen diffusion channels. Hence, the over-accumulation of discharge products can lead to the increase in polarization during charging of the Na–air battery and eventual termination of the oxygen evolution reaction.7
To reduce the accumulation of discharge products for decreased charge potential and improved cycling performance, morphological properties of the cathode (e.g. surface area, pore volume, and pore size) need to be tailored while employing different catalysts. However, to the best of our knowledge, there have been no reports of research efforts to confine the size or arrangement of discharge products in the vicinity of the cathode to decrease the charge potential and improve the cycling behavior of Na–air batteries. In the present work, OMC having 2.7 nm size pore (OMC-2.7) was employed as a cathode material to control the formation and subsequent decomposition of discharge products, and thus to reduce polarization and improve cycling behavior.
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