Metal-air batteries, which utilize conversion chemistry rather than intercalation mechanisms, have attracted large research interest due to their high theoretical energy density. Much work has been devoted to investigate and optimize Li-O₂ cell, which suffer from large overpotential and poor energy efficiency due to complex cell chemistry and undesired side reactions. Recently, Janek et al. have reported the approach of substituting lithium with sodium in an air battery system and surprised the research community with outstanding performance. Their Na-O₂ was reversibly charged/discharged at very low overpotentials using a pure carbon cathode without the addition of a catalyst [1]. They further more claimed that low surface area can provide a more efficient cycling performance as well as high absolute capacity [2]. To further understand the impact of the carbon material used as air cathode inside the Na-O₂ system, we investigated a range of carbonized fiber based materials. We found that commercially available and heat-treated filter paper provides outstanding oxygen reduction reaction and oxygen evolution reaction activities without any additional catalyst. An initial absolute capacity of 1.26 mAh cm^-2 and low overpotential <400 mV could be achieved when cycled between 1.8 and 3.0 V at 100 µA cm^-2 without any capacity restriction.

References:

[1] P. Hartmann, C.L. Bender, J. Janek et al., Nat. mater. 2013, 12, 228-232.

[2] C.L. Bender, P. Hartmann, J. Janek et al. Adv. Energy Mater. 2014, 4, 1301863