In this regard, porous carbon is widely adopted as the air cathode due
to its large variety,high specific surface area, good conductivity and
low cost. For example, Liu et al. investigated graphene nanosheets
(GNS) as the air cathode and obtained a high discharge capacity of
8268 mA h g1 at a current density of 200 mA g1 [35]. Jian et al.
used a carbon nanotube paper as a binder-free air cathode. Results
showed a discharge capacity of 7530 mA h g1 at current density of
500mA g1 and a charge overpotential less than 200mV [36].