Abstract
Iron air/flow battery is the next promising battery system that can bridge the drawbacks of a static battery, at least in medium to high storage systems, due to the distinguishing difference from its static counterpart. It comes with the main advantages: the high current discharge and a flowing electrolyte, which can significantly suppress the formation of dendrite and passivation without imposing permanent damage to the cell structure. Iron, the fourth most abundant metal on the earth's crust, comes at a lower cost and requires less corrosion protection.
This technology has received less attention than others due to overpotential/overvoltage and high hydrogen evolution reaction on the anode. Different promising approach has been explored to improve the cycling stability of iron air batteries; by adding different electrolyte additives to suppress passivation and hydrogen evolution during discharge, improving the air cathode design by including dual or bifunctional electrocatalyst, and recent modification of the anode has helped realize a better iron air battery by facilitating a high surface area iron electrode using nanosized iron particle, and these create more electrode available to electrolyte and further adding a suitable additive to the electrode and electrolyte and increase charge capacity.
Nonetheless, the battery working components begin to degrade as they interact; these cannot be stopped as batteries are consumable objects, but they can be delayed by improving the membrane separator's physical-chemical properties like conductivity, swelling ratio, permeability, and membrane stability. Membrane's critical role aid in the improvement of the battery performance by separating the air cathode and metal anode electrode compartments to prevent short-circuiting, facilitate proton transfer, act as an electron insulator, and prevent fuel crossover, therefore improving the battery cycle life.
This work focused on proton exchange membrane (PEM) fabrication from sulfonated poly (2,6- dimethyl – 1,4-phenylene oxide) (SPPO) attached to sulfonated graphene oxide (SGO) for iron-air/flow battery application. The characteristic properties of all membranes with varying composition of SGO (0, 0.25, 0.5, 0.75, 1.0, 1.5%) were investigated with thermogravimetric analysis (TGA) for thermal stability, scanning electron microscope (SEM) for morphology, and energy dispersive X-ray spectroscopy (EDX) for elemental
PHELA MC vii
ABSTRACT
composition and distribution. The successful fabrication of SPPO was confirmed by the FTIR spectroscopy and proton nuclear magnetic resonance (1H NMR), whilst SGO was confirmed by FTIR, Raman spectroscopy and SEM. The composite membrane properties such as ion exchange capacity (IEC), water uptake (WU), ion conductivity (IC), chemical stability and permeability were also evaluated.
The presence of SGO improved water uptake of all membranes and lowered the swelling ratio of the composite membranes. The 1%(SPPO/SGO) showed good properties with ion exchange capacity of 2.310503 (mmol/g), higher water uptake (44.1% at 25 oC) and water retention of 44.48% with a lower swelling ratio (21.4% at 25 oC). However, the 0.75% was found to pose the highest proton conductivity and had better dispersion, elemental distribution and morphology. Additionally, SGO has improved the thermal stability of the membrane as we observe the shift of the SPPO/SGO 1%, 0.75%, and 0.25% exceeding the pristine PPO decomposition temperature. The chemical stability of SPPO (0%) was at 100% after 7 days in 1 M of HCl(aq) and SGO constituent maintained a fluctuation between (70 and 100%). The results suggest that SGO is a good in-organic filler for the composite proton exchange membrane, and stable enough for possible application in iron-air/flow battery.