Global energy consumption is one of the greatest problems humanity is facing and the need for viable and environmentally friendly alternative energy sources is rising. One of these alternative technologies is Direct Formic Acid Fuel Cells (DFAFCs) a promising alternative energy source for the constantly increasing energy demand; they have major potential for use in portable devices as they can perform extremely well at ambient temperatures and have a low environmental footprint.

Due to the low permeability of formic acid through the polymer exchange membrane (PEM) it allows work at higher concentrations leading to higher energy production compared to other fuel cells. Working under similar operating conditions DFAFCs can generate power densities of 233 mW/cm² outperforming Direct Methanol Fuel Cells (DMFCs) with power densities of 53 mW/cm^2 (1).

However, no fundamental studies about the intrinsic conductivity and dimensional stability of PEM have been carried out whilst under use of formic acid with the purpose of understanding how PEM behave under such highly acidic conditions. This is vital for understanding the long term performance and durability of such fuel cells, should they be used on a wider scale.

The studies carried out have examined how the PEM, including Nafion 115,117,211 and 212, behave and perform under varying acidic conditions. For the dimensional stability study optical analysis was carried out to determine the changes occurring in-situ to the material. In addition, determining changes in resistance using impedance spectroscopy allows for the selection of the most efficient membrane configuration for optimal cell operation.

Previous research has shown that Nafion with a lower equivalent weight has an increased hydrophilic region, compared with membranes with higher equivalent weight. Using this relationship to understand the performance of Nafion suggests that a higher hydrophilic region leads to deformity by the formic acid on the membrane. We have observed this as a change in the dimension of the membrane in only one direction; a change that is not observed when the membrane is immersed in water alone, where the changes in the dimensions are uniform in two directions. There are two possible causes of this; firstly by the production process of the membrane or that a change is taking place in the hydrophobic regions the continuous semi- crystalline TFE structure of the material. In this work we will explain the cause of the deformation.

1. 2-D Crystals Significantly Enhance the Performance of a Working Fuel Cell. Stuart M. Holmes*, Prabhuraj Balakrishnan, Vasu. S. Kalangi, Pulickel M. Ajayan, Xiang Zhang, Marcelo Lozada-Hidalgo and Rahul R. Nair. 27.09.2016., Advanced Energy Materials.