Coin cells were assembled in Cambridge Energy Solutions CR2032 SS316 coin cell cases. All cells were two-electrode cells and did not utilise a third reference electrode. Electrodes were cut from freestanding composite films using either 3 16 ⁄ , 1 4 ⁄ , or 3 loadings of between 9 -11 mg cm -2 . The cells were assembled in a N2 glovebox (O2 < 0.1 ppm; H2O < 0.1 ppm).