The impact of graphene oxide nanosheet lateral dimensions on the electrochemical performance of nanoporous graphene-based electrodes

Electrodes based on nanoporous reduced graphene oxide (rGO) have been developed as the interfacing component in different designs of neural implants in a variety of therapeutic and monitoring applications. The starting graphene oxide (GO) nanosheets lateral dimensions influenced the staking order, roughness and thickness of the derived rGO films, including the formation of nanochannels. Apart from the morphological differences observed, the GO lateral dimension also impacted on the film conductivity, and on the overall electrochemical performance of the rGO electrodes. While electrodes fabricated from nano-scale GO sheets (us-GO) only showed diffusion-limited impedance in the high frequency regime, the electrical response of electrodes from micron-scale GO sheets (L-GO) was limited by diffusion in the whole frequency range due to a less disordered nanoporous film. At 1 kHz, us-GO electrodes, due to their larger capacitance, presented a higher charge injection limit (Q_inj.l.) than L-GO electrodes. Due to the higher conductivity of L-GO, electrodes exhibited half the ohmic drop (IR) of electrodes made of us-GO. This work highlights the importance of GO nanosheet engineering to optimize the performance of rGO electrodes in terms of Q_inj.l. and IR, two key figures of merit in neuroelectronic applications.