The overall experimental device length scale is of order mm, but it incorporates features of the nm length scale, presenting us with the computational challenge of bridging this disparity in one computational model. Therefore, we let a single nanochannel represent the complex porous structure of an electrode. The mm scale of the device is then approximated by placing diffusion barriers at either end of the nanochannel which slows down diffusion via a simple linearised diffusive flux 𝑗 𝑖 = -𝐷 𝑖,𝑏 (ρ 𝑖 (𝑥 + ) -ρ 𝑖 (𝑥 -))/𝑑 b . Here 𝐷 𝑖,𝑏 = 10 -2 𝐷 𝑖 to account for the phenomenon that effective self-diffusion coefficients of ions, when situated in a nanoporous material, are decreased by over two orders of magnitude compared with bulk electrolyte, 𝜌 𝑖 (𝑥 + )