Improved kinetics from ion advection through overlapping electric double layers in nano-porous electrodes

A novel device architecture is presented for laminar flow fuel cell by introducing an ion advection flux within the electric double layer (EDL). Typically advection in the EDL is negligible because the near wall electrolyte velocity is zero. However, by using nano-pores, a non-negligible ion advection flux can be developed in the charged regions of the EDL. In this article we study how advection in the EDL affects the kinetic performance of electrochemical cells. To accomplish this we use a laminar flow fuel cell model based on the Poisson–Nernst–Planck and Frumkin–Butler–Volmer equations. The model contains nonlinear physics with very disparate length scales due to the complex 3-dimensional nature of the nano-porous device. To account for these difficulties, the full mathematical model is solved numerically using a novel numerical algorithm developed based on domain decomposition method. The presented algorithm allows the simulation of complex near wall electrode effects, such as overlapping double layers in a nano-pore, in the context of a complete device, which would have been numerically prohibitive otherwise. The presence of an advection flux through nano-pores on the order of the EDL width yields some novel phenomena that affect the structure of electrode–electrolyte interface. The most surprising result is the development of a region of zero charge at the electrodes in the upstream regions of longer nano-pores. We also show that electrolyte advection within the EDL can be used to enhance the kinetic performance of electrodes in electrochemical cells.

► A novel device concept is presented for laminar flow fuel cell using nano-porous electrodes.
► The overall device performance of a laminar flow fuel cell can be improved by manipulating the electric double layer using advection in nano-pores.
► The presence of advection within the electric double layer affects its structure significantly.
► The device performance increases with flow velocity and nano-pore length.
► For very long nano-pores, the advection effect produces a highly nonlinear distribution of continuum variables.