The Influence of Electrolyte Flow Hydrodynamics on the Performance of a Microfluidic Dye-Sensitized Solar Cell

Abstract

The dye-sensitized solar cells microfluidically integrated with a redox flow battery (µDSSC-RFB) belong to a new emerging class of green energy sources with an inherent opportunity for energy storage. The successful engineering of microfluidically linked systems is, however, a challenging subject, as the hydrodynamics of electrolyte flow influences the electron and species transport in the system in several ways. In the article, we have analyzed the microflows hydrodynamics by means of the lattice-Boltzmann method, using the algebraic solution of the Navier-Stokes equation for a duct flow and experimentally by the micro particle image velocimetry method. Several prototypes of µDSSC were prepared and tested under different flow conditions. The efficiency of serpentine µDSSC raised from 2.8% for stationary conditions to 3.1% for electrolyte flow above 20 mL/h, while the fill factor increased about 13% and open-circuit voltage from an initial 0.715 V to 0.745 V. Although the hexagonal or circular configurations are the straightforward extensions of standard photo chambers of solar cells, those configurations are hydrodynamically less predictable and unfavorable due to large velocity gradients. The serpentine channel configuration with silver fingers would allow for the scaling of the µDSSC-RFB systems to the industrial scale without loss of performance. Furthermore, the deterioration of cell performance over time can be inhibited by the periodic sensitizer regeneration, which is the inherent advantage of µDSSC.

Drift-Diffusion Phenomenon in the Presence of Reversible Trapping Reaction

“…Let us consider an infinite homogeneous system containing at t = 0 a uniform distribution of mobile neutral particles with density n 0 . In the presence of a first order trapping reaction, the time evolution of mobile and fixed densities particles, n m and n f , are described by the system of ordinary differential equations 17,32 The (6) to be solved with the initial conditions n m (0) = n 0 , and n f (0) = 0. From (6), it is evident that τ κ = 1/κ and τ λ = 1/λ are characteristics times related to the trapping and to the release phenomena.…”

“…In the presence of a first order trapping reaction, the time evolution of mobile and fixed densities particles, n m and n f , are described by the system of ordinary differential equations 17,32 The (6) to be solved with the initial conditions n m (0) = n 0 , and n f (0) = 0. From (6), it is evident that τ κ = 1/κ and τ λ = 1/λ are characteristics times related to the trapping and to the release phenomena. From (6), taking into account the initial conditions, it follows that n m (t) + n f (t) = n 0 .…”

“…From (6), it is evident that τ κ = 1/κ and τ λ = 1/λ are characteristics times related to the trapping and to the release phenomena. From (6), taking into account the initial conditions, it follows that n m (t) + n f (t) = n 0 . A simple calculation gives…”

“…In the following, our analysis will be conducted within this framework. However, in other contexts, such as the study of trapping phenomena in microfluidic systems , or investigations into the physical properties of charged colloidal systems, − or the transport properties of highly concentrated electrolytes, hydrodynamic coupling plays a fundamental role in analyzing the medium’s response to external stimuli. In these cases, considering hydrodynamic coupling allows for defining the effective dielectric constant and the diffusion coefficient of the electrolyte itself. − …”