Mass transfer and cell performance of a unitized regenerative fuel cell with nonuniform depth channel in oxygen‐side flow field

Abstract

Summary In this study, the cell performance of nonuniform depth and conventional straight channel in a unitized regenerative fuel cell (URFC) is compared. Various shapes of oxygen‐side channel cases are also proposed. Several parameters, such as the distribution of reactants and products and current density and powers in fuel cell (FC) and electrolytic cell (EC) modes, are investigated. A steady‐state model of two‐dimensional, two‐phase, nonisothermal, and coupled electrochemical reaction is developed. Five oxygen‐side channel shapes are also designed, in which the depth along the flow direction is narrowed. Result shows that narrowing the average channel depth can promote and guide the reactant transfer to the catalyst layer and avoid the blocking of the production. Thus, in comparison with the conventional channel, the cell performances of nonuniform depth and shallow straight channel cases are improved in both modes. In addition, with the decrease of average channel depth, the temperature uniformity gets better, which is also conductive to the improvement of cell performance. Furthermore, in FC mode at low voltage and EC mode, the cell net power basically increases with the decrease of the average channel depth ratio. And when the average channel depth is the same, the net power of straight channel is always lower than nonuniform depth case. This study introduces the round‐trip energy efficiency as an evaluation indicator of URFC. This efficiency can be increased by improving the cell performance of both modes, especially at high current density.

Combination effect of flow channel configuration and anode GDL porosity on mass transfer and performance of PEM water electrolyzers

“…This is because the reduction of the flow space leads to an increase in the pressure drop, which is similar to the phenomenon of occlusion. The pumping power in all cases can be described as: 19 P pumping = Δ pA in u in where Δ p (Pa) is the pressure drop from the inlet to the outlet, A in is the cross-section of the channel inlet, and u in is the average velocity at the anode inlet.…”

“…In addition, it was found that removing the shoulders between the channels and using metal foam as the flow distributor also improved the performance. 18 Song et al 19 designed a non-uniform depth channel in which the depth is narrowed along the flow direction, and found that narrowing the average channel depth can improve reactant transfer to the catalyst layer and avoid product blockage. Zhang et al 20 also found that decreasing the channel depth and increasing the width of the flow channel can enhance the transfer of water and heat in the electrolyzer, but too much width of the flow channel leads to an increase in the ohmic overvoltage.…”

3D two‐phase and non‐isothermal modeling for PEM water electrolyzer: Heat and mass transfer characteristic investigation

“…Based on Ohm's law, the charge conservation equation for electrons and protons can be expressed as 27 :…”

“…Where c i is the molar concentration of gas phase species i, S i is the source term of species i and it is related to the rate of electrochemical reaction in the CLs. D eff is the effective diffusion coefficient, and given by 22,27,34 :…”

“…The computational domain is meshed using a structured hexahedral mesh and the relative residuals of all variables are set to 1:0 Â 10 À5 . The numerical simulation was carried out on Cathode reference exchange current density, A m À2 i ref,c 10,000 [9] Anode and cathode transfer coefficient α a , α c 0.5 [9] Anode and cathode activation energy, kJ mol À1 E act,a , E act,a 62.836, 24.359 [22] Contact angle, θ 80 [35] Surface tension, N m À1 σ 0.0625 [35] Porosity (GDL, CL) in anode ε GDL , ε CL 0.5, 0.25 [34] Porosity (GDL, CL) in cathode ε GDL , ε CL 0.5, 0.25 [34] Electrolyte volume fraction in CLs ε m 0.26 [27] Absolute permeability of GDLs and CLs, m 2…”