Coupled Multi-Physics Modeling of Integrated Photoelectrochemical Hydrogen Processing Devices Using Concentrated Irradiation
Fig. 1 (a) Schematic (not to scale) showing 3D structure of the integrated PEC device. The 2D simulation domain is the xy-plane.
We developed, a coupled 2D multi-physics model of the proposed concentrated PEC device. The model includes radiative heat transfer in the concentrator, electromagnetic wave propagation in the semiconductors (a triple junction solar cell), charge generation and transport in the photoabsorbers and the integrated electrolyzer (polymeric electrolyte and solid electrode), electrochemical reaction at the catalytic sites, fluid flow and species transport in the channels delivering the reactant (water) and removing the products (hydrogen and oxygen), and heat transfer in all components. Finite element and finite volume methods were used to solve the governing equations and the corresponding boundary conditions. Complex temperature dependencies of the material properties were included in different physics’ models.
Fig. 2 shows the simulation flow and coupling between different physical nodes. The EM simulation is performed for the given temperature field, starting with a constant initial temperature (Tinit = 293K). After taking heat dissipation density from electromagnetic wave propagation, the heat transfer simulation is performed along with (reactive) fluid flow and electrochemistry simulations. In parallel, the semiconductor device simulation is performed starting with Tinit. After the calculation of the operating point, the simulation iterations are repeated until the temperature field converges.
The model allowed to investigate and optimize the thermal management in the integrated PEC device, highlighting that the PV performance benefited with decreasing temperature (water acting as coolant, taking the heat from PV) while the electrochemical performance benefited from the increasing temperature (heated water used as reactant). Cooling power of the water was found to be dependent on its mass flow rate and length of the water channel. The device was designed to work in the plateau region of the PV – a triple junction cell made of Ga0.51In0.49P/GaAs/Si – and hence its operation was unaffected by the decreasing open circuit voltage with increasing temperatures. We observed an increase in the amount of H2 produced with increasing light concentration as the operating current of the integrated PEC increases. Parametric studies on device dimensions, light concentration, anodic and cathodic catalyts, water mass flow rate, and PV materials allowed to provide an optimum range for different device design and material characteristics for the best perfoming integrated concentrated PEC.
The model developed shows promise to be a valuable design and optimization tool for integrated PEC cells working with concentrated irradiation and at elevated temperatures.
Fig. 2 The simulation flow of the Integrated PEC system.
 S. Haussener et al. Simulations of the irradiation and temperature dependence of the efficiency of the tandem photoelectrochemical water-splitting systems, Energy Environ. Sci., 2013.