Abstract
In this paper, a simplified model of a Polymer Electrolyte Membrane (PEM) water electrolysis cell is presented and compared with experimental data at 60 °C and 80 °C. The model utilizes the same modelling approach used in previous work where the electrolyzer cell is divided in four subsections: cathode, anode, membrane and voltage. The model of the electrodes includes key electrochemical reactions and gas transport mechanism (i.e., H2, O2 and H2O) whereas the model of the membrane includes physical mechanisms such as water diffusion, electro osmotic drag and hydraulic pressure. Voltage was modelled including main overpotentials (i.e., activation, ohmic, concentration). First and second law efficiencies were defined. Key empirical parameters depending on temperature were identified in the activation and ohmic overpotentials. The electrodes reference exchange current densities and change transfer coefficients were related to activation overpotentials whereas hydrogen ion diffusion to Ohmic overvoltages. These model parameters were empirically fitted so that polarization curve obtained by the model predicted well the voltage at different current found by the experimental results. Finally, from the efficiency calculation, it was shown that at low current densities the electrolyzer cell absorbs heat from the surroundings. The model is not able to describe the transients involved during the cell electrochemical reactions, however these processes are assumed relatively fast. For this reason, the model can be implemented in system dynamic modelling for hydrogen production and storage where components dynamic is generally slower compared to the cell electrochemical reactions dynamics.
Highlights
With the increasing production of electricity from intermittent renewable energy sources, the need for an effective energy storage is becoming imperative
It is estimated that between 2006 and 2016 there was an increase in renewable energy production by two-thirds [1]
Among the different options for energy storage, Polymer Electrolyte Membrane (PEM) electrolysis has recently attracted attention because it utilizes the same technology as PEM fuel cells, which has been developed for a long time and Energies 2018, 11, 3273; doi:10.3390/en11123273
Summary
With the increasing production of electricity from intermittent renewable energy sources (e.g., wind and solar), the need for an effective energy storage is becoming imperative. Electrolyzer models and simulations in Matlab/Simulink® were developed among others by [4,5] Such a dynamic modelling software platform is well suited for energy case scenarios where input and output are continuously changing over the time. In particular in [4], the authors describe a model with all the components from renewable energy generation including the wind turbines, electrolyzer, fuel cell and power conditioning. One of the first Simulink mathematical models of the gas porous diffusion electrode and ion exchange membranes of a PEM electrolyzer can be attributed to Görgün et al [6] This model is a steady state model, as it does not consider thermal and electrical capacitance dynamic effects. Choi et al [10] developed an electrolyzer model with the Butler-Volmer kinetics including the effect of cell temperature on the exchange current density. The model is detailed described and the experimental results are used to validate the model
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