Quantifying Temperature Effects in Large-Scale PEM Water Electrolysis Stacks
Authors: Krenz Tobias , Weiland Oskar , Trinke Patrick , Helmers Lennard , Bensmann Boris , Hanke-Rauschenbach Richard 
Published: November 2022

Introduction

Large-scale water electrolysis is needed for scaling up the production of hydrogen as a renewable energy carrier. The required size and number of cells of the PEMWE stack exceed laboratory-scale settings, which leads to additional effects that could impact the operation and performance [1]. The interaction of large, neighbouring cells with each other are expected to lead to significant temperature differences within the stack of cells, which cause deviations in the contribution to the loss mechanisms and uneven stresses or loading of the members.

Methods

This contribution presents a dynamic PEMWE-stack model, which is formulated in two dimensions: through the stack and along the channel. Due to the high electric conductivity of the bipolar plates the cell voltage of each cell is independent of the cell/channel flow coordinate. The model is based on mass and enthalpy balances of the fluids on the anodic and cathodic side. Conductive heat transport along the cell and through the stack is considered as well as convective transport by the fluids. Time-dependency of mass and enthalpy balances is considered to capture unsteady operation of the stack. In addition, a temperature-dependent polarisation model for determining the cell voltage is included in the model. The polarisation model includes the contributions of activation overpotentials, mass transport losses and ionic membrane and contact resistances. The cells on both edges of the stack are modelled with dedicated boundary conditions to capture the physical arrangement and convective heat exchange with the environment. Water flow and electrical settings are prescribed as external boundary condition. The model is validated with experimental data from industrial stacks.

Results

The temperature profile inside the stack is found unevenly distributed in both spatial directions between the cells with colder boundary and warmer inner cells. The colder outer cells operate at a higher cell voltage in an electrical series connection. For the inner cells, a significant temperature gradient is found in flow direction. As the polarisation loss mechanisms depend on temperature, the share of the losses is unevenly distributed in both coordinates. This leads to higher current densities at the parts of a cell that experience elevated temperatures (Fig. 1). These mechanisms depend on the macroscopic design of the cell, boundary and operating conditions. Load variations induce a dynamic stack response in temperature, cell voltage and the fluids until a steady state is reached. At the same time local temperature and current density variation, can be analyzed as performance drivers, including degradation. Both aspects can be used for design and optimization of industrial scale PEMWE stacks.

References

[1] S. Siracusano, V. Baglio, N. Briguglio, G. Brunaccini, A. Di Blasi, A. Stassi, R. Ornelas, E. Trifoni, V. Antonucci and A. S. Aricò, International Journal of Hydrogen Energy,
37(2), 1939–1946 (2012).

Figure 1