PEM Introduction
PEM water electrolyzers utilize Proton Exchange Membrane (PEM) technology to facilitate proton conduction and gas isolation on both sides of the electrode. This design overcomes the limitations associated with alkaline liquid electrolytes used in AWE systems. The PEM water electrolytic cell employs a PEM as the electrolyte and pure water as the reactant. The PEM exhibits low hydrogen permeability and produces high-purity hydrogen, requiring only the removal of water vapor. The zero spacing structure and low ohm resistance of the electrolytic cell significantly enhance the overall efficiency of the electrolysis process and enable a more compact design. It offers a wide pressure control range, allowing for hydrogen output pressure of several MPa, making it suitable for rapid changes in renewable energy inputs. As a result, PEM electrolysis is a promising pathway for green hydrogen production.
It is worth noting that the main challenges for PEM electrolysis are cost and lifetime. In the cost breakdown of an electrolytic cell, the bipolar plate accounts for approximately 48%, while the membrane electrode comprises around 10%. Currently, the international advanced level of PEM technology includes a single cell performance of 2 A·cm^-2 at 2 V, a total platinum catalyst load of 2-3 mg/cm^2, and a stable operating time of 6×10^4 to 8×10^4 hours. The production cost of hydrogen is approximately $3.7 per kg. Efforts to reduce the cost of PEM electrolytic cells focus on core components such as membrane electrodes, gas diffusion layers, and bipolar plates based on catalyst and PEM materials.
The bipolar plate and flow field contribute significantly to the cost of the electrolytic cell. Therefore, reducing the cost of the bipolar plate is crucial for controlling overall expenses. In PEM electrolyzers, the anode operates under harsh conditions, leading to bipolar plate corrosion and subsequent metal ion leaching, which can contaminate the PEM. To address this issue, common protective measures include applying anti-corrosion coatings on the surface of the bipolar plate. Lettenmeier et al. conducted research where a Ti layer was prepared using vacuum plasma spraying on a stainless steel bipolar plate to prevent corrosion. Subsequently, a Pt layer was deposited through magnetron sputtering to prevent the conductivity reduction caused by Ti oxidation. Further studies demonstrated that a similar cell performance could be maintained by substituting the expensive Pt coating with a more affordable Nb coating while achieving stable operation for over 1000 hours. The research group at the University of Tennessee employed additive manufacturing methods to create a 1 mm thick flow field made of stainless steel on a cathode bipolar plate. and then deposited a 0.15 mm thick net gas diffusion layer on it. This design exhibited a very small cathode impedance and achieved a cell performance of up to 2 A·cm^-2 at 1.715 V, although surface improvements were still required for enhanced stability. Additionally, institutions such as Oak Ridge National Laboratory and the Korea Institute of Science and Technology have also conducted extensive research on bipolar plate development for PEM electrolytic cells.
The electrode material currently used, the most commonly used is Titanium fiber felt and Porous titanium plate, which has good resistance and corrosion resistance.
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