Investigation of electrode composition of polymer fuel cells by electrochemical impedance spectroscopy

Argyrodite Solid Electrolyte-Integrated Ni-Rich Oxide Cathode with Enhanced Interfacial Compatibility for All-Solid-State Lithium Batteries

All-solid-state lithium batteries (ASSLBs) paired with an argyrodite sulfide solid electrolyte have become a candidate to take the world by storm for achieving high energy and safety. However, the undesirable interface design between a sulfide solid electrolyte and cathode is difficult to address its scalability production challenge. Particularly, the inferior interfacial contact between a sulfide solid electrolyte and cathode is an intractable obstacle for the large-scale commercial application of ASSLBs. Herein, an elaborately designed conformally in situ integration of a sulfide solid electrolyte onto a Ni-rich oxide cathode is proposed to overcome this issue through a facile tape casting method. In this unique integrated electrode structure, the sulfide solid electrolyte intimately makes contact with the Ni-rich oxide cathode, which significantly strengthens the solid-solid interfacial compatibility, as well as decreases the interfacial reaction resistances, thereby enabling rapid Li+ transportation and a stable interfacial structure. As a result, ASSLBs consisting of a sulfide solid electrolyte-integrated Ni-rich oxide cathode and Li anode exhibit high discharge capacity, excellent cyclic stability, and remarkable rate performance, which are superior to the cells with segregated structures composed of a Ni-rich oxide cathode, sulfide solid electrolyte, and Li anode. The features clearly indicate that the advanced interfacial contact between the cathode and solid electrolyte is responsible for ASSLBs with low polarization and fast reaction kinetics. Therefore, this work provides a rational proof-of-concept fabrication protocol for the reliable interfacial structure design of high-performance ASSLBs.

The Influence Catalyst Layer Thickness on Resistance Contributions of PEMFC Determined by Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy is an important tool for fuel-cell analysis and monitoring. This study focuses on the low-AC frequencies (2–0.1 Hz) to show that the thickness of the catalyst layer significantly influences the overall resistance of the cell. By combining known models, a new equivalent circuit model was generated. The new model is able to simulate the impedance signal in the complete frequency spectrum of 105–10−2 Hz, usually used in experimental work on polymer electrolyte fuel cells (PEMFCs). The model was compared with experimental data and to an older model from the literature for verification. The electrochemical impedance spectra recorded on different MEAs with cathode catalyst layer thicknesses of approx. 5 and 12 µm show the appearance of a third semicircle in the low-frequency region that scales with current density. It has been shown that the ohmic resistance contribution (Rmt) of this third semicircle increases with the catalyst layer’s thickness. Furthermore, the electrolyte resistance is shown to decrease with increasing catalyst-layer thickness. The cause of this phenomenon was identified to be increased water retention by thicker catalyst layers.