4 research outputs found
Exploring critical parameters of electrode fabrication in polymer electrolyte membrane fuel cells
Microstructure and electrochemical properties of the cathode catalyst layers (CCL) of a polymer electrolyte
membrane fuel cells (PEMFC) have great impact on the performance and durability of the cell. The aim of this
work is to establish a link between CCL structure and fuel cell performance. To obtain CCLs with unique
structures six types of electrodes were prepared, each with a different coating technique but with the same Pt
loading. The coating techniques are airbrush, screen printing, inkjet printing, dry spraying, doctor blade and
drop casting. Moreover, intrinsic properties of PEMFC electrodes such as porosity, permeability, diffusivity as
well as ionomer distribution are determined by Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) and
Atomic Force Microscopy (AFM). Overall, 12 parameters have been evaluated. Generally, CCLs with low fractions of uncovered Pt/C show higher performance at low current densities. In this case the more homogeneous ionomer distribution leads to a higher catalyst utilization. At high current densities transport properties of the
CCL have to be considered in addition to the catalyst utilization to explain their performance. The CCL prepared by screen printing shows a low fraction of uncovered Pt/C in combination with good transport properties, leading to the best performance at high currents
Influence of cycling profile, depth of discharge and temperature on commercial LFP/C cell ageing: postāmortem material analysis of structure, morphology and chemical composition
The paper presents post-mortem analysis of commercial LiFePO4 battery cells, which are aged at 55 Ā°C and ā 20 Ā°C using dynamic current profiles and different depth of discharges (DOD). Post-mortem analysis focuses on the structure of the electrodes using atomic force microscopy (AFM) and scanning electron microscopy (SEM) and the chemical composition changes using energy dispersive X-ray spectroscopy (SEM-EDX) and X-ray photoelectron spectroscopy (XPS). The results show that ageing at lower DOD results in higher capacity fading compared to higher DOD cycling. The anode surface aged at 55 Ā°C forms a dense cover on the graphite flakes, while at the anode surface aged atā 20 Ā°C lithium plating and LiF crystals are observed. As expected, Fe dissolution from the cathode and deposition on the anode are observed for the ageing performed at 55 Ā°C, while Fe dissolution and deposition are not observed atā20 Ā°C. Using atomic force microscopy (AFM), the surface conductivity is examined, which shows only minor degradation for the cathodes aged atā 20 Ā°C. The cathodes aged at 55 Ā°C exhibit micrometer size agglomerates of nanometer particles on the cathode surface. The results indicate that cycling at higher SOC ranges is more detrimental and low temperature cycling mainly affects the anode by the formation of plated Li
Influence of Cycling Profile, Depth of Discharge and Temperature on Commercial LFP/C Cell Ageing: Cell Level Analysis with ICA, DVA and OCV Measurements
This paper uses several techniques to monitor the ageing of commercial LiFePO4 cells, which are cycled at 55Ā°C and -20Ā°C and with a variety of depths of discharges. Ageing at lower depth of discharge leads to higher capacity fading, as compared to higher depth of discharge. The highest capacity fading is observed using 50% depth of discharge cycling at 55Ā°C, while the lowest capacity fading is observed for the cells aged at 100% depth of discharge at -20Ā°C. Using incremental capacity analysis and differential voltage analysis the capacity fading is monitored and underlying ageing mechanisms are described. The loss of lithium inventory and the loss of active material, especially on the cathode side, are the major degradation mechanisms for the cells. The first incremental capacity analysis peak of the discharge process can be used in our case to predict remaining life and cell capacit
LongāTerm Operation of NbāCoated Stainless Steel Bipolar Plates for Proton Exchange Membrane Water Electrolyzers
Proton exchange membrane water electrolysis (PEMWE) is the most promising technology for green hydrogen production using renewable electricity, but it is expensive due to the Ti bipolar plates (BPPs). Herein, a PEMWE stack with coated stainless steel (ss) BPPs (Nb/Ti/ss-BPP and Nb/ss-BPP) is reported, which operates for about 14 000 h at 1.63 +/- 0.12 A cmĀ² and 65 Ā°C. The average degradation rate is as low as 1.2% or 5.5 ĀµV h-1. Scanning electrode microcopy reveals no signs of corrosion of the ss beneath the coatings. The interfacial contact resistance increases due to the formation of poorly conductive amorphous Nb oxides, as shown by atomic force microscopy and X-Ray photoelectron spectroscopy, although it does not affect the cell performance. The results prove that Ti is not needed anymore as base material for manufacturing the BPPs, thus the cost of PEMWE can be significantly reduced