Differential analysis of SOFC current-voltage characteristics

Abstract

Solid Oxide Fuel Cells (SOFC) are regarded as a promising technology for economic power generation due to their high efficiency and large fuel flexibility. Durability is a severe hurdle towards their deployment. The near future targets in respect to Degradation Rate (DR) are about 0.1%.kh-1, which needs improved monitoring and diagnostics. This work aims at introducing new approach based on Differential Analysis of the i-V curves, named DiVA. It operates with the Differential Resistance (DR) Rd and its evolution during long term testing. Since derivatives are more sensitive to small deviations, the Differential Resistance Analysis (DRA) ensures increased sensitivity and information capability in respect to degradation monitoring and diagnostics, which is demonstrated on a small stack during thermal cycling conditions-before and after the first thermal cycle, on button cells tested up to 9000 hours, as well as on button cells operating in fuel cell and in electrolysis mode. The results show that DRA is several times more sensitive in comparison with the classical DR evaluation based on registration of the voltage decrease at constant current.

Zdravko Stoynov – the scientist who created new scientific horizons - Review

“…This method surprises and fascinates with simplicity and originality that provide over 10 times higher sensitivity when assessing degradation rate. This approach could eliminate some difficult and risky accelerated stress tests on batteries and fuel cells [31][32][33].…”

“…The method operates with the differential resistance Rd = dU/dI, i.e. with the derivative of the potential U with respect to the current I, which changes its value according to the working point, following the shape of the volt-ampere curve [31][32][33].…”

“…The introduction of a spectral transform procedure additionally increases the noise immunity and sensitivity of the method (Figure 5b) [32,33]. The intensity of the individual spectral peak (A Ω -1 cm -4 ) is proportional to the length of the current range with similar values of the differential resistance.…”

“…The Differential Resistance Analysis, which uses the new characteristic indicator Rd,min, is several times more sensitive than the classical approach for measurement of the degradation rate based on the voltage change over time at constant current [30][31][32]. Figure 6 demonstrates the high selectivity and sensitivity of the method that makes visible changes in the system which are unnoticeable in the current-voltage characteristics and ensures their quantitative evaluation.…”

In-situ temperature monitoring directly from cathode surface of an operating solid oxide fuel cell

“…However, premature degradation of cells and stacks is a significant challenge to ensure the longevity of SOFCs and to make them a commercially viable technology to produce cleaner electricity [11], [12], [13]. Among various factors affecting the premature degradation of SOFCs, thermal cycling at high temperatures (usually in a range from 600 °C to 900 °C) and uneven temperature distribution are two dominant factors [14], [15]. Severe mechanical failures such as formation and propagation of cracks and failures in gas sealing are typical temperature-driven failures at cell level, while failures of interconnect sealing is one of the stack level problems aggravated by uneven temperature distribution [4], [5].…”