Limitations and Challenges

With reasonable OCVs and power outputs in the milliwatts range, SC-SOFCs with coplanar electrodes are a promising approach for compact, robust, and small-scale 

Reactant gases and reaction products from one electrode can also easily diffuse to the adjacent electrode and affect the oxygen partial pressure. While reasonable OCVs can be achieved with microscale interdigitated electrode patterns [71], very low OCVs are attributed to turbulent flow and gas intermixing between the closely spaced microelectrodes [72, 78], especially under wet gas conditions [20, 76]. 

In combination with a LSM-based cathode, a Ni-YSZ anode and YSZ electrolyte appeared blackened after sintering whereas cells with a LSCF cathode did not exhibit such a color change [73]. The black coloration was attributed to the diffusion of manganese from the cathode to the anode through the electrolyte. Chemical interaction between closely spaced coplanar anodes and cathodes could affect the cell performance and material compatibility studies could facilitate the selection of suitable ceU component materials. 

The cell efficiency of SC-SOFCs with interdigitated electrodes was estimated to be below 1%, with a fuel utilization of less than 0.1% [63]. In addition to insufficient catalytic selectivity of the electrode materials, the small size of SC-SOFCs with coplanar electrodes limits the electrochemical conversion of fuel. 

The small electrode size not only imposes fabrication challenges and hmits the feasibility of SC-SOFCs with coplanar microscale electrodes, it also limits detailed analyses of these cells. SC-SOFCs with coplanar microscale electrodes yield very low conversion of the reactant gases, so that differences between input and output gases cannot be easily detected by mass spectrometry and information about the reactions that occur cannot be obtained. Similarly, the small electrode size makes impedance analysis difficult. The lack of fundamental studies and appropriate characterization and fabrication techniques leaves the working principles of SC-SOFCs with coplanar electrodes to a great extent unexplored. 

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Keyes R W 1991 Limits and challenges in electronics Contemp. Rhys. 32 403... 

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Chapter 8 by Van Doorslaer builds on Chapter 2 by Harmer et al., applies the ideas to a range of heme proteins, and provides a brief review of these methods, highlighting the advantages, limitations, and challenges for the future. In particular, there is a focus on multifrequency EPR, which has provided important insights into... 

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