Conclusions
Concentrating on the effects of operational disturbances, a robustness criterion is creatively developed based on the newly modified efficiency criterion, for comprehensive evaluations of the energy conversion process in DMFCs. On the basis of experimental and numerical techniques, careful analyses are performed on classical efficiency criteria. Systematic investigations have also been performed on the integrated use of newly proposed efficiency and robustness evaluations in DMFC systems with different operating conditions and different MEAs. The main findings in the present study can be summarized as follows,
(1) Compared with classical criteria which consider the system efficiency is integrated by several sub-parts, a newly modified efficiency criterion is developed from the global perspective of the whole DMFC systems. It proposes to use Gibbs free energy to substitute the low heating value, which can be beneficial for avoiding misinterpretations of energy conversion process in DMFCs. Comparative study with existing criteria shows that, the newly modified criterion could provide efficient, effective and physically meaningful energy conversion evaluations for undisturbed DMFC operations.
(2) Effect of uncertainty propagations is experimentally revealed to be non-ignorable in disturbed DMFC operations, and it cannot be completely assessed by independently using of efficiency evaluations. A robustness evaluation is then creatively extended from the newly modified efficiency criterion to consider the effects of operational disturbances. Preliminary applications in experimental analysis show that the robustness evaluations provide a guidance to determine the appropriate current densities for stable operations.
