Micro-solid state energy conversion membranes: influence of doping and strain on oxygen ion transport and near order for electrolytes†
Enhancing the efficiency of micro-energy conversion devices through engineering of the structure–transport relationship is a prerequisite toward next generation micro-electrolysers and fuel cells. Here, oxygen ion conducting free-standing thin films are key elements, forming buckled and strained membranes for gas exchange and energy conversion. The electro-chemo-mechanics of free-standing membranes vs. substrate-supported films are investigated as model device structures to study the factors influencing the ionic transport, and answer the fundamental question: how strongly does solid solution doping vs. lattice strain affect the defect-induced oxygen ion transport in buckled electrolyte membrane films for solid state micro-devices? Importantly, we demonstrate that tuning the electro-chemo-mechanics of doped ceria films can influence the ionic transport through the effect of opposed strained volumes altering the clustering of oxygen vacancy defects. Strain is studied by comparing flat substrate-supported films to compressive buckled membrane devices and observing subsequent changes in atomistic near order via Raman spectroscopy. The buckling resulted in a significant increase of the activation energy for ionic transport, greater than classical extrinsic doping. The power of electro-chemo-mechanic engineering of ceramic films is demonstrated in finding the best strategy for optimizing ionic conduction and thereby enhancing future performance in thin film electrolytes for micro-energy conversion devices.