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Solid oxide fuel cells are of technological interest as they offer high efficiency for energy conversion in a clean way. Understanding fundamental aspects of oxygen self-diffusion in solid state ionic systems is important for the discovery of next-generation electrolyte and cathode material compositions and microstructures that can enable the operation of SOFCs at lower temperatures more efficiently, durably, and economically. In the present perspective article, we illustrate the important role of modelling and simulations in providing direct atomic scale insights on the oxygen ion transport mechanisms and conduction properties in the cathode and electrolyte materials, and in accelerating the progress from old materials to new concepts. We first summarize the ionic transport mechanisms in the traditional cathode and electrolyte materials which have been widely studied. We then pay our attention to the non-traditional materials and their oxygen transport paths from recent studies, focusing on structural and transport anisotropy and lattice dynamics. Lastly, we highlight the new developments in the potential to increase the ionic conductivity of the traditional materials through external mechanical stimuli, bringing about the mechano-chemical coupling to drive fast ionic transport.

Three dimensional printing technologies represent a revolution in the manufacturing sector because of their unique capabilities for increasing shape complexity while reducing waste material, capital cost and design for manufacturing. However, the application of 3D printing technologies for the fabrication of functional components or devices is still an almost unexplored field due to their elevated complexity from the materials and functional points of view. This paper focuses on reviewing previous studies devoted to developing 3D printing technologies for the fabrication of functional parts and devices for energy and environmental applications. The use of 3D printing technologies in these sectors is of special interest since the related devices usually involve expensive advanced materials such as ceramics or composites, which present strong limitations in shape and functionality when processed with classical manufacturing methods. Recent advances regarding the implementation of 3D printing for energy and environmental applications will bring competitive advantages in terms of performance, product flexibility and cost, which will drive a revolution in this sector. Broader contextIntensive research on additive manufacturing has been carried out during the last three decades to allow the fabrication of three dimensional objects by assembling materials without the use of tools or molds. Three dimensional printing technologies represent a potentially low-cost, new paradigm for the manufacture of energy conversion technologies offering unique capabilities in terms of shape/geometry complexity and enhancement of specific performance per unit of mass and volume of the 3D printed units. However, the fabrication of highly complex devices for the energy sector by using 3D printing is an almost unexplored field. In this work we review the state of the art of 3D printing technology to fabricate components or devices for energy and environmental applications, focusing on aspects related to the control of the microstructure, functionality and performance of the 3D printed structures.