Probing proton transport in solid oxide energy conversion and storage systems
As there are increasing demands on society to decarbonise power generation and transport, there is an increasing requirement to provide alternative sources of energy. Currently there are several competitive options, many of which however have intermittency issues and/or require coupling with storage technologies. One promising solution gathering commercial interest is the solid oxide cell, with the possibility of operation as i) a fuel cell to produce electricity, heat and hot water as a combined heat and power (CHP) solution, ii) as an electrolyser to produce hydrogen or synthesis gas (syngas; CO/H2) or iii) combining these as a reversible device, all operating in the 400-800oC temperature range.
There are two main underpinning technologies: oxide ion conducting and proton conducting electrolytes. For the proton conducting systems, the presence of protons in the electrolyte is fundamental to operation whilst in the oxide ion conducting systems the role of protons is less clear. The incorporation and mobility of protons in oxides such as CeO2, ZrO2 and new phases such as NdBaInO4 and the Ba-Mo hexagonal perovskite-based electrolytes has been of interest, but unambiguously determining transport parameters has proven challenging. Direct measurement of proton diffusion through isotopic labelling is fraught with difficulties due to the low concentrations and background interferences in high vacuum systems. The intention of this work is to unambiguously determine if protons are present in the bulk of a range of oxide electrolytes over the technologically interesting temperature regimes, and if they are mobile.