Non-stoichiometric oxides can undergo reversible redox reactions without crystallographic phase transformations – a unique property that remains underexplored in energy storage applications. The reduction of non-stoichiometric oxides, like SrFeO3 δ, is an energy sink, whilst its oxidation leads to energy release. Together, these reactions can be used for energy charging and discharging in the storage cycles. Here, we look into redox reactions of SrFeO3 δ, triggered by manipulating the oxygen partial pressure (pO2). The experimental work was carried out at 600°C, with SrFeO3 δ in a packed bed, exposed to mixtures of N2 and air, with a higher value pO2 in the discharging step (oxidation) and a lower pO2 in the charging step (reduction). The extent of reaction in the bed was associated with heat and reaction fronts, the first describing the energy distribution, the latter - the uptake or release of oxygen in the reactions with particles of SrFeO3 δ. Propagation of both fronts was deduced from spatial-temporal changes in temperatures of the SrFeO3-δ bed, measured with an array of thermocouples, and with the content of oxygen in the off-gas, detected with a paramagnetic sensor. Our experiments demonstrate that large shifts in pO2 cause the reaction front to lead the heat front, whilst smaller variations in pO2 result in the reversed order and even overlapping of the fronts. These results, hence, exemplify the versatility of operation and usage of non-stoichiometric oxides for energy storage.