Extended Data Fig. 3: Conversion rates measured using different heating rates.

a, Relative mass loss over time measured using 5, 10, and 20 °C/min heating rates. To stay consistent with the main text results (Fig. 1g), all the specimens were heated up to 700 °C, followed by 1 hr isothermal holding period. b, Conversion rate curves as a function of temperature acquired using three different heating rates. The same conversion rate is reached at higher temperature as the heating rate increases (see for example, the \(\alpha =0.2\) isoconversion line as a guide to the eye), signifying the thermal activation nature of the operating reduction mechanisms. Inset of b reveals the time derivative of the conversion rate with respect to the progression of the reduction. Two peaks are present in all three \({\rm{d}}\alpha /{\rm{d}}t\) curves, proving the involvement of multiple reduction micro-events. These results are further utilized to determine effective activation energy following isoconversional principle^31,32. c, SXRD diffraction patterns of the pellets after the measurements. It is seen that complete reduction is achieved only with 5 °C/min heating rate, while discernible amounts of FeO_x oxide remain in the pellets when higher heating rates were utilized. The presence of the residual FeO_x phase aligns well with the in situ SXRD results revealed in main text Fig. 3, where the reduction of FeO_x is recognized as the most sluggish reaction mechanism.