To further analyze the activation energy in the QED region, an Arrhenius analysis is performed, and the activation energies Ea at different energy gaps ΔE are provided in Figure . Here, Marcus theory (black line) predicts a parabolic dependence centred at ΔE = -Er, whereas the QED-ET theory (red line) gives that the activation energy decreases substantially at ΔE ≈ -1.02 eV. To illustrate the energy gap dependence of Ea, we divide the range of ΔE into three regions and present the relevant mechanisms in Figure -4f. In the normal and inverted regions, Marcus theory and the QED-ET theory exhibit similar activation energies owing to the dominance of nonradiative ET processes (kMarcus ≫ kQED) (Figure ). In the QED region (ΔE < ΔEM-Q), Marcus theory predicts that Ea continues to increase due to the increasing vibrational displacements of the crossing seams (corresponding to the intersection of the black parabola and blue parabola in Figure ). By contrast, the QED-ET theory exhibits barrier-free radiative ET rates and the energy gap power law [recall eq 3] because the radiative ET mechanism dominates the ET process (kQED ≫ kMarcus), resulting in the elimination of the activation barrier due to the formation of new activationless points from the vacuum fluctuations between zero-photon and one-photon states (corresponding to the intersections of the black parabola and the multiple red parabolas in Figure ). Therefore, this 'activationless' phenomenon can be regarded as evidence for QED-driven radiative ET processes. In the highly negative Marcus inverted region (corresponding to the QED region in the QED-ET theory), the weak temperature dependence (or temperature independence) of ET rates has been reported numerous times. Although some pioneering theoretical studies have proposed that a vibrational tunnelling process is the main mechanism of the temperature independence, there is room for investigating this issue. We believe that the concept of "QED-induced barrier-free ET reactions" can be utilized to design barrier-free redox reactions, and its extension deserves further exploration.