fig5

Figure 5. (A) The reaction path of β-MnO2; (B) The XRD patterns of α-MnO2; This figure is reprinted (adapted) with permission from Pan et al. Copyright (2016) Nature Research[65]. (C) In situ pH changes of β-MnO2/Zn. This figure is reprinted (adapted) with permission from Liu et al. Copyright (2021) Elsevier[78].