fig4

Figure 4. Summary and perspective of MIDs. (A) Horizontal comparisons of the five main self-powered systems. (B) Summary of material selection for MID preparation. (C) Summary of challenge for MIDs. (D) Forward-looking roadmap for advancing MIDs. MID: Moisture-induced iontronic device; TEG: thermoelectric generators; SC: solar cells; EMG: electromagnetic generators; NG: nanogenerators.