Water splitting performance. (a) LSV curves of the PNC || PNC and Pt/C || RuO2 electrolyzers in 1.0 M KOH. (b) Chronopotentiometry curves of PNC || PNC and Pt/C || RuO2 electrolyzers at 1000 mA cm−2. (c) Illustration of the PNC as a bifunctional electrode for overall water electrolysis. (d) DFT calculated the relative energy diagram of the water dissociation process for PNC. The inset shows the structural diagram of PNC at different water decomposition states.