Materials synthesis: The KFeFe-PBA samples were synthesized by the potassium citrateassisted co-precipitation method. Firstly, 2.5 mmol K4Fe(CN)6•3H2O and 2.5 mmol FeSO4•7H2O were separately dissolved into 50 ml 0.2 mol L -1 C6H5K3O7 solutions. The two solutions were mixed by slowly dropping the FeSO4 solution into the K4Fe(CN)6 solution with magnetic stirring. After overnight stirring, the precipitate was centrifuged and washed thoroughly by DI water and isopropanol. Finally, the product was collected after overnight vacuum drying at 60°C. The samples synthesized at room temperature and 60°C were donated as KFeRT and KFe60, respectively.