Fe nanopowder-assisted fabrication of FeO_x/porous carbon for boosting potassium-ion storage performance

The electrode materials of potassium ion storage system have attracted considerable attention given the promising prospect of a potassium ion system in large-scale electrochemical energy storage applications. Despite the excellent anode performance of metal oxides in Li⁺ and Na⁺ batteries, the study on their K⁺ storage performance is still rarely reported. In this study, we report a safe and low-cost strategy to prepare FeO_x/N-doped carbons by using NaHCO₃ and Fe nanopowder. Benefiting from the oxidation of Fe to Fe₃O₄, an interesting "one stone, two birds" role of the Fe powder can be identified in the heating process. As a reduction agent, the Fe powder can consume the excess oxygen in the bio-massed carbon framework, facilitating the formation of short-range-ordered domains in the biomass-derived carbon materials (FeO_x@GBHCs). Moreover, the close combination of oxidization products (Fe₃O₄ particles) and carbon matrix leads to numerous FeO_x clusters grafted on the surface of the carbon framework via the strong C-O-Fe binding. Therefore, the resultant FeO_x/porous carbon exhibits a high reversible capacity of 410 mA h g^-1 and an excellent cycling capability. The assembled FeO_x@GBHCs//AC potassium-ion hybrid supercapacitor delivers a high energy density of 133 W h kg^-1 at a power density of 700 W kg^-1, demonstrating a potential prospect of metal oxides in boosting the potassium ion storage performance.