Coordinately unsaturated single Fe-atoms with N vacancies and enhanced sp ³ carbon defects in Fe–N(sp ² )–C structural units for suppression of cancer cell metabolism and electrochemical oxygen evolution

Installing coordinately unsaturated Fe-N-C structural units on polymer-composite-derived N-doped carbon offers highly active Fe-N_x sites for the electrochemical oxygen evolution reaction (OER) and reactive oxygen species (ROS) generation in tumor cells. An NH₄Cl-driven high-temperature etching method was employed for the formation of FeSA950NC with coordinately unsaturated single Fe-atoms in an Fe-N(sp²)-C structural unit together with N vacancies (V_N) and sp³ defects. The carbonization of Fe-phen@ZIF-8 at 800 °C for 30 min under argon, followed by grinding Fe-ZIF-8@RF-urea with NH₄Cl at 950 °C for 2 hours, resulted in sp³ carbon defects and V_N sites with coordination unsaturation in Fe-N_x due to NH₄Cl decomposition to NH₃ and HCl, which produced substantial internal stress for etching the carbon matrix. FeSA950NC was used to treat both A549 lung cancer cells and NIH3T3 mouse fibroblast cells to determine its potential as an efficient tumor therapeutic strategy using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and ROS assays. Additionally, FeSA950NC provided high stability and excellent OER activity through the Fe-N(sp²)-C structural unit on pyridinic nitrogen by delivering at a minimum overpotential of 300 mV, which is much lower than that of structurally similar Fe-atom sites. The significantly stronger ROS and OER activities of FeSA950NC suggested the role of V_N and sp³-carbon defects with coordinately unsaturated Fe-N₂ sites in improving its catalytic performance.