Phosphorus-doped [Ni(x)Co(x)Fe(1-2x)]O–Fe2O3 inverse spinel nanosheets anchored on starch-derived carbon microspheres for efficient and durable overall water splitting

Efficient bifunctional electrocatalysts are vital for boosting water electrolysis performance. Herein, starch-derived porous carbon microspheres were synthesized under high-salinity conditions to serve as conductive templates for the in situ growth of transition metal species. Through carbonization and phosphorization, an inverse spinel composite, P-[Ni (0.15) Co (0.15) Fe (0.7) ]O–Fe 2 O 3 , was generated. The carbon microspheres provided excellent conductivity and mechanical stability, while the nanosheets offered abundant active sites and porous structures, ensuring enhanced electron transfer and strong synergistic interactions. Consequently, the optimized catalyst exhibited outstanding bifunctional performance, with low overpotentials of 217 mV for oxygen evolution and 125 mV for hydrogen evolution at 10 mA cm −2 . The assembled electrolyzer delivered 10 mA cm −2 at 1.58 V and maintained stability for 100 h. This work demonstrates a sustainable route for fabricating high-performance transition metal-based electrocatalysts using renewable starch biomass.