Anthropogenic CO2 emission greatly contributes to global climate change. Discovering sustainable, energy- and cost-efficient materials that can capture and store CO2 is a crucial step towards mitigating the adverse effects of global warming. Here we report an effective power-to-decarbonization approach based on atmospheric pressure plasma (APP) assisted synthesis of carbon-MgO nanohybrids for efficient CO2 capture. MgO nanoparticles were derived from inexhaustible plasma-electrified seawater while abundantly available biomass was used as the carbon source, making the whole process sustainable. The APP treatment introduced nitrogen species on the sample's surface and enhanced the CO2 capture. The amount of seawater and the pyrolysis temperature were optimized; the sample prepared using 50 mL of seawater at 500 °C of pyrolysis temperature showed the highest CO2 capture amount of 6 % (mass). This study demonstrates a green and sustainable pathway for CO2 capture through materials recovery from seawater and biomass, while using renewable electricity-driven plasmas as an effective, low-cost energy source for process electrification.