Utilizing　solar　energy　to　convert　CO2　into　fuels　and　chemicals　represents　a　promising　solution　to　reduce　reliance　on　fossil　fuels,　but　it　is　hampered　by　the　lack　of　highly-efficient　catalysts.　Herein,　we　report　unique　cobalt　nitride/nitrogen-rich　carbons　(Co4N/NCs),　which　can　work　as　noble-metal-free　catalysts　for　CO2-to-CO　conversion.　The　mass　activity　of　Co4N/NCs　is　two　orders　of　magnitude　higher　than　those　of　previously　reported　CO2　photoreduction　catalysts.　The　quantum　yield　for　CO　production　at　450　nm　reaches　7.2%　with　a　turnover　frequency　per　Co　atom　of　0.97　s-1.　The　electronic　structure　and　coordinated　environment　of　catalysts　are　analyzed　by　X-ray　absorption　fine　structure　spectroscopy　and　X-ray　photoelectron　spectroscopy.　The　reaction　processes　are　investigated　by　in-situ　diffuse　reflectance　infrared　fourier　transform　spectroscopy　and　density　functional　theory　calculations.　Results　suggest　that　the　synergetic　effects　between　the　Co4N　and　the　NCs　can　consolidate　the　adsorption　and　activation　of　CO2　and　accelerate　the　interfacial　electron-transfer　kinetics　between　the　Co4N/NCs　catalysts　and　light-harvesting　antenna,　thereby　resulting　in　the　outstanding　activity　for　synthesizing　CO　from　CO2.　This　work　offers　the　possibility　to　design　Co-based　host-guest　topology　for　highly-efficient　CO2　reduction.　©　2020　Elsevier　B.V.