Electrochemical　carbon　dioxide　reduction　reaction　(ECO2RR)　to　produce　high　value-added　products　is　a　promising　and　effective　strategy　for　closing　the　artificial　carbon　cycle　and　achieving　sustainable　development　of　resource.　However,　catalyst　structural　reorganization　and　agglomeration　caused　by　the　reduction　process　will　reduce　the　catalytic　performance.　In　this　study,　a　carbon　nitrogen　shell　with　cupper-doped　(CNCu　shell)　catalyst　was　prepared　using　silicon　dioxide　(SiO2)　as　a　template.　The　selectivity　of　the　catalyst　was　controlled　by　precisely　adjusting　the　form　of　Cu　doping　in　the　catalyst.　When　doped　as　single-atoms　(CNCu2.5),　the　catalyst　exhibited　a　Faraday　efficiency　of　up　to　85　%　for　formate　at　−0.9　V　versus　reversible　hydrogen　electrode　(vs.　RHE).　In　contrast,　when　both　Cu　clusters　and　single-atoms　coexisted　(CNCu25),　the　catalyst　favored　multi-carbon　products,　with　a　Faraday　efficiency　of　45　%　for　ethanol　and　23　%　for　acetic　acid.　Density　functional　theory　(DFT)　calculations　revealed　the　key　mechanism　for　the　difference　in　catalyst　selectivity　between　the　two　doping　forms.　Cu　single-atoms　provided　suitable　binding　energy　to　HCOO*,　which　increased　the　rate　of　CO2　conversion　to　formate,　while　the　combination　of　Cu　clusters　and　single-atoms　increased　the　adsorption　of　HCOO*,　raising　the　rate-determining　step　energy　of　the　formate　pathway,　which　favored　multi-carbon　products.　This　study　fundamentally　revealed　how　different　doping　forms　of　metals　affect　catalyst　selectivity,　providing　new　insights　and　strategies　for　developing　superior　metal–carbon–nitrogen　(M[sbnd]C[sbnd]N)　catalysts.　©　2024　Elsevier　Inc.