Heterogenized　phthalocyanine-based　molecular　catalysts　are　the　ideal　electrocatalytic　platforms　for　CO2　reduction　reaction　(CO2RR)　because　of　their　well-defined　structures　and　potential　properties.　In　addition　to　the　pursuit　of　catalytic　performances　at　industrial　potentials,　it　is　equally　important　to　explore　experimental　rules　and　design　considerations　behind　activity　and　selectivity.　Herein,　we　successfully　developed　a　series　of　nickel　phthalocyanines　(NiPcs)　with　different　alkyl　chains　immobilized　on　multi-walled　carbon　nanotubes　(CNT)　to　unveil　the　structure—performance　relationship　for　electrocatalytic　CO2RR　in　neutral　electrolyte.　Interestingly,　a　volcano-type　trend　was　found　between　the　activity　for　CO2-to-CO　conversion　and　alkyl　chain　lengths　of　NiPcs　on　CNT.　Experimental　results　further　indicate　that　their　electrocatalytic　CO2RR　activities　are　highly　related　to　the　molecular　dispersion　and　the　heterointerfacial　charge　transfer　capability　adjusted　by　the　alkyl　chains.　Particularly,　the　optimized　electrocatalyst　via　accurate　clipping　at　the　molecular　level　exhibits　an　ultrahigh　activity　with　Faradaic　efficiency　of　CO　up　to　99.52%.　©　2022,　Tsinghua　University　Press.