We　demonstrate　a　new　case　of　materials–gene　engineering　to　precisely　design　photocatalysts　with　the　prescribed　properties.　Based　on　theoretical　calculations,　a　phase-doping　strategy　was　proposed　to　regulate　the　pathways　of　CO2　conversion　over　Au　nanoparticles　(NPs)　loaded　TiO2　photocatalysts.　As　a　result,　the　thermodynamic　bottleneck　of　CO2-to-CO　conversion　is　successfully　unlocked　by　the　incorporation　of　stable　twinning　crystal　planes　into　face-centered　cubic　(fcc)　phase　Au　NPs.　Compared　to　bare　pristine　TiO2,　the　activity　results　showed　that　the　loading　of　regular　fcc-Au　NPs　raised　the　CO　production　by　18-fold　but　suppressed　the　selectivity　from　84　%　to　75　%,　whereas　Au　NPs　with　twinning　(110)　and　(100)　facets　boosted　the　activity　by　nearly　40-fold　and　established　near　unity　CO　selectivity.　This　enhancement　is　shown　to　originate　from　a　beneficial　shift　in　the　surface　reactive　site　energetics　arising　at　the　twinned　stacking　fault,　whereby　both　the　CO　reaction　energy　and　desorption　energy　were　significantly　reduced.　©　2022　Wiley-VCH　GmbH.