Bismuth-based　materials　have　attracted　broad　research　interest　as　catalysts　for　electrocatalytic　CO2　reduction　(ECR)　to　formate　in　recent　years.　Most　studies　have　been　focused　on　exploring　materials　with　high　activity,　selectivity,　and　durability,　while　little　attention　has　been　paid　to　the　catalysts　structure　stability　especially　under　working　conditions　of　CO2　electrolysis.　Here,　starting　from　the　precursor　of　bismuth　oxide　formate　nanowires　(BiOCOOH　NWs),　it　was　found　that　BiOCOOH　NWs　were　easy　to　electrochemically　evolve　into　two-dimensional　sheet　structure　in　CO2-saturated　KHCO3　solution　and　would　further　reconstitute　into　larger　ultrathin　bismuth　nanosheets　covered　with　amorphous　oxide　thin　layer　(Bi/BiOx　NSs).　However,　in　Ar-saturated　HCOONa　solution,　the　one-dimensional　structure　could　be　maintained　and　reconstructed　into　rough　porous　bismuth　nanowires　(Bi　NWs).　Bi　NWs　showed　less　stability　during　ECR,　which　also　generated　surface　amorphous　oxide　layer　and　further　fragmentated　into　nanoparticles　or　nanosheets.　Bi/BiOx　NSs　showed　better　activity,　selectivity,　and　stability　than　Bi　NWs,　thanks　to　the　high　exposing　active　sites,　enhancing　CO2　adsorption　and　charge　transfer.　The　demonstrated　electrolyte　dependence　of　structure　evolution　for　bismuth-based　catalysts　and　their　performance　for　CO2　electroreduction　could　provide　guidance　for　the　design　and　synthesis　of　efficient　catalysts.　[Figure　not　available:　see　fulltext.]　©　2023,　Tsinghua　University　Press.