Double　perovskite-type　Sr11Mo4O23　material　exhibits　unusual　structural　flexibility　and　oxygen　ion　mobility.　However,　the　transition　of　Sr11Mo4O23　cubic　phase　to　SrMoO4　tetragonal　phase　around　400　degrees　C　makes　the　conductivity　drop　by　45.8　%.　Hence,　it　is　necessary　to　stabilize　the　phase　structure　and　improve　the　elec-trochemical　performance　of　Sr11Mo4O23　in　order　to　be　used　for　implementing　into　intermediate　tempera-ture　solid　oxide　fuel　cells　(IT-SOFCs).　In　this　work,　a　novel　Sr10.8A0.2Mo3.5Ta0.5O23-delta　(A　=Li,　Na,　K)　electrolyte　powders　are　synthesized　by　a　citrate-nitrate　combustion　method.　X-ray　diffraction,　scanning　electron　mi-croscopy　and　electrochemical　impedance　spectroscopy　are　used　to　investigate　the　effects　of　acceptor-type　Ta　and　alkali　metals　co-doping　on　phase　structural,　microstructure　and　electrical　properties　of　Sr11Mo4O23.　All　Sr10.8A0.2Mo3.5Ta0.5O23-delta　samples　show　the　same　single　phases　as　Sr11Mo4O23　(Fdm　space　group,　JCPDS　27-1441).　Doping　Ta　element　at　the　B-site　of　Sr11Mo4O23　can　inhibit　the　phase　transition　of　Sr11Mo4O23　to　SrMoO4　so　as　to　improve　the　structure　stability　of　Sr11Mo4O23.On　this　basis,　doping　alkali　metal　at　the　A-site　further　enhances　the　electrical　conductivity　of　Sr11Mo3.5Ta0.5O23-delta(SMTO).　Among　them,　Sr10.8K0.2Mo3.5Ta0.5O23-delta　(SKMTO)　sample　has　the　conductivity　of　2.02　x　10-2　S/cm　in　the　air　at　800　degrees　C,　which　is　similar　to　233　%　higher　than　that　measured　for　Sr11Mo4O23.　Moreover,　the　reliable　chemistry　stability　of　the　SKMTO　samples　was　demonstrated　under　wet　reducing　5　%　H2　or　dry　3　%　CO2　atmospheres,　respectively.　Finally,　the　single　cells　with　SKMTO　and　SMTO　electrolytes　supported　were　successfully　prepared　by　screen-printing　method,　respectively.　The　power　density　of　SKMTO-cell　is　improved　by　at　least　254　%　compared　to　SMTO-cell.　It　can　be　deduced　that　co-doped　Sr10.8K0.2Mo3.5Ta0.5O23-delta　can　be　considered　as　potential　elec-trolyte　for　IT-SOFCs.(c)　2022　Elsevier　B.V.　All　rights　reserved.