H+-ion　concentration　cell,　which　can　harvest　thermal　energy　to　generate　electricity　by　hydrogen　concentration　difference　principle　with　a　fuel　cell　structure,　is　an　innovative　thermoelectric　conversion　device.　In　this　system,　phosphoric　acid-doped　polybenzimidazole　(PA-doped　PBI)　membrane　is　a　key　component　influencing　the　power　generation　performance　of　the　cell.　Herein,　30,　45,　60,　75,　and　90　μm　thick　PBI　membranes　are　successfully　synthesized　and　doped　with　phosphoric　acid.　To　achieve　a　good　compromise　between　the　proton　conductivity　and　durability,　the　properties　of　PA-doped　PBI　membranes　are　experimentally　evaluated　to　clarify　the　effect　of　the　acid　doping　time　and　membrane　thickness　on　cell　performance.　The　results　indicate　that　the　higher　the　acid　doping　level,　the　worse　the　dimensional　stability　of　the　membrane.　Also　the　thinner　the　PBI　membrane,　the　smaller　the　membrane　resistance　to　ions　motion,　while　the　poorer　the　stability.　Upon　reaction　at　170　°C,　this　cell　can　boast　a　power　density　from　3.0　to　8.0　W　m−2,　which　results　in　a　thermoelectric　conversion　efficiency　of　5.97–14.32%.　This　study　potentially　boosts　the　practical　application　of　thermal-to-electrical　conversion　technology.　©　2020　Hydrogen　Energy　Publications　LLC