Ion-selective　membranes　have　long　faced　a　trade-off　between　nanoscale　precision　and　macroscopic　durability,　especially　in　systems　with　large　pores　(＞1　mu　m),　where　traditional　overlapping　electrical　double　layer　mechanisms　fail.　Organic　membranes　offer　high　ion　selectivity　but　poor　stability,　while　inorganic　membranes　are　durable　yet　limited　by　high　internal　resistance　from　ultralong,　tortuous　pathways.　Here,　these　challenges　are　overcome　by　designing　robust　porous　titanium　membranes　patterned　with　TiO2　nanotube　arraysvia　a　simple　electrochemical　anodization　process.　Uniquely,　these　membranes　reverse　ion　selectivity　from　cation　to　anion　transport,　enabled　by　the　enhanced　charge　separation　and　high　surface　area　of　the　TiO2　nanotubes.This　allows　cation　adsorptionon　channel　walls　and　selective　anion　transport　through　the　central　tunnel-even　in　microchannels　up　to　100　mu　m,　far　beyond　conventional　nanoscale　designs.　The　membranes　demonstrate　proof-of-concept　osmotic　energy　conversion　with　remarkable　durability　of　110　days,　attributed　to　the　mechanical　and　chemical　stability　of　TiO2　nanotubes.　This　work　redefines　the　ion-selective　membrane　design　by　bridging　nanoscale　control　with　macroscopic　robustness　and　offers　new　insights　into　ion　transport　mechanisms　within　microchannels.