This　study　investigates　the　ethanol　gas-sensing　mechanisms　of　ZnO　nanocrystals　with　distinct　morphologies,　synthesized　via　a　hydrothermal　method　using　various　alkali　sources.　Significant　differences　in　the　gas-sensing　performance　and　morphology　of　ZnO　samples　synthesized　with　ammonium　carbonate　(Na2CO3),　hexamethylenetetramine　(HMTA),　ammonia　solution　(NH3·H2O),　and　sodium　hydroxide　(NaOH)　were　observed.　ZnO　were　confirmed　to　be　impurity-free　through　XRD　analysis,　and　their　morphological　features　were　characterized　by　SEM.　TEM,　XPS,　and　FTIR　were　employed　to　further　analyze　the　crystal　structure　and　binding　energy　of　ZnO.　To　elucidate　the　underlying　mechanisms,　density　functional　theory　(DFT)　calculations　combined　with　electron　depletion　layer　theory　were　applied　to　assess　charge　transfer　processes　and　identify　the　most　sensitive　ZnO　crystal　planes　for　ethanol　detection.　Experimental　gas-sensing　tests,　conducted　across　5–1000　ppm　ethanol　concentrations　within　a　150–350　°C　range,　showed　that　ZnO　prepared　with　Na2CO3,　HMTA,　and　NaOH　was　responsive　at　high　ethanol　concentrations　as　low　as　100　°C,　while　ZnO　synthesized　with　ammonia　required　250　°C　to　exhibit　sensitivity.　All　ZnO　samples　demonstrated　excellent　recovery　at　low　concentrations　at　250　°C.　By　integrating　experimental　findings　with　theoretical　insights,　this　study　provides　a　comprehensive　understanding　of　ethanol　gas-sensing　mechanisms　in　ZnO,　highlighting　the　role　of　crystal　plane　engineering　and　charge　transfer　dynamics　as　critical　factors　influencing　gas　response.　©　2024　by　the　authors.