Water Self-Dissociation is Insensitive to Nanoscale Environments

SOLANA DI PINO; YAMILA PEREZ SIRKIN; URIEL N. MORZAN ; VERÓNICA M. SÁNCHEZ; ALI HASSALANI; DAMIAN A. SCHERLIS

Angewandte Chemie - International Edition

John Wiley and Sons Inc

Año: 2023 vol. 62

Nanoconfinementeffectson waterdissociationandreactivityremaincontroversial,despitetheirimpor-tanceto understandthe aqueouschemistryat interfaces,pores,or aerosols.ThepKwin confinedenvironmentshas beenassessedfromexperimentsandsimulationsin afewspecificcases,leadingto dissimilarconclusions.Here,withtheuseof carefullydesignedab initiosimulations,we demonstratethatthe energeticsof bulkwaterdissociationis conservedintactto unexpectedlysmalllength-scales,downto aggregatesof onlya dozenmoleculesor poresof widthsbelow2 nm.Thereasonisthatmostof thefree-energyinvolvedin waterauto-ionizationcomesfrombreakingthe OH covalentbond,whichhasa comparablebarrierin the bulkliquid,in asmalldropletof nanometersize,or in a nanoporein theabsenceof stronginterfacialinteractions.Thus,dissocia-tionfree-energyprofilesin nanoscopicaggregatesor in2D slabsof 1 nmwidthreproducethebehaviorcorre-spondingto thebulkliquid,regardlessof whetherthecorrespondingnanophaseis delimitedby a solidor a gasinterface.Thepresentworkprovidesa definiteandfundamentaldescriptionof the mechanismandthermo-dynamicsof waterdissociationat differentscaleswithbroaderimplicationson reactivityandself-ionizationatthe air-liquidinterface.