氨氮还原成氮气机理方面

Poweringdenitrification:theperspectivesofelectrocatalyticnitratereductionMatteoDuca*abandMarcT.M.Koper*aReceived3rdAugust2012,Accepted24thSeptember2012DOI:10.1039/c2ee23062cImbalancesinthenitrogencyclecausedbyhumanactivities(combustion,fertiliser-intensiveagriculture)haveresultedinalarminglyincreasedlevelsofnitrateingroundwaterandotherwaterbodies,withpotentiallyhealth-threateningconsequences.Theelectrocatalyticremovalofnitratefrompollutedwaterisapromisingalternativetobacterialdenitrification,providedthatfullselectivitytoharmlessN2,whichcanbereturnedtotheatmosphere,isachieved.Thisperspectivearticlediscussesthestate-of-the-artofresearchonelectrocatalyticdenitrification,criticallyevaluatingtheobstaclesstillhamperinglarge-scaleapplicationofthistechnique.Themilestonesoffundamentalresearchfocussingonthecathodereactionwillfirstbedealtwith,followedbytheirtranslationintoelectrochemicalreactorsofpracticalinterest.Finally,ashortforayintothenovelfieldofbioelectrochemicalreactorswillclosethearticle.Challengesandopportunitiespertainingtothesethreetopicswillbeanalysed.IntroductionAmongthevariousenvironmentalissuesthataffecttheEarth,theanthropogenicperturbationofthenitrogencycleposesthemostimpendingthreatontheshorttimescale,bothforhumanhealthandthebiosphere.1–3Theveryetymologyofthenamenitrogen(‘‘generatingnitre’’,i.e.KNO3)bearswitnesstooneofthemostworrisomeconsequencesofhuman-drivenimbalancesinthenitrogencycle:anincreasedrunoffofnitratetoground-water,riversandcoastalwater.Thereisagrowingconsensusinthescientificcommunitythatthenitrogencyclehassufferedthemostextensivehuman‘‘footprint’’sincethebeginningoftheAnthropocene,4whichhascausedthiscycletoexceedthesafetythresholdforasustainablefuture(theso-called‘‘tippingpoint’’).5,6Theinfluenceofhumanactivitiesisoftenquantifiedintermsof‘‘reactivenitrogen’’(Nr)producedwithinabiogeochemicalsystemoveracertaintime-span.Nr,definedas‘‘thebiologicallyactive,photochemicallyreactiveandradiativelyactivenitrogencompoundsintheatmosphereandthebiosphereoftheEarth’’,2representsanaccurateindicatorofthehumanfootprintbecausenaturalNrformationhasbeensluggishandrate-limitingthroughoutthegeologiceras.7Thestartoftheanthropicnitrogencyclewasthediscoveryandsubsequentlarge-scaleimplementationoftheHaber-Boschprocess8(whichisnowthemaincontributortoNr(ref.3)),onwhichreliesourabilitytoproducefertilisersand,inturn,toaLeidenInstituteofChemistry,LeidenUniversity,POBox9502,2300RA,Leiden,TheNetherlands.E-mail:[e-mail];Fax:[phone];Tel:[phone]bLaboratoired’ElectrochimieMol
eculaire,Unit
eMixtedeRechercheUniversit
e,CNRSNo.7591,Universit
eParisDiderot,15rueJeandeBa€ıf,75205ParisCedex13,France.E-mail:[e-mail]-Boschprocessrepresentsamilestoneinthehistoryofchemistry,providingmankindwithaplentifulandinexpensivesupplyoffertilisers.Yet,growingevidencefromenvironmentalscienceresearchindicatesthattheexcessiveuseoffertilisers,alongwithfossil-fuelcombustion,hascausedalarmingimbalancesinthenitrogencycle,leadingtonitrateaccumulationingroundwaterandcoastalareas.Thisenvironmentalissuecallsforefficientdenitrificationstrategiesancillarytothewidespreadbiologicaldeni-trification.Electrocatalyticdenitrificationisaverypromisingalternative,sinceitcouldbefedwith‘‘green’’electricityfromrenewablesourcesanditcantargetnitrate-ladenliquidindustrialwastesunsuitableforbiologicaltreatmentorwaterforhumanconsumption.However,dauntingproblemsaretobesolvedforelectrocatalyticdenitrificationtobecomealarge-scaletechnology,theachievementof100%selectivitytoharmlessN2beingtheforemostchallenge.FundamentalresearchhasshedlightontheelementaryunderpinningsofN2formation,suggestingafewstrategiestosteerselectivity;someofthem,suchasbimetalliccatalystscombininga‘‘promoter’’anda‘‘selector’’,havebeenimplementedinelectrochemicalreactors.Theprogressofelectrocatalyticdenitrificationwillincreasinglyrelyonthisrelaybetweenfundamentalandappliedresearch,alongwiththeallianceofspectroscopy,computationandexperimentalelectrochemistrytounravelreactionmechanisms.9726|EnergyEnviron.Sci.,2012,5,9726–9742ThisjournalisªTheRoyalSocietyofChemistry2012DynamicArticleLinksCEnergy&EnvironmentalScienceCitethis:EnergyEnviron.Sci.,2012,5,9726:05:20.ViewArticleOnline/JournalHomepage/TableofContentsforthisissueensurefoodsupplyforagrowingpopulation.However,theinefficientuseoffertilisers,alongwithNOxformationduringcombustion,1hasresultedinasteadilygrowingrunoffofNrintotheenvironment,notonlycausingthewell-known‘‘acidrain’’butalsomoreinsidiousconsequences,suchasthedevelopmentofalgalblooms,whichtransformscoastalandhumidareasin‘‘dead-zones’’,9creatingabreedinggroundfordisease-carryinginsectsandparasites,too10(Fig.1).Nitrateisthemostoxidizedformofnitrogenandthemainnitrogen-containingpollutantofgroundwater,riversandlakes.11Threesourcescontributetotheaccumulationofnitrate:theabove-mentionedaciddepositionofairborneNOx,theoxidationofammonia(fromoverfertilisation)byterrestrialco