ChineseJournalofCatalysis36(2015)175–180
催化学报2015年第36卷第2期|www.chxb.cn a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r. c o m / l o c a t e / c h n j c Article Elucidationofoxygenreductionreactionpathwayon
carbon‐supportedmanganeseoxides
LuhuaJianga,*,QiwenTanga,b,JingLiua,b,GongquanSuna,#
DalianInstituteofChemicalPhysics,ChineseAcademyofSciences,Dalian116023,Liaoning,China
UniversityofChineseAcademyofSciences,Beijing100049,China
a
b
A R T I C L E I N F O
A B S T R A C T
Articlehistory:
Received30September2014
Accepted10November2014
Published20February2015
Keywords:
Oxygenreductionreactionpathway
Alkalineelectrolyte
Carbon‐supportedelectrocatalyst
Manganeseoxide
The oxygen reduction reaction (ORR) is a complex process. This is particularly the case for car‐
bon‐supportedelectrocatalystsinalkalineelectrolytes,becausecarboncancatalyzetheORRviaa
two‐electron transfer to generate hydroperoxide (HO2−), which subsequently undergoes either
chemical decomposition to generate O2 and OH− (HODR) or electrochemical reduction to OH−
(HORR).Inthisstudy,weelucidatedtheORRpathwayonaseriesofcarbon‐supportedmanganese
oxides,whichhavebeenextensivelystudiedaselectrocatalystsinalkalineelectrolytes.Acompari‐
son of the turnover frequencies of the HODR and HORR showed that although an apparent
four‐electrontransferprocesswasidentifiedwhentheHO2−yieldwasmeasuredusingtherotating
ring disk electrode technique, the real ORR pathway involved a two‐electron transfer process to
generateHO2−,withsubsequentchemicaldecompositionofHO2−.Theseresultswillhelpustoun‐
derstandtheintrinsiccatalyticbehaviorofcarbon‐supportedtransition‐metaloxidesfortheORRin
alkalineelectrolytes.
©2015,DalianInstituteofChemicalPhysics,ChineseAcademyofSciences.
PublishedbyElsevierB.V.Allrightsreserved.
1. Introduction
Theoxygenreductionreaction(ORR)isveryimportantbe‐
causeitisthecathodicreactioninfuelcellsandmetal–airbat‐
teries.Pt‐basedmaterialsareextensivelyusedasORRcatalysts
under acidic conditions, but under alkaline conditions, a wide
range of non‐noble metals and their oxides are stable and ac‐
tive for practical applications [1–3]. An understanding of the
ORR pathway on a catalyst surface is critical in both funda‐
mental and practical terms. Although the ORR pathway on a
smoothcatalystsurfacecanbeeasilystudiedusingtherotating
ringdiskelectrode(RRDE)technique,foracarbon‐basedprac‐
ticalporouselectrode,theORRpathwayiscomplexbecausethe
considerable amount of intermediate HO2− generated at the
carbonsurfacecanbereadsorbedforfurtherreactions.Specif‐
ically, hydroperoxide species have three possible subsequent
pathways,asshowninScheme1,i.e.,(1)diffusiondirectlyinto
theelectrolyteasaproduct,(2)furtherelectrochemicalreduc‐
tion to form OH−, and (3) chemical decomposition to produce
O2 and OH−. Unlike case (1), cases (2) and (3) are apparent
four‐electron processes, although only case (2) is a real
four‐electronprocess.Ourpreviousstudyofcarbon‐supported
cobalt oxides [4,5] clearly showed that although the apparent
electrontransfernumberwasclosetofourinalargepotential
*Correspondingauthor. Tel:+86‐411‐84379603;Fax:+86‐411‐84379063;E‐mail:[email protected] #Correspondingauthor. Tel:+86‐411‐84379603;Fax:+86‐411‐84379063;E‐mail:[email protected] ThisworkwassupportedbytheStrategicPriorityResearchProgramofChineseAcademyofSciences(XDA09030104),theNationalBasicResearch
Program of China (973 Program, 2012CB215500), the National Natural Science Foundation of China (21033009), and the 100‐Talent Program of
ChineseAcademyofSciences. DOI:10.1016/S1872‐2067(14)60249‐7|http://www.sciencedirect.com/science/journal/18722067|Chin.J.Catal.,Vol.36,No.2,February2015 176
LuhuaJiangetal./ChineseJournalofCatalysis36(2015)175–180
2.2. Workingelectrodepreparation k4 (4e ), direct 4e pathway
O2
k1 (2e)
k 3 (2e)
HO2
k2
O2+OH
OH
2e +2e
2e + HODR
Scheme 1. Various possible mechanisms for O2 reduction in alkaline
solution.
window, differentelectrochemicalreactionsoccurreddepend‐
ingontheelectrodepotential,i.e.,atwo‐electrontransferpro‐
cess followed by chemical decomposition of hydroperoxide at
low overpotentials, but two‐electron transfer followed by fur‐
ther electrochemical reduction of hydroperoxide, namely a
serialfour‐electrontransferprocess,athighoverpotentials.
Other promising transition‐metal oxides, e.g., manganese
oxides, are also worth investigating to help us to understand
catalysis of the ORR by transition‐metal oxides. Previously, it
was concluded that a two‐electron transfer process with sub‐
sequentchemicaldecompositionofhydroperoxideoccurredon
amanganeseoxidesurface[6,7].However,thereisstillalackof
experimentalevidencetosupportthisdeduction.Inthispaper,
continuingourpreviousstudyontheeffectsofmanganeseva‐
lencesinmanganeseoxidesonORRactivity[8],weaimtoelu‐
cidate the ORR pathway on carbon‐supported manganese ox‐
ides.Themanganeseoxidesamplesusedinthisstudyarethe
same as those used in our previous study [8]; therefore, the
preparation procedures will not be described again. First, we
calculated the electron transfer number of the ORR according
totheKoutecky–LevichequationbymeasuringtheORRpolar‐
izationcurvesviatherotatingdiskelectrode(RDE)technique.
We then distinguished between direct and indirect
four‐electrontransferprocessesbydetectingtheHO2yieldsat
manganese oxides of different catalyst thicknesses via the
RRDEtechnique.Finally,wedeterminedthemainreactionsin
peroxidechemicaldecomposition(HODR)andelectrochemical
reduction (HORR) by measuring the turnover frequencies
(TOFs)ofthetworeactions. 2. Experimental
2.1. Experimentalsetup
Atraditionalthree‐electrodesystemwasusedforRDEand
RRDE measurements. The RDE (Φ 5 mm, glassy carbon (GC)]
measurements were performed using a CHI 760D electro‐
chemical workstation. The RRDE measurements were per‐
formedusingaBi‐potentiostat(PineInstruments).GCcovered
by a porous catalyst film was used as the working electrode,
andPtwireandaHg/HgOelectrode(MMO,in1mol/LNaOH,
0.93 V vs reversible hydrogen electrode after calibration)
served as the counter and reference electrodes, respectively.
ThepotentialofthePtringelectrodewaskeptat0.2Vvsthe
MMOduringtheRRDEtests. The preparation of the working electrode has been de‐
scribedindetailintheliterature[9].Briefly,catalystpowder(3
mg) was dispersed in ethanol (2 mL). Carbon powder (2 mg;
VulcanXC‐72,CabotCorp.)wasaddedtoincreasetheconduc‐
tivity,and5wt%Nafionsolution(50μL;DuPont)wasaddedas
a binder. The mixture was ultrasonicated to form a well‐dis‐
persedink.Acertainamountoftheinkwaspipettedontothe
GC electrode and then the solvent was evaporated at room
temperaturetoformacatalyst thinfilm. AlltheMnOxcatalyst
sampleswerefresh,withoutanyelectrochemicalpretreatment.
2.3. DeterminationofORRandHORRpolarizationcurves
The ORR and HORR polarization curves were recorded in
O2‐saturated1mol/LNaOHsolutionandN2‐saturated1mol/L
NaOHcontaining0.85mmol/LH2O2solution,respectively,ata
scanningrateof10mV/s. 2.4. TOFmeasurements(HODR)
GCcoveredwithaPt/Ccatalystwasusedasaprobetode‐
tect the changes with time in the H2O2 concentration in the
electrolyteafteraddingMnOxastheHODRcatalyst.Themeas‐
urements were also carried out in a three‐electrode system
[10]. The preparation procedure for the thin‐film electrode
withPt/Castheelectrocatalystwasthesameasthatdescribed
abovefortheMnOxelectrode.Afterelectrochemicallycleaning
theelectrodesurfaceatascanningrateof100mV/sin1mol/L
NaOH,theORRlimitingcurrent(ilim,ORR)wasrecordedbyhold‐
ingtheelectrodepotentialat0.5Vfor10s,withtheelectrode
rotatingataspeedof1600rpm.ThenH2O2(30%)wasadded
to the electrolyte to ensure a concentration of 0.85 mmol/L
(the same concentration as that of O2 in the O2‐saturated 1
mol/L NaOH solution) [11]. Then MnOx (300 μg) dispersed in
water (1 mL) was quickly added to the H2O2‐containing elec‐
trolyte under magnetic stirring to ensure good contact of the
MnOxcatalystwithH2O2.ThePtelectrodewasheldat0.5Vfor
10stocollectthecurrent(ilim)atintervals.Theconcentration
ofresidualHO2intheelectrolytecouldbecalculatedaccording
to the current difference on the Pt electrode (ilim,HORR = ilim −
ilim,ORR).Themeasurementscontinuedforonly10sateachin‐
tervalandthenthePtelectrodewasrapidlyremovedfromthe
electrolyte after the tests, therefore it was assumed that no
extraHO2decomposedatthePtsurface. 3. Resultsanddiscussion
3.1. MeasurementofORRelectrontransfernumbersof carbon‐supportedmanganeseoxideelectrocatalysts
TheORRpolarizationcurvesofthecarbon‐supportedman‐
ganeseoxideelectrocatalystsweremeasuredinO2‐saturated1
mol/L NaOH electrolyte; the results are shown in Fig. 1. The
ORRonsetpotentialsofthefourcarbon‐supportedMnOxcata‐
lystswithdifferentmanganesevalences,i.e.,MnOOH/Mn(OH)4,
LuhuaJiangetal./ChineseJournalofCatalysis36(2015)175–180
0.0
MnOOH/Mn(OH)4
i/mA
-0.2
MnO2
(1)
(1)
(2)
(2)
(3)
(3)
(4)
(4)
177
Mn2O3
Mn3O4/Mn2O3
(1)
(1)
(2)
(2)
-0.4
-0.6
(3)
(3)
(4)
(4)
-0.8
-0.6
-0.4
-0.2
E/V vs MMO
0.0
-0.6
-0.4
-0.2
E/V vs MMO
0.0
-0.6
-0.4 -0.2
0.0
E/V vs MMO
0.2-0.6
-0.4 -0.2 0.0
E/V vs MMO
0.2
Fig.1.ORRpolarizationcurvesforMnOx+Ccatalystsatdifferentrotationrates.(1)400rpm;(2)900rpm;(3)1600rpm;(4)2500rpm.
1.2
MnOOH&Mn(OH)4
MnO2
1.0
Mn2O3
Mn3O4&Mn2O3
XC-72
0.8
2
Toelucidatetheapparentfour‐electrontransferprocess,we
investigatedthechangesintheHO2yieldwithvaryingcatalyst
thickness:ifHO2istheintermediateintheORR,theHO2yield
shoulddecreasewithincreasingcatalystthickness,becausethe
HO2 species has a greater probability of chemically decom‐
posingtoform O2[10,13];otherwise,the ORR shouldbe adi‐
rect four‐electron transfer process with negligible HO2 pro‐
duction[14,15]. To avoid any changes in the surface manganese valence,
fresh MnOx samples were used for the RRDE tests. The RRDE
measurements were performed in an O2‐saturated 0.1 mol/L
NaOH electrolyte. The measured disk currents are shown in
Fig.3(a).TheHO2yieldcanbecalculatedfromEq.(2):
XHO2−=(2iring/N)/(idisk+iring/N)
(2)
where iring and idisk are the ring current and disk current, re‐
1
3.2. InfluenceofcatalystthicknessonHO2yields
spectively, and N is the collecting efficiency of the RRDE (N =
0.38 after calibration). The calculated HO2 yield (XHO2) is
shown in Fig. 3(b). To enable a clear comparison, the HO2−
yields (@–0.4 V vs MMO) for different electrocatalysts are
listedinTable1.Itcanbeseenthatforallcatalysts,asthecata‐
lyst loading increases from 3.75 to 30 μg, the quasi‐limiting
currentincreases,buttheORRonsetpotentialremainsalmost
constant. For the MnOOH/Mn(OH)4 sample, with a catalyst
loading of 3.75 μg, the maximum XHO2 is 87.4%, indicating a
dominant two‐electron process. The HO2 yield sharply de‐
creaseswithincreasingcatalystloading.Asthecatalystloading
increasesto30μg,theHO2yielddecreasestoaround21%.For
the MnO2 sample, XHO2 decreases from 26% to 6.6% with in‐
creasing catalyst loading from 3.75 to 30 μg, suggesting a
four‐electron process at high catalyst loading. These results
clearlyshowthatO2isfirstreducedtoHO2,whichisthenre‐
duced or chemically decomposes in a thick catalyst layer,
therefore the HO2 yield detected by the Pt ring electrode de‐
creaseswithincreasingcatalystlayerthickness.Bonakdarpour
etal.[13]investigatedtheORRatFe/N/Celectrodesandmade
similar observations, i.e., the HO2 yield decreased from
60%–80%to2%–15%asthecatalystlayerincreasedfrom40
μg/cm2to800μg/cm2.
i / (cm /mA)
MnO2, Mn2O3, and Mn3O4/Mn2O3[8],areverysimilar, andthe
ORR limiting currents increase with increasing electrode ro‐
tatingrate.Forcomparison,theORRlimitingcurrentwithVul‐
can®XC‐72carbonastheelectrocatalystislowerthanthatwith
MnOx.AccordingtotheKoutecky–Levichequation[12]:
ilim = 0.62nFADo2/3ω1/2ν−1/6Co* (1)
(wherenistheORRelectrontransfernumber,FistheFaraday
constant,Aisthegeometricareaoftheelectrode,Disthediffu‐
sioncoefficientofO2intheelectrolyte,ωistherotationspeed
oftheelectrodeinradians,νistheviscosityoftheelectrolyte,
andCo*istheconcentrationofO2attheelectrodesurface),the
limitingcurrentisproportionaltothesquarerootoftheelec‐
trode rotating rate, therefore the relationship between 1/ilim
andω0.5(@E=0.5V)islinear,asshowninFig.2.Afterfitting,
the electron transfer numbers for MnOOH/Mn(OH)4, MnO2,
Mn2O3, and Mn3O4/Mn2O3 were calculated to be 3.5, 3.5, 3.6,
and3.5,respectively,suggestingthatafour‐electrontransferis
the dominant process for carbon‐supported MnOx. For com‐
parison, the electron transfer number for Vulcan® XC‐72 car‐
bonisonly2.1,suggestingthatatwo‐electronprocessisdomi‐
nantwithHO2asthemainproduct. 0.6
0.4
0.02
0.03

0.04
0.5
0.5
/rpm
0.05
Fig. 2. Koutecky–Levich plots of ORR on MnOx + C catalysts (derived
fromFig.1). 178
LuhuaJiangetal./ChineseJournalofCatalysis36(2015)175–180
XHO2_
0.6
XHO2_
0.4
MnOOH/Mn(OH)4
0.8
0.4
0.2
0.2
(b)
(b)
0.0
0.0
-0.2
3.75 g
7.5 g
15 g
30 g (a)
-0.4
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
idisk/mA
0.0
0.0
idisk/mA
MnO2
-0.2
3.75 g
7.5 g
15 g
30 g (a)
-0.4
-0.6
0.1
-0.5
-0.4
E vs MMO/V
Mn2O3
0.6
0.4
0.2
0.1
0.6
0.4
0.2
(b)
0.0
0.0
(b)
0.0
0.0
-0.2
3.75 g
7.5 g
15 g
30 g
-0.4
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
E vs MMO/V
0.0
idisk/mA
idisk/mA
0.0
Mn3O4/Mn2O3
0.8
XHO2_
XHO2_
0.8
-0.3
-0.2
-0.1
E vs MMO/V
(a)
(a)
0.1
3.75 g
7.5 g
15 g
30 g
-0.2
-0.4
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
(a)
0.1
E vs MMO/V

2
Fig.3.Diskcurrents(a)andHO yields(b)onMnOx/Ccatalystswithdifferentcatalystloadingsatrotationrateof1600rpmandscanningrateof10
mV/s.CollectionefficiencyN=0.38;ringpotentialwasmaintainedatEring=0.2V.
3.3. DeterminationofORRpathwaysatcarbon‐supportedMnOx
catalysts
3.3.1. CalculationofTOF(HODR)
Tofurtherclarifywhetherchemicaldecompositionorelec‐
trochemical reduction of the generated HO2 intermediate is
dominant,wecalculatedandcomparedtheTOFsoftheHORR
andHODR.TheHODRTOFwascalculatedasdescribedinthe
Experimentalsection.ThedifferencebetweentheORRlimiting
current(ilim,ORR),measuredinO2‐saturated1mol/LNaOH,and
the time‐dependent limiting current of ilim, measured in
O2‐saturated 1 mol/L NaOH + 0.85 mmol/L H2O2, gives the
limitingcurrentforHO2electrochemicalreduction(ilim,HORR)as
ilim − ilim,ORR. The changes in ilim,HORR with time can be used to
Table1 HO2−yieldsfordifferentelectrocatalysts(@–0.4VvsMMO).
Catalystmass (g)
Mn(OH)4
3.75
87.4
7.5
55.0
15.0
41.8
30.0
21.3
HO2yield(%)
MnO2
Mn2O3
26.2
65.3
21.4
37.4
15.3
13.2
6.6
4.9
Mn3O4/Mn2O3
65.4
58.7
19.0
9.7
calculatetheTOFoftheHODRattheMnOxsurface,asdescribed
below[10].ItshouldbenotedthattheNaOHsolutionwassat‐
urated with O2 in measuring the H2O2 reduction current, to
eliminatetheinfluenceofO2onHO2chemicaldecomposition.
ItshouldalsobementionedthatthecalculationofTOFHODRwas
basedonthehypothesisthat(1)TOFHODRisindependentofthe
HO2concentrationand(2)alltheMnOxtakespartinthereac‐
tion.Theoretically,theHORRlimitingcurrentcanbeexpressed
as ilim,HORR=2FD2c2*/ (3)
whereD2isthediffusioncoefficientofHO2intheelectrolyte,
c2*isthebulkconcentrationofHO2,andisthediffusionlayer
thicknessoftheelectrodeatarotatingspeedof1600rpm. TheHODRisapproximatelyfirstorderatlowHO2concen‐
trations,thereforethereactionratecanbeexpressedas νHODR=−dc2*/dt=kHODRc2*
(4)
wherekHODRistheapparentreactionrateconstantoftheHODR,
which is related to the amount of catalyst in the electrolyte.
Combining Eqs. (3) and (4), the relationship between ilim,HORR
andkHODRisexpressedas kHODR=−ln(10)dlog(ilim,HORR)/dt
(5)
The changes in log(ilim,HORR) with time are shown in Fig. 4,
LuhuaJiangetal./ChineseJournalofCatalysis36(2015)175–180
MnOOH/Mn(OH)4
MnO2
Mn2O3
Mn3O4&Mn2O3
MnOOH/Mn(OH)4
MnO2
Mn2O3
Mn3O4/Mn2O3
0.00
i3/mA
ilim,HORR/(mA/cm2)
1
179
-0.05
(a)
-0.10
0.1
-0.6
0
1
2
t/(103 s)
3
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
E vs MMO/V
4
-0.05
Fig. 4. Time‐dependent plots of HO2 reduction current density (pro‐
portionaltobulkHO2concentration)in1mol/LNaOHsolution. (b)
E vs MMO/V
-0.10
whichisfittedlinearly,indicatingthattheHODRisafirst‐order
reaction,assupposed.Ifthecatalystamountaddedtotheelec‐
trolyteisthesamefordifferentsamples,theslopesofthelines
reflect the HODR rates for different MnOx catalysts, i.e.,
Mn3O4/Mn2O3>Mn2O3>MnO2>MnOOH/Mn(OH)4. Furthermore,kHODRisrelatedtotheTOFbyEq.(6)[10]:
TOFHODR=kHODRVc2*MMn/(mW)
(6)
whereVisthevolumeoftheelectrolyte,misthemassofMnOx,
c2*isthebulkconcentrationofHO2,Wisthemasspercentage
of manganese in MnOx, and MMn is the atomic weight of man‐
ganese(54.95g/mol).ThecalculatedresultsarelistedinTable
2. Fig. 5. (a) Polarization curves for HORR with MnOx catalysts in
N2‐saturated 0.85 mmol/L H2O2 + 1 mol/L NaOH electrolyte and (b)
derivedTafelplotsforHORR(currentsarenormalizedtomassofMnOx
catalyst).Electroderotatingspeed:1600rpm,scanningrate:10mV/s.
3.3.2. CalculationofTOF(HORR)
TheHORR polarization curves forthe MnOx catalysts were
measuredinaN2‐saturated0.85mmol/LH2O2+1mol/LNaOH
electrolyte and are shown in Fig. 5(a). To eliminate the influ‐
ence of mass transport, the kinetic HORR currents were de‐
rivedfromFig.5(a)accordingto[12]:
1/ilim=1/i+1/ik
(7)
TheobtainedTafelplotsareshowninFig.5(b).Itcanbeseen
thatreductioncurrentsaredetectedforthefourMnOxcatalysts
andtheonsetpotentialsarearound−0.05V.Mn2O3andMnO2
havethemostpositiveandthemostnegativehalf‐wavepoten‐
tial,respectively.Thelimitingcurrentsareintherange0.06to
0.10 mA. For comparison, the theoretical limiting current of
the HORR was calculated according to the Koutecky–Levich
equation;at around1.6mA/cm2, it is ca. 0.31 mA for anelec‐
trodeof 5mm,withadiffusioncoefficientofHO2in1mol/L
NaOHof1.3×10–9m2/s,electrolyteviscosityof1×10–4m2/s,
and electrode rotating speed of 1600 rpm. The much lower
experimental limiting current compared with the calculated
valueshowsthatonlysomeHO2iselectrochemicallyreduced,
andsomeischemicallydecomposedtoformO2,whichiseither
electrochemically reduced or released to the atmosphere. In
thefollowingcalculation,itisassumedthatthelimitingcurrent
resultsentirelyfromreductionofHO2,toobtainthemaximum
TOFoftheHORR.TheTOFoftheHORRiscalculatedas[10] TOFHORR=ik,HORRMMn/(nFW)
(8)
whereik,HORRisthekineticcurrentoftheHO2electrochemical
reduction,nistheelectrontransfernumber,andF,W,andMMn
have the same meanings as in Eqs. (3) and (6). The values at
0.12VarelistedinTable2forcomparison. FromTable2,itisclearlyseenthatforthefourMnOxcata‐
lysts,theTOFfortheHODRistwoordersofmagnitudehigher
than that for the HORR, indicating that the intermediate HO2
mainly undergoes subsequent chemical decomposition. These
MnOx samples have similar morphologies; one reason for the
better ORR activities of Mn2O3 and Mn3O4/Mn2O3 is probably
faster chemical decomposition of the HO2 intermediate on
thesecatalysts. Table2 ReactionratesofHO2electroreductionanddecomposition.
Catalyst
TOFHODR(10−2s−1)
MnOOH&Mn(OH)4
2.41 MnO2
2.74 2.87 Mn2O3
Mn3O4&Mn2O3
3.39 TOFHORRat0.12V(10−4s−1)
4.36
3.35
5.03
3.96 -0.15
MnOOH/Mn(OH)4
MnO2
Mn2O3
Mn3O4/Mn2O3
-0.20
-0.25
-0.30
10-1
100
ik,HORR/(A/g)
101
4. Conclusions
A comparisonoftheTOFsoftheHODRand HORRshowed
that although apparent four‐electron transfer processes were
observedbymeasuringtheHO2−yieldviatheRRDEtechnique,
therealORRpathwayinvolvesatwo‐electrontransferprocess
to generate HO2−, with subsequent chemical decomposition.
180
LuhuaJiangetal./ChineseJournalofCatalysis36(2015)175–180
GraphicalAbstract
Chin.J.Catal.,2015,36:175–180 doi:10.1016/S1872‐2067(14)60249‐7
Elucidationonoxygenreductionreactionpathwayoncarbon‐supported
manganeseoxides LuhuaJiang*,QiwenTang,JingLiu,GongquanSun*
DalianInstituteofChemicalPhysics,ChineseAcademyofSciences;
UniversityofChineseAcademyofSciences
O2
The real ORR pathway behind the apparent four‐electron process on car‐
bon‐supportedmanganeseoxideswasshowntobeatwo‐electrontransferreac‐
tionfollowedbyhydroperoxidedisproportionation.
Theseresultsareexpectedtohelpustounderstandtheintrin‐
sic catalytic behavior of carbon‐supported transition‐metal
oxidesfortheORRinalkalineelectrolytes.
k4 (4e), direct 4e pathway
k1 (2e  )
HO2
k3
O2
+OH
k2 (2e  )
OH
MnOx/C
ElectrochimActa,2003,48:1015
[7] OhsakaT,MaoLQ,AriharaK,SotomuraT.ElectrochemCommun,
2004,6:273
[8] TangQW,JiangLH,LiuJ,WangSL,SunGQ.ACSCatal,2014,4:
457
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碳载氧化锰表面氧还原反应路径研究
姜鲁华a,*, 唐琪雯a,b, 刘
静a,b, 孙公权a,#
中国科学院大连化学物理研究所, 大连洁净能源国家实验室(筹), 辽宁大连116023
b
中国科学院大学, 北京100049
a
摘要: 氧还原反应(ORR)是一个复杂的过程, 尤其在碱性电解液中, 炭载型催化剂表面的ORR路径尤为复杂, 因为碳本身可以催化
ORR以二电子转移过程发生, 产生过氧化氢, 继而过氧化氢或者发生化学分解生成氧气(HODR), 或者发生电化学还原生成OH–
(HORR). 本文详细研究了ORR在常用氧化锰催化剂表面的反应路径. 通过比较HODR和HORR的转换频率发现, 尽管利用旋转环
盘电极方法得到的表观电子转移数接近4, 真实的ORR主要是2电子过程, 反应生成的过氧化氢继而大部分发生化学分解生成氧
气. 该结果有助于理解碱性电解质中炭载型过渡金属氧化物电催化剂对ORR的催化行为.
关键词: 氧还原反应路径; 碱性电解质; 碳载氧化锰电催化剂
收稿日期: 2014-09-30. 接受日期: 2014-11-10. 出版日期: 2015-02-20.
*通讯联系人. 电话: (0411)84379603; 传真: (0411)84379063; 电子信箱: [email protected]
#
通讯联系人. 电话: (0411)84379603; 传真: (0411)84379063; 电子信箱: [email protected]
基金来源: 中国科学院战略性先导科技专项(XDA09030104); 国家重点基础研究发展计划(973计划, 2012CB215500); 国家自然
科学基金(21033009); 中国科学院“百人计划”.
本文的英文电子版由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).