there has been extensive 
 study of metallic nanoparticles as a result 
 of the interesting properties that can arise at short length scales . advances in synthesis have allowed the preparation of gold nanoparticles 
 with good control over size and shape , affording opportunities to 
 understand the effect of these parameters on their properties . bimetallic systems provide further means to tune the properties 
 of nanoparticles through variation of composition and chemical ordering 
 within the nanoparticles . in particular , 
 au  pt and au pd nanoparticle systems have attracted 
 interest because of their potential applications as catalysts , and 
 the composition and distribution of the two metals have been shown 
 to impact on their activity and selectivity . pt systems , 
 a pt core with a au shell should be the most thermodynamically stable 
 arrangement at the nanoscale . despite this , it has been possible both 
 to synthesize alloyed au pt nanoparticles and to deposit pt 
 onto au seed nanoparticles to produce au nanoparticles with pt shells . however , the formation of a smooth pt overlayer 
 on au is difficult ; for example , small pt particles form on the surface 
 of au nanorods ( nrs ) . similarly , growth of rh on au nrs is uneven . in contrast , however , pd easily forms smooth 
 layers on au . this could result from 
 a number of factors , including the high surface and cohesive energies 
 of pt ( 2.49 j m and 5.48 ev / atom , respectively ) . for bulk systems , it is possible to form monolayers 
 of pt on au through galvanic displacement of cu monolayers deposited 
 by underpotential deposition ( upd ) , although upd 
 of cu monolayers is less straightforward at the nanoscale . pt 
 core  shell particles , although a recent paper showed that the 
 structure of au nrs with pt shells alters over time or upon annealing . the incomplete coverage of au by pt may provide 
 channels for au diffusion to the outside of the nanoparticle . the 
 purpose of the present study was to develop a method of forming smoother , 
 more complete coatings of pt on au nrs both to enhance the stability 
 of the core we show that a method involving sequential 
 deposition using selective blocking can be successfully employed to 
 produce au core  pt shell nrs with considerably enhanced stability 
 and catalytic activity . au nrs were synthesized using the method reported by nikoobakht 
 and el - sayed . platinum was deposited 
 onto the au nrs at a au : pt molar ratio of 1:0.5 by modification of 
 the method of grzelczak et al . one sample was subjected simply to 
 further deposition with the same quantity of pt salt . a second sample 
 was first bubbled with carbon monoxide for 30 min , left to stand for 
 1 h , and then bubbled with ar for 40 min before the second deposition 
 of pt was performed . the idea behind the additional step in the procedure 
 was to block some of the pt sites with co ( which binds more strongly 
 to pt than to au ) in order to encourage further pt deposition to take 
 place on exposed au sites . for electrochemical measurements , au or 
 au  pt nrs were dispersed on carbon powder and deposited on 
 a glassy carbon rotating - disk electrode ( rde ) using nafion as a binder . the residual surfactant on the nr surfaces was removed by an electrochemical 
 cleaning procedure as described in the supporting 
 information . high - angle 
 annular dark - field scanning transmission electron microscopy 
 ( haadf - stem ) images of the nrs are presented in figure 1 . the au rods have an average width of 23.5 nm and an average 
 length of 59.2 nm , giving an aspect ratio of 2.6  0.5 . the first deposition 
 of pt mainly results in deposition at the ends of the rods . it could arise from blocking of the sides of 
 the nrs by bromide or underpotentially deposited ag , higher surface 
 energy of the rod end facets compared with the side facets , or enhanced 
 mass transport of platinum precursor to the ends of the rods ( hemispherical 
 diffusion compared with planar diffusion conditions ) . in addition , 
 once pt has nucleated on the rods , there is a thermodynamic preference 
 for additional pt to grow on pt rather than on exposed au because 
 of the higher cohesive and surface energies of pt as well as the lattice 
 strain ( 3.9% ) caused by the mismatch in lattice parameters 
 ( table 1 ) . haadf - stem 
 images of ( a ) au nrs , ( b1 , b2 ) au  pt nrs prepared 
 without the co blocking step , and ( c1 , c2 ) au  pt nrs of same 
 composition prepared with the co blocking step . also shown are edx 
 maps of the ( b3 , c3 ) au and ( b4 , c4 ) pt distributions in the nrs from 
 ( b2 ) and ( c2 ) , respectively . data were taken from refs ( 22 ) and ( 23 ) . when additional pt is deposited , the pt does indeed 
 continue to 
 grow more at the ends of the rods , as shown in figure 1b . figure 1c shows that the second 
 deposition is more even when the first layer of pt is blocked by co. 
 the au  pt rods are smoother in figure 1c1 than in figure 1b1 , and the contrast is 
 more even across the rod . au and pt have similar atomic numbers , which 
 means that contrast observed in the images is mainly related to the 
 thickness . panels b2 and c2 in figure 1 are 
 higher - magnification images of a typical nr from each sample , and 
 energy - dispersive x - ray analysis ( edx ) maps of the au and pt distributions 
 for each sample are presented in panels b3,4 and c3,4 , respectively . pt nr samples have greater 
 pt concentration at the ends of nrs ( figure 1b4 ) , whereas the samples prepared with selective blocking by co have 
 a more even pt distribution , with more pt in the middle of the rod 
 ( figure 1c4 ) . measurements of the mean aspect 
 ratios and indications of the degrees of outgrowth at the corners 
 are shown in figure 2 ( lengths and widths are 
 provided in the supporting information ) . the mean aspect ratio of the au  pt nrs prepared by selective 
 blocking ( 2.7  0.6 ) is close to that of the original au nrs , 
 whereas that of nrs prepared without selective blocking is higher 
 ( 3.5  0.8 ) , indicating preferential growth of pt at the ends 
 when the existing pt deposits are not blocked . in addition , there 
 is a greater propensity for pt to grow on the corners than on the 
 ends or the sides of the rods . these elemental mapping and morphological 
 observations all indicate that co blocking is effective in producing 
 a more even distribution of pt on the au nr seeds . images acquired for the 
 samples after 5 and 17 months ( figure s2 
 in the supporting information ) showed that 
 au  pt nrs prepared without a blocking step underwent significant 
 morphological changes , akin to those reported previously for similar 
 samples . in contrast , nrs prepared with 
 the selective blocking method retained their original size and shape . shell 
 nrs that exhibit greater long - term stability than nrs obtained by 
 standard chemical deposition . figure 3 presents uv  vis spectra 
 of au nrs and au nrs coated with pt . two absorption peaks are observed , 
 corresponding to localized surface plasmon resonances in the transverse 
 ( tspr ) and longitudinal ( lspr ) directions . as pt is deposited onto the nrs , the lspr peak is red - shifted and 
 broadened , in line with previous observations for deposition of transition 
 metals onto nrs . the tspr peak is often less sensitive 
 to the deposition of metals , and this is observed also in figure 3 . the red shift is usually related to an increase 
 in the aspect ratio of the nr . pt nr samples : 
 ( a ) au ; ( b ) au  pt ( 1:0.5 ) ; ( c ) au  pt ( 1:1 ) prepared 
 without the co blocking step ; ( d ) au  pt ( 1:1 ) prepared with 
 the co blocking step . we confirmed these observations via computational simulation 
 using 
 the discrete dipole approximation , as 
 implemented in the software package ddscat ( further details concerning the ddscat configuration and calibration 
 are given in the supporting information , and calculated spectra are shown in figures 
 s3s6 ) . a cylindrical au nr was constructed with aspect 
 ratio close to those of the nrs shown in figure 1a : the rod length ( l ) was set to 30 nm , and the 
 radius was set to 5 nm , giving a width ( w ) of 10 
 nm and an aspect ratio ( ar = l / w ) of 3 . the incoming radiation was set at an angle of 45 relative 
 to the principal axis of the nr , ensuring excitation of both the tspr 
 and lspr modes , as appropriate . the calculated max for the au nr was 630 nm , which is a little lower than that 
 in the experimental spectrum ( figure 3 ) , but 
 there is dispersion in the experimental aspect ratios . it is well - known 
 from experiment and calculations that increasing the ar in homogeneous 
 au nrs results in a red shift of the lspr ; this is verified in figure s6 in the supporting 
 information , which shows calculated spectra for au nrs with 
 ars of 35 . calculations of extinction spectra for nonhomogeneous 
 models of 
 nrs are not widely seen in the literature . by adding pt deposits at 
 the ends of the au nr ( in a  capping  position ; figure 4a middle ) and on the sides of the au nr ( in what 
 we have named a  coating  position ; figure 4a right ) , we were able to calculate the effect of 
 pt deposition on the optical extinction spectrum . figure 4b shows the extinction spectra for a bare au nr 
 ( l = 30 nm , w = 10 nm , ar = 3 ) , 
 a pt - capped au nr with cap thickness  = 5 nm ( overall ar = 
 4 ) , and au nrs with initial pt caps ( 1 = 5 nm ) and 
 then a secondary pt capping and coating ( i.e. , a universal covering ) 
 with a thickness of 1 or 2 nm ( 2 =  = 1 or 
 2 nm , overall ar = 3.5 or 3.14 , respectively ) , corresponding to the 
 experimentally observed structures . there are multiple changes to 
 the extinction spectrum resulting from the additions of pt , the predominant 
 factors being the geometric dependence of max on 
 the ar and the quenching effects of the 
 pt dielectric medium . our calculations 
 ( figure 4b ) show a clear red shift of the lspr 
 from max = 627 to 688 nm for the pt - capped au nr 
 ( ar = 4 ) . the red shift in the lspr is not as large as that for a 
 pure au nr with ar = 4 ( figure s6 ) . pt nr models : ( left ) 
 bare au nr with ar = 3 ( length l = 30 nm , width w = 10 nm ) ; ( middle ) au nr with added pt caps ( thickness 
  ) ; ( right ) au nr with a pt coating ( thickness  ) . the 
 angle of the incoming incident radiation relative to the principal 
 ( long ) axis is 45. ( b ) calculated extinction spectra ( qext ) of au the spectrum for the bare au nr ( ar 
 = 3 ) is 
 shown by a black solid line . the spectrum for a pt - capped au nr (  
 = 5 nm , ar = 4 ) is plotted as a red dotted line . spectra for geometric 
 models with initial pt caps ( 1 = 5 nm ) and a secondary 
 pt capping and coating ( 2 =  = 1 or 2 nm , 
 ar = 3.5 or 3.14 , respectively ) are plotted with blue short - dashed 
 and green long - dashed lines , respectively , illustrating clear quenching 
 of the spectral features with increasing pt coating . in our experimental spectra ( figure 3 ) , 
 little difference is apparent between the spectra of rods prepared 
 by direct pt deposition and by deposition onto selectively blocked 
 nrs . figure 4b shows that pt coating leads 
 to rapid quenching of the recognizable au lspr spectral feature , even 
 for a thickness  of only 1 nm . blue shifts of the lspr peaks , 
 resulting from the decrease in ar for these thicker nrs , were also 
 observed . referring back to our experimental uv  vis spectra , 
 from these calculations we can postulate that the second pt deposition 
 would need to be prominently on the end of the pt - capped au nr to 
 ensure a further red shift in the lspr peak as seen in figure 3 . considering the haadf - stem images in figure 1 and the compositional au : pt ratio of 1:1 ( which 
 would require a pt coating of between 1 and 2 nm in our model ) , it 
 seems plausible that the au lspr is in fact quenched , resulting in 
 similar spectral signatures for the two samples of higher pt content 
 [ spectra ( c ) and ( d ) in figure 3 ] . figure 5 shows cyclic voltammograms ( cvs ) 
 of carbon - supported au and au a pair of redox waves centered at 0.3 v vs sce arises 
 from the redox reactions of functional groups on the carbon surface , 
 most likely quinones . this 
 current is larger for the au / c sample and decreases as the ratio of 
 accessible pt surface area to au surface area increases . in view of 
 the fact that the total active surface areas of the catalysts are 
 similar ( vide infra ) the effect is not discussed in the literature , but there 
 is precedent for mixed au pt nanoparticle systems to produce 
 lower capacitive currents at greater pt : au surface ratios . the cv of the au nrs displays a wave at 0.8 
 v on the cathodic scan that corresponds to the reduction of gold oxide . this feature is decreased when the au nrs are coated with pt . if it 
 is assumed that a charge of 400 c cm is 
 required to reduce gold oxide , the accessible 
 area of au can be evaluated . table 2 lists 
 the values of the charge and electrochemically active au surface area 
 for each sample . the au  pt sample prepared by the selective 
 blocking method displayed the smallest gold oxide reduction wave , 
 indicating that the accessible surface area of gold is smallest for 
 this sample . the scan rate was 0.05 v s , and the current density ( j ) is 
 referred to the electrochemically active surface area ( see table 2 ) . the wave at 0.3 v on the 
 negative - going potential sweep 
 corresponds to the reduction of platinum oxide and is indicative of 
 the accessible surface area of pt . this peak appears to increase in 
 size as more pt is deposited and also appears to be largest for the 
 sample produced by selective blocking . however , the overlap of this 
 peak with that arising from carbon functional groups precludes its 
 quantitative analysis . the peaks corresponding to metal oxide reduction 
 are a little negative of those obtained for polycrystalline pt and 
 au under similar conditions , suggesting slower kinetics for the reduction 
 of these oxides . at the negative limit , hydrogen adsorption and desorption 
 can be observed on the pt  au surfaces . the area under the peaks 
 indicates that the surface coverage with pt is larger for the particles 
 prepared by the selective blocking method . table 2 also provides values for the samples active pt surface 
 areas , obtained by integrating the area under the background - corrected 
 desorption wave and assuming a charge of 209 c cm for the same reaction on polycrystalline pt . under the assumption that the loading of nrs is similar 
 for each experiment , the total surface area for an estimate of the 
 coverage of au with pt can be obtained by comparing 
 the au and pt areas for each sample . these estimates are provided 
 in table 2 and show that the sample prepared 
 with selective blocking has the highest coverage of pt ( despite the 
 fact that two samples contain the same pt : au molar ratio ) . the shape 
 of the peaks corresponding to hydrogen desorption provides information 
 on the types of pt surface sites available . the voltammetric profile 
 for the nrs prepared by selective blocking resembles that of polycrystalline 
 pt and indicates a high proportion of { 110 } and { 100 } step sites on 
 the surface , whereas those of the other two catalysts suggest fewer 
 { 110}-type sites . the co was 
 adsorbed at 0.055 v and displaced from solution with ar before the 
 cvs were recorded . as expected , each cv shows an absence of features 
 relating to hydrogen desorption ( co adsorption blocks hydrogen adsorption 
 on the surface ) , and a new current peak on the anodic scan is present , 
 which corresponds to the oxidative desorption of co. interestingly , 
 the onset potentials of co oxidation are similar for the three samples . 
 however , the breadth of the peak decreases as the pt surface area 
 increases . the nanoparticles with the lowest pt coverage exhibit the 
 lowest activity , with a broad wave followed by another wave at more 
 positive potentials . the nanoparticles prepared by the selective blocking 
 method produce cvs with a sharp peak centered at more negative potentials , 
 reminiscent of similar measurements on polycrystalline pt , and with higher overall charge than for cvs 
 of the other samples . the sharpness of the peak , along with the cvs 
 of the clean nr surfaces , indicates that the selective blocking method 
 yields nrs with more extended regions of pt surface . the higher activity 
 of the particles prepared by selective blocking could also be related 
 to the larger number of { 110}-type sites observed in the cv data . co stripping voltammograms for the carbon - supported 
 catalysts in 
 0.05 m h2so4 electrolyte . the scan rate was 
 0.05 v s , and the current density is referred 
 to the electrochemically active surface area ( see table 2 ) . rotating - disk electrode polarization 
 curves acquired for the catalysts 
 at a rotation rate of 1600 rpm in o2-saturated sulfuric 
 acid electrolyte are compared in figure 7 ( full 
 sets of rde polarization curves at different rotation rates for each 
 catalyst are provided in figure s6 in the supporting 
 information ) . the shape of the curve observed for au nrs is 
 similar to those previously reported for au surfaces and nanoparticles in acidic media and reflects the slow 
 kinetics of oxygen reduction on au in acidic solutions : the onset 
 of the current is at a significantly more negative applied potential , 
 and the current does not reach a plateau , indicating that the rate 
 of reaction does not reach a point where it is limited by mass transport 
 alone in the potential range employed ( i.e. , it is limited by both 
 kinetics and mass transport , even at the negative potential limit ) . hydrodynamic 
 voltammograms acquired for carbon - supported catalysts 
 in oxygen - saturated 0.05 m h2so4 . the scan rate 
 was 0.002 v s , and the rotation rate was 1600 
 rpm . the pt - coated au nrs exhibit faster 
 kinetics , in that the rde curves 
 all reached a mass - transport - limited current at negative potentials 
 and the onset of current was at a much more positive potential than 
 for au , albeit at a slightly more negative potential than previously 
 reported for carbon - supported 3 nm diameter pt particles . it is immediately apparent that the catalyst 
 prepared by the selective blocking method is the most active , as the 
 current in the mixed - control region is significantly higher . the current 
 plateaus in the mass - transport - limited region indicate differing selectivities 
 of the catalysts toward the oxygen reduction reaction ( orr ) . oxygen 
 can be reduced via a four - electron reduction to water ( directly or 
 in two sequential two - electron steps ) or via a two - electron reduction 
 to hydrogen peroxide ( scheme 1 ) . the larger current densities observed for the catalyst produced 
 with the selective blocking method indicate that a higher proportion 
 of water is produced as a product in the orr . the average number of electrons transferred per oxygen 
 molecule 
 can be evaluated from the data in figure 7 using 
 the koutecky levich equation:1where j is the current density , jl is the limiting 
 current density , jk is the kinetic current 
 density , n is 
 the number of electrons transferred , k is the standard rate constant ( referred to the standard potential , e ) , e is the applied potential , r is the gas constant , t is the absolute 
 temperature ,  is the transfer coefficient , na is the number of electrons transferred in the rate - determining 
 step , f is the faraday constant , ca is the bulk concentration of species a and da is its diffusivity , v is the kinematic 
 viscosity , and  is the rotation rate ( in rpm ) . representative 
 plots of j versus  ( at an applied potential of 0.1 v ) for 
 the catalysts are provided in figure 8a , along 
 with lines having the slopes expected for four - electron and two - electron 
 reductions . these plots assume an oxygen solubility of 1.26  
 10 mol cm in the solution , 
 a diffusivity of 1.93  10 cm s , and a kinematic viscosity of 0.01009 cm s. from 
 eq 1 , values of n as a function 
 of potential can be evaluated , and these data are presented in figure 8b . ( a ) examples of koutecky  levich plots derived from 
 the data 
 in figure 7 at e = 0.1 
 v. the thick blue and green lines have the theoretical slopes for 
 two- and four - electron pathways , respectively ( the two - electron line 
 has been shifted for clarity ) . ( b ) values of the number of electrons 
 transferred ( n ) as a function of applied potential , 
 derived from the koutecky levich plots : red  , au nrs ; 
 blue  , au  pt ( 1:0.5 ) ; black  , au pt 
 ( 1:1 ) ; green  , au  pt ( 1:1 ) prepared by selective blocking . a range of means to compare the 
 activities of catalysts have been 
 reported in the literature . we chose to estimate standard rate constants 
 ( referred to the standard potential for reduction of oxygen to water ) 
 as well as specific activities at 0.55 v vs sce , for ease of comparison 
 with other au - supported pt systems . to estimate the standard rate 
 constants , data were fitted to eq 1 with igor 
 pro using nonlinear regression analysis with e = 1.23 v , na = 1 , and ca , da , and v as above . the value of  had to be constrained 
 to 0.5 , and n and k were 
 allowed to vary . each polarization curve was fitted to eq 1 , 
 and the values of n and k were averaged . the values of n were found to be 
 similar to those obtained in figure 8 ; they 
 are given in table 3 along with the values 
 of k , the latter normalized to the active 
 surface area ( estimated as the sum of the electrochemically active 
 areas of au and pt in table 2 ) . the values of 
 the standard rate constant are of similar magnitude , with the catalyst 
 prepared by selective blocking being slightly more active than the 
 other two materials . the main advantage of this catalyst would thus 
 appear to be the larger currents obtained and greater selectivity 
 toward water . the exchange current density 
 reported for carbon - supported pt nanoparticles 
 is 1.66  10 a cm , corresponding roughly to a rate constant on 
 the order of ( 3.77 )  10 cm s ( depending on the value of n ) . the 
 rate constants in table 3 are a little larger 
 than this value . the reason why the rate constants measured for the 
 catalysts in the present work are larger is not obvious , and literature 
 relating to the orr on au  pt systems reports various effects : 
 some reports show increased activity relative to pt and others 
 show lower activity than pt . van brussel and co - workers reported 
 higher activity for au - supported pt in the positive - going sweep ( orr 
 on the reduced surface ) but lower activity relative to pt in the negative - going 
 sweep ( orr on the oxidized surface ) . in the catalyst 
 samples prepared in the present work , pt was grown epitaxially on 
 the au nr surface , and the lattice parameters 
 of au and pt ( 4.08 and 3.92  , respectively ) indicate a strain 
 of 3.9% . lattice strain has previously 
 been suggested to affect the electronic structure of a metal , shifting 
 its d - band center to higher energy , with the effect that binding of 
 small adsorbates is enhanced . thus , for au - supported 
 pt , the adsorption of o2 would be stronger , enhancing the 
 reaction rate , but the binding of o and oh intermediates is also predicted 
 to be stronger than on pt , decreasing the reaction rate . the overall 
 predicted effect is lower orr activity for pt / au(111 ) compared with 
 pt(111 ) . in line with this argument , 
 the activities for au core  pt shell particles and au - supported pt layers displayed a dependence on the thickness of the pt layer , with thicker 
 deposits approaching the activity of bulk pt . on the other hand , lattice 
 strain arguments alone do not take into account ligand effects , and a recent publication examining the orr on the ( 111 ) and ( 100 ) 
 facets suggested that expansion or compression alone is unlikely to 
 be responsible for changes in the binding energies of oh and hence 
 the activity . pt systems suggest 
 a synergistic relationship between au and pt sites and/or a positive shift in the pt oxidation potential . to compare our data more easily with those for other au - supported 
 pt samples , the specific activity ( jk at 
 0.55 v vs sce ) was obtained from koutecky levich plots and 
 normalized to the electrochemically active surface area and also to 
 the pt surface area , the latter following sarapuu et al . at this potential , it was assumed that the activity 
 arose from pt sites because negligible current was observed for the 
 au catalysts . pt 1:1 catalyst prepared without 
 selective blocking exhibits a specific activity ( with respect to pt 
 area ) similar to that of the au pt 1:0.5 catalyst ; these activities 
 are similar to those reported by sarapuu et al . for au - supported pt deposits catalyzing oxygen reduction 
 in sulfuric acid ( for which little dependence of the activity on pt 
 thickness was observed as a result of the dominating effect of sulfate / bisulfate 
 adsorption ) . the catalyst prepared by selective 
 blocking exhibited 25% higher specific activity with respect 
 to pt area , suggesting that the different morphology of the pt - on - au 
 support has an influence on the activity , in line with previous reports . the specific activity observed for this catalyst 
 approaches that reported for bulk ( polycrystalline ) pt . the increase in current density at this potential is related largely 
 to the increase in the number of electrons transferred , which is higher 
 for the catalyst prepared by selective blocking . conversion of the 
 current densities to rate constants using the values of n at 0.55 v gives k values of 3.04  
 10 and 3.33  10 cm s for the au pt catalysts prepared without and 
 with selective blocking , respectively . these may be compared with 
 the rate constants ( normalized to pt surface area ) obtained by van 
 brussel and co - workers for pt deposits on au prepared by displacement 
 of cu . the rate constant for the catalyst prepared 
 by selective blocking is a little higher but has a similar order of 
 magnitude . the main advantage of this catalyst would thus appear to 
 be the larger specific currents obtained and greater selectivity toward 
 water . perhaps obtaining a uniform dispersion of pt over au rather 
 than concentrating it in particular regions of the nrs enables peroxide 
 generated at au sites to be reduced at nearby pt sites , as suggested 
 by adzic and co - workers . a new method for the 
 preparation of smoother films of pt on au 
 nanoparticle supports has been described . sequential deposition with 
 selective blocking of the initial pt deposits by co results in a more 
 uniform distribution of pt on au nanorods . the catalytic activity 
 of these au  pt nrs toward electrochemical oxidation of co and 
 reduction of oxygen is superior to that of au the nr structure 
 also has greater long - term stability when prepared with the blocking 
 method . this method could easily be extended to coverage of smaller 
 au supports and further refined by increasing the number of blocking 
 steps . it could prove useful as a general means of synthesizing pt 
 ( or other transition metal ) shell catalysts on nanometallic supports , 
 producing catalysts with enhanced stability and performance .
a method 
 for the preparation of smooth deposits of pt on au nanorods 
 is described , involving sequential deposition steps with selective 
 blocking of surface sites that reduces pt - on - pt deposition . the au 
 pt 
 nanorods prepared by this method have higher long - term stability than 
 those prepared by standard pt deposition . 
 electrochemical data show 
 that the resulting structure has more extended regions of pt surface 
 and enhanced activity toward the carbon monoxide oxidation and oxygen 
 reduction reactions .