You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
in a low - temperature fuel cell , polarization often occurs at the oxygen electrode . in order to reduce the effect of polarization on the electrode , it is necessary to enhance the activity of the electrocatalysts involved in the oxygen reduction reaction .
frequently , spherical pt nanoparticles are used as the electrocatalysts [ 1 - 3 ] . on the basis of the catalytic model , increasing
the number of active sites on the surface of an electrocatalyst is an option for improving its electrochemical activity .
recently , nonspherical nanoparticles have also been found to be promising catalysts [ 4 - 8 ] .
these nanoparticles promote catalytic reactions because higher atomic fractions are located at the corners and edges of the nanoparticles .
additionally , hollow metallic nanoparticles have attracted interest in the field of optics   and catalysis   due to their unique properties .
we have recently found that triangular ag / pd nanocatalysts in an electroless copper bath exhibit high activity .
the present study investigates the catalytic potential of hexagonal ag / pt nanoshells prepared via the galvanic displacement reaction for the oxygen reduction reaction .
initially , 0.05 ml of 0.05 m agno3aqueous solution was added to 10 ml of 2.5  10 m sodium citrate aqueous solution .
subsequently , 0.025 ml of 0.1 m nabh4solution was gradually added to a stirred mixed solution of sodium citrate and agno3 , and a light yellow ag seed solution was obtained .
furthermore , 10 ml of 0.05 m agno3was added to 200 ml of 0.1 m hexadecyltrimethyl ammonium bromide ( c16tab ) aqueous solution , and 10 ml of 0.1 m ascorbic acid and 0.266 ml of the prepared ag seed solution were slowly dropped into the aqueous solution .
hexagonal ag nanotemplates were obtained on adding 0.8 ml of 2 m naoh aqueous solution to the c16tab aqueous solution .
two hundred milliliters of the solution containing the synthesized ag hexagonal nanoplates was precipitated by centrifugation at 4000 rpm , and the solution was then redispersed using 3 ml of deionized water to reduce the interaction of free c16tab molecules with the synthesized ag / pt nanoshells . in order to prevent the interaction of clions with the synthesized nanoshells ,
13.9 mg of k2ptcl4was added and slowly dissolved in a 1-ml aqueous solution of 25 mm agno3 ; white solid agcl was obtained .
the white precipitate was removed by the centrifugation method , and a 1-ml solution was then formed with a ptconcentration of 33.5 mm .
an amount of 0.0083 ml of ptsolution was added to 3 ml of the stirred solution of ag nanotemplates at a fixed controlled temperature of 60 c .
the solution containing the prepared ag / pt nanoshells was dropped onto a copper grid covered with a carbon film and was dried naturally ; the characteristic size , shape , and composition of the nanoshells were obtained by performing observations of the dried material by using a high - resolution transmission electron microscope ( hrtem ; jeol jem-3000f ) and an energy dispersive x - ray spectroscope ( edx ) .
x - ray diffraction ( xrd ) spectroscopy ( shimadzu xd-3a , cu anode ) was also employed for the analysis of xrd patterns of the nanoshells .
first , 0.772 mg of carbon powder ( xc-72 ) was added to a 1-ml aqueous solution and dispersed via ultrasonic vibration .
an amount of 30 l of the resulting aqueous solution was dropped onto a 0.07-cmglassy carbon electrode ( gce ) and heated to 70 c to evaporate the water .
simultaneously , in order to make a comparison with the electrochemical activity of the ag / pt nanoshells , spherical ag / pt nanoparticles and pt nanoparticles with the same pt and ag concentration were prepared .
fifty - microliter solutions concentrated from 1-ml solutions of the prepared ag / pt nanoshells , the ag / pt nanoparticles , and the pt nanoparticles were dropped onto a carbon powder / gce electrode . in order to prevent the catalyst from falling into the electrolyte during the measurement ,
the gce was rinsed with 3 l of 5 wt% nafion solution and heated at 70 c for 20 min .
a three - electrode cell , consisting of a gce working electrode , a pt counter electrode , and an ag / agcl ( 3 m kcl ) reference electrode , was used for the lsv measurement . to measure the oxygen reduction activity ,
the lsv experiment was performed in 1 m h2so4(aq ) solution at a scan rate of 20 mv / s .
figure 1a and b presents hr - tem images of the ag / pt nanoshells prepared by the galvanic displacement reaction .
the images clearly reveal that hexagonal ag / pt nanoshells were successfully prepared via the galvanic displacement reaction by adding pt ions to a prepared solution of ag hexagonal nanotemplates , as shown in the inset of fig .
1b ) , the color of the nanoshell edge was significantly darker than that of the nanoshell center .
the edx was utilized to ensure that the hexagonal ag / pt nanoshells were synthesized by this method .
figure 2 shows the line scanned edx spectrum obtained from the edx analysis of a single nanoshell .
on the basis of an analysis of the hr - tem image , the lattice spacing of a hexagonal ag / pt nanoshell was measured , and is shown in fig .
the plane distance of ( 111 ) for the pt and ag nanoparticles was ~2.28    and ~2.33  , respectively .
this indicates that the distance of ~2.30  , which lies between these two values , corresponds to a shell structure formed by the pt and ag atoms .
similar results have been obtained from hr - tem experiments for mixtures of spherical ag / pt nanoparticles .
tem images of ag / pt hexagonal nanoshells : ahigh order;bhr - tem image.inset : hexagonal ag nanotemplates line scanned edx spectrum and xrd pattern of ag / pt hexagonal nanoshells : aline scanned edx spectrum of single nanoshells;bxrd pattern additional information on the nanoshell composition was provided by the xrd pattern shown in fig .
the four peaks , located at 38.25 , 44.65 , 64.85 , and 77.55 , that were detected for the dry ag / pt nanoshell powders were attributed to the ( 111 ) , ( 200 ) , ( 220 ) , and ( 311 ) diffraction planes of the face - centered cubic ( fcc ) structure , respectively .
089 - 3722 ) corresponding to the ( 111 ) , ( 200 ) , ( 220 ) , and ( 311 ) faces of the fcc structure are located at 38.12 , 44.31 , 64.46 , and 77.41 , respectively .
the ( 111 ) , ( 200 ) , ( 220 ) , and ( 311 ) peaks in the pt standard xrd spectrum ( jcpds no .
087 - 0644 ) are located at 38.69 , 44.97 , 65.49 , and 78.73 , respectively .
the locations of the peaks of the ag / pt nanoshells were between those of ag and pt .
figure 3 depicts lsv curves that compare the oxygen reduction reactions in which the prepared hexagonal ag / pt nanoshells , ag / pt nanoparticles , and pt nanoparticles were used as electrocatalysts .
in contrast to the spherical pt and ag / pt nanocatalysts , the hexagonal ag / pt nanoshells showed excellent activity starting from ~0.68 v in the oxygen - saturated acid solution . in the tem image ( fig .
1 ) of the hexagonal ag / pd nanoshells , pores are observed to form on the nanoshells surface .
it is possible that the trapping of the electrolyte species by pores with high - surface areas resulted in the high activity of the nanoshells for oxygen reduction .
recently , pt - based alloy nanoparticles with an optimized electronic structure were reported to show high activity for the electroreduction of oxygen . in the present study ,
another reason for the high activity of the nanoshells is that pt s electronic structure was modified by ag during the formation of the alloy nanoshells .
the comparative lsv curves of the hexagonal ag / pt nanoshells , spherical ag / pt nanoparticles and pt nanoparticles for electroreducing oxygen .
the weight of hexagonal ag / pt nanoshells , spherical ag / pt nanocatalysts and spherical pt nanoparticles : 5  10 mg in conclusion , hexagonal ag / pt nanoshells were successfully synthesized using the galvanic displacement reaction ; in the reaction , the added ptions slowly reacted with the prepared ag nanoplates that were used as templates .
the prepared hexagonal ag / pt nanoshells were successfully used as electrocatalysts in an oxygen reduction process .
the authors thank the national science council of the republic of china , taiwan , for financially supporting this research under contract no .
hexagonal ag / pt nanoshells were prepared by using a hexagonal ag nanoplate as the displacement template and by introducing pt ions . the prepared 
 ag / pt nanoshells played the role of an electrocatalyst in an oxygen reduction process . 
 compared to spherical pt and ag / pt nanoparticles , the hexagonal ag / pt nanoshells showed higher activity for oxygen electroreduction .