Imaging the electrocatalytic activity of single nanoparticles (original) (raw)

The electrocatalytic properties of nanoparticles depend on 2 their size, shape and composition 1,2. These properties are 3 typically probed by measuring the total electrocatalytic 4 reaction current of a large number of nanoparticles, but this 5 approach is time-consuming and can only measure the 6 average catalytic activity of the nanoparticles under study. 7 However, the identification of new catalysts requires the 8 ability to rapidly measure the properties of nanoparticles 9 synthesized under various conditions and, ideally, to measure 10 the electrocatalytic activity of individual nanoparticles. Here, 11 we show that a plasmonic-based electrochemical current-12 imaging technique 3 can simultaneously image and quantify 13 the electrocatalytic reactions of an array of 1.6 3 10 5 platinum 14 nanoparticles printed on an electrode surface, which could 15 facilitate high-throughput screening of the catalytic activities 16 of nanoparticles. We also show that the approach can be used 17 to image the electrocatalytic reaction current and measure 18 the cyclic voltammograms of single nanoparticles. 19 Scanning electrochemical microscopy (SECM) can be used to 20 rapidly screen the electrocatalytic Q2 of nanoparticles 4. However, 21 SECM relies on mechanical scanning of a microelectrode across a 22 sample surface, which limits the imaging speed and can interfere 23 with the electrocatalytic reactions of the nanoparticles 5. Methods 24 that can probe the catalytic reactions of individual nanoparticles 25 have also been developed 6-9 , including nanoelectrodes 8 and super-26 resolution fluorescence microscopy 9. In particular, ultramicroelec-27 trodes have been used to monitor current spikes associated with 28 individual collision events of nanoparticles dissolved in an electro-29 lyte 6,7. However, this non-imaging method cannot assign spikes to a 30 specific nanoparticle and it is difficult to measure the entire cyclic 31 voltammogram (CV) of each nanoparticle. 32 Unlike conventional electrochemical techniques (including 33 SECM), which measure the electrical current associated with chemi-34 cal reactions taking place on an electrode surface, our plasmonic-35 based electrochemical current imaging (P-ECi) approach measures 36 the conversion between oxidized and reduced species near the elec-37 trode 3,10-12. We have shown 3 that the plasmonic signal in P-ECi is 38 directly related to the electrical current, allowing us to determine 39 the current optically and to image the local current density of the 40 entire electrode surface quickly (microsecond to millisecond) and 41 non-invasively. This capability allows us to image and measure 42 the electrocatalytic current of multiple individual nanoparticles 43 versus time or potential, simultaneously. 44 Platinum nanoparticles are well known for their electrocatalytic 45 activities. Q3 An important example is the electrocatalytic reduction 46 of protons to generate hydrogen. To demonstrate the capability of P-ECi for high-throughput screening of the electrocatalytic reactions of platinum nanoparticles, we synthesized nanoparticles and LETTERS