Advanced Electrocatalysts on the Basis of Bare Au Nanomaterials for

Subscriber access provided by EPFL | Scientific Information and Libraries

Article

Advanced Electrocatalysts on Basis of Bare Au Nanomaterials for Biofuel Cell Applications Seydou Hebie, Yaovi Holade, Ksenia Maximova, Marc Sentis, Philippe Delaporte, Kouakou Boniface Kokoh, Teko W. Napporn, and Andrei V. Kabashin ACS Catal., Just Accepted Manuscript • Publication Date (Web): 25 Sep 2015 Downloaded from http://pubs.acs.org on October 1, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Advanced Electrocatalysts on Basis of Bare Au Nanomaterials for Biofuel Cell Applications Seydou Hebié1, Yaovi Holade1, Ksenia Maximova2, Marc Sentis2, Philippe Delaporte2, Kouakou Boniface Kokoh1, Teko W. Napporn1*, Andrei V. Kabashin2* 1

Université de Poitiers, IC2MP UMR 7285 CNRS, 4, rue Michel Brunet B-27, TSA 51106, 86073 Poitiers Cedex 9, France

2

Aix Marseille University, CNRS, UMR 7341 CNRS, LP3, Campus de Luminy – case 917, 13288, Marseille Cedex 9, France

ABSTRACT: We report a drastic enhancement of electrocatalytic activity toward glucose oxidation by using novel electrocatalysts on the basis of “bare” unprotected Au nanoparticles synthesized by methods of laser ablation in pure deionized water. The recorded current density of 2.65 A cm-2 mg-1 for glucose electrooxidation was higher than a relevant value for conventional chemically synthesized Au nanoparticles by an order of magnitude and outperformed all data reported in the literature for metal and metal alloy-based electrocatalysts.

The

enhanced

electrocatalytic

characteristics

of

laser-synthesized

nanoparticles are explained by the absence of any organic contaminants or protective ligands on their surface, relatively small size of nanoparticles and their particular crystallographic structure. The employment of bare nanomaterials in glucose electrooxidation schemes promises a radical improvement of current biofuel cell technology and its successful application in bio-implantable devices.

1 ACS Paragon Plus Environment

ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 27

KEYWORDS: laser ablation in liquids, bare gold nanoparticles, glucose electrocatalysts, electrooxidation, biofuel cells.


Page 3 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

INTRODUCTION Biofuel cells have recently emerged as novel power generation systems, which convert chemical energy of abundant bio-organic materials (typically glucose or other sugars) into electrical one via electrochemical reactions with the help of biological catalysts (enzymes).1,2 Having excellent biocompatibility, biofuel cells can efficiently operate in physiological conditions, including in vivo environment.3 Combined with good miniaturization prospects, not possible with conventional batteries,4 biofuel cells promise novel attractive applications, including micro scale output power sources for medical implants such as pacemakers and a variety of other functional devices.1,2 In biofuel cells, enzymes are normally used both for the oxidation of glucose (anode) and for the reduction of oxygen (cathode). However, the regeneration of the cathode catalyst requires a constant supply of dioxygen, which generates hydrogen peroxide leading to an inevitable degradation of cell performance.3,5 As a result, the lifetime of enzymatic fuel cells does not exceed several weeks, which limits their application area by short-term implantable sensors.6 The stability of characteristics of biofuel cells can be much improved by employing hybrid schemes, such as one shown in Fig. 1a, in which abiotic anode catalyst is used to oxidize glucose instead of enzymes.7 Noble metal nanoparticles (NPs) are of particular interest for these tasks, as they can not only offer long-term chemical stability,8 but also enable good catalytic activity in oxidation reactions.7,9,10 However, as the electrocatalytic activity of metal NPs mainly originates from high energy surface states,11,12 the performance of the nanoparticle-based electrode is critically dependent on surface conditions, namely on the purity of NPs. As an example, the activity of Au NPs can be drastically decreased by the adsorption of organic species, which cause the modification of surface states.12,13 Unfortunately, high purity of noble metal nanomaterials is not always the case when conventional chemical routs for the fabrication of NPs are involved. Indeed, Au-based


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 27

nanomaterials are normally synthesized in reverse micelles or by the reduction of a gold precursor in the presence of capping agents.12,14-18 When the synthetic method involves the use of organic molecules as a capping or surfactant agent, the surface of the as-prepared NPs may be covered by organic layers, which strongly affects their electro-catalytic activity. Alternative synthetic routes such as template growth,19 electrochemical routes,20 microwave rapid heating,21 water-in-oil growth22 are not always consistent with the purity requirement as well. Gold NPs prepared by laser ablation in water present an essentially novel object, which can be exempt of any surface contamination.23 Indeed, a common experimental setup implies laser radiation-caused ablation of material from a solid target in pure aqueous environment, resulting in a natural formation of gold nanoclusters.24,25 The nanoclusters then cool down and coalesce forming a colloidal nanoparticle solution. When ultra-short radiation is used for the laser synthesis,24-28 the formed NPs can have low size dispersion, while nanoparticle solutions remain extremely stable even in the absence of any protecting ligand due to electric repulsion effects. It is important that when this synthesis is performed in deionized water in the absence of any organic or other by-products, the surface of the formed nanoparticles remains clean and uncontaminated.24,28 Furthermore, such a “bare” surface of the nanoparticles can provide much stronger reactivity28 and different surface chemistry29 compared to conventional chemically-synthesized colloidal nanomaterials. Such properties of bare laser-synthesized nanomaterials look promising for catalytic applications and the first tests confirm high efficiency of laser-synthesized nanomaterials in catalytic tasks.30-32 This paper is conceived as an exploratory research to assess the potential of bare Au nanomaterials as electro-catalysts in biofuel cell applications. Employing ultrapure, ligandfree Au NPs prepared by methods of laser ablation in deionized water, we reveal their much enhanced activity toward the electrooxidation of glucose compared to conventional


Page 5 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

chemically synthesized Au counterparts. Studies of electrochemical reactions on bare surfaces of Au NPs fabricated by laser ablation provide fundamental data on surface reactivity and guidelines for the understanding and design of catalytic materials.

METHODS Reagents, Apparatus and Measurements: For all experiments, the glassware was cleaned successively in an acidic potassium permanganate solution and then in an acidic hydrogen peroxide solution. Afterwards, the glassware was rinsed with hot water. It was then kept in aqua regia solution for 1 h and finally rinsed abundantly with ultra-pure water (18.2 MΩ cm at 20 °C). The supporting electrolyte solution was 0.1 mol L-1 NaOH (97%, Sigma-Aldrich®), prepared with ultra-pure water. Lead (II) nitrate (99.5%, Merck) and the D-(+)-glucose (99.5%) were purchased from Sigma-Aldrich®. All reactants were used without any purification. Laser-ablative fabrication of gold nanoparticles: Au Nanoparticles were prepared by femtosecond laser ablation in liquid medium.24,25 Gold target (99.99%, GoodFellow) was placed at the bottom of the glass vessel filled with deionized water (18.2 MΩ cm). A 2.3 mm diameter beam from a Yb:KGW laser (Amplitude Systems, 1025 nm, 480 fs, 95 µJ, 1 kHz) was focused with a 75-mm lens on the surface of a target. The target was moved constantly in the focusing plane with the speed of 0.5 mm/s, while keeping the same thickness of the liquid above the target of about 1 cm. The ablation was performed till the solution obtained deep red color. In order to obtain the sample of gold nanoparticles in pure water with narrow size distribution, the nanoparticles produced by the laser ablation underwent the laser fragmentation step, as it was described before.26,27 Briefly, 5 mL of the previously prepared solution was placed in a glass cuvette and was irradiated for 30 min by a femtosecond laser beam of a Yb:KGW laser, focused in the very middle of the cuvette using with the same 5 ACS Paragon Plus Environment

ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 27

focusing lens. The energy of the laser beam was varied from 10 to 100 µJ in order to get the nanoparticles with different mean sizes and narrow size distribution. The solution was stirred with a magnetic stirrer during the whole fragmentation process.

Chemical synthesis of Au nanoparticles: (i) CTAB-stabilized NPs: The synthesis of Au nanoparticles was made according to the method described in the literature.17 In a vial tube of 10 mL, 0.125 mL of 10 mmol L-1 HAuCl4 was mixed with 3.75 mL of an aqueous solution of 0.10 mol. L-1 CTAB. Then, 0.30 mL of an ice-cold 0.05 mol L-1 NaBH4 solution was added to the solution, all at once under stirring. Rapidly, the mixture turned to a light-brown color indicating the formation of gold nanoparticles. In order to remove the excess of the surfactant CTAB, the synthesized nanoparticles solution was centrifugated at a controlled temperature of 27 °C, at 14000 rpm for 12 min. The supernatant was removed and the bottom part containing nanoparticles was redispersed in 2 mL of ultra-pure water for another centrifugation in the same conditions. This step permitted to collect all the synthesized particles but also to eliminate most of the surfactant used during the synthesis. Afterwards, three centrifugation cycles were made at different rotation rates (5000, 8000 and 14000 rpm). The last one permitted to collect the synthesized nanoparticles. This purification step is very important for removing most of the CTAB contained in the solution. The few remaining surfactant physically bonded on the surface of the nanoparticles was removed electrochemically by cyclic voltammetry. The formed CTAB-Au NPs had the mean size of 20 nm and exhibited a plasmonic peak around 520 nm in extinction spectra (see supporting information). (ii) Citrate method: Turkevich method or citrate method is commonly used to fabricate spherical gold nanoparticles with different size distributions.18 2.0 mL of 0.25 mmol L-1 chloroauric acid was mixed with 1.25 ml of 20 mM NaOH solution in a flask. This mixture


Page 7 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

was completed with water in order to reach a final volume of 20 mL. The flask was installed in a temperature controlled bath at 80 °C. Afterwards, 0.6 mL of sodium citrate solution (50 mg mL-1) was added to the mixture under vigorous stirring. Finally, the reaction was performed at 80 °C for 2 h. The pink color of the solution indicates the presence of gold nanoparticles (Cit-Au NPs). Then, the centrifugation of the solution is carried out similarly to the case of CTAB-stabilized NPs. The formed Cit-Au NPs had the mean size of 10 nm and also exhibited a plasmonic peak around 520 nm in extinction spectra (see supporting information). Structural characterization of Nanoparticles: The morphology and the size of the prepared gold nanoparticles were observed by transmission electron microscopy (TEM), JEOL 2100 UHR (200 kV) electron microscope equipped with LaB6 filament. A droplet of solution containing laser-synthesized nanoparticles were dropped onto the surface of carbon-coated TEM copper grid, dried and finally examined by the TEM system. Electrochemical tests: All the electrochemical experiments were carried out at controlled temperature. The supporting electrolyte was a 0.1 mol L-1 NaOH solution. A typical threeelectrode Pyrex glass cell was employed. The reference electrode was a reversible hydrogen electrode (RHE). All potentials in the text are referred to this reference electrode. The working electrode was a glassy carbon disk (GC) of 0.071 cm2 mounted in Teflon. The counter electrode was a glassy carbon slab electrically connected with a gold wire. Before any electrochemical measurement, the electrolyte was purged with nitrogen to expel oxygen. The nitrogen flow is maintained during the experiment for avoiding any oxygen introduction in the electrolyte. Prior to each experiment, the GC electrode was polished with alumina 1 µm and 0.05 µm, respectively, followed by several ultrasonic cleanings in ultra-pure water. Afterwards, a cyclic voltammogram of the GC electrode is recorded in the supporting


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 27

electrolyte to insure the cleanliness of the cell. Then, 20 µL of the catalytic ink (0.11 mg mL1

) was dispensed onto the glassy carbon disk and thereafter, the working electrode was

introduced into the electrolyte under potential control. The voltammetric experiments were performed with a potentiostat (EG&G Princeton Applied research Model 362) monitored by a computer. All the current densities in the present work were normalized with the metal weight and by the electrochemical active surface area of the gold electrode. The electrochemical active surface of gold can be estimated by the charge corresponding to the reduction of the oxide monolayer on gold surface. This charge depends also on the value of the upper potential limit chosen. In the present investigation, this charge is ca. 482 µC cm-2 in alkaline.33

RESULTS AND DISCUSSION Nanoparticle solutions prepared by laser ablation in deionized water look deep red, as shown in the inset of Fig. 1b. Samples of bare LA-Au NPs exhibited a characteristic peak around 520 nm in the extinction spectrum (Fig. 1b), which is associated with the excitation of surface plasmons over the nanoparticles. All samples demonstrated exceptional stability as they did not show any sign of nanoparticle precipitation after several months of their storage in glass vials. As shown in Fig. 1c, the mean size of LA-Au NPs was about 20 nm with the size dispersion less than 10 nm full width at half maximum (FWHM). Electron diffraction studies (1st inset to Fig. 1c) revealed the multicrystalline structure of LA-Au NPs, containing various facets (111), (220), (311), (200) etc. The measured interplanar space for all lattice fringes measured by high resolution transmission electron microscopy (TEM) roughly corresponded to values obtained from electron diffraction data. As an example, the measured interplanar space of 2.35 Å (2nd inset of Fig. 1c) is in good agreement with the (111) lattice plane of face-centered-cubic (fcc) gold.34,35 As we previously showed29, the laser-synthesized Au nanoparticles are negatively charged, which conditions the exceptional stability of


Page 9 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

colloidal nanoparticles solutions. For comparison, we synthesized Au NPs by chemical reduction of chloroauric acid (HAuCl4) using CTAB as a stabilizer (CTAB-Au NPs) and using a citrate (Turkevich) method (Cit-Au NPs). In our tests, we used colloidal suspensions of LA-Au NPs, CTAB-Au NPs and Cit-Au NPs having relatively small and similar size (~ 10-20 nm) as catalyst inks. The nanoparticles were deposited on glassy carbon substrate without any additional reagents. We first compared responses of NPs-based electrodes in cyclic voltammetry using a model of under potential deposition (UPD) of lead, which has proved its efficiency for characterizing surface purity of metal nanostructures, as well as for the assessment of crystallographic structure and ratio between the existing facets.12,36 Fig. 2a displays the evolution of the first ten cycles of the cyclic voltammogram of Au NPs prepared by colloidal chemistry (CTAB-Au NPs)17 and the first and second cycles of the LA-Au NPs prepared by laser ablation. These voltammograms were recorded in 0.1 mol L-1 NaOH, at 20 mV s-1 and 20 °C. As follows from the Figure, CTAB-Au NPs demonstrate a very low electrochemical response for first CV cycles, which is obviously related to their contamination. Indeed, the first cycles are characterized by low current densities associated with a low activity of the catalytic sites, which are apparently blocked by adsorbed organic molecules. Nevertheless, the current densities corresponding to the oxide formation increase from the first to the tenth cycle showing a gradual cleaning of such nanoparticles. Although citrate anions used during the synthesis of Cit-Au NPs should mostly be removed by preliminary cleaning steps, we observed similar “cleaning” effect on Cit-Au NPs as well. We explain this effect by the presence of residual traces of citrate anions on gold NPs surface. Furthermore, such traces of citrate anions are known to enhance their adsorption on Au surface starting from a potential value of 0.4 V vs. RHE where the onset potential of glucose oxidation is often observed.37 This adsorption must obviously lead to a decrease in the electrocatalytic activity of gold nanoparticles toward glucose oxidation. In


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 27

contrast, laser-ablated nanoparticles (LA-Au NPs) demonstrate excellent catalytic activity starting from 1-2 CV cycles, suggesting an exceptional purity of LA-Au NPs (Fig. 2a). In fact, the tenth cycle of CTAB-Au NPs is similar to the first-second cycle of nanoparticles the prepared by laser ablation (LA-Au NPs). It is important that LA-Au NPs demonstrate excellent oxidation properties from the very first cycles. In particular, one can see a small faradaic current density at 0.40 V vs. RHE during the positive scan, which corresponds to the chemisorption of OH- leading to the formation of Au(OH) species. The oxidation process is reversible in this low potential region (E < 1.10 V vs. RHE) and is accompanied by the appearance of an additional peak around 1.20 V vs. RHE13,38 (as shown in Fig. 2a, for CTABAu NPs this peak could be observed only after several cycles of nanoparticle cleaning). Then, at 1.25 V vs. RHE one can observe a sharp oxide peak, followed by two other oxidation waves.12,13,39 In general, the surface oxide formation on LA-Au NPs and chemicallysynthesized NPs electrodes takes place at 1.20 V vs. RHE and the anodic current density gradually increases until the upper potential limit set at 1.55 V vs. RHE. Such formed oxides are reduced in a single CV transient at 1.07 V vs. RHE during the negative scan rate. The inset in Fig. 2 depicts the UPD of lead (PbUPD) for LA-Au NPs based electrode in 0.1 mol L-1 NaOH + 1 mmol L-1 Pb(NO3)2 at 20 mV s-1. Here, one can see two reduction peaks around 0.52 V and 0.38 V. RHE during the negative potential sweep, which are typically assigned to the deposition of lead on (110) and (111) Au facets, respectively. Similarly, two stripping peaks around 0.42 V and 0.58 V are recorded during the positive scan. These peaks are normally attributed to a reversible desorption of the Pb layer on (111) and (110) Au facets, respectively. The presence of low coordination (110) and (111) facets is indeed confirmed by electron diffraction data (1st inset of Fig. 1c). It worth noting that in some cases lead can additionally be deposited on (100) facets.12 However, our UPD tests were not sensitive


Page 11 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

enough to reveal the presence of (100) facets, although facets from the same family (namely (200) facets) were visible from electron diffraction data. As shown in Fig. 2b, the shapes of the CVs strongly depend on temperature. The first peak related to Au oxide formation becomes sharp and shifts towards lower potential values when temperature (T) is gradually increased, while the gold oxides reduction-related peak shifts to higher potentials. The inset graph in the Fig. 2b depicts the surface oxide charge qox and the potential of oxides reduction peak Epeak as function of temperature (T). The values of qox were evaluated by integrating the oxides reduction peaks at different temperatures. The data show a small and linear increase of qox, from 82 to 258 mC cm-2 mg-1 when T is varied from 5 to 55 °C, whereas Epeak shifts by 90 mV towards higher potentials. Similar behaviour for Au surface oxides formation was already observed for polycrystalline bulk gold electrode in acidic medium.40 A gradual increase of oxide charge qox under temperature increase gives evidence of the efficient formation of oxide states (OH)ads on Au, which are known to play a crucial role in electrochemical oxidation of glucose.41 Indeed, the oxidation of glucose is due to the interaction between the adsorbed hemiacetal group and (OH)ads, where AuOH sites on the Au surface act as active species for the glucose oxidation.42 Thus, the oxidation of glucose strongly depends on the number of AuOH sites. The first step of the glucose oxidation in alkaline media involves its adsorption on the AuOH layer followed by the dehydrogenation of the anomeric carbon. The adsorbed species reacts at the AuOH sites to lead to gluconolactone. Then, a further desorption of gluconolactone gives reaction products, which could involve more than a two-electron process as a result of the carbon–carbon bond cleavage.43,44 In addition, the hydrolysis of the gluconolactone occurs in the bulk solution to form sodium gluconate.41,42 In order to assess the potential of Au nanoparticles for biofuel cell applications, we carried out a series of comparative tests on glucose oxidation using LA-Au, CTAB-Au and


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 27

Cit-AuNPs – based electrodes. To make a correct comparison, CTAB-Au NPs and Cit-Au NPs were preliminarily cleaned by at least 10 cycles of cyclic voltammogram in 0.1 mol L-1 NaOH at controlled temperature of 25 °C. Fig. 3a presents the cyclic voltammograms of LAAu and cleaned chemically-synthesized NPs –based electrodes in alkaline medium containing 10 mmol L-1 glucose. One can see that for both electrodes, the glucose oxidation starts during the positive scan at 0.40 V vs. RHE (onset potential). The first peak is associated with the oxidative transformation to gluconolactone species at the Au NPs electrode.43,44 This peak is reached at 0.60 V vs RHE and 0.50 V vs RHE for LA-Au NPs and CS-Au NPs, respectively. This lactone is then successively oxidized in the broad potential from 0.80 to 1.35 V for both types of NPs. However, the oxidation efficiency appears to be quite different for LA-Au and chemically-synthesized NPs. While the magnitude of the oxidation peak Ep located at 1.30 V vs RHE and 1.15 V vs RHE for CTAB-Au NPs and Cit-Au NPs does not exceed the current density of 0.41 A cm-2 mg-1 and 0.27 A cm-2 mg-1, respectively, the relevant value for LA-Au NPs was recorded at Ep = 1.20 V vs. RHE and reached 2.65 A cm-2 mg-1. Thus, despite preliminary cleaning of chemically-synthesized NPs, laser-ablated counterparts provided almost an order of magnitude higher efficiency in glucose oxidation. We believe that such a difference of catalytic activities is due to different purity of the nanomaterials. LA-Au NPs are known to exhibit ultra-clean bare surface, while even after preliminary cleaning active facets of chemically-synthesized NPs still look contaminated by residual organic molecules and other by-products (although this contamination was not visible by the UPD), resulting in the decrease of their catalytic activity. Thus, our tests showed that laser-ablated NPs can exhibit a much improved electrocatalytic efficiency compared to chemically synthesized counterparts. It is interesting that in terms of the onset potential, the specific activity (A cm-2) and the mass activity (A g-1), laser-ablated Au NPs outperform all other nanomaterials used for biofuel cell applications. In


Page 13 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

particular, the mass activity of 65 A g-1 (or 6 mA cm-2) corresponding to the measured current density of 2.65 A cm-2 mg-1 is 3.3 and 2.6-fold larger than relevant parameters for chemicallysynthesized Au/Vulcan and bimetallic Au70Pt30/Vulcan catalysts,7,35 which are known to provide record up to date values, and much larger than data for all other nanomaterials reported in the literature.45,46 It is important that the onset potential in our case is shifted towards low electrode potential, which makes possible delivering high cell voltages. Indeed, glucose electrooxidation on LA-Au NPs electrode starts ca. 0.35 V vs. RHE in alkaline medium. Here, the catalyst shows impressive activity in the potential widow 0.4-0.7 V vs. RHE. At this potential range, the present catalyst shows unpredictable high catalytic activity (sharp increase of the current) compared to Au NPs reported in previous studies.12,35,45-48 Such a behaviour typically evidences excellent kinetics of the catalytic reaction.45,48,49 Furthermore, all our data were obtained in the geometry of simple deposition of LA-Au NPs on a glassy carbon substrate, while in most previous studies NPs were dispersed inside a porous matrix of Vulcan carbon powder in order to maximize the surface area of the NPs catalysts and improve the electron transfer process. This means that even under much lower surface area of NPs exposed to glucose, LA-Au NPs outperformed all their chemical counterparts. We suppose that similar porous substrate strategy can be used to maximize the surface area of LA-Au NPs and thus further improve their electrocatalytic performance. We believe that there are at least three reasons for such a high electrocatalytic activity of laser-synthesized nanomaterials. First, this is bare uncontaminated surface of laser-ablated nanomaterials as a result of their physical synthesis in pure environment (deionized water). In contrast to chemically synthesized nanomaterials, this surface is not blocked by any organic by-products, which ensures very high electrocatalytic efficiency toward glucose oxidation. The second reason can be related to the presence of some specific crystallographic facets, which enhance the catalytic response. As follows from electron diffraction data, laser-synthesized nanoparticles can exhibit low


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 27

coordination facets (110), (111), (100), which are known to exhibit enhance electrocatalytic activity toward glucose oxidation.12,17,50 It should be noted that experiments at higher potentials on oxygen evolution reaction on a bulk Au electrode did not confirm the importance of preferential crystallographic facets.10 The third factor can be related to a proper mean size and good dispersion of LA-Au NPs. Studying organics oxidation in heterogeneous catalysis, Haruta suggested that the Au/oxide perimeter acts as the reaction site for the catalytic reaction according to the cluster size dependence of the catalytic activity.51 On the other hand, Valden et al.52 proposed that the catalytic activity of the Au cluster is strongly related with the band gap of the Au cluster, which is provided by the quantum size effects. The electronic interaction between nano-sized Au cluster and the TiO2 surface for understanding the chemical properties of Au/TiO2 has been widely studied.51-54 It seems a relative small mean size of LA-Au NPs (~ 20 nm) and their good dispersion with no signs of agglomeration effects could also have a favourable role in recorded high electrocatalytic activity. In order to assess the potential of laser-ablated Au NPs for biofuel cell applications, it is important to determine the regime of glucose electrooxidation reaction on Au NPs-based electrode. This regime can be determined by the assessment of the electrochemical activation energy, which characterizes minimal necessary energy to initiate an electrocatalytic reaction.55 Here, the diffusion control is characterized by a steady oxidation process in a large volume and a constant supply of glucose to the electrode. This regime is typically achieved at relatively low activation energy value (< 50 kJ mol-1). In contrast, the regime of adsorption control mainly involves glucose molecules adsorbed on the electrode and is characterized by high activation energies (> 50 kJ mol-1). The activation energy can be determined experimentally from Arrhenius’ law,55 whose electrochemical formulation is given by the following equation56:


Page 15 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

E − a jp = Ae RT

(1)

where R is the gas constant value (8.314 J mol-1 K-1), Ea is expressed in J mol-1, T is temperature (in Kelvin). In this case, we can derive the following expression for the activation energy Ea:   ∂ log( j ) p  = − 2.3R Ea  1 ∂ T E, c 

()

     

(2)

Here E is the potential where the reaction takes place and c is the concentration of glucose. Fig. 3b shows temperature dependence of the voltammograms of the LA-Au NPs electrode in 0.1 mol L-1 NaOH recorded at 20 mV s-1 in the presence of 10 mmol L-1 glucose for different temperatures varied from 5 to 55 °C. It is visible that current densities of the oxidation peaks increase with the temperature. More importantly, the onset potential centred at ca. 0.40 V vs. RHE at 5 °C shifts toward the lower potentials when the temperature is increased up to 35 °C. The oxidation current peaks A and B also increase with the temperature, while at 55 °C the current density decreases dramatically. The latter phenomenon is accompanied by the appearance of the coloration of the electrolytic solution due to a decomposition of the glucose molecule.57 Additionally, the main oxidation peak (peak B) and a shoulder become more distinguishable at 1.25 V and ca. 1.0 V, respectively. The curves in the inset of Fig. 3b reveal a linear relationship between log (jpeak) and 1/T. From the slopes of these straight lines and Equation (2), we can estimate activation energies as 18 and 22 kJ mol-1 for the oxidation peaks A and B, respectively. It is clear that the measured activation energies are much lower than 50 kJ mol-1, indicating the diffusion control of the glucose electrooxidation reaction on the LA-Au NPs electrode.58 Thus, the LA-Au NPs provided low activation energies consistent with steady electrooxidation process and a


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 27

constant supply of glucose. This result illustrates excellent prospect of laser-synthesized nanopamaterials in biofuel cell applications.

CONCLUSIONS We reported a radical improvement of the efficiency of glucose electrooxidation by employing bare Au nanoparticles synthesized by ultraclean laser ablative synthesis in deionized water. First, our tests using UPD of lead demonstrate much higher electrocatalytic response of laser-synthesized nanoparticles compared to nanoparticles prepared by conventional chemical reduction methods. Then, by using bare Au nanoparticles as electrodes in glucose electrooxidation, we report almost one order of magnitude higher efficiency of bare nanoparticles compared to chemical counterparts. Furthermore, the recorded current density of 2.65 A cm-2 mg-1 appeared to outperform all values reported in the literature for metal and metal alloy-based electrocatalysts. The recorded low activation energy for glucose oxidation is consistent with the diffusion control regime, which is characterized by a steady electrooxidation process and a constant supply of glucose. We explain such a high activity of laser-synthesized nanoparticles by the cleanness of bare surface, small nanoparticle size and the presence of some preferential crystallographic facets enhancing catalytic response. The employment of such bare Au-based nanomaterials for glucose electrooxidation schemes promises a radical improvement of current state-of-the-art biofuel cell technology. Finally, presented results offer a novel ample and rational pathway to design novel active nanomaterials for energy conversion and storage based on properties of bare nanomaterials.

ASSOCIATED CONTENT Supporting information Supporting Information presents UV-Visible absorption spectra, TEM/HRTEM images and corresponding size distributions of nanoparticles chemically synthesized in the presence of 16 ACS Paragon Plus Environment

Page 17 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

CTAB (CTAB-Au NPs) and sodium citrate (Cit-Au NPs). This information is available free of charge via the Internet at http://pubs.acs.org/.

AUTHOR INFORMATION Corresponding Authors Andrei V. Kabashin: *E-mail:[email protected],Address: Aix Marseille University, CNRS, UMR 7341 CNRS, LP3, Campus de Luminy – case 917,13288, Marseille Cedex 9, France Teko W; Napporn: *E-mail: [email protected]; Address : Université de Poitiers, IC2MP, CNRS UMR 7285, Équipe SAMCat, 4 rue Michel Brunet-B27, TSA 51106, 86073 Cedex 9, France Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT KM, PD, MS and AVK acknowledge the support of the AMIDEX project (no ANR-11IDEX-0001-02) funded by the ‘Investissements d’Avenir’ French Government program, managed by the French National Research Agency (ANR) by the LASERNANOBIO project (ANR-10-BLAN-919) of the ANR, and by LASERNANOCANCER project of the INCA INSERM (INCa-DGOS-Inserm 6038). SH, YH, KBK and TWN acknowledge the CNRS and the Région Poitou Charentes for their support.


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 27

Figure captions Figure 1. (a) Schematic presentation of a hybrid biofuel cell for implantable bio-devices. Gold NPs serve as catalysts to initiate a biocatalytic reaction of glucose oxidation, which is possible due to the presence of glucose and oxygen in biofuels. Glucose is oxidized on NPsbased anode leading to the loss of electrons. The electrons then migrate to the cathode via an external circuit to reduce oxygen to water. The energy released by this process can then be used to activate bioelectronics devices such as pacemakers. (b) Typical extinction spectrum of laser-synthesized Au nanoparticles. The inset shows a glass cuvette with a solution of lasersynthesized Au NPs in deionized water. (c) Typical Transmission Electron Microscopy (TEM) image (inset) and corresponding size distribution of Au nanoparticles prepared by fs laser ablation in water. Insets show a high resolution TEM image of a typical lasersynthesized Au nanoparticle and electron diffraction image from LA-Au NPs. Figure 2. (a) Cyclic voltammograms of the Au electrodes formed by laser-ablated (LA-Au NPs, red) and chemically-synthesized (CTAB-Au NPs, 1-9 cycles indicted by dotted black, 10th cycle by blue) in 0.1 mol L-1 NaOH recorded at 20 mV s-1 and at controlled temperature of 20 °C. The inset shows the UPD of lead in 0.1 mol L-1 NaOH + 1 mmol L-1 Pb(NO3)2 for LA-Au NPs-based electrode under the same conditions. (b) Series of CVs profiles for LA-Au NPs in 0.1 mol L-1 NaOH recorded at 20 mV s-1 illustrating the effect of temperature on the surface oxidation behaviour. The inset shows the charge density (qox), and Epeak as a function of T. Figure 3. (a) Voltammograms of CTAB-Au NPs (red curve), Cit-Au NPs (blue) and LA-Au NPs (black) electrodes in 0.1 mol L-1 NaOH recorded at 20 mV s-1 and at 25 °C in the presence of 10 mmol L-1 glucose. (b) Voltammograms of LA-Au NPs electrodes in 0.1 mol L-


Page 19 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

1

NaOH recorded at 20 mV s-1 in the presence of 10 mmol L-1 glucose and at different

temperatures from 5 to 55 °C. The inset represents the plots of log(jpeak) as function of 1/T.


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 27

REFERENCES (1) Barton, S. C.; Gallaway, J.; Atanassov, P. Chem. Rev. 2004, 104, 4867. (2) Chen, T.; Barton, S. C.; Binyamin, G.; Gao, Z.; Zhang, Y.; Kim, H.-H.; Heller, A. J. Am. Chem. Soc. 2001, 123, 8630. (3) Zebda, A.; Gondran, C.; Le Goff, A.; Holzinger, M.; Cinquin, P.; Cosnier, S. Nat. Commun. 2011, 2, 370. (4) Steele, B. C. H.; Heinzel, A. Nature 2001, 414, 345. (5) Willner, I. Science 2002, 298, 2407. (6) Heller, A. Phys. Chem. Chem. Phys. 2004, 6, 209. (7) Habrioux, A.; Servat, K.; Tingry, S.; Kokoh, K. B. Electrochem. Commun. 2009, 11, 111. (8) Cui, C.; Gan, L.; Heggen, M.; Rudi, S.; Strasser, P. Nat. Mater. 2013, 12, 765. (9) Heck, K. N.; Janesko, B. G.; Scuseria, G. E.; Halas, N. J.; Wong, M. S. ACS Catal. 2013, 3, 2430. (10) Yeo, B. S.; Klaus, S. L.; Ross, P. N.; Mathies, R. A.; Bell, A T. ChemPhysChem 2010, 11, 1854. (11) Blizanac, B. B.; Arenz, M.; Ross, P. N.; Marković, N. M. J. Am. Chem. Soc. 2004, 126, 10130. (12) Hebié, S.; Cornu, L.; Napporn, T. W.; Rousseau, J.; Kokoh, B. K. J. Phys. Chem. C 2013, 117, 9872. (13)

Habrioux, A.; Hebié, S.; Napporn, T.; Rousseau, J.; Servat, K.; Kokoh, K. B.

Electrocatalysis 2011, 2, 279. (14) Brust, M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman, R. J. Chem. Soc., Chem. Commun. 1994, 801. (15) Gole, A.; Murphy, C. J. Chem. Mater. 2004, 16, 3633. 20 ACS Paragon Plus Environment

Page 21 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

(16) Lohse, S. E.; Murphy, C. J. Chem. Mater. 2013, 25, 1250. (17) Hebié, S.; Kokoh, K. B.; Servat, K.; Napporn, T. Gold Bull. 2013, 46, 311. (18) Kimling, J.; Maier, M.; Okenve, B.; Kotaidis, V.; Ballot, H.; Plech, A. J. Phys. Chem. B 2006, 110, 15700. (19) Foss, C. A.; Hornyak, G. L.; Stockert, J. A.; Martin, C. R. J. Phys. Chem. 1992, 96, 7497. (20) Yu; Chang, S.-S.; Lee, C.-L.; Wang, C. R. C. J. Phys. Chem. B 1997, 101, 6661. (21) Liu, F.-K.; Chang, Y.-C.; Ko, F.-H.; Chu, T.-C. Mater. Lett. 2004, 58, 373. (22)

Napporn, T.; Habrioux, A.; Rousseau, J.; Servat, K.; Léger, J.-M.; Kokoh, B.

Electrocatalysis 2011, 2, 24. (23) Kabashin, A. V.; Delaporte, P.; Pereira, A.; Grojo, D.; Torres, R.; Sarnet, T.; Sentis, M. Nanoscale Res. Lett. 2010, 5, 454. (24) Kabashin, A. V.; Meunier, M. J. Appl. Phys. 2003, 94, 7941. (25) Kabashin, A. V.; Meunier, M. J. Phys.: Conf. Series 2007, 59, 354. (26) Besner, S.; Kabashin, A. V.; Meunier, M. Appl. Phys. A 2007, 88, 269. (27) Ksenia, M.; Andrei, A.; Marc, S.; Andrei, V. K. Nanotechnology 2015, 26, 065601. (28) Wagener, P.; Schwenke, A.; Barcikowski, S. Langmuir 2012, 28, 6132. (29) Sylvestre, J.-P.; Poulin, S.; Kabashin, A. V.; Sacher, E.; Meunier, M.; Luong, J. H. T. J. Phys. Chem. B 2004, 108, 16864. (30) Li, S.; Zhang, J.; Kibria, M. G.; Mi, Z.; Chaker, M.; Ma, D.; Nechache, R.; Rosei, F. Chem. Commun. 2013, 49, 5856. (31) Blakemore, J. D.; Gray, H. B.; Winkler, J. R.; Müller, A. M. ACS Catal. 2013, 3, 2497. (32) Singh, R.; Soni, R. K. J. Nanosci. Nanotechnol. 2014, 14, 6872. (33) Finot, M. O.; Braybrook, G. D.; McDermott, M. T. J. Electroanal. Chem. 1999, 466, 234.


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 27

(34) Sun, J.; Guan, M.; Shang, T.; Gao, C.; Xu, Z.; Zhu, J. Cryst. Growth Des. 2008, 8, 906. (35) Pradel Tonda-Mikiela; T. W. Napporn; Cláudia Morais; Karine Servat; Aicheng Chen; Kokoh., B. J. Electrochem. Soc. 2012, 159, H828. (36)

Hernández, J.; Solla-Gullón, J.; Herrero, E.; Feliu, J. M.; Aldaz, A. J. Nanosci.

Nanotechnol. 2009, 9, 2256. (37) Huerta, F.; Mele, C.; Bozzini, B.; Morallón, E. J. Electroanal. Chem. 2004, 569, 53. (38) Burke, L. D.; O'Sullivan, J. F. Electrochim. Acta 1992, 37, 585. (39) Adžić, R. R.; Avramov-Ivić, M. J. Catal. 1986, 101, 532. (40) Tremiliosi-Filho, G.; Dall’Antonia, L. H.; Jerkiewicz, G. J. Electroanal. Chem. 2005, 578, 1. (41) Hsiao, M. W.; Adžić, R. R.; Yeager, E. B. J. Electrochem. Soc. 1996, 143, 759. (42) Aoun, S. B.; Dursun, Z.; Koga, T.; Bang, G. S.; Sotomura, T.; Taniguchi, I. J. Electroanal. Chem. 2004, 567, 175. (43) Adzic, R. R.; Hsiao, M. W.; Yeager, E. B. J. Electroanal. Chem. Interf. Electrochem. 1989, 260, 475. (44) Kokoh, K. B.; Léger, J. M.; Beden, B.; Lamy, C. Electrochim. Acta 1992, 37, 1333. (45) Basu, D.; Basu, S. Int. J. Hydrogen Energy 2011, 36, 14923. (46) Zhu, C.; Guo, S.; Dong, S. Adv. Mater. 2012, 24, 2326. (47) Li, Q.; Cui, S.; Yan, X. J. Solid State Electrochem. 2012, 16, 1099. (48) Yan, L.; Brouzgou, A.; Meng, Y.; Xiao, M.; Tsiakaras, P.; Song, S. Appl. Catal. B: Env. 2014, 150–151, 268. (49) Chen, C.-C.; Lin, C.-L.; Chen, L.-C. J. Power Sources 2015, 287, 323. (50) Wang, J.; Gong, J.; Xiong, Y.; Yang, J.; Gao, Y.; Liu, Y.; Lu, X.; Tang, Z. Chem. Commun. 2011, 47, 6894. (51) Haruta, M. CATTECH 2002, 6, 102.


Page 23 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

(52) Valden, M.; Lai, X. Science 1998, 281, 1647. (53) Tauster, S. J.; Fung, S. C.; Baker, R. T. K.; Horsley, J. A. Science 1981, 211, 1121. (54) Minato, T.; Susaki, T.; Shiraki, S.; Kato, H. S.; Kawai, M.; Aika, K.-i. Surf. Sci 2004, 566–568, Part 2, 1012. (55) Damjanovic, A. J. Electroanal. Chem. 1993, 355, 57. (56) Conway, B. E.; White, R. E.; Bockris, J. O. M. Modern Aspect of Electrochemistry No. 16; Plenum Press, New York, USA, 1985. (57) Yei, L. H. E.; Beden, B.; Lamy, C. J. Electroanal. Chem. Interf. Electrochem. 1988, 246, 349. (58) Parpot, P.; Kokoh, K. B.; Beden, B.; Lamy, C. Electrochim. Acta 1993, 38, 1679.


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 27

Table of Contents (TOC) Graphic


Page 25 of 27

(a)

(b)

(c) 1000

Rel. Abundance (Counts)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

800

600

400

200

0

5

10

15

20

25

30

35

40

Particles size / nm

Fig. 1 (a-c) Hebie et. al., ACS Catalysis

ACS Paragon Plus Environment

ACS Catalysis

(a)

1 - 9 CVs CTAB-Au NPs th

10

nd

20

-2

2

gold oxides formation

CTAB-Au-NPs

cycle LA-Au NPs

0 (111)

-40

-1

(110) 50

-2

mg )

-20

0

j (mA cm

-1

mg )

40

j (mA cm

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 27

(111) 0.2

-60

gold oxides reduction

-50 0.4

(110) 0.6

0.8

E / V vs. RHE

0.0

0.4

0.8

1.2

E / V vs. RHE)

Fig. 2 (a,b) Hebie et. al., ACS Catalysis


1.6

Page 27 of 27

2.5

2.0

j / A cm-2 mg-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

(a) LA-Au NPs CTAB-Au NPs Cit-Au NPs

1.5

1.0

0.5

0.0 0.0

0.4

0.8

1.2

E / V vs. RHE

Fig. 3 (a,b) Hebie et. al., ACS Catalysis


1.6

Advanced Electrocatalysts on the Basis of Bare Au Nanomaterials for

Recommend Documents