Applications of Scanning Electrochemical Microscopy

Allen J. Bard,Fu-Ren F. Fan 한국분석과학회 1995 분석과학 Vol.8 No.4

Applications of Scanning Electrochemical Microscopy

Bard, Allen J.,Fan, Fu-Ren F. The Korean Society of Analytical Sciences 1995 분석과학 Vol.8 No.4

The application of scanning electrochemical microscopy to the imaging of surfaces in water and air and to the study of the electrochemistry of single molecules is discussed.

Assessment of the Stability and Operability of Cobalt Phosphide Electrocatalyst for Hydrogen Evolution

Ahn, Hyun S.,Bard, Allen J. American Chemical Society 2017 ANALYTICAL CHEMISTRY - Vol.89 No.16

<P>Transition metal phosphides have been investigated heavily as hydrogen evolution reaction (HER) catalysts. One of the most active transition metal phosphides, CoP, has been tested for its stability and operability under mild conditions that it may be exposed to in its applications (photoelectrochemistry and artificial photosynthesis). Surface-interrogation scanning electrochemical microscopy (SI-SECM) revealed that CoP HER catalyst is vulnerable to oxidation (by oxygen and chemical oxidants). The degradation mechanism was shown to be surface oxidation by dioxygen, followed by acid etching of the oxidized layer. The compositional integrity (unity ratio of cobalt and phosphorus) was maintained throughout the film decomposition progress.</P>

Surface Interrogation Scanning Electrochemical Microscopy for a Photoelectrochemical Reaction: Water Oxidation on a Hematite Surface

Kim, Jae Young,Ahn, Hyun S.,Bard, Allen J. American Chemical Society 2018 ANALYTICAL CHEMISTRY - Vol.90 No.5

<P>To understand the pathway of a photoelectrochemical (PEC) reaction, quantitative knowledge of reaction intermediates is important. We describe here surface interrogation scanning electrochemical microscopy for this purpose (PEC SI-SECM), where a light pulse to a photoactive semiconductor film at a given potential generates intermediates that are then analyzed by a tip generated titrant at known times after the light pulse. The improvements were demonstrated for photoelectrochemical water oxidation (oxygen evolution) reaction on a hematite surface. The density of photoactive sites, proposed to be Fe<SUP>4+</SUP> species, on a hematite surface was successfully quantified, and the photoelectrochemical water oxidation reaction dynamics were elucidated by time-dependent redox titration experiments. The new configuration of PEC SI-SECM should find expanded usage to understand and investigate more complicated PEC reactions with other materials.</P> [FIG OMISSION]</BR>

CHARGE TRANSPORT THROUGH CARBON NANOTUBE OR FULLERENE–MOLECULE–SILICON JUNCTIONS

FU-REN F. FAN,BO CHEN,AUSTEN K. FLATT,JAMES M. TOUR,ALLEN J. BARD 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2007 NANO Vol.2 No.5

We report here the current–voltage (i–V) characteristics of several (n++-Si/MNOPE/C60/Pt-tip) or (n++-Si/MNOPE/SWCNT/Pt-tip) junctions, where MNOPE = 2'-mononitro-4, 4'-bis(phenylethynyl)-1-phenylenediazonium and SWCNT = single wall carbon nanotube. A layer of C60 or SWCNT-derivatized MNOPE has strong effect on the i–V behavior of the junctions, including rectification, negative differential resistance (NDR) and switching behaviors. The i–V curve of a grafted molecular monolayer (GMM) of MNOPE atop n++-Si shows NDR behavior, whereas those of C60- and SWCNT-derivatized GMMs of MNOPE on n++-Si show strong rectifying behavior with opposite rectification polarities. With C60, larger currents were found with negative tip bias, while with SWCNT, the forward top bias was positive. Because C60 tends to be a good electron acceptor and SWCNTs tend to be good electron donors, they show different i–V behavior, as observed. Some of the (n++-Si/MNOPE/SWCNT/Pt-tip) junctions also show reversible bistable switching behavior.

Electrochemical Formation of a <i>p–n</i> Junction on Thin Film Silicon Deposited in Molten Salt

Zou, Xingli,Ji, Li,Yang, Xiao,Lim, Taeho,Yu, Edward T.,Bard, Allen J. American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.45

<P>Herein we report the demonstration of electrochemical deposition of silicon <I>p–n</I> junctions all in molten salt. The results show that a dense robust silicon thin film with embedded junction formation can be produced directly from inexpensive silicates/silicon oxide precursors by a two-step electrodeposition process. The fabricated silicon <I>p–n</I> junction exhibits clear diode rectification behavior and photovoltaic effects, indicating promise for application in low-cost silicon thin film solar cells.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2017/jacsat.2017.139.issue-45/jacs.7b09090/production/images/medium/ja-2017-09090m_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja7b09090'>ACS Electronic Supporting Info</A></P>

Improved Photoelectrochemical Water Oxidation by the WO₃/CuWO₄ Composite with a Manganese Phosphate Electrocatalyst

Nam, Ki Min,Cheon, Eun Ah,Shin, Won Jung,Bard, Allen J. American Chemical Society 2015 Langmuir Vol.31 No.39

<P>We describe a composite of the n-type semiconductors for the photoelectrochemical oxygen evolution reaction (OER). A simple drop-casting technique of mixed precursors and a one-step annealing process were used in the synthesis of the WO<SUB>3</SUB>/CuWO<SUB>4</SUB> composite. The composite showed improved photocurrent for water oxidation compared to either of the two compounds individually. We discuss possible electron–hole separation mechanisms in two semiconductors comprising a primary photon-absorbing semiconductor of CuWO<SUB>4</SUB> with a secondary semiconductor of WO<SUB>3</SUB>. When the WO<SUB>3</SUB>/CuWO<SUB>4</SUB> composite is simultaneously irradiated, the photogenerated hole from the WO<SUB>3</SUB> valence band transfers to CuWO<SUB>4</SUB>, which results in an enhanced charge separation of CuWO<SUB>4</SUB>. Furthermore, the OER catalytic activity of manganese phosphate (MnPO) was compared to manganese oxide nanoparticles (Mn<SUB>2</SUB>O<SUB>3</SUB>) by electrochemical measurements, showing that the manganese phosphate was more efficient for the OER reaction. To investigate the effect of catalysts on semiconductors, manganese phosphate was deposited on the WO<SUB>3</SUB>/CuWO<SUB>4</SUB> composite. The result demonstrates the promise of manganese phosphate for improving the photocurrent as well as the stability of the WO<SUB>3</SUB>/CuWO<SUB>4</SUB> composite.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2015/langd5.2015.31.issue-39/acs.langmuir.5b01780/production/images/medium/la-2015-017808_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la5b01780'>ACS Electronic Supporting Info</A></P>

Visible Light Photoelectrochemical Properties of PbCrO₄, Pb₂CrO₅, and Pb₅CrO₈

Lee, Heung Chan,Cho, Sung Ki,Park, Hyun S.,Nam, Ki Min,Bard, Allen J. American Chemical Society 2017 The Journal of Physical Chemistry Part C Vol.121 No.33

<P>Photoactivities of lead chromates with various combinations of Pb and Cr are rapidly screened using scanning electrochemical microscopy (SECM): In the rapid screening investigation, the metal oxide spot electrode With a Pb/Cr ratio of 2:1 exhibits the highest photoactivity among the semiconductor prepared with different compositions. The pliotoadtivity electtoChemical properties. of electrodes of PbCrO4; Pb(2)crO(5), and Pb(5)crO(8) are further studied following the combinatorial screening. In the bulk electrode measurements, the Pb2CrO5 bulk electrode displays the highest photocutrent of 0.23 mA/cm(2) for SO32- oxidation at 0.4 V vs Ag/Agcl under 100 mW/cm(2) UV vis light irradiation. Pb2CrO5- presents visible, light activity with an absorption wavelength up to 550 nm and an incident photon to current conversion efficiency (IPCE) of 10% at the wavelength of 340 nm. The onset wavelength observed in the UV vis absorption spectrum increases with increasing Pb contents in lead chromates. Optically obtained direct band gaps decreased from 2.38 to 2.26 to 2.07 eV for PbCrO4, Pb2CrO5, and Pb5CrO8, respectively. However, the onset wavelength that appeared in IPCE is 2.26 +/- 0.02 eV for all three lead chromates where the photocurrent under longer wavelength light irtacliatinn is insignificant. The results imply that more Pb 6s orbitals form interband states, increasing optical transitions in lead chromates. The band structures of PbCrO4, Pb2CrO5, and Pb5CrO8 are also determined by electrochemical analyses and ultraviolet photoelectron spectroscopy (UPS).</P>

Stochastic electrochemistry with electrocatalytic nanoparticles at inert ultramicroelectrodes—theory and experiments

Kwon, Seong Jung,Zhou, Hongjun,Fan, Fu-Ren F.,Vorobyev, Vasily,Zhang, Bo,Bard, Allen J. Royal Society of Chemistry 2011 Physical chemistry chemical physics Vol.13 No.12

<P>Collisions of several kinds of metal or metal oxide single nanoparticles (NPs) with a less catalytic electrode surface have been observed through amplification of the current by electrocatalysis. Two general types of current response, a current staircase or a current blip (or spike) are seen with particle collisions. The current responses were caused by random individual events as a function of time rather than the usual continuous current caused by an ensemble of a large number of events. The treatment of stochastic electrochemistry like single NP collisions is different from the usual model for ensemble-based electrochemical behaviour. Models for the observed responses are discussed, including simulations, and the frequency of the steps or blips investigated for several systems experimentally.</P> <P>Graphic Abstract</P><P>Electrochemical measurements of single nanoparticle collisions at an electrode correlate with random walk simulations. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0cp02543g'> </P>