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Title: Inhibition of tafel kinetics for electrolytic hydrogen evolution on isolated micron scale electrocatalysts on semiconductor interfaces

Abstract

Semiconductor-liquid junctions are ubiquitous in photoelectrochemical approaches for solar-to-fuels energy conversion. Electrocatalysts are added to the interface to improve catalytic efficiency, but they can also impair the photovoltage-generating energetics of the electrode without appropriate microscopic organization of catalytically active area on the surface. This balance is more complicated when gas products are evolved, like hydrogen on water splitting electrodes. Discrete catalysts can be blocked by the gas liquid-solid boundary of a bubble stuck to the surface. Here, we study the kinetics of hydrogen evolution on semiconductor electrodes fabricated with an isolated, micronscale platinum electrocatalyst pad. Movies of in operando bubble evolution were recorded with synchrotron-based high-speed x-ray phase-contrast imaging in a compatible electrochemical cell. The self-limited growth of a bubble residing on the isolated electrocatalyst was measured by tracking the evolution of the gas-liquid boundary through the sequence of images in the movie. As a result, the effect of pad size on the catalytic currents and the issues with reactant transport can be inferred from these dynamics.

Authors:
 [1];  [1];  [2];  [2]
  1. Univ. of Arkansas, Fayetteville, AR (United States)
  2. Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1373585
Grant/Contract Number:
AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Applied Materials and Interfaces
Additional Journal Information:
Journal Volume: 8; Journal Issue: 37; Journal ID: ISSN 1944-8244
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; electrochemistry; catalysis; x-ray phase-contrast microscopy; solar fuels; bubbles; bubble evolution; hydrogen evolution reaction

Citation Formats

Coridan, Robert H., Schichtl, Zebulon G., Sun, Tao, and Fezzaa, Kamel. Inhibition of tafel kinetics for electrolytic hydrogen evolution on isolated micron scale electrocatalysts on semiconductor interfaces. United States: N. p., 2016. Web. doi:10.1021/acsami.6b07729.
Coridan, Robert H., Schichtl, Zebulon G., Sun, Tao, & Fezzaa, Kamel. Inhibition of tafel kinetics for electrolytic hydrogen evolution on isolated micron scale electrocatalysts on semiconductor interfaces. United States. doi:10.1021/acsami.6b07729.
Coridan, Robert H., Schichtl, Zebulon G., Sun, Tao, and Fezzaa, Kamel. 2016. "Inhibition of tafel kinetics for electrolytic hydrogen evolution on isolated micron scale electrocatalysts on semiconductor interfaces". United States. doi:10.1021/acsami.6b07729. https://www.osti.gov/servlets/purl/1373585.
@article{osti_1373585,
title = {Inhibition of tafel kinetics for electrolytic hydrogen evolution on isolated micron scale electrocatalysts on semiconductor interfaces},
author = {Coridan, Robert H. and Schichtl, Zebulon G. and Sun, Tao and Fezzaa, Kamel},
abstractNote = {Semiconductor-liquid junctions are ubiquitous in photoelectrochemical approaches for solar-to-fuels energy conversion. Electrocatalysts are added to the interface to improve catalytic efficiency, but they can also impair the photovoltage-generating energetics of the electrode without appropriate microscopic organization of catalytically active area on the surface. This balance is more complicated when gas products are evolved, like hydrogen on water splitting electrodes. Discrete catalysts can be blocked by the gas liquid-solid boundary of a bubble stuck to the surface. Here, we study the kinetics of hydrogen evolution on semiconductor electrodes fabricated with an isolated, micronscale platinum electrocatalyst pad. Movies of in operando bubble evolution were recorded with synchrotron-based high-speed x-ray phase-contrast imaging in a compatible electrochemical cell. The self-limited growth of a bubble residing on the isolated electrocatalyst was measured by tracking the evolution of the gas-liquid boundary through the sequence of images in the movie. As a result, the effect of pad size on the catalytic currents and the issues with reactant transport can be inferred from these dynamics.},
doi = {10.1021/acsami.6b07729},
journal = {ACS Applied Materials and Interfaces},
number = 37,
volume = 8,
place = {United States},
year = 2016,
month = 8
}

Journal Article:
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  • Calculations of the isotopic ratio of exchange currents (i/sub o/) for cathodic hydrogen and deuterium evolution were made for limiting cases, aad the dependence of the ratio upon reaction mechanism is discussed. Experimental values of (i/sub o/)/sub H/(i/sub o/) were obtained for nickel, copper, silver, gold, platinized platinum, aad palladium under conditions of high solution purity and cleanliness of electrode surface. Control experiments on the kinetics of hydrogen evolution at each of the above metals were also carried out. The isotopic ratios of exchange currents are discussed in terms of reaction mechanisms. The calculations are improved by takig into accountmore » surface coverage by adsorbed hydrogen or deuterium. A series of new limiting values for the isotopic ratios of exchange currents is presented and assignments of rate- determining mechanism in cathodic hydrogen and deuterium evolution are suggested for several metals. (auth)« less
  • The significance of the new-established situation that the Tafel slopes, b, ( = d{eta}/d In i) for simple charge-transfer processes at electrodes are usually not represented with respect to variation with temperature, T, by the conventional relation b = RT/{beta} cpF, where {beta} is a constant-valued electrochemical charge-transfer barrier-symmetry coefficient, is examined in the light of recent comments on the problem. Clear evidence is given that b has the form b = RT({beta}sub H + T{beta}{sub s})F for proton transfer at Hg in water and various other solvents, where {beta}{sub H} and T{beta}{sub s} are enthalpic components of the overallmore » {beta}, corresponding to experimentally observable potential-dependence of both the enthalpy and the entropy of activation, respectively. The frequent deviation from conventional behavior thus arises because the entropy of activation, as well as the energy of activation, can be potential-dependent, a situation that, until recently, has been neglected in inter-pretations of electrode-kinetic experiments. The origin of the conventional effect of potential on electrode reaction rates, through the change of electrode work function,{Phi}, with overpotential or electrode potential, V, ({Phi}{sub v} = {Phi}{sub v = O}{plus minus} eV), is examined critically in relation to the potential-dependent surface-potential component, {chi}{sub d}, in {Phi}, which can also be T-dependent.« less
  • The anodic polarization for the oxygen evolution reaction of many metals and metal alloys results in the measurement of two Tafel regions, one for low overpotentials and one for high overpotentials. The polarization of the amorphous Ni{sub 50}Co{sub 25}P{sub 15}B{sub 10} alloy resulted in the measurement of a Tafel plot which appeared to have two different states linked by a transition potential region that was dependent on electrode pretreatment. A ``limiting current`` phenomenon in the transition region, in which the current appears to be independent of the potential, on the amorphous Ni{sub 50}Co{sub 25}P{sub 15}B{sub 10} alloy was observed. Themore » limiting-current phenomenon in the transition region may reflect changes of the electrodes surface oxidation states and the oxygen reaction mechanisms in the two Tafel regions. This limiting current transition region was investigated by dc anodic polarization, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy (XPS). A time-dependent impedance behavior was observed coincident with a limiting current in the Tafel plot within the same potential region. This was further characterized by means of a fixed frequency impedance measurement. XPS spectra of oxidation species of Ni were obtained from the amorphous Ni{sub 50}Co{sub 25}P{sub 15}B{sub 10} alloy and were compared with the spectra of chemically synthesized Ni oxide and hydroxides. The XPS results from the amorphous Ni-Co alloy electrode polarized in the two Tafel regions revealed different surface chemistries. The ``limiting current`` phenomenon could thus be attributed to a slow, surface place exchange between Ni and Co sites and a further oxidation of the surface from the low overpotential Tafel region to the high overpotential Tafel region.« less