Photoinduced Electrochemical Reduction of Nitrite at an Electrochemically Roughened Silver Surface

Article abstract of DOI:10.1021/jp990928h

Photoelectrochemical reduction of nitrite and nitrate was studied on the surface of an electrochemically roughened silver electrode. The dependence of the photocurrent on photon energy, applied potential, and concentration of nitrite was determined. It was concluded that the photoelectrochemical reduction proceeds via a photoemission process followed by the capture of hydrated electrons by electron acceptors. The excitation of plasmon resonances in nanosize metal structures produced during the roughening procedure resulted in the enhancement of the photoemission process. Ammonia was detected as one of the final products in this reaction. Mechanisms for the photoelectrochemical reduction of nitrite and nitrate are proposed.

Full text of DOI:10.1021/jp990928h

J. Phys. Chem. B 1999, 103, 6567-6572
6567
Photoinduced Electrochemical Reduction of Nitrite at an Electrochemically Roughened
Silver Surface
Junwei Zheng,† Tianhong Lu,‡ Therese M. Cotton,† and George Chumanov*,†
Department of Chemistry, Iowa State UniVersity, Ames, Iowa 50011, and Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences, Changchun, 130023, P. R. China
ReceiVed: March 17, 1999; In Final Form: May 24, 1999
Photoelectrochemical reduction of nitrite and nitrate was studied on the surface of an electrochemically
roughened silver electrode. The dependence of the photocurrent on photon energy, applied potential, and
concentration of nitrite was determined. It was concluded that the photoelectrochemical reduction proceeds
via a photoemission process followed by the capture of hydrated electrons by electron acceptors. The excitation
of plasmon resonances in nanosize metal structures produced during the roughening procedure resulted in the
enhancement of the photoemission process. Ammonia was detected as one of the final products in this reaction.
Mechanisms for the photoelectrochemical reduction of nitrite and nitrate are proposed.
Introduction
certain electrode potentials and photon energies the observed
photocurrent arises from photoelectron emission from the metal
The reduction of nitrite is of significant importance for many
reasons including remediation of environmental pollutants and
chemical technology. Nitrites are present in high concentration
in caustic radioactive waste from nuclear plants, and the
reduction to gaseous products would greatly lessen the volume
of such waste.1,2 The reduction of nitrite to various compounds
(for example, hydroxylamine) would provide industrially useful
intermediates for the production of many chemicals.3 Methods
based on electrochemical reduction can also be potentially used
for the detection of nitrite in different analytical applications.4,5
Despite considerable effort, efficient electrochemical reduc-
tion of nitrite could not be achieved because of the large
overpotential that is required at neutral and alkaline pH’s (ca.
-1.4 V in 1 M NaOH at a Ag cathode6). The reduction can
occur at less negative potentials in acidic media; however, under
these conditions, nitrite is unstable and decomposes to form
different species, thereby complicating the process.7 Various
approaches that have yielded some measure of success in
lowering the high overpotential include the use of catalytic
electrode materials, such as Ni,6 Zn,6 Cd,8 and Cu,6 the addition
of catalysts such as metal cyclams to the electrolytic solution,9
and the adsorption of the catalyst on the electrode, as in the
case of copper-phenanthroline complexes on graphite.10 Highly
promising photoassisted reduction of nitrate has been also
studied at mercury electrodes immersed in suspensions of
semiconductor particles.11-13
into the electrolyte solution.16 Prior to his work, Berg attributed
experimentally observed photocurrent at a mercury electrode
to the absorption of light by the metal and production of “hot
electrons” causing an increase of the electron transfer rate to
the solute in the solution.17 Heyrovsky invoked the concept of
photodecomposition of surface charge transfer complexes
formed between a metal and a solvent or solute.18 The absorption
of light by these complexes resulted in bond rupture and electron
transfer either to the metal or to the adsorbate, depending upon
whether the latter functions as an electron donor or an electron
acceptor, respectively. Both of these mechanisms are feasible
and, at different experimental conditions, can contribute to
varying extents to the observed photocurrent. However, the
fundamental photoemission process is the direct ejection of an
electron into the solution and does not depend on the presence
of photoactive species. Ejected electrons undergo rapid ther-
malization and hydration in solution. The hydrated electron may
then react with species in solution (scavengers) or, if none are
present, return to the electrode thereby reducing the net
photocurrent to zero.
From the dependence of the photocurrent on photon energy
and electrode potential, Barker noted that the experimental
results did not fit the model developed for photoemission into
a vacuum.16 The presence of the electrical double layer in a
condensed medium has a strong influence on the photoemission
process. A new quantum mechanical theory was required to
describe the photoemission phenomena at metal/electrolyte
interfaces. Based on the method of threshold approximation,
a so-called “2/5 law” was developed by Brodsky and
Gurevich.19,20 The “2/5 law” has been widely accepted for
determining the relationship between the applied potential and
the photoemission current.
The first observation of the photoelectric effect at a metal-
electrolyte interface is attributed to Becquerel, who in 1839
noted an electric current between two electrodes immersed in
dilute acid solution when one of the electrodes was illuminated
with light.14 Following his observation, this effect was exten-
sively studied and finally demonstrated to result from photo-
emission process (reviewed in ref 15). The concept was
postulated as early as 1965 by Barker et al. who proved that at
The effects of the surface roughness on the photoemission
have been addressed in several studies. In 1974, Sass et al.
demonstrated that the photocurrent for proton reduction at
roughened silver electrodes increased by approximately 100 fold
over that at smooth Ag surface.21 The dependence of the
* To whom all correspondence should be addressed. E-mail: gchumak@
iastate.edu. Phone: (515) 294-1066. Fax: (515) 294-0105.
† Iowa State University.
‡ Chinese Academy of Sciences.
10.1021/jp990928h CCC: $18.00 © 1999 American Chemical Society
Published on Web 07/14/1999

6568 J. Phys. Chem. B, Vol. 103, No. 31, 1999
Zheng et al.
photoemission upon photon energy was found to correlate with
the surface plasmon absorption in silver. Corrigan and Weaver
studied laser-induced electron transfer at metal surfaces for Co-
(III) and Cr(II) amine complexes.22 A substantial enhancement
of the photocurrent was obtained after electrochemical roughen-
ing of silver and gold surfaces. More recently, Kostecki and
Augustynski have observed strong cathodic photocurrents for
silver electrodes immersed in saturated CO2 solutions.23,24 The
maximum of the photocurrent also corresponded to the peak of
the plasmon resonance in silver.
In the present study, the excitation of surface-plasmon
resonances on the surface of electrochemically roughened silver
electrode was used to enhance electroreduction of nitrite. It is
demonstrated that the photoinduced electroreduction occurred
via photoemission of electrons from the metal with subsequent
capturing by the electron acceptor. Ammonia was identified as
one of the final products in this reaction.
Experimental Methods
Electrochemical measurements were carried out in a con-
ventional three-electrode cell. A platinum wire served as the
auxiliary electrode. A saturated calomel electrode (SCE) was
used as the reference electrode. All potentials are reported with
respect to the SCE. Working electrodes were constructed from
a polycrystalline silver wire that was sealed into glass tubing
with Torr Seal (Varian Associates, Palo Alto, CA) epoxy resin.
The surface area of the electrodes was ca. 0.09 cm2. Before
each experiment, the electrode surface was polished in sequence
with aqueous suspensions of 5, 0.3, and 0.05 µm alumina until
a shiny, mirrorlike finish was obtained. The electrodes were
cleaned by sonication three times (total 30 min) in Milli-Q water.
The silver surface was electrochemically roughened using
double-potential step oxidation-reduction cycles performed with
a custom-built potentiostat/integrator. The supporting electrolyte
was 0.1 M Na2SO4. All solutions were purged with nitrogen
gas for 15 min prior to each experiment. Three cycles of the
following sequence were performed: the potential was initially
stepped to +0.55 V, at which poiny 25 mC/cm2 of charge was
allowed to pass, and then the potential was stepped to -0.60 V
until the current reached a minimum. The electrochemical
roughening increased the surface area of the electrode from 0.09
to 0.15 cm2 as determined by underpotential lead deposition.
Cyclic voltammetric measurements were performed at room
temperature with a model 173 potentiostat/galvanostat connected
to a model 175 universal programmer (Princeton Applied
Research). The cyclic voltammograms (CVs) were plotted on
an X-Y recorder. The scan rate was 10 mV/s in all of the
experiments.
The working electrode was irradiated with 362, 413, 647 457,
476, 488, 496, and 514 nm light using Kr+ (Coherent, Innova
100) and an Ar+ (Coherent, Innova 200) lasers. The light was
focused to a 2 mm spot on the electrode surface. The power
was measured with model 210 (Coherent) power meter. Unless
otherwise stated, the laser power was 100 mW in all of the
experiments.
In the bulk electrolysis experiments, the electrode potential
was maintained at -1.0 V. The surface was irradiated continu-
ously and the solution was stirred. The concentration of NH3
formed during the photoelectrolysis was determined by the
Nesslor method.25
Figure 1. Cyclic voltammograms of 1 mM NaNO2 in 0.1 M Na2SO4
solution at the (A) Hg, (B) polished Ag, and (C) roughened Ag
electrodes: (solid curve) in dark; (dashed curve) with 413 nm
irradiation.
nitrite (1 mM NaNO2 in the 0.1 M Na2SO4 solution, pH ) 7)
at different electrodes is shown in Figure 1. Cathodic currents
measured in the dark and under irradiation were compared for
different electrodes. The comparison was performed at -1.0 V
where there was almost no electrochemical nor photoelectro-
chemical evolution of hydrogen. In the case of the mercury
electrode, very little difference (less than -0.1 µA) can be noted
between CVs measured in the dark and in the light (Figure 1A).
A somewhat greater photocurrent (ca. -0.4 µA) was observed
at the polished silver surface (Figure 1B). The roughened silver
electrode, in contrast, exhibited a large increase (approximately
26-fold, from ca. -0.4 to -10.7 µA) in cathodic current during
illumination (Figure 1C). This increase cannot be simply
attributed to the small (ca. 1.5-fold) increase in the surface area
resulting from the roughening. Moreover, the onset potential
of the current was also shifted positively by approximately 400
mV from -1.0 to -0.6 V under illumination (Figure 1C). These
facts indicate that the photocurrent at the roughened electrode
is enhanced due to the excitation of plasmon resonances in
nanoscale metal structures generated during the roughening
procedure.
Effect of Excitation Wavelength on the Photoelectro-
chemical Response. Cyclic voltammograms measured in 1 mM
NaNO2 and 0.1 M Na2SO4 solution in the dark and under
irradiation with a series of excitation wavelengths are shown
in Figure 2. Curve a depicts the dark current for the potential
scan from -0.2 to -1.2 V. The successive curves b-h were
obtained with laser irradiation using 647, 514, 496, 488, 476,
457, and 413 nm wavelengths, respectively. Two important
features should be noted: the photocurrent increases with photon
energy and the onset potential for the reduction of nitrite shifts
positively as the photon energy is increased. The overall shapes
of curves a-g are very similar, but curve h (413 nm excitation)
has a distinct shoulder near -0.85 V and a relatively larger
photocurrent in the potential region between -0.8 and -1.0 V.
The shoulder is even more pronounced at higher excitation
Results and Discussion
Effect of Electrode Material and Surface Treatment. The
effect of irradiation on the electrochemical reduction of the

Reduction of Nitrite at a Roughened Silver Surface
J. Phys. Chem. B, Vol. 103, No. 31, 1999 6569
Figure 4. Excitation wavelength dependence of photocurrent at -1.0
V for nitrite reduction at the roughened Ag electrode. Data obtained
from Figures 2 and 3.
Figure 2. Excitation wavelength dependence of cyclic voltammograms
of 1 mM NaNO2 in 0.1 M Na2SO4 solution at the roughened Ag
electrode: (a) dark; (b) 647; (c) 514; (d) 496; (e) 488; (f) 476; (g)
457; (h) 413 nm.
of the excitation photon (pω) and the threshold photon energy
(pωo),
I ≈ (pω - pωo)2
(1)
This is known as Fowler’s parabolic law for the photocurrent,
where the threshold photon energy is equal to the work function
of the metal. In the case of the photoemission into an electrolyte
solution, the theoretical description by Brodsky and Gurevich19
predicts the “5/2 law”
I ≈ (pω - pωo(E))5/2
(2)
where the threshold photon energy is now dependent upon the
electrode potential E. Thus, the two distinct features of
photoemission into an electrolyte solution include the 5/2 power
dependence and the shift in the threshold photon energy with
the electrode potential
Figure 3. Excitation wavelength dependence of cyclic voltammograms
of 1 mM NaNO2 in 0.1 M Na2SO4 solution at the roughened Ag
electrode: (a) dark; (b) 413 nm; (c) 363.8 nm.
pωo ) pωo(Eo) + e(E - Eo)
(3)
energy (363.8 nm) and appears shifted to more positive
potentials (Figure 3). Two peaks in the potential scan under
irradiation suggest the presence of two photoinduced electro-
chemical processes that are “hidden” in an inaccessibly negative
region without irradiation.
where Eo is the potential of zero charge. Data obtained for the
photoreduction of nitrite ion will next be analyzed in terms of
the above two predictions.
The plot of the photocurrent raised to the 0.4 power versus
potential measured at -1.0 V is shown in Figure 5. In the case
of 1 mM NaNO2 in a 0.1 M Na2SO4 solution, a nonlinear
behavior can be observed near the onset potential (Figure 5,
curve a). A similar phenomenon was also reported by Pleskov
et al., who claimed that the nonlinearity is related to the low
concentration of electrolyte or electron acceptor in the double
layer.27 The “5/2 law”, which is based on the threshold
approximation, is only valid for concentrated electrolytes where
the potential drop between metal and solution is confined to
the dense part of the double layer. As can be seen in the case
of 0.5 M NaNO2 in the 1 M Na2SO4 solution, the data fit the
expected linear relationship quite well (Figure 5, curve b).
The plot of the onset potential versus photon energy is shown
in Figure 6. The onset potential was determined from Figure 2
as the potential at which the current started to flow in the
cathodic scan. The relationship is linear, in agreement with eq
3; however, the slope is ca. -2.0 instead of -1.0 expected for
concentrated acceptor solutions.28 The larger slope could result
from low acceptor concentration.15
The dependence of the photocurrent at -1.0 V on the
excitation wavelength is plotted in Figure 4. Although, this
“action spectrum” is not of sufficiently high resolution to
determine accurately the maximum in the curve, it is clear that
the photocurrent increases rapidly in the spectral region from
500 to 400 nm and decreases below ca. 400 nm. The data,
therefore, indicate a resonance behavior of the photocurrent,
corresponding to the plasmon resonance absorption in silver.
The possibility that the photocurrent at a roughened silver
electrode may result from a photoemission process in which
nitrite functions as a scavenger of hydrated electrons is
considered next. The dependence of the photocurrent on photon
energy and applied potential is well-characterized for the
photoemission process from metals into a vacuum.26 However,
this is not an appropriate model for metals in contact with
electrolytes, as shown in the study of Barker et al.16 In the case
of the photoemission into a vacuum, the photocurrent is known
to depend quadratically on the difference between the energy

6570 J. Phys. Chem. B, Vol. 103, No. 31, 1999
Zheng et al.
Figure 5. Potential dependence of photocurrent for nitrite reduction
at roughened Ag electrodes in (a) 1 mM NaNO2 + 0.1 M Na2SO4
solution and (b) 0.5 M NaNO2 + 1 M Na2SO4 solution.
Figure 7. Cyclic voltammograms of NaNO2 with different concentra-
tion at the roughened Ag electrode with 413 nm irradiation: (dashed
curve) dark; (a) 0.5; (b) 1; (c) 2; (d) 5; (e) 10 mM. Insert: plot of
photocurrent at -1.0 V versus concentration.
Figure 6. Photon energy dependence of onset potential. Data obtained
from Figures 2 and 3.
The photoelectrochemical response as a function of nitrite
concentration in the range between 0.5 and 10 mM exhibits
nonlinear behavior (Figure 7, insert). According to the model
in which hydrated electrons are captured by electron scavengers,
it is expected that this response should follow square root
dependence at low concentrations and reach saturation at high
concentrations.19 Indeed, the corresponding plot in Figure 8
confirms this model for the photoreduction of nitrite at
electrochemically roughened silver surface. The square root
dependence reflects the fact that not all photoemitted electrons
were captured by nitrite ions; some electrons returned to the
electrode. This back current is affected by nitrite concentration.
The dependence of the photocurrent on the incident laser power
follows linear behavior which is characteristic of a one-photon
process29 and is expected for the power used in these experi-
ments (Figure 9).
Figure 8. Plot of photocurrent as a function of C1/2. Data obtained
from Figure 7.
The time evolution of the photocurrent in a quiescent, 1 mM
nitrite solution is shown in Figure 10. When the electrode was
first irradiated, the photocurrent reached the initial value of 24
µA. After ca. 40 s of continues irradiation, the photocurrent
decayed exponentially to its steady state value of 12 µA. It is
important to mention that this current remained nearly constant
as long as the concentration of nitrite ions remained unchanged,
indicating little or no poisoning of the electrode surface by
reaction intermediates or products. Electrolysis experiments at
the controlled potential were further performed under the
irradiation with 413 nm light, and ammonia was detected as
one of the products.
On the basis of the experimental results, possible mechanisms
for the photoelectrochemical reduction of nitrite at a roughened
silver electrode are proposed. Photogenerated hydrated electrons
e- (aq) are captured by nitrite to form NO22-, which undergoes
hydrolysis. Following this initial photochemical step, several
electrochemical reactions take place:

Reduction of Nitrite at a Roughened Silver Surface
J. Phys. Chem. B, Vol. 103, No. 31, 1999 6571
Figure 11. Cyclic voltammograms of 1 mM NaNO2 in 0.1 M NaOH
solution at the roughened Ag electrode: (dashed curve) in dark; (solid
curve) with 413 nm irradiation.
when determining the photoelectrochemical efficiency. In the
proposed mechanism, the total number of the electrons crossing
the interface is six and only one electron is photogenerated.
Even though no measurements of nitrogen gas were per-
formed in this study, its formation could also take place. As
the concentration of NO-• product in the diffusion layer
increases, the dimeric species (N2O2)2- can be formed with
further decomposition into N2O.29 Nitrous oxide can then react
with the hydrated electron and undergo the following reactions:
Figure 9. Photoresponse of 1 mM NaNO2 in 0.1 M Na2SO4 solution
at -1.0 V at the roughened Ag electrode with 413 nm irradiation.
N2O + e- (aq) f N2O-
N2O- + H2O f N2 + OH• + OH-
OH• + e- f OH-
Three photoelectrons among a total of six are required for the
reduction of 2NO2- to nitrogen gas N2 according to this scheme.
Finally, any electrochemical reaction following the photochemi-
cal step can “utilize” hydrated electrons as well. This fact
complicates even more the exact determination of the number
of photoelectrons that contribute to the measured photocurrent
making calculations of the photoefficiency difficult. Neverthe-
less, we estimated the quantum efficiency of about 0.04% for
nitrite photoreduction on the electrochemically roughened silver
surface. The estimate is based exclusively on the assumption
that only one photoelectron is captured.
Figure 10. Power dependence of cyclic voltammograms of 1 mM
NaNO2 in 0.1 M Na2SO4 solution at the roughened Ag electrode with
413 irradiation. Insert: plot of photocurrent at -1.0 V versus power
of irradiation.
Effect of pH. The pH of the solution strongly affects the
reduction potential of nitrite, as demonstrated for a number of
different electrodes.30-33 For the silver electrode, Cattarin6
reported that the nitrite reduction in the 1 M NaOH begins in
the potential region of hydrogen evolution, ca. - 1.4 V. The
product formed was identified as ammonia. Our results obtained
in the dark in 1 mM NaNO2 and 0.1 M NaOH solution are
consistent with that report (Figure 11, dashed curve). However,
when irradiated with 413 nm light, the onset potential for the
reduction was shifted to -0.6 V (Figure 11, solid curve).
Comparing to that at neutral pH (Figure 1, C), two new features
at -1.08 and -1.35 V appeared in the cathodic scan. These
features could represent the reduction of different intermediates,
2-
NO2- + e- (aq) f NO2
NO22- + H2O f NO + 2OH-
NO + e- f NO-•
NO-• + 2e- f NH2OH
NH2OH + 2e- f NH3
It is important to emphasize that the measured current is the
sum of the photocurrent and the current due to subsequent
electrochemical reactions. This issue must be taken in to account

6572 J. Phys. Chem. B, Vol. 103, No. 31, 1999
Zheng et al.
electrochemical reduction involves a photoemission process
from the metal followed by capture of the hydrated electrons
by nitrite. The dependence of the photocurrent on irradiation
power and wavelength suggests a one-photon process that
involves the excitation of plasmon resonances in nanoscale metal
structures on the roughened silver surface. Electrolysis experi-
ments at the controlled potential and under irradiation revealed
ammonia as one of the products. Two mechanisms are proposed
for nitrite reduction. In the case of nitrate reduction, it is
suggested that nitrate was first reduced to nitrite via a two-
electron electrochemical step followed by photoelectrochemical
reduction of nitrite.
Acknowledgment. Research at Ames Laboratory is sup-
ported by the Division of Chemical Sciences, Office of Basic
Energy Sciences, U.S. Department of Energy. Ames Laboratory
is operated for the U.S. Department of Energy by Iowa Sate
University under Contract W-7405-Eng-82.
Figure 12. Cyclic voltammograms of 1 mM NaNO3 in 0.1 M Na2SO4
solution at the roughened Ag electrode: (dashed curve) in dark; (solid
curve) with 413 irradiation.
References and Notes
(1) Genders, J. D.; Hartsough, D.; Hobbs, D. T. J. Appl. Electrochem.
1996, 26, 1.
reduction potentials of which are shifted to more positive values
in alkaline pH. It should be noted that under irradiation the onset
potentials for the nitrite reduction were the same at -0.6 V in
both neutral and alkaline solutions, thereby indicating that the
photoemission process is essentially independent of pH.
Reduction of Nitrate. A photoelectrochemical response was
also observed in the solution of nitrate (Figure 12). Nitrate can
be electrochemically reduced to nitrite without irradiation via
a two-electron step process (Figure 12, dashed curve). The
reduction peak at -1.1 V reflects a large overpotential that is
required for this reaction because of the rapid reoxidation of
(2) Coleman, D. H.; White, R. E.; Hobbs, D. T. J. Electrochem. Soc.
1995, 142, 1152.
(3) Van de Moesdijk, C. G. M. Chem. Ind. 1984, 18, 189.
(4) Strehlitz, B.; Grundig, B.; Schumacher, W. Anal. Chem. 1996, 68,
807.
(5) Wu, Q.; Storrier, G. D.; Pariente, F. Anal. Chem. 1997, 69, 4856.
(6) Cattarin, S. J. Appl. Electrochem. 1992, 22, 1077.
(7) Nishimura, K.; Machida, K.; Enyo, M. Electrochim. Acta 1991,
36, 877.
(8) Xing, X.-K.; Scherson, D. A. J. Electroanal. Chem. 1986, 199,
485-488.
(9) Taniguchi, I.; Nakashima, N.; Matsushita, K.; Yasukouchi, K. J.
Electroanal. Chem. 1987, 224, 199-209.
(10) Fung, C.-S.; Wong, K.-Y. J. Electroanal. Chem. 1996, 401, 263.
(11) Halman, M.; Tobin, J.; Zuckerman, K. J. Electroanal. Chem. 1986,
209, 405.
(12) Baldwin, R. P.; Perone, S. P. J. Electrochem. Soc. 1976, 123, 1647.
(13) Babenko, S. D.; Benderskii, V. A.; Zolotovitskii, Y. A. M.;
Krivenko, A. G. J. Electroanal. Chem. 1977, 76, 347.
(14) Becquerel, E. Compt. Rend. 1839, 9, 145.
(15) Brodsky, A. M., Pleskov, Y. V. Surface Sci. 1972, 2, 1.
(16) Barker, G. C.; Gardner, A. W.; Sammon, D. C. J. Electrochem.
Soc. 1966, 113, 1183.
the high energy NO3 intermediate ion.29 Since no light is
2-
required to convert nitrate to nitrite, the observed photocurrent
was attributed mainly to the photoelectrochemical reduction of
nitrite according to mechanisms described above. The limiting
step in the overall reaction is the electrochemical reduction of
NO3- to NO2- that occurs at the potentials more negative than
the onset potential for the photoelectrochemical reduction of
NO2-. For this reason, no dependence of the onset potential on
irradiation is expected. Indeed, the reduction current under
irradiation (Figure 12, solid curve) increased ca. twice relative
to the dark current with no or very little shift in the onset
potential. A small shift that can be assumed in Figure 12 is due
to the fact that the reduction of nitrate to nitrite can also occur
by capturing hydrated electrons generated by photoemission.
This reaction will compete with the electrochemical reduction
of nitrate, and depending upon relative contributions of these
two pathways, more or less shift in the onset potential will be
observed.
(17) Berg, H. ReV. Polarogr. 1963, 11, 29.
(18) Heyrovsky, M.; Norrish, R. G. W. Nature 1965, 200, 1356.
(19) Brodsky, A. M.; Gurevich, Y. Y. SoV. Phys. JETP 1968, 54, 213.
(20) Brodsky, A. M. In Excess Electrons in Dielectric Media; Ferradini,
C., Jay-Gerin, J.-P., Eds.; CRC Press: Boca Raton, 1991; Chapter 11.
(21) Sass, J. K.; Sen, R. K.; Meyer, E.; Gerischer, H. Surface Sci. 1974,
44, 515.
(22) Corrigan, D. S.; Weaver, M. J. J. Electroanal. Chem. 1987, 228,
265.
(23) Kostecki, R.; Augustynski, J. J. Appl. Phys. 1995, 77, 4701.
(24) Fedurco, M.; Shklover; Augustynski, J. J. Phys. Chem. 1997, 101,
5158.
(25) Marczenko, Z. In Separation and Spectrophotometric Determination
of Elements; Masson, M., Ed.; Ellis Harwood Limited: Chichester, England,
1986; Chapter 35.
Conclusion
(26) Fowler, R. H. Phys. ReV. 1931, 38, 45.
(27) Pleskov, Y. V.; Rotenberg, Z. A. J. Electroanal. Chem. 1969,
20, 1.
Enhanced photoelectrochemical reduction of nitrite and nitrate
was observed on roughened silver surfaces compared to
“smooth” silver and mercury when irradiated with light in the
blue-green spectral region. In the case of nitrite, the irradiation
resulted in an increase of the reduction current along with a
shift of the onset potential, as was determined from the
comparison of CVs measured in the dark and under illumination
conditions. It was determined that the photocurrent is propor-
tional to the 5/2 power of the applied potential and to the square
root of the nitrite concentration in the solution. On the basis of
these data as well as the linear relationship between the onset
potential and photon energy, it was concluded that the photo-
(28) Gurevich, Y. Y.; Pleskov, Y. V.; Rotenberg, Z. A. In Photoelec-
trochemistry; Wroblowa, H. S., Conway, B. E., Eds.; Consultants Bureau:
New York, 1980; Chapter 4.
(29) Benderskii, V. A.; Benderskii, A. V. Laser Electrochemistry of
Intermediates; CRC Press: New York, 1995; Chapter 7.
(30) Ehman, D. L.; Sawyer, D. T. J. Electroanal. Chem. 1968, 16, 541.
(31) Vicente, F.; Garcia-Jaren˜o, J. J.; Tamarit, R.; Cervilla, A.; Dome-
nech, A. Electrochim. Acta 1995, 40, 1121.
(32) Reuben, C.; Galun, E.; Cohen, H.; Tenne, R.; Kalish, R.; Muraki,
Y.; Hashimoto, K.; Fujishima, A.; Butler, J. M.; Le´vy-Cle´ment, C. J.
Electroanal. Chem. 1995, 396, 233.
(33) Fung, C.-S.; Wong, K.-Y. J. Electroanal. Chem. 1996, 401, 263.