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Fig. 2. Peak potential E, vs. the logarithm of the concentration c° of pereinodisalfGre in 10 mM HCIO, (A) or the concentration cj of HCIO, with | mM Na,S,0, (B) for the flame-annealed Au(110) and Au(111) (empty points) and the non-annealed Au() 11) (fol! points), Sweep rate of 100 mV s~!

Figure 2 Peak potential E, vs. the logarithm of the concentration c° of pereinodisalfGre in 10 mM HCIO, (A) or the concentration cj of HCIO, with | mM Na,S,0, (B) for the flame-annealed Au(110) and Au(111) (empty points) and the non-annealed Au() 11) (fol! points), Sweep rate of 100 mV s~!

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Fig. 1. Cyclic voltammogram of the stationary Au(110) electrade in 10 mM HClO, (and in 10 mM HCIO, +1 mM Na,S,0, with the sweep starting at 0.8 V towards more positive ( ) or more negative (---) potentials, ata sweep rate of LOO mV 8°! surface oxides and polarized straight from 0.8 V towards more negative potentials (the dashed line in Fig. 1), and on the surface, which is oxidized first in a potential sweep from 0.8 V to 1.4 V (the full line in Fig. 1). Besides, the rate of the reduction of surface oxides is approximately the same as in the absence of peroxodisulfate, i.e. the two reduction processes appear to be additive. In order to minimize the possible interference with the surface oxida- tion and/or reduction, all polarization measurements were performed starting at 0.8 V towards more negative poten- tials on the electrodes previously polarized by a single sweep excursion from 0.8 V to ~0.4 V and the reverse.
Fig. 1. Cyclic voltammogram of the stationary Au(110) electrade in 10 mM HClO, (and in 10 mM HCIO, +1 mM Na,S,0, with the sweep starting at 0.8 V towards more positive ( ) or more negative (---) potentials, ata sweep rate of LOO mV 8°! surface oxides and polarized straight from 0.8 V towards more negative potentials (the dashed line in Fig. 1), and on the surface, which is oxidized first in a potential sweep from 0.8 V to 1.4 V (the full line in Fig. 1). Besides, the rate of the reduction of surface oxides is approximately the same as in the absence of peroxodisulfate, i.e. the two reduction processes appear to be additive. In order to minimize the possible interference with the surface oxida- tion and/or reduction, all polarization measurements were performed starting at 0.8 V towards more negative poten- tials on the electrodes previously polarized by a single sweep excursion from 0.8 V to ~0.4 V and the reverse.
Fig. 3. Cyclic voltammograms of the rotating AUCLED) Ceres") and Aud tO) (electrodes in 0.1 M HCO, + 1 mM Na,$,0, at the rotation velocity of 1040 rpm and the sweep rie of 2 mVos°'. Both electrodes were fame-annealed prior to the measurement.
Fig. 3. Cyclic voltammograms of the rotating AUCLED) Ceres") and Aud tO) (electrodes in 0.1 M HCO, + 1 mM Na,$,0, at the rotation velocity of 1040 rpm and the sweep rie of 2 mVos°'. Both electrodes were fame-annealed prior to the measurement.
Fig. 4. Rate constant & of the peroxodisulfate reduction at the fanie-ai- nealed Au(110) empty points) and Au 11) (full points and dotted fine) electrodes in the solution containing 1 mM Na, 5,0, and 0.01 M (9.0). 0.1 M (88.0) or IM (a.a) M HCIO, of 0.01 M H,S0, ©) evaluated from the RDE voltammograms measured at the rotation veloe- ity of 1040 rpm and the sweep rate of 2 mV s- ' going towards more negative potentials. behaviour (Fig. | and Fig. 3), the dependence of the rate constant & on the electrode potential £ has the shape of a volcano curve, which for the Au(11) electrode has the maximum at the potential that is about 350 mV_ more positive than for the Au(110) electrode. At far negative potentials, the rate constant increases with the increasing concentration of the base electrolyte on both electrodes. At far positive potentials, a similar effect is seen on Au 11), while on Au(110) the rate constant first decreases and then increases. An increase in the rate constant is apparently responsible ok the change in the voltammetric peak poten- tial E, with cy, which is about the same for both Au 11) and Au(l 10), cf. the slope G£,,/0 log c} = 90 mV in Fig. 2B. On the other hand, in the HORACE ‘of sulfate, which adsorbs specifically at E> 0.4 V [7], the reduction rate on
Fig. 4. Rate constant & of the peroxodisulfate reduction at the fanie-ai- nealed Au(110) empty points) and Au 11) (full points and dotted fine) electrodes in the solution containing 1 mM Na, 5,0, and 0.01 M (9.0). 0.1 M (88.0) or IM (a.a) M HCIO, of 0.01 M H,S0, ©) evaluated from the RDE voltammograms measured at the rotation veloe- ity of 1040 rpm and the sweep rate of 2 mV s- ' going towards more negative potentials. behaviour (Fig. | and Fig. 3), the dependence of the rate constant & on the electrode potential £ has the shape of a volcano curve, which for the Au(11) electrode has the maximum at the potential that is about 350 mV_ more positive than for the Au(110) electrode. At far negative potentials, the rate constant increases with the increasing concentration of the base electrolyte on both electrodes. At far positive potentials, a similar effect is seen on Au 11), while on Au(110) the rate constant first decreases and then increases. An increase in the rate constant is apparently responsible ok the change in the voltammetric peak poten- tial E, with cy, which is about the same for both Au 11) and Au(l 10), cf. the slope G£,,/0 log c} = 90 mV in Fig. 2B. On the other hand, in the HORACE ‘of sulfate, which adsorbs specifically at E> 0.4 V [7], the reduction rate on
Fig. 5. Differential capacity C vs, the potential £ for the Aud 10) (A) and Au(111) (B) electrodes in 10 mM HCIO, in the absence (full lines) and the presence (points) of peroxodisulfate at a concentration of 0.4 (4). 0.8 (2), 1.0(0) and 1.6(@) mmol dim” * measured at the rotation velocity of 1040 rpm and the sweep rate of § mV 8”! on going towards more positive potentials,
Fig. 5. Differential capacity C vs, the potential £ for the Aud 10) (A) and Au(111) (B) electrodes in 10 mM HCIO, in the absence (full lines) and the presence (points) of peroxodisulfate at a concentration of 0.4 (4). 0.8 (2), 1.0(0) and 1.6(@) mmol dim” * measured at the rotation velocity of 1040 rpm and the sweep rate of § mV 8”! on going towards more positive potentials,
Fig. 6. A G15 nmX615 am (inset 151 nm x 142 nm) STM image of Au(1Tf) (A) and a 11.3 nm x 12.9 nm STM image of Au(110) (B) in air after flame-annealing, cycling in HCIO, and rinsing with water. The surface of Au(111) is covered with holes and multilayer islands (clusters), which are separated by densely spaced steps. All holes and islands comprise terraces as seen in the inset. Four narrow terraces on Au(110) with a (1 X 1)-structure are shown (slightly distorted due to thermal drift). There are two reasons why this conclusion is important. Firstly, owing to a coupling between the rates of the specific ion adsorption and the faradaic reaction, the fitting of impedance data to a particular equivalent circuit may not be straightforward, unless the contribution of one of these processes can be neglected [9]. Secondly, if the contribution of the faradaic impedance is negligible, the data can be fitted to the simple equivalent circuit above.
Fig. 6. A G15 nmX615 am (inset 151 nm x 142 nm) STM image of Au(1Tf) (A) and a 11.3 nm x 12.9 nm STM image of Au(110) (B) in air after flame-annealing, cycling in HCIO, and rinsing with water. The surface of Au(111) is covered with holes and multilayer islands (clusters), which are separated by densely spaced steps. All holes and islands comprise terraces as seen in the inset. Four narrow terraces on Au(110) with a (1 X 1)-structure are shown (slightly distorted due to thermal drift). There are two reasons why this conclusion is important. Firstly, owing to a coupling between the rates of the specific ion adsorption and the faradaic reaction, the fitting of impedance data to a particular equivalent circuit may not be straightforward, unless the contribution of one of these processes can be neglected [9]. Secondly, if the contribution of the faradaic impedance is negligible, the data can be fitted to the simple equivalent circuit above.
Fig. 7. Surtuce excess concentration [of peroxodisultate vs. the poten- tial £ (A) and vs. the surface charge density on the metal @ (B) for AUCH10) (2) and AuCLED (@) in 0.01 M HCIO, +0.4 mM Na,S,0,. Adsorption data for Au(111) in 0.1 M HCIO, +0.5 mM K,S0, (a) were taken from Ref, [7], Simulated plots for Au(110)(- - and Au(HID) (~ >) represent the sum 2) = 7 + °° evaluated by using Eq. (8) for the values of the parameters given in Table 1, and the commen values of the parameters ae = y" = 0.5, y + y' = 0.36, B = 0.64 and assuming that T° reaches the maximum corresponding to one-third of the atom density on the Au surface (1.39 10"* atoms em™*), @ in panel A relates the Sutface concentration to the atom density.
Fig. 7. Surtuce excess concentration [of peroxodisultate vs. the poten- tial £ (A) and vs. the surface charge density on the metal @ (B) for AUCH10) (2) and AuCLED (@) in 0.01 M HCIO, +0.4 mM Na,S,0,. Adsorption data for Au(111) in 0.1 M HCIO, +0.5 mM K,S0, (a) were taken from Ref, [7], Simulated plots for Au(110)(- - and Au(HID) (~ >) represent the sum 2) = 7 + °° evaluated by using Eq. (8) for the values of the parameters given in Table 1, and the commen values of the parameters ae = y" = 0.5, y + y' = 0.36, B = 0.64 and assuming that T° reaches the maximum corresponding to one-third of the atom density on the Au surface (1.39 10"* atoms em™*), @ in panel A relates the Sutface concentration to the atom density.
Fig. 8. Rate constant k of the peroxodisulfate reduction on the flame-an- nealed Au(110) (©), Au(t11) (@), non-annealed Au(111)[3) ( ) and Au(poly) [2] (- - -) electrodes in 0.1 M HCIO, + 1 mM Na.§.0. evaluated from the RDE voltammograms.
Fig. 8. Rate constant k of the peroxodisulfate reduction on the flame-an- nealed Au(110) (©), Au(t11) (@), non-annealed Au(111)[3) ( ) and Au(poly) [2] (- - -) electrodes in 0.1 M HCIO, + 1 mM Na.§.0. evaluated from the RDE voltammograms.
Fig. 9, Corrected rate constant vs. the corrected potential of the direct reduction pathway on the AgCE1) (2) and Aw(1 10) (O) electrodes in 0.1 M HCIO, +1 WM Na,8,0, evatuated for 2 = = 2.
Fig. 9, Corrected rate constant vs. the corrected potential of the direct reduction pathway on the AgCE1) (2) and Aw(1 10) (O) electrodes in 0.1 M HCIO, +1 WM Na,8,0, evatuated for 2 = = 2.
Fig. 10. Simulation of the potential dependence of the rate constants kp and & of the direct (lires) and the electrocstalytic (points) reduction pathway, respectively, on the Au(110) (O.---) and Au(1ID (6. ) electrodes in 0.1 M HCIO, or in 0.01 MH, SO, (t8) for the values of the parameters given in Table 1. and the common values of the parameters ae = y' = 0.5, y + y’ = 0.36, B = 0.64, @p = 0.28 and k®=8x 107? ems. A kinetic model of the electrocatalytic pathway has been developed in the previous study (3). The model assumes that the steady-state is established in the reaction (la) as a result of balancing the rates of the adsorption, the desorption and the first one-electron transfer step. It has been argued (3] that the latter step determines the rate of the electrocatalytic pathway, while the second electron transter to the highly reactive radical-anion SO)” is much faster. For electrostatic reasons, the rate of the simple or a
Fig. 10. Simulation of the potential dependence of the rate constants kp and & of the direct (lires) and the electrocstalytic (points) reduction pathway, respectively, on the Au(110) (O.---) and Au(1ID (6. ) electrodes in 0.1 M HCIO, or in 0.01 MH, SO, (t8) for the values of the parameters given in Table 1. and the common values of the parameters ae = y' = 0.5, y + y’ = 0.36, B = 0.64, @p = 0.28 and k®=8x 107? ems. A kinetic model of the electrocatalytic pathway has been developed in the previous study (3). The model assumes that the steady-state is established in the reaction (la) as a result of balancing the rates of the adsorption, the desorption and the first one-electron transfer step. It has been argued (3] that the latter step determines the rate of the electrocatalytic pathway, while the second electron transter to the highly reactive radical-anion SO)” is much faster. For electrostatic reasons, the rate of the simple or a
Parameters of the kinetic model of the electrocatalytic pathway in the peroxadisulfate reduction on Au(110) and Au(1 11)
Parameters of the kinetic model of the electrocatalytic pathway in the peroxadisulfate reduction on Au(110) and Au(1 11)
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