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Figure 1.(a) Cyclic voltammograms obtained in 0.1 MH2so4 at a bare ITO electrode and an AuNP-modified ITO electrode.(bd) Cyclic voltammograms obtained in 0.1 M carbonate buffer (pH 10.0) containing 1.0 mM H2O2 at (b) bare ITO electrodes and (c, d) AuNP-modified ITO electrodes.(e, f) Cyclic voltammograms obtained in a solution containing 0.25 M formic acid and 0.5 M NaHCO3 at AuNP-modified ITO electrodes. The scan rate of all voltammograms was 50 mV/s. In Figures bf, the voltammograms were recorded (i) before,(ii) just after,(iii) one week after, and (iv) three months after the anodic treatment (the experiment of Figure a).

The electrocatalytic activity of metal electrodes depends on electrode-treatment history1, 2 and surface contamination, 3 which makes it difficult to obtain reproducible electrochemical data. Generally, to address such problem, the electrocatalytic activity of metal electrodes is enhanced prior to their use; the enhancement is based on thermal, 4 chemical, 5 cathodic6 (application of a potential at which hydrogen is generated), and anodic treatment1, 2, 7, 8 (formation of metal oxide and its subsequent reduction). In particular, multiple anodic treatments of metal electrodes offer highly enhanced electrocatalytic activity, which even enables one to observe substantial currents of hydrogen sorption and desorption at Au electrodes. 1, 2 We have recently shown that the electrocatalytic activity of Au nanoparticles (AuNPs) can be enhanced via NaBH4 treat-