The electrochemical reduction of peroxycitric acid (PCA) coexisting with citric acid and hydrogen peroxide (H2O2) in the equilibrium mixture was extensively studied at a gold electrode in acetate buffer solutions containing 0.1 M Na2SO4 (pH 2.0-6.0) using cyclic and hydrodynamic voltammetric, and hydrodynamic chronocoulometric measurements. The reduction of PCA was characterized to be an irreversible, diffusion-controlled process, and the cyclic voltammetric reduction peak potential (E-p(c)) was found to be more positive by ca. 1.0 V than that of the coexisting H2O2, e.g., the E-p(c) values obtained at 0.1 V s(-1) for PCA and H2O2 were 0.35 and -0.35V, respectively, vs. Ag vertical bar AgCl vertical bar KCl (sat.) at pH 3.3. The E-p(c) of PCA was found to depend on pH, i.e., at pH>4.5, the plot of E-p(c) vs. pH gave the slope (-64mV decade(-1).) which is close to the theoretical value (-59mVdecade(-1)) for an electrode process involving the equal number of electron and proton in the rate-determining step, while at pH<4.5, the E-p(c) was almost independent of pH. The relevant electrochemical parameters, Tafel slope, number of electrons, formal potential (E-0'), cathodic transfer coefficient and standard heterogeneous rate constant (k(0)') for the reduction of PCA and the diffusion coefficient of PCA were determined to be ca. 100 mV decade(-1), 2, 1.53 V (at pH 2.6), 0.29, 1.2 x 10(-12) cm s(-1) and 0.29 x 10(-5) cm(2) s(-1), respectively, and except for E-0', the obtained values were almost independent of the solution pH. The overall mechanism of the reduction of PCA was discussed. (C) 2007 Elsevier Ltd. All rights reserved.