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    STUDIA CHEMIA - Issue no. 3, Tom I / 2016  

  Abstract:   The increase of the graphite electrocatalytic activity toward hydrogen peroxide (HP) electrosynthesis (HPE) by the partial electroreduction of O2 can be achieved by in-situ electroactivation (EA). Our previous studies completed in strong alkaline media (1 M NaOH) by galvanostatic multi-sequence EA techniques (MSETs) revealed that an adequate graphite EA can improve HPE current efficiency (CE) up to 35 % compared to the unmodified graphite. In order to implement the optimised operational parameters to a micro-pilot scale electrochemical reactor, in a first step, several systems for the on-line HP concentration monitoring were designed and tested. Unfortunately, the preliminary test, even in moderate alkaline media (0.1 M NaOH) revealed that, at concentrations greater that 50 ppm, the HP decomposes intensively in contact with the setup components, disallowing the HP accumulation. As a consequence, for all further experiments, the alkaline supporting electrolyte was replaced with 0.1 M Na2SO4. In these new conditions, two models of HP on-line detectors (spectrophotometrical and amperometrical) were designed and tested, presenting adequate limit of detection (L.O.D. = 10 ppm and L.O.D. = 0.23 ppm, respectively). Also, the HPE process was studied in sulphate media, using a Pt/graphite wall-jet ring disk electrode system, revealed that the CE can reach a 46 % value for the unmodified electrode and increases up to 52 % when the auto-adaptive galvanostatic MSETs protocol is used.

Keywords: hydrogen peroxide electrosynthesis, graphite electroactivation, hydrogen peroxide on-line monitoring, wall-jet ring disk electrode, auto-adaptive techniques
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