Reduction behavior of neptunium(V) at a gold or platinum electrode duringcontrolled potential electrolysis and procedures for electrochemical preparationsof neptunium(IV) and (III)

摘要

Unique current-time relations were observed during the controlled potential electrolysis for the reduc-tion of NpO_2 to Np4+or Np3+at a gold platinum electrode in perchloric acid solution. The reductionprocess of Np0_2 was elucidated based on controlled potential electrolysis and voltammetry as follows:Though Np0_2 is not reduced directly at a gold electrode, it is reduced by chemical reaction with Np3+which is produced by the electrode reduction of Np4+. Here, Np4+ is initially produced through the dispro-portionation of Np02 , and generated progressively through the reduction of NpO_2 . The reduction of Np02at a platinum electrode is initiated by the electrocatalytic reduction to Np4+ with the hydrogen atomwhich is produced by the electrode reduction of H+ and adsorbed on the platinum electrode surface.The Np4+ produced functions as an electron transfer mediator to reduce Np02 similar to the reactionat a gold electrode. The above described catalytic reduction processes of Np02 were elucidated withthe aid of digital simulation of bulk electrolyses. Methods useful for the preparation of Np4+ and Np3+by bulk electrolysis were proposed based on the experimental results.