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

Unique current–time relations were observed during the controlled potential electrolysis for the reduction of NpO2+ to Np4+ or Np3+ at a gold or platinum electrode in perchloric acid solution. The reduction process of NpO2+ was elucidated based on controlled potential electrolysis and voltammetry as follows: Though NpO2+ 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 disproportionation of NpO2+, and generated progressively through the reduction of NpO2+. The reduction of NpO2+ at a platinum electrode is initiated by the electrocatalytic reduction to Np4+ with the hydrogen atom which 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 NpO2+ similar to the reaction at a gold electrode. The above described catalytic reduction processes of NpO2+ were elucidated with the 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.