Reduction of sodium boron oxide by atmospheric pressure hydrogen plasma

Abstract Sodium borohydride (NaBH 4 ) is a promising hydrogen carrier whose practical use requires efficient regeneration from sodium metaborate (NaBO 2 ), the hydrolysis by-product. Thermochemical, mechanochemical, and electrochemical routes have been explored, and here we employ atmospheric-pressure hydrogen plasma in a planar dielectric barrier discharge reactor. Solid NaBO 2 powders were irradiated under hydrogen atmosphere while varying the applied voltage, repetition rate, reactor configuration, gas flow rate, and irradiation time. NaBH 4 formation was confirmed by X-ray diffraction and by quantifying hydrogen evolved during post-irradiation acid hydrolysis after irradiation process. NaBO 2 -to-NaBH 4 conversion was typically 0.3%–0.9%, with a maximum of 1.74% at 16 kV, 10 kHz, and 10 h. Analysis of parametric trends suggests that NaBH 4 formation is mainly limited by the overlap between the discharge and powder bed and by NaBH 4 decomposition induced by water. These results demonstrate direct NaBO 2 reduction by atmospheric-pressure hydrogen plasma and identify design targets to complement NaBH 4 regeneration routes.