Abstract: The present invention provides a hydrogen storage and release material including a two-dimensional hydrogen boride-containing sheet including a two-dimensional network containing n(HxBy) (n?4, 0.001?x/y?0.999) having a molar ratio of boron to hydrogen from 1:0.999 to 1:0.001, the molar ratio being determined by thermal desorption spectroscopy, and mass measurement before and after a temperature rise, wherein the hydrogen storage and release material has: peaks derived from B1s of boron at 187.5±1.0 eV and 191.2±1.0 eV to 193±1.0 eV in X-ray photoelectron spectroscopy, and a peak derived from a B—H stretching vibration at from 2400 cm?1 to 2600 cm?1 and also a peak derived from a B—H—B stretching vibration at from 1200 cm?1 to 1800 cm?1 in infrared spectroscopy.

Abstract: A reducing material including a two-dimensional hydrogen boride-containing sheet having a two-dimensional network composed of (BH)n (n?4). A composite including a two-dimensional hydrogen boride-containing sheet having a two-dimensional network composed of (BH)n (n?4) and a metal nanoparticle. A reduction method including: a step of dispersing the reducing material according to any one of Claims 1 to 5 in an organic solvent to prepare a dispersion liquid containing the reducing material; and a step of reducing a metal ion having a redox potential which is given as a standard electrode potential of ?0.26 V/SHE or higher by mixing the dispersion liquid with the metal ion.