Abstract Changes in the physicochemical properties of aqueous-alkaline solutions of sodium borohydride upon prolong storage have been studied. It was shown that in solutions water slowly interacts with the hydride to produce sodium tetrahydroxoborate which precipitates as NaB(OH) 4 ·2H 2 O. The effect of NaBH 4 decomposition in aqueous-alkaline solutions on the in situ reduction of cobalt chloride has been investigated. It was found that sodium tetrahydroxoborate interacts with cobalt chloride to form purple amorphous cobalt borate which is reduced by NaBH 4 to an active catalyst. The properties of the active components in freshly prepared solutions and in solutions after a one-year storage have been compared using HR TEM, XPS and IR spectroscopy. It was found that with the decreasing content of NaBH 4 there was a decrease in the extent of reduction of the catalyst precursors while the increase in the pH of up to 13 leads to the formation of cobalt hydroxide which has low activity towards hydrolysis.