Since the late 1990s, sodium borohydride (NaBH₄, denoted SB) is presented as a promising hydrogen storage material and an attractive fuel (aqueous solution) of the direct fuel cell (or direct liquid-feed fuel cell). In 2007, the U.S. Department of Energy recommended a no-go for SB for vehicular applications and suggested work on ammonia borane (AB), another promising hydrogen storage material, which is also considered as a fuel for the direct fuel cell. Both boron hydrides in hydrogen and fuel cell applications are the topics of the present paper. The basics, issues, solutions to the issues and state-of-the-art are tackled but the discussion aims to compare the hydrides for either application. It is shown that there are many similarities between SB and AB in their features and applications. Nevertheless SB and AB as hydrogen storage materials do not compete. Rather, SB is intended more to portable technologies while AB to vehicular applications. Otherwise, when these hydrides are utilised as fuels of direct fuel cell, one question arises: what can be the advantage of developing the AB-powered fuel cell when it seems to be less effective, practical, and more complex than the SB-powered fuel cell? These aspects are discussed. However that may be, it is concluded that both SB and AB are not mature enough for the applications considered.

Cobalt-catalyzed hydrolysis of sodium borohydride (NaBH₄) has attracted great attention since the hydride is believed to be promising hydrogen storage material. Cobalt is an efficient metal catalyst and has already proven to be a potential alternative to noble metals. Nevertheless it is not stable. Indeed it transforms into a Co- and B-based material when on contact with NaBH₄. Through ex situ characterizations (e.g. ICP, XRD, XPS and SEM), the Co- and B-based material has been supposed to be either a cobalt boride Co_xB (with x from 1 to 3) or a Co–B alloy. This contradiction is the topic of the present paper. Herein, the literature dedicated to the Co-catalyzed NaBH₄ hydrolysis is exhaustively surveyed. The results of the ex situ characterizations are largely discussed, for example that: (i) the ex situ characterized Co_xB or Co–B might be different from the in situ formed Co- and B-based catalyst; (ii) there is no clear evidence of the formation of either Co_xB or Co–B; (iii) the in situ formed catalyst would change in accordance with a cycle in the course of the hydrolysis; and (iv) in situ characterizations are clearly required but their setting up is a challenge. These conclusions, among others, are argued.