Improved H2 production rate by hydrolysis of Ammonia Borane using quaternary alloy catalysts

Co–M–B–P quaternary alloy catalyst powders (where M = Cr, Mo, W, and Cu) were synthesized by chemical reduction method to improve the catalytic performance of Co–B catalyst for hydrogen production by hydrolysis of Ammonia Borane (AB). The catalytic activity increases significantly due to the combined promoting effects induced by M and P in quaternary alloy as compared to binary Co–B catalyst. The promoting roles of each doping element in Co–B catalyst during AB hydrolysis were studied using XPS, XRD, SEM, and BET surface area analyses. Each transition element, present in the form of either oxides or metal, acts as an atomic barrier to prevent Co–B particle agglomeration to increase the effective surface area. At the same time these species also act as Lewis acid sites to improve the absorption of the reactants on to the surface. Inclusion of phosphorous, in addition, is able to create higher number of Co-active sites on the surface, which was inferred from XPS analysis. Among all the alloy catalysts, Co–Cr–B–P showed the highest H2 generation rate, which was mainly attributed to the collective effects of Cr and P in forming the catalyst surface having higher surface area and more Co-active sites. On the contrary, in the case of Cu doped Co–B catalyst, the inclusion of P considerably lowers the surface area, which decreases the catalytic activity.