Sodium borohydride production and utilisation for improved hydrogen storage

Abstract

Sodium borohydride (NaBH 4 ) has been the subject of extensive investigation as a potential hydrogen storage material. Its advantages include its ability to be stored as a stabilised aqueous solution and hydrolysed catalytically on demand, providing hydrogen safely, controllably, and at mild conditions. However, several drawbacks were identified by the US Department of Energy (DOE) in their "No-Go" recommendation in 2007; namely, the limitations on its gravimetric hydrogen storage capacity (GHSC) and its prohibitive manufacturing cost.This thesis aims to address some of the major issues associated with the use of NaBH 4 for hydrogen storage. Efforts have been spread across three key research areas, which were identified in a review of the recent literature: Synthesising an efficient, durable, and inexpensive catalyst for the hydrolysis of aqueous NaBH 4 solution  The design of a hydrogen storage system based on NaBH 4 which can overcome the GHSC constraints imposed by the solubility of its hydrolysis by-product, NaBO 2  The development of a novel recycling process for regenerating NaBH 4 from NaBO 2 , with the goal of reducing its production cost to within the DOE's target range of $2-4 per gallon of gasoline equivalent (gge) To achieve the first goal, a new electroless plating method was developed for preparing cobalt-boron (Co-B) catalysts supported on shaped substrates. This method involves mixing the plating solutions at low temperature (<5 o C), in contrast to previously employed methods, which are generally carried out at room temperature or higher. The new method requires only one plating step to achieve the desired catalyst loading, and has higher loading efficiency than processes requiring multiple plating steps, due to reduced catalyst wastage. The catalysts produced by this method show significantly higher NaBH 4 hydrolysis activity than those prepared by conventional methods, with a hydrogen generation rate over 24000 mL/min/g recorded at a temperature of 30 o C and a NaBH 4 concentration of 15 wt%. The improved activity of these catalysts was thought to be due to their increased boron content and nanosheet-like morphology, both of which are products of the low temperature preparation method.ii The stability of these catalysts was examined over several usage and deactivation cycles, which involved long-term exposure to alkaline solution. It was found that the deactivated catalysts were able to recover 80-90% of their initial activity even after 10 cycles, if operated at 40 o C or higher. Characterisation of the deactivated catalysts revealed that a layer of NaBO 2 had formed on the surface, blocking the catalytically active Co sites. The improved cyclic stability is most likely due to the dissolution of this layer at higher temperatures.A new reactor design for a NaBH 4 -based hydrogen storage system was developed, with the goal of overcoming the GHSC limitations encountered by conventional system designs. The new design is based on a fed-batch configuration in which solid NaBH 4 is added ...

Synthesis Of Black Titanium Dioxide And Effect Of Calcination Conditions And Reducing Agent On Photocatalytic Degradation Of Methyl Orange

“…Sodium borohydride (NaBH 4 ), or called sodium tetrahydroborate, is widely used as a reducing agent in laboratory and industrial applications. It has many advantages, including use in the catalytic hydrolysis due to its high potential to be used as hydrogen storage material for mobile application [26] or as a synthetic fuel for a direct borohydride fuel cell. Also, hydrogen storage material required good properties including fast sorption kinetics and convenient working temperatures and working pressures.…”

“…26 Fits and diagnostics for all observations of the removal from photocatalytic degradation, excluding the adsorption under UV light irradiation…”