Effect of Water on the Electrochemical Oxidation of Gas-Phase SO2 in a PEM Electrolyzer for H2 Production

Water plays a critical role in producing hydrogen from the electrochemical oxidation of SO2 in a proton exchange membrane (PEM) electrolyzer. Not only is water needed to keep the membrane hydrated, but it is also a reactant. One way to supply water is to dissolve SO2 in sulfuric acid and feed that liquid to the anode, but this process results in significant diffusion resistance for the SO2. Alternatively, we have developed a process where SO2 is fed as a gas to the anode compartment and reacts with water crossing the membrane to produce sulfuric acid. There was concern that the diffusion resistance of water through the membrane is as significant as SO2 diffusion through water, thus limiting the benefit of a gas-phase anode feed. We show here that water diffusion through the membrane is not as limiting as liquid-phase SO2 diffusion. Therefore, we can control the cell voltage, the limiting current, and the sulfuric acid concentration by varying the diffusion resistance of the membrane via thickness or temperature. Catalyst loading, however, has a negligible effect on cell performance

Synthesis, Characterization, and Atomistic Modeling of Stabilized Highly Pyrophoric Al(BH_4)_3 via the Formation of the Hypersalt K[Al(BH_4)_4]

The recent discovery of a new class of negative ions called hyperhalogens allows us to characterize this complex as belonging to a unique class of materials called hypersalts. Hyperhalogen materials are important while serving as the building blocks for the development of new materials having enhanced magnetic or oxidative properties. One prime example of a hydperhalogen is the Al(BH_4)_4^– anion. Aluminum borohydride (17 wt % H) in itself is a volatile, pyrophoric compound that has a tendency to release diborane at room temperature, making its handling difficult and very undesirable for use in practical applications. Here we report that the combination of Al(BH_4)_3 with the alkaline metal borohydride KBH_4 results in the formation of a new compound KAl(BH_4)_4 which is a white solid that exhibits remarkable thermal stability up to 154 °C and has the typical makeup of a hypersalt material. Using a variety of characterization tools and theoretical calculations, we study and analyze the physical characteristics of this compound and show its potential for stabilizing high hydrogen capacity, energetic materials

Alanate-borohydride material systems for hydrogen storage applications

Alteration of the thermodynamic stability of selected borohydride/alanate systems, including the combination of LiBH_4 with NaAlH_4 and LiBH_4 with CaCl_2 and LiAlH_4, was investigated to determine the possibility of forming intermediate stability mixed AlH_(4)^(−)–BH_(4)^(−) phase. Facile metathesis exchange reactions were observed when NaAlH_4 was combined with LiBH_4 resulting in the formation of LiAlH_4 and NaBH_4. Thermal analysis of this system showed that the 1st and 2nd decomposition of LiAlH_4 occurred irrespective of NaBH_4 illustrating the absence molecular level interaction between the AlH_(4)^(−) and the BH_(4)^(−) anions. On the other hand, in the case of CaCl_2, LiAlH_4, LiBH_4 combination, the results showed the formation of a calcium alanate type phase. Evaluation of the thermal property of this system showed an endothermic one step decomposition between 130 °C and 200 °C (2.3 wt% loss). Structural examination of this calcium alanate type phase revealed a different local coordination geometry of AlH_(4)^(−) from that observed in calcium alanate. The formation and properties of this phase are being attributed to molecular level AlH_(4)^(−)–BH_(4)^(−) interactions. These findings provide a pathway toward designing novel alanates-borohydrides systems for hydrogen storage applications. This article will show the methodologies followed and explain the results obtained

Synthesis, Characterization, and Atomistic Modeling of Stabilized Highly Pyrophoric Al(BH₄)₃ via the Formation of the Hypersalt K[Al(BH₄)₄]

The recent discovery of a new class of negative ions called hyperhalogens allows us to characterize this complex as belonging to a unique class of materials called <i>hypersalts</i>. Hyperhalogen materials are important while serving as the building blocks for the development of new materials having enhanced magnetic or oxidative properties. One prime example of a hydperhalogen is the Al­(BH₄)₄^– anion. Aluminum borohydride (17 wt % H) in itself is a volatile, pyrophoric compound that has a tendency to release diborane at room temperature, making its handling difficult and very undesirable for use in practical applications. Here we report that the combination of Al­(BH₄)₃ with the alkaline metal borohydride KBH₄ results in the formation of a new compound KAl­(BH₄)₄ which is a white solid that exhibits remarkable thermal stability up to 154 °C and has the typical makeup of a hypersalt material. Using a variety of characterization tools and theoretical calculations, we study and analyze the physical characteristics of this compound and show its potential for stabilizing high hydrogen capacity, energetic materials