New electrolytic synthesis of borohydride anions from boron oxide in a molten salt melt

An electrolytic reduction leading to the formation of borohydride, starting from boron oxide and hydrogen gas, was studied. Supplying voltage to an electrochemical cell containing molten lithium-potassium-cesium bromide eutectic would result in electrochemical synthesis of lithium metal and bromine gas. At operating temperature of 300°C, the amount of hydrogen dissolved in the melt was low, and therefore might not readily react with lithium. The lithium ended up in large pieces, which would not easily react to form the hydride. Addition of B₂O₃ made the melt viscous even 75°C above the stated melting point. The electrolysis in effect withdrew lithium from the melt, further altering the composition and the melt of 10 solidified near the cathode. The formation of solid often blocked the pores in the cathode through which hydrogen enters the cell. Once blockage occurred, the formation of borohydride stops due to the loss of hydrogen to react with lithium, even if the electrolysis continues. This is an abstract of a paper presented at the ACS Fuel Chemistry Meeting (Washington, DC Fall 2005).