(157g) Nano-Scale Atomic Layer Deposited Films for Water Splitting Cycles
Iron oxide (Fe3O4) can be reduced to iron metal using synthesis gas (CO, H2, CO2) at moderate temperatures (700 ? 1200°C). Iron metal is then used to split water at lower temperatures (300 ? 600°C), producing a stream of pure, uncontaminated hydrogen and regenerating the Fe3O4 for syngas reduction again. However, both the reduction and oxidation reactions are controlled by diffusion through the reacted layer, making the reaction slow when bulk iron is used. The higher temperature reduction step also results in sintering of the powder, decreasing the surface area for diffusion and greatly slowing the reaction rate. This limits the number of reduction and oxidation cycles that bulk iron can undergo. By coating high surface area substrates with nano-thin films of iron using Atomic Layer Deposition (ALD), the reaction can be completed more quickly than with bulk iron powder for the same mass of iron. The thin films and high surface area substrates also mitigate the effects of sintering. In this study, the kinetics of the syngas reduction and water oxidation of these iron thin films on different substrate materials (SiO2, Al2O3, and ZrO2) have been studied and compared with the kinetics of the reactions when using bulk iron powder.