RESUMO
Epilayers of single-crystal GaAsPN and GaPN semiconductor samples with varying nitrogen compositions were photoelectrochemically characterized to determine their potential to serve as water splitting photoelectrodes. The band gap and flatband potentials were determined and used to calculate the valence and conduction band edge energies. The band edges for all compositions appear to be too negative by more than 500 mV for any of the materials to effect light-driven water splitting without an external bias. Corrosion analysis was used to establish material stability under operating conditions. GaPN was found to show good stability toward photocorrosion; on the other hand, GaAsPN showed enhanced photocorrosion as compared to GaP.
RESUMO
Electrokinetic flow provides a mechanism for a variety of fluid pumping schemes. The design and characterization of an electrochemically driven pump that utilizes porous carbon electrodes, iodide/triiodide redox electrolytes, and Nafion membranes is described. Fluid pumping by the cell is reversible and controlled by the cell current. Chronopotentiometry experiments indicate that the total available fluid that can be pumped in a single electrolysis without gas evolution is determined solely by the initial concentration of electrolyte and the applied current. The magnitude of the fluid flow at a given current is determined by the nature of the cation in the electrolyte and by the water absorption properties of the Nafion membrane. For 1 M aqueous electrolytes, pumping rates ranging from 1 to 14 microL/min were obtained for current densities of 10-30 mA/cm2 of membrane area. Molar volume changes for the I3-/I- redox couple and for the alkali cation migration contribute little to the observed volumetric flow rates; the magnitude of the flow is dominated by the migration-induced flow of water.
