Hydrogen can be used as a replacement for fossil fuels in many applications. However,commercially relevant scales of hydrogen production utilize either electrolysis or a combination of steam methane reforming and the water gas shift reaction which are energy intensive and non-renewable. Here I report on a portion of work toward understanding the fundamental physical and chemical phenomena that constrain the maximum solar-to-hydrogen (STH) conversion efficiency for photoelectrochemical particle-slurry reactors. Using Rh-doped strontium titanate (SrTiO 3 :Rh), a variable power light source, and an inline-mass spectrometry the rate of hydrogen production can be controlled and optimized.In the second part of my work, I report on the spectro-electrochemical behavior of crystalline titanium dioxide (TiO2) mesoporous films as a model system for aqueous redox flow battery charging/discharging. The effects of potential determining ions on the density of states in the materials are discussed
