Transparent Porous Conductive Substrates for Gas-Phase Photoelectrochemical Hydrogen Production

Gas diffusion electrodes are essential components of common fuel and electrolysis cells but are typically made from graphitic carbon or metallic materials, which do not allow light transmittance and thus limit the development of gas-phase based photoelectrochemical devices. Herein, the simple and scalable preparation of F-doped SnO2 (FTO) coated SiO2 interconnected fiber felt substrates is reported. Using 2-5 mu m diameter fibers at a loading of 4 mg cm(-2), the resulting substrates have porosity of 90%, roughness factor of 15.8, and Young's Modulus of 0.2 GPa. A 100 nm conformal coating of FTO via atmospheric chemical vapor deposition gives sheet resistivity of 20 +/- 3 omega sq(-1) and loss of incident light of 41% at illumination wavelength of 550 nm. The coating of various semiconductors on the substrates is established including Fe2O3 (chemical bath deposition), CuSCN and Cu2O (electrodeposition), and conjugated polymers (dip coating), and liquid-phase photoelectrochemical performance commensurate with flat FTO substrates is confirmed. Finally, gas phase H-2 production is demonstrated with a polymer semiconductor photocathode membrane assembly at 1-Sun photocurrent density on the order of 1 mA cm(-2) and Faradaic efficiency of 40%.