Transparent Porous Conductive Substrates for Gas‐Phase Photoelectrochemical Hydrogen Production

Abstract

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 µm 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 Ω 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 H2 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%.

Porous Transport Photoelectrodes Fabricated on Felt Substrates and Applications to Polymer Electrolyte Photoelectrochemistry

“…[5,6] Several porous photoanodes (ntype TiO 2 , WO 3 , BiVO 4 , Fe 2 O 3 , and SrTiO 3 ) and photocathodes (ptype CuInS 2 and Cu 2 O) have been prepared on porous felt substrates composed of carbon and titanium microfibers. [4][5][6][7][8][9][10][11][12][13] Carbon microfibers could be oxidatively decomposed during thermal treatments and photoanodic reactions. In contrast, titanium microfibers have better tolerance under oxidative conditions compared with carbon microfibers.…”

“…[6] (C) Photographic and SEM images of FTO-coated transparent porous conductive substrates (TPCS). [13] (D) Photographic and SEM image of a bulk-heterojunction (BHJ)/CuSCN/TPCS photocathode and its PEC response toward Eu 3 + reduction (pH 2) under 1-sun simulated illumination (AM1.5G, 100 mW cm À 2 ). Adapted from Ref.…”

Gas-fed photoelectrochemical reactions sustained by phosphotungstic acid as an inorganic surface electrolyte

“…Prototype gas-fed PEC systems have been developed using a proton exchange membrane (PEM) with a porous photoanode and cathode electrocatalyst. 7–23 We found that the surface coating of the porous photoelectrodes with perfluorinated sulfonic acid (PFSA) ionomers significantly enhanced the PEC performance of the vapour-fed system operating without liquid electrolyte. 13–17 The surface ionomer decorated on the porous photoanodes forms a triple-phase boundary, allowing gas, semiconductor particles, and electrolyte to come into contact simultaneously, facilitating proton-coupled electron transfer (PCET) and charge transport in the gas-fed PEC cell.…”

Porous silicon-nanowire-based electrode for the photoelectrocatalytic production of hydrogen

“…2 Based on the design of polymer electrolyte membrane (PEM) electrolyzers, gas-phase PEM-PEC cells have recently emerged as a scalable design for green hydrogen production. 3 This device improves ion conductivity and allows the creation of higher surface area photoelectrodes. 4,5…”