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

<jats:title>Abstract</jats:title><jats:p>Photoelectrochemistry is used to develop solar energy technologies for fuel production and chemical transformations. Semiconductor materials such as TiO<jats:sub>2</jats:sub>, WO<jats:sub>3</jats:sub>, BiVO<jats:sub>4</jats:sub>, Fe<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>, and Cu<jats:sub>2</jats:sub>O are often investigated in devices designed to convert light energy into chemical energy, including for the production of hydrogen by photoelectrochemical (PEC) water splitting. The oxide electrodes are of significant interest due to their potential for efficient PEC reactions with high durability and their relatively low costs compared to other semiconductor materials. This review highlights the roles played by macroporous photoelectrodes in the development of highly efficient photoelectrodes and advanced PEC systems using polymer electrolytes. Three‐dimensional conductive fiber substrates, such as titanium felt and carbon paper, outperform their two‐dimensional counterparts owing to their larger interfacial areas that enhance PEC properties. The macroporous structures facilitate mass‐transport‐limited reactions when integrated with polymer electrolytes in membrane electrode assemblies. Such configurations are promising for PEC splitting of pure water, and for transforming gaseous molecules such as water vapor, volatile organic compounds, and methane. Optimizing the configuration, including electrode materials selection and ionomer‐coating treatment, can potentially improve the performance of polymer electrolyte membrane PEC cells. Porous transport photoelectrodes integrated with proton/anion‐exchange membranes offer significant opportunities for advanced PEC applications.</jats:p>