All chemicals were received from commercial sources and used without further treatment. Ultrapure water (Arium, resistivity 18 MΩ cm) and potassium hydrogen carbonate (Sigma-Aldrich) were used for the electrochemical experiments. PTFE substrates (Sartorius TM , with 0.45 μm pore size) and Sigracet BB39 (Fuel Cell Store) carbon-based GDEs were used as substrates.