The Cu2O-GDL was prepared by brush-coating commercial Cu2O particles (EPRUI Nanoparticles & Microspheres Co. Ltd.) onto the surface of a 1cm×1cm commercial GDL (Fuel cell systems). Specifically, 15 mg of Cu2O was dispersed in 200 μL of isopropanol (>99.8%, VWR Chemicals) and 66 μL of a 5 wt% Nafion suspension (Sigma-Aldrich) to create the catalyst ink. This mixture was sonicated for 20 minutes, and the ink was then coated to a 1 cm 2 GDL surface by brush, using a layer-by-layer coating technique. After each layer, the coating was dried at 40-50°C for 1-3 minutes. This process was repeated until the target catalyst loading of 4-5 mg cm -2 was achieved.