Highly Porous Iridium Thin Electrodes with Low Loading and Improved Reaction Kinetics for Hydrogen Generation in PEM Electrolyzer Cells.

Highly efficient electrodes with simplified fabrication and low cost are highly desired for the commercialization of proton exchange membrane electrolyzer cells (PEMECs). Herein, highly porous Ir-coated thin/tunable liquid/gas diffusion layers with honeycomb-structured catalyst layers were fabricated as anode electrodes for PEMECs via integrating a facile and fast electroplating process with efficient template removal. Combined with a Nafion 117 membrane, a low cell voltage of 1.842 V at 2000 mA/cm 2 and a high mass activity of 4.16 A/mg Ir at 1.7 V were achieved with a low Ir loading of 0.27 mg/cm 2 , outperforming most of the recently reported anode catalysts. Moreover, the thin electrode shows outstanding stability at a high current density of 1800 mA/cm 2 in the practical PEMEC. Moreover, with in-situ high-speed visualizations in PEMECs, the catalyst layer structure's impact on real-time electrochemical reactions and mass transport phenomena was investigated for the first time. Increased active sites and improved multiphase transport properties with favorable bubble detachment and water diffusion for the honeycomb-structured electrode are revealed. Overall, the significantly simplified ionomer-free honeycomb thin electrode with low catalyst loading and remarkable performance could efficiently accelerate the industrial application of PEMECs.