Low Loading and High Utilization Ratio of Iridium Catalyst Coated Smoltek Carbon Nanofibers Used as Anode Material for PEM Water Electrolyzers

Pro­ton exchange mem­brane water elec­trolyz­ers (PEMWE) are a core tech­nol­o­gy for the future green hydro­gen pro­duc­tion mar­ket. The installed pow­er for PEMWE is esti­mat­ed to be 40 GW by 2030. The oxy­gen evo­lu­tion reac­tion (OER) cat­a­lyst on the anode side is dom­i­nat­ed by Irid­i­um (Ir)-based mate­ri­als, one of the rarest noble met­als in the crust of Earth. It is crit­i­cal to low­er the load­ing of Ir-based cat­a­lyst to ≈ 0.1 mg Ir/​cm2 with­out com­pro­mis­ing the over­all per­for­mance to enable the mass man­u­fac­tur­ing tar­gets. It is a big chal­lenge due to the poor elec­tri­cal con­tact between the result­ing cat­a­lyst lay­ers and the anode sub­strate. To reach this goal, Smoltek invent­ed an advanced porous trans­port elec­trode (PTE) con­cept using its pro­pri­etary car­bon nanofiber (CNF) tech­nol­o­gy and unique Ir coat­ing tech­nol­o­gy. An anode porous trans­port lay­er (PTL) is first mod­i­fied by ver­ti­cal­ly aligned CNFs to increase sur­face area, fol­lowed by coat­ing a cor­ro­sion-resis­tant and con­duc­tive lay­er (e.g. Plat­inum) and a sub­se­quent OER cat­a­lyst lay­er. Cathod­ic elec­trode­po­si­tion in a three-elec­trode sta­t­ic cell was per­formed for Ir-based cat­a­lyst depo­si­tion. We demon­strate that with this method, the mor­phol­o­gy and depo­si­tion process of Ir are con­trol­lable at very low load­ing amounts (≥ 0.1 mg Ir/​cm2). An Ir coat­ing lay­er can be formed on the high­ly struc­tured CNF-based sur­face. The elec­trode­posit­ed Ir has strong adhe­sion with the CNF PTEs, result­ing in a high elec­tri­cal conductivity.

This unique Ir-elec­trode­posit­ed CNF PTEs struc­ture max­i­mizes the anode sur­face area and paves a new way to increase the uti­liza­tion ratio of cat­a­lyst sur­face at a low load­ing amount, which makes it a com­pet­i­tive anode mate­r­i­al in today’s PEMWE market.