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.