β-FeOOH nanorod as a highly active and durable self-repairing anode catalyst for alkaline water electrolysis powered by renewable energy

A β-FeOOH nanorod was investigated as a highly active and durable self-repairing anode catalyst for alkaline water electrolysis with repeated potential change, simulating power from renewable energy. The β-FeOOH nanorod was synthesized by coprecipitation, using an organic buffer of tris(hydroxymethyl)aminomethane. The β-FeOOH nanorods dispersed in 1 M KOH aq. as an alkaline electrolyte were electrochemically deposited on a nickel electrode by a constant current electrolysis. The deposited β-FeOOH nanorods formed bundled network on the surface of the electrode and exhibited high oxygen evolution reaction (OER) activity, where the minimum OER overpotential was 285 mV at 100 mA cm –2 . The durability of the nickel electrode coated with β-FeOOH nanorods were tested via shutdown-based accelerated durability test, where electrolysis at 600 mA cm –2 for 1 min and the potential control at 0.5 V vs. reversible hydrogen electrode (RHE) for 1 min are repeated in the presence of β-FeOOH nanorod in the electrolyte. The catalyst coated electrode showed the low OER overpotential for 4000 cycles, whereas the OER overpotential of a bare nickel electrode increased within only 200 cycles. The β-FeOOH nanorod efficiently suppressed the corrosion of the nickel substrate and the layer of β-FeOOH nanorod was continuously repaired by accumulating the β-FeOOH nanorod from the electrolyte. Therefore, the β-FeOOH nanorod is useful as a self-repairing anode catalyst with high OER activity and durability. Graphical abstract Highlights β-FeOOH nanorod is synthesized via coprecipitation in the presence of organic buffer. Quite low overpotential for oxygen evolution reaction (285 mV at 100 mA cm –2 ) was achieved. The catalyst layer was self-repaired to show high durability under accelerated durability test.