Composition–Activity Relationships of Multicomponent Hydroxide/Titania Nanotube Arrays for Water Electrolysis under Quasi-Industrial Condition

MOH (M = Ti 4+, Mn 2+, Fe 3+, Co 2+, Ni 2+, Cu 2+ ) containing one to six species of metal ions were deposited onto titania nanotube arrays (TNTA) to prepare a series of multicomponent composite electrodes (MOH@TNTA). The effects of the MOH composition on the catalytic activity of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were investigated in detail. Results show that the dominant influential factor for HER is the component number of MOH. Increasing the metallic components can enhance HER performance and the sexenary hydroxide composite (s-MOH@TNTA) exhibits optimal HER performance, with η 10 being 42 mV and k Tafel being 52 mV/dec, both outperforming benchmark Pt/C. In contrast, the dominant influential factor for OER is the ion species in MOH and the electrode containing Fe 3+ or Co 2+ outperforms the other electrodes. Notably, the Fe 3+ /Co 2+ binary hydroxide composite CoFe(OH) x @TNTA exhibits the best OER catalytic activity, with η 10 being 318 mV and k Tafel of only 31 mV/dec. The η 10 is comparable to benchmark IrO 2, yet its ultralow k Tafel leads to superior performance under high current densities. Moreover, the unique structure of nanotube arrays endows MOH@TNTA with more prominent performance under quasi-industrial condition. The overall water splitting (OWS) electrolyzer with CoFe(OH) x @TNTA and s-MOH@TNTA serving as anode and cathode achieves 200 mA/cm 2 at 1.73 V with operational stability for approximately 200 h.