Composition-Activity Relationships of Multicomponent Hydroxide/Titania Nanotube Arrays for Water Electrolysis under...

MOH (M = Ti⁴⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺) 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 η₁₀ 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 Fe³⁺ or Co²⁺ outperforms the other electrodes. Notably, the Fe³⁺/Co²⁺ binary hydroxide composite CoFe(OH)_x@TNTA exhibits the best OER catalytic activity, with η₁₀ being 318 mV and k_Tafel of only 31 mV/dec. The η₁₀ is comparable to benchmark IrO₂, 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/cm² at 1.73 V with operational stability for approximately 200 h.