Abstract: The development of bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at high current density under industrial temperatures is crucial for large-scale industrial hydrogen production from water splitting. In this work, M-MnO₂@TNTA composite electrodes were prepared by depositing various metal ion-doped manganese oxide nanoparticles on the titania nanotube array (TNTA) by successive ionic layer adsorption reaction (SILAR) method, and their HER and OER electrocatalytic performances were investigated in 1 M KOH. Results show that the CoFe-MnO₂@TNTA composite electrode prepared by simultaneous doping of Co³⁺ and Fe³⁺ in MnO₂ exhibits optimal catalytic performance. Compared with MnO₂@TNTA without ion doping, the overpotentials of CoFe-MnO₂@TNTA at 10 mA cm^-2 (η₁₀) for HER and OER are reduced by 571 and 665 mV. In addition, the electrode performance can be significantly enhanced by increasing the test temperature, and the porous array structure enables CoFe-MnO₂@TNTA to exhibit better performance at high current densities. At 50 °C, which is the common industrial electrolytic water temperature, the η₁₀ of CoFe-MnO₂@TNTA for HER is almost equal to that of the Pt/C electrode. The η₁₀₀ of CoFe-MnO₂@TNTA for HER is reduced by 35 mV compared with the Pt/C electrode. Moreover, η₂₀₀ of CoFe-MnO₂@TNTA for OER is significantly lowered by 111 and 184 mV compared with IrO₂ and RuO₂ electrodes. Utilizing CoFe-MnO₂@TNTA as both the cathode and anode for overall water splitting, the electrolysis voltage is merely 2.33 V under the current density of 200 mA cm^-2, much lower than that of IrO₂ (+)||Pt/C (-) (2.68 V). The present work may provide a valuable reference for the development of self-supporting bifunctional electrodes suitable for high-current-density water splitting at industrial temperatures.

Key words: MnO₂, Titania nanotube array, Ion doping, Electrocatalytic water splitting, Hydrogen evolution reaction, Oxygen evolution reaction