Tailoring TiO2 nanotubes photoanodes with electrodeposited Co3O4 and CoOOH cocatalysts for enhanced electrocatalytic and photoelectrocatalytic oxygen evolution

• ChA-controlled cobalt electrodeposition yields effective Co 3 O 4 and CoOOH cocatalysts. • CoOOH’s 157 mV/dec Tafel slope vs Co 3 O 4 indicates faster OER kinetics. • Proton-assisted electron transfer in CoOOH outperforms Co 3 O 4 pathways. • CoOOH electrodes deliver higher photocurrent and stability than Co 3 O 4 . In this work, titanium dioxide nanotubes (TiO 2 -NTs) were functionalised with cobalt-based cocatalysts — Co 3 O 4 and CoOOH — via controlled electrodeposition to improve their performance in electrocatalytic and photoelectrocatalytic oxygen evolution reaction (OER). TiO 2 -NTs, prepared by anodization and hydrothermal annealing, provided a stable and photoactive platform. Structural and chemical characterisation (SEM, EDX, XRD, ATR-FTIR, XPS) confirmed successful deposition of the cocatalyst layers. Electrochemical measurements revealed a markedly superior performance of CoOOH-modified electrodes, which exhibited a significantly reduced OER onset potential (0.80 V vs. Ag/AgCl) compared to pristine TiO 2 -NTs and TiO 2 -NTs/Co 3 O 4 . Under illumination, TiO 2 -NTs/CoOOH generated up to twice the photocurrent of their Co 3 O 4 -modified counterparts. Mechanistic analysis attributed this enhancement to the proton-coupled electron transfer capability of CoOOH. Additionally, photocatalytic degradation of methylene blue confirmed that the presence of CoOOH enhances the catalytic performance of TiO 2, indicating improved overall activity of the composite material. These findings highlight CoOOH as a more effective cocatalyst than Co 3 O 4 for enhancing TiO 2 -NTs based systems in solar-assisted water splitting and pollutant degradation applications.