Three-dimensional (3D) nanoporous nickel oxyhydroxide (NiOOH) films were prepared on a TiO₂ nanoarray substrate by a novel surfactant-assisted photodeposition method using Ni²⁺-containing solutions as precursors, and their energy storage and conversion behaviors were investigated. In the photodeposition process, photogenerated holes were used to oxidize Ni²⁺ ions to Ni³⁺ ions, resulting in the precipitation of NiOOH onto the TiO₂ nanoarray substrate. The amount of photochemically deposited NiOOH increased with an increase in the surfactant (sodium lauryl sulfate, SDS) concentration in the deposition solution. If the SDS concentration did not surpass 0.3 wt%, the photochemically deposited NiOOH composite film exhibited a 3D nanoporous structure, and the pore size decreased with an increase in the SDS concentration. The 3D nanoporous NiOOH composite film which was prepared by photodeposition for 5 h in the presence of 0.3 wt% SDS presented the largest discharge capacity in our experimental range, implying enhanced UV-induced oxidative energy storage. The as-photodeposited NiOOH nanoflakes with a quasi two-dimensional structure exhibited close contact with TiO₂ nanorods, originating from the fact that NiOOH was deposited at the sites where the photogenerated holes were available. It was demonstrated that the as-photodeposited 3D nanoporous NiOOH composite film could be used for the removal of trace amounts of indoor formaldehyde gas, which was mainly due to the stored oxidative energy. The photodeposition method demonstrated here can be used as a general route to fabricate photocatalyst-based composite materials.