Methods of seawater desalination and carbon dioxide (CO₂) reduction using clean and renewable energy have attracted much attention withing the reducing fresh water and growing CO₂ concentration. Here, we propose a synergistic method for solar-driven desalination and CO₂ reduction at the surface of sea using a three-dimensional titanium oxide-gold semiconductor/metal (TiO₂-Au NW/NPs (NW: nanowire, NP: nanoparticle)) photothermal conversion membrane that can efficiently harvest a broad solar spectrum (200 to 2500 nm, 94%) to undertake the conversion of light-to-heat and light-to-electricity. The TiO₂-Au NW/NPs membrane demonstrated a high solar vapor conversion efficiency of ~ 90%, CO₂ reduction yields of 0.066 μmol·cm⁻² CH₄ and 0.015 μmol·cm⁻² CO within 5 h. In addition, the membrane efficiently evaporated seawater with different salt concentrations to produce drinking water which meet World Health Organization (WHO) and US Environmental Protection Agency (EPA) standards. This work provides an integrated solution for solar desalination and CO₂ reduction at the surface of sea to reduce the harm to marine life caused by ocean acidification while producing pure water.