Hydrogen　generation　by　photoreforming　of　methanol　is　being　one　of　the　most　intensely　investigated　photochemical　transformations　in　pursuing　a　sustainable,　zero　waste　circular　economy.　This　transformation　usually　produces　a　significant　amount　of　gaseous　carbon　in　the　form　of　CO2　and　CO　that　disqualifies　many　active　photocatalysts　as　being　fully　sustainable.　Here,　we　demonstrate　the　atomically　dispersed　Cu　on　TiO2　composite　nanoparticles　synthesized　by　the　wet　impregnation　method　that　are　highly　active　and　selective　in　hydrogen　production　by　photoreforming　of　methanol　solution.　Our　photocatalyst　exhibits　an　apparent　quantum　efficiency　of　10%　at　365　nm　wavelength　and　the　low　power　0.45　W　light　emitting　diode　(LED)　source.　The　only　gaseous　product　found　is　molecular　hydrogen,　whereas　all　carbon　is　trapped　in　the　downstream　liquid　mixture　of　formaldehyde　and　formic　acid,　making　the　process　fully　sustainable　and　clean.　We　used　various　experimental　techniques　and　density　functional　theory　calculations　(DFT)　to　characterize　our　photocatalysts　and　provide　an　insight　into　the　exceptional　behavior　of　the　Cu/TiO2　system.　A　combination　of　ab　initio　DFT　and　X-ray　photoelectron　spectroscopy　(XPS)　measurements　allowed　us　to　identify　the　Cu+-Cu0-Cu+　redox　cycle　under　the　reaction　conditions.　Bypassing　the　Cu2+　oxidation　state　is　crucial　to　keep　the　oxidation　potential　of　photogenerated　holes　low　enough　to　prevent　CO2　generation　and　keeping　all　carbon　in　the　liquid　phase.　This　work　paves　the　way　toward　an　efficient　and　clean　generation　of　hydrogen　by　photoreforming　of　methanol　over　well-established　and　cheap　Cu/TiO2　photocatalyst.