| Summary: | Energy recycling and production using abundant atmospheric CO<sub>2</sub> and H<sub>2</sub>O have increasingly attracted attention for solving energy and environmental problems. Herein, Pt-loaded Ti sheets were prepared by sputter-deposition and Pt<sup>4+</sup>-reduction methods, and their catalytic activities on both photocatalytic CO<sub>2</sub> reduction and electrochemical hydrogen evolution were fully demonstrated. The surface chemical states were completely examined by X-ray photoelectron spectroscopy before and after CO<sub>2</sub> reduction. Gas chromatography confirmed that CO, CH<sub>4</sub>, and CH<sub>3</sub>OH were commonly produced as CO<sub>2</sub> reduction products with total yields up to 87.3, 26.9, and 88.0 μmol/mol, respectively for 700 °C-annealed Ti under UVC irradiation for 13 h. Pt-loading commonly negated the CO<sub>2</sub> reduction yields, but CH<sub>4</sub> selectivity was increased. Electrochemical hydrogen evolution reaction (HER) activity showed the highest activity for sputter-deposited Pt on 400 °C-annealed Ti with a HER current density of 10.5 mA/cm<sup>2</sup> at −0.5 V (vs. Ag/AgCl). The activities of CO<sub>2</sub> reduction and HER were found to be significantly dependent on both the nature of Ti support and the oxidation states (0,II,IV) of overlayer Pt. The present result could provide valuable information for designing efficient Pt/Ti-based CO<sub>2</sub> recycle photocatalysts and electrochemical hydrogen production catalysts.
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