The combination of metal cocatalysts with light-harvesting semiconductors is a promising route to improving the photocatalytic performance in CO2 reduction reaction. However, owing to the high H2O activation ability of metal surface, the H-2 evolution from water as a side reaction greatly decreases the activity and selectivity for CO2 reduction. Herein, we demonstrate that the photocatalytic performance in CO2 reduction can be promoted by grain boundaries (GBs) on metal cocatalysts. In this work, metal (Rh and Pd) nanowires with high density of GB were loaded on TiO2 nanosheets, which acting as cocatalysts effectively reduce the H-2 evolution and greatly enhance the photocatalytic performance in CO2 reduction as compared with the corresponding metal nanoparticle cocatalysts without GBs. Two effects are believed to contribute to this enhancement: (1) nanowire structure facilitates the interfacial electron transfer from TiO2 to metal cocatalysts; (2) the GB terminations on the surface of metal cocatalysts are catalytically active sites for CO2 reduction reaction. This work highlights the rational architectural design of cocatalyst for enhanced photocatalytic performance. (C) 2017 Elsevier B.V. All rights reserved.