Composition-tunable Cu-In and Cu-Sn bimetallic foams with dendritic nanomorphology were synthesized via a simple co-electrodeposition approach. Their compositions were tuned and optimized to achieve high CO2 electroreduction selectively towards either HCOO -or CO. The selectivity of the prepared bimetallic foams towards CO2ER strongly depends on the catalyst composition. The Cu-rich bimetallic foams (85% Cu, Cu85In15 and Cu85Sn15) showed a high CO-selectivity, while the Cu-poor bimetallic foams (25-40% Cu, Cu25In75 and Cu40Sn60) showed a high HCOO --selectivity. Despite both Cu-Sn and Cu-In bimetallic systems showing a similar CO2ER dependency on the surf ace composition (Cu/Sn and Cu/In surf ace ratios), these b imetallic electrocatalysts showed significant differences in their surface speciation and CO2ER enhancing mechanisms. Specifically, the indium and tin surface speciation are strongly dependent on the composition and the applied potentials. The surf ace of HCOO-selective bimetallic f oams (Cu40Sn60 and Cu25In75) exhibited exclusively metallic surface species (Cu 0 , Sn 0 and In 0 ) at potential with the highest HCOO -selectivity (-0.9 V), however they f ound to enhance the HCOO -pathway via different mechanisms. Cu40Sn60 enhances the HCOO -selectivity at the expense of the parasitic hydrogen evolution reaction, while Cu25In75 improves HCOO -production at the expense of CO. At all potentials below -0.9 V, 80% of the surf ace indium of Cu25In75 exists as metallic In (In 0 ) with low contribution of oxidized indium species, while under same conditions the surface speciation of Cu40Sn60 (HCOOselective) showed that ~52% of the surface tin persists as oxidized tin species. This may explain the observed dif ferences in their CO2-perf ormance at low potentials, where Cu40Sn60 mainly produces H2, while Cu25In75 showed a high tendency for CO-formation under similar conditions. On the other hand, CO-selective bimetallic f oams (Cu-rich), Cu85In15 and Cu85Sn15, exhibited a similar CO2ER behavior, despite the significant differences of their surface speciation. Cu85In15 (CO-selective) exhibited the optimal CO-selectivity at -0.6 V, while Cu85Sn15 showed the same CO-selectivity (90%) at slightly higher potential (-0.7 V). The surf ace speciation of Cu85In15 showed that its surf ace mainly composed of metallic Cu and metallic In with low contribution of oxidized In species, while the surf ace of Cu85Sn15 was f ound to compose of metallic Cu and oxidized Sn species with a very low contribution of metallic Sn.